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Insect and Arthropod Pest Identification and Management
Editor: Ronald Oetting UGA/CAES/Griffin Campus
Handout for Southeast Greenhouse Conference Workshops 2000 to 2004 (Text only)
Contributors and Participants:
Trade and brand names are used only for information. The Cooperative Extension Service, Universities, and the participants do not guarantee nor warrant published standards on any product mentioned; neither does the use of a trade or brand name imply approval of any product to the exclusion of others which may also be suitable. |
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Introduction Detection and identification of pests is basic to any type of management program. This is especially true when using alternatives to chemical control, such as biological control. There are many pesticides registered for greenhouse use (see list of registered pesticides at the end of this handout.) Many of the pesticides are broad spectrum with some residual but most of the newer compounds are more target specific and have a short residual. There are problems with resistance to many of the compounds that are available. Most of the chemical companies have added resistance management tactics to their labels and as a result there are limitations on how many applications can be made on a crop or season. In addition, the broad spectrum pyrethroids, organophosphates and carbamates are lost to many ornamentals with the enforcement of FQPA. As a result, growers need to implement an integrated pest management (IPM) program starting before insects enter the greenhouse and become a pest problem. The first step is to maintain good sanitation by clearing the greenhouse of all plant material before bringing new plant material in for a new crop. The house needs to be clear of plants long enough (preferably a week or more) to allow all insects in the soil to emerge and die. In situations where the house can not be emptied, new plant material should be isolated and observed before introducing this new plant material and incorporating them into the rest of the plants. Keep greenhouses clean by maintaining a constant weed control program and removing unwanted host plants. The area surrounding the greenhouse should also be kept as free of plants as possible, especially broadleaf plants. This will delay the movement of pests into the greenhouse and infesting the new crop. The use of screening to exclude pests from entering the greenhouse is another method of delaying the onset of pest problems. The selection of screens is critical because they must be correctly matched in surface area and pore size (opening in screen) to avoid reducing air flow for evaporative cooling in the greenhouse. Next, develop a program of scouting to check plants regularly. If possible an employee(s) should be assigned the responsibility of scouting for insects and other pests. The scout should check for insects, mites, and diseases on a weekly basis to maintain effective pest management. While looking for pests the scout should be constantly alert to any horticultural problem that might be affecting the crop. The selection of proper spray equipment and use of good application technique is important in obtaining good coverage. Most of the major insect and mite pests of ornamentals are found on the underside of the leaves making it difficult to reach them without good application technique. These pests will not be controlled unless there is penetration of the spray cloud into plant canopy. Many of the new pesticides control by smothering (soaps and oils) and must come in contact with the pest to be effective. This makes good coverage especially critical. Research is being conducted on incorporating selective insecticides and natural enemies into IPM programs for the management of pests. These programs will allow for better management of the chemical insecticides that we have. However, they also require more knowledge about the plant/pest interactions and scouting is a necessity. When considering implementing these new programs, start with a single greenhouse to become familiar with their use. You should be aware of the pests that commonly occur on the crop and have an idea of what pesticides can be used to control these pests and which are the most compatible with the biological control agents being used. Pest detection and identification is key to developing any management program. When pesticides are the only tool used for pest management, the pest must be properly identified in order to select the best pesticides to use. The identification and detection of the major pests of greenhouse crops are discussed. The pests listed are the most common ones encountered and some are difficult to manage and therefore detection and identification of these major pests is critical to good pest management. There are several pesticides that have been registered for greenhouse use in the last few years. The most recent introductions were TriStar, a general use insecticide, TetraSan, a miticide, and Pedestal, an IGR registered against thrips, whiteflies, armyworms, and leafminers. Other recent introductions are miticides Pylon, Hexagon, Ovation, Akari, and Floramite; insecticides Endeavor, Conserve and Confirm; and other compounds Triact (neem oil) and iron phosphate (for slugs and snails). |
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MITES Description and Biology There are four major groups of mites that attack ornamental plants. They are the spider mites, the false spider or flat mites, tarsonemid mites and the gall or eriophyid mites. Mites are not insects, but more closely related to spiders and ticks. After hatching from the egg, the first immature stage (larva) has three pairs of legs. The following nymphal stages and the adult has four pairs of legs except for the in the Eriophyidae. Spider mites are the most common mites attacking plants. The tarsonemid mites, such as broad and cyclamen mites are common but not as common as the spider mites. False spider mites and eriophyid mites are less common but are experiencing a significant increase in grower complaints about damaging levels of both groups. Eriophyid mites exhibit great modification of body structure. They have only two pairs of legs; the four rear legs are absent. They are microscopic, elongate, spindle-shaped and translucent, and the abdomen usually has transverse rings present. Important Species. The most common spider mites found in Florida infesting ornamental plants are the two-spotted spider mite (Tetranychus urticae), Glover mite (Tetranychus gloveri), Lewis mite (Eotetranychus lewisi), southern red mite (Oligonychus ilicis), six-spotted spider mite (Eotetranychus sexmaculatus) and the spruce spider mite (Oligonychus ununguis). The most common tarsonemid mites are the broad mite (Polyphagotarsonemus latus) cyclamen mite (Phytonemus pallidus) and the 'maranta' mite (Steneotarsonemus furcatus). The predominant false spider mites are the privet mite (Brevipalpus obovtus), B. californicus (no common name), B. phoenicis (no common name) and Tenuipalpus spp. There are hundreds of species of eriophyid mites. Many species attack foliage plants, bedding plants and woody plants. Some of the most common are Eriophyes buceras on black olive, Acaphylla steinwedeni on camellia, Trisetacus quadrisetus on juniper, Paracalacarus podocarpi on podocarpus, Phytoptus canestrinii on boxwood, and a unidentified species severely impacting Loropetalum in Florida. The two spotted spider mite (TSSM) is a very common pest of greenhouse crops and is found throughout the United States. This pest has often been referred to as 'a red-spider'. Classified in the spider group (Arachnida), mites are not true insects and adult mites have 8, rather than 6 legs. The TSSM is soft bodied, oval-shaped, the back arched and bearing bristles, measuring about 0.3 to 1 mm. in length and has two dark spots (sometimes four), one on either side of the top. The color can vary from greenish or yellowish, pearly amber, to red depending upon the host plant and environment. Developmental rate is significantly determined by temperature. The developmental threshold, temperature above which development begins, is approximately 51.6 EF (10.9 EC). The number of degree days needed to develop from egg to egg (1 generation) is approximately 265.3 (147.4 above 10.9 EC). Under greenhouse conditions, the average development time from egg to adult is 14-21 days. However, mites develop quickly under hot, dry conditions and may mature in as few as 7 days during these periods. It has been estimated that in a months time one female and her progeny are capable of producing: 20 mites at 60E F, 13,000 mites at 70E F, and well over 13 million mites at 80E F average temperature. Thus it is easy to understand why mites can be such a problem in the hot days of summer. Eggs are laid singly on the surface of leaves. The eggs are spherical and found on the underside of the leaf often where mite feeding is noticeable. The color of eggs varies from transparent to opaque straw yellow. The immature is lighter in color than the adult, usually pale green or yellow. Young mites only have six legs. The older immature is slightly smaller than the adult and pale green to brownish green and has eight legs. Feeding Damage and Symptoms When two-spotted spider mites remove the sap, the mesophyll tissue collapses and a small chlorotic spot forms at each feeding site. An estimated 18 to 22 cells are destroyed per minute. Continued feeding causes a stippled, bleached effect and later, the leaves turn yellow, gray or bronze. Complete defoliation may occur if the mites are not controlled. Southern red mites first attack the lower leaf surface. As the population increases, the mites move to the upper surface. Injured leaves appear gray. Six-spotted mites feed along the midrib on the underside of the leaf. The upper surface has yellow spots. When heavy infestations occur, the entire leaf becomes yellow, distorted and drops prematurely. Spruce spider mite feeding causes the plants to appear off-color and eventually turn completely brown when high numbers are present. False spider mites produce no webbing. Damage from these mites varies considerably, ranging from faint brown flecks to large chlorotic areas on the upper leaf surface to brown areas on the lower leaf surface, depending on the host. Eriophyid mite feeding results in the following damage symptoms: (1) russeting of leaf and fruit (citrus); (2) leaf galls (juniper); (3) leaf blistering on top with hairy growth underneath (black olive); (4) discolored and stunted terminal growth (podocarpus); and (5) discolored bud scales, floral parts and leaves (camellia). These mites are thought to possess chemicals in their salivary secretions that act as growth regulators. When the mites feed, these chemicals are injected into the plant. Leaves may become discolored or plant growth patterns may be changed. On foliage growth, modifications are initially more readily found on embryonic plant tissue. Russeting, which is discoloration, occurs on mature leaves and fruits. Eriophyid mites induce plant galls developed from epidermal cells that are infected by injected growth regulators. Each species of mite has particular chemicals that cause galls to form which are of specific benefit to the mite. After the induced change has altered the behavior of the affected cell or cells, the mite does not have to remain on the site to insure continuation of gall growth. Eriophyid galls occur on soft plant parts, usually on green tissue that was infested when the plant was young. Galls occur in many different shapes. These include pouch or purse galls, bladder galls, nail galls, finger galls and head galls. Detection and Sampling Mites form a protective webbing over their eggs and themselves. Although they feed and leave cast skins on the underside of the leaf, first look for the presence of mites as evidenced by stippling on the upper side of leaves. To sample for mites, sharply tap an affected leaf over a sheet of white paper and look for green, red or yellow specks the size of a grain of pepper crawling on the paper. When checking plants for presence of mites, wash hands thoroughly after checking plants to prevent transferring mites to uninfested plants. Fine strands of silk are spun by spider mites, although these webs may not be detected until large numbers are present. Small mites can use this webbing to balloon and migrate from one place to another. When the infestation is severe, parts of the plant may be completely covered in sheets of webbing, and masses of mites can be detected in the webbing and clustered on tips of leaves and on flowers. Eriophyid (0.1) and tarsonemid (0.15mm) mites are so small, they are virtually impossible to see without a microscope and a trained eye. If damage symptoms indicate a possible infestation, take the affected plant parts to your county extension office. Management Chemical Control. Mite control is a constant battle and requires vigilance. Mites are very key pests for many ornamental crops and, according to Dr. Hudson, responsible for a significant portion of all pesticides used on ornamentals. Seldom are mites ever eradicated once they are present but they can be reduced and managed at levels that are almost undetectable even by the best of scouts. Scouting is essential in order to reduce/prevent wild fluctuations in mite densities, enable detection of poor coverage or lack of control, reduce chances of resistance development and increase the efficiency of the entire pest management program. A scouting program can be as simple or complicated as one desires. However, scouting a given crop should take place and be as thorough as possible. Plants should be inspected by turning over leaves and viewing them with the aid of a hand lens. Leaves from within the center of the plant often harbor low level infestations. You should look for signs of damage (yellow speckles), active adult and immature mites as well as eggs. If mites are found, it is often necessary to blow on them or prod them with your fingernail to determine if they are alive. Some compounds kill mites, but they look alive until they fall over when prodded. (Note: Plants with live mites should be tagged so that you can return to that exact plant and determine the impact of any control measures. Don't mark the plant in such away that the plant receives "EXTRA" attention by the spray crew!). It also helps to determine the sex of two-spotted spider mites. Males have pointed abdomens and are more slender than the rounded and plump females. If most of the surviving mites are male, it could be an indication that you have a developing resistance problem. Resistance management is critical for all the pests we are addressing in this conference. Alternating compounds, along with using biological controls, is one method to help reduce the potential of resistance developing. The exact method of alternating between compounds is open for some discussion - alternate every time you spray, make a couple of applications of the same compound before changing, or changing materials at a rate or frequency which is dictated by the length of the pests generation. For mites, I feel that the first alternative is the most feasible - change chemistry every time you make an application. This is because the generation time of mites can be as short as 5-7 days and many compounds have limitations on how many applications can be made during a given period or to a single crop, i.e., Hexygon® is limited to one application per crop per year. There are several miticides registered for use on ornamentals. In the last few years Akari™, Floramite®, Hexygon®, Ovation™, Pylon®, Sanmite® , Tetrasan™ and Vendex® have been introduced or reintroduced to the greenhouse market. Pesticide resistance can develop quickly with repeated use of the same chemical. The use of insecticides to control insect pests (on a crop infested with mites) can induce spider mite outbreaks by killing the beneficial arthropods that normally feed on mites. In addition, there are natural fungi that attack mites during cool, damp weather and these natural agents are killed when using fungicides against plant pathogens. Keep it clean! Discard severely infested plants and prune infested tissue from remaining plants. Keep greenhouses clean by maintaining a constant weed control program removing unwanted host plants. Segregate new plants before introducing them to make sure they are clean before placing them with existing plants. Segregate infested plants in one area for treatment. Be proactive, find them first. Scout greenhouses using random sampling techniques. Use this information as a decision basis for the timing of chemical applications. Start any control practice early, when the first mites are detected. Spot sprays can be used at this time. Control is difficult once populations have increased to high levels. When spraying for mites you should always pay close attention to coverage, water quality and phytotoxicity. Biological Control. Several biological agents are available, including predatory mites (i.e. Mesoseiulus (=Phytoseiulus) longipes, Neoseiulus(=Amblyseius) californicus, Neoseiulus(=Amblyseius) fallacia, Phytoseiulus macropilis, Phytoseiulus persimilis) which can be introduced into the greenhouse to attack mites. Florida growers have experienced excellent results using either P. persimilis or N. californicus depending on the crop. I prefer N. californicus for most crops. This species is very mobile and is used to control spider mites in peppers, roses, strawberries, and ornamental crops. Relative to P. persimilis, it tolerates lower relative humidity, and it can survive longer without food, making preventive releases possible. Even though it attacks all stages of prey mites and it develops twice as fast as T. urticae at some temperatures, N. californicus reduces dense populations of spider mites more slowly than P. persimilis. Many growers use both mites together, N. californicus as the primary control agent and P. persimilis applied to plants with high mite densities. In Florida, it is also an effective predator of broad mite, Polyphagotarsonemus latus. The development of N. californicus is greatly influenced by temperature as it is for the two-spotted spider mite. The developmental threshold, temperature above which development begins, is approximately 50.6 EF (10.3 EC). The number of degree days needed to develop from egg to egg (1 generation) is approximately 187.6 (104.2 above 10.3 EC). |
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LEAFMINERS Description and Biology Leafminers are housefly-like flies and about the size of fruit flies. There are three species of Liriomyza leafminers that are pests on ornamental plants. The vegetable leafminer, Liriomyza sativae, is an occasional pest and the pea leafminer, Liriomyza huidobrensis, is a major pest in many parts of the world. Liriomyza huidobrensis has been detected in one location in Georgia but the population was eradicated. The primary leafminer pest in the Southeast is the serpentine leafminer, Liriomyza trifolii. These species are called serpentine leafminers because of the twisting mines left by the larvae feeding in the leaf tissue. The adults become active in the early morning and reach their activity peak before noon. This is also the time that mature larvae pupate and adults emerge from the pupae. Adults puncture leaf tissue with their ovipositor and feed on the juices that exude from the puncture. These punctures can easily be detected as a spot on the leaf surface. A female will lay an egg beneath the leaf surface in one of the punctures. When the egg hatches the larvae will start to feed on the tissue between the upper and lower leaf surface. In the third-larval stage the larva will chew a hole to the surface of the leaf and exit, dropping to the soil to pupate. Pupation can take place in any secluded area the larvae can find to hide. The adult emerges in 10 to 12 days. The total development time is less than 3 weeks with warm temperatures. Leafminers are pests on many plants but chrysanthemums, Gerbera daisies, and several bedding plants are the primary hosts. Characters to Separate Species Liriomyz trifolii Adults are 1.3 to 2.3 mm long, with a yellow head, thorax and abdomen blackish-grey, feet and scutellum bright yellow. The male is much smaller than the female. The eggs are 0.2 x 0.1 mm, cream colored, semi-transparant at first. Eggs are lightly inserted under the leaf epidermis. Larvae develop in the leaf but when they emerge they are about 3 mm and bright yellow. The pupa is brown and usually in or on the soil beneath the plant but sometimes they will pupate on the leaf surface. Adults of the three species have a yellow spot in the middle of a dark dorsum. The sides are yellowish, especially in L. trifolii and L. sativiae. L. huidobrensis has some cream to yellow on the side but there is more black than on the other two species. Liriomyza sativae is shiny black on the upper surface except for a prominent yellow triangle between the bases of the wings; the underside and the face between the eyes are yellow. Liriomyza trifolii differs in having the thorax covered with overlapping bristles that give fresh specimens a silvery gray color; specimens that are on sticky cards or placed in alcohol lose the gray and appear shiney black. Also, the portion of the head behind the eyes is mostly yellow in L. trifolii, with only a small black area touching the rear edge of the eye; in L. sativae, the area behind the eyes is predominantly black. Liriomyza huidobrensis adults are similar to L. trifolii, but slightly larger. The black on L. huidobrensis is a mat black. The character that is easiest to detect is that L. huidobrensis has a large black area that touches the posterior part of the ocular of the eye while L. trifolii has yellow or a very narrow black area touching the eye. The mines can be used to differentiate between two species. The mines of L. huidobrensis tend to follow the leaf veins when larvae encounter a vein while feeding. Mines are also common near the petiole of the leaf. The mines of L. trifolii usually do not follow veins but are random within the leaf. Feeding Damage and Symptoms The adults and larvae feed on plant tissue but the larvae are the most damaging as they mine the mesophyll portion of the leaves between the surface layers, creating the very noticeable serpentine mines. High populations of leafminer larvae can result in most of the tissue being mined and most of the chlorophyll removed. As a result, the leaf is very unsightly and also the plant is weakened with reduced photosynthesis. The punctures made by adults are not as noticeable as the mines but also reduce plant quality. Both mines and punctures can easily be detected on the upper leaf surface. Detection and Sampling Yellow sticky cards are used to detect leafminers coming into a greenhouse crop. The adults can easily be separated from other small flies on the monitoring card by the yellow spot in the center of the back. Crops susceptible to leafminers should also be scouted for the presence of adult ovipostion/feeding punctures and the mines of larvae. The mines are often low on the plant so care should be taken to check lower leaves when walking through the crop scouting. Management Chemical Control. The larvae is inside the leaf and the pupae is in the soil making it difficult to reach these stages with pesticides. The insecticides that are effective usually have some transluminar or systemic activity allowing penetration of the leaf tissue. The insecticides in this category are abamectin (Avid), azadirachtin (Azatin), cyromazine (Citation), and spinosad (Conserve). The insecticide novaluron (Pedestal) was recently registered for suppression of leafminers. No foliar insecticide can reach the pupae in the soil so repeat application is necessary to make sure the life cycle is broken. Three applications at 7 day intervals are required to make sure that control is achieved, especially with a heavy infestation. Keep it clean! Ornamentals (obtained as plugs or cuttings) can be infested with leafminer eggs or immatures. Check these cuttings to make sure they are clean of pests. Screening is very effective in excluding leafminer adults. Be proactive, find them first. Scout greenhouses using random sampling techniques. Larval mines and adult punctures are easy to detect. Yellow sticky cards are effective in attracting adults. Biological Control. Biological agents are available. There are parasites that find the larvae in the mines and penetrate the leaf to lay an egg directly on the maggot. There are two genera of these parasites: Dacnusa and Diglyphus. |
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APHIDS Description and Biology Although many species of aphids (sometimes called plant-lice) are pests of ornamentals, green peach and melon aphids are especially troublesome on greenhouse crops. Aphids can have a very short life cycle of only 7 days. The unique reproductive capability of aphid females to bear live young females allows an aphid population to explode to extremely high levels in only a few weeks. Up to 30 generations per year are common in the greenhouse environment. Adults normally range from 1 to 3 mm in length. Aphids are normally wingless but produce winged forms that move to new plants to feed when populations levels increase. A high reproductive rate and an overall resistance to pesticides makes the aphid a formidable pest in the greenhouse. Characters to Separate Species Color is variable in both melon and green peach aphids and can not be used as a distinguishing character. Green peach aphids range from light to dark green or pink, with red eyes. Three dark lines run down its back. The melon aphid is smaller than most aphids and yellow to dark green with a black head and thorax. Wings are held roof-like over the abdomen when at rest. The cornicles are the two tube-like projections (tail-pipes) on the rear of the aphid. In the green peach aphid these cornicles are long, slender, and pale in color but usually dark at the tip. The melon aphid has short cornicles which are uniformly dark. The melon aphid is smaller (1- 1.8 mm long) than the green peach aphid (2.9 mm long). A single female may produce from 60 to 100 progeny before dying at an age of 20 to 30 days. The young in turn may mature in 6 or 7 days after birth. Feeding Damage and Symptoms Aphids feed on most greenhouse-grown ornamentals. Green peach aphids are often found on the new terminal or on the whole plant while melon aphids are more common on the lower leaves, but they can be found higher on the plant as the population increases. Aphids suck plant sap and contaminate the host plant with honeydew and cast skins. The aphid's honeydew secretion promotes the growth of sooty mold which significantly reduces plant quality. Plant damage symptoms from aphid feeding include the distortion of new growth, stunting and reduced quality. Aphid feeding activity can also transmit viruses to some plants. Detection and Sampling Monitor aphid population levels by trapping winged adults on yellow sticky cards and inspecting leaves for presence of feeding aphids. Yellow sticky cards that are strategically placed throughout the greenhouse, especially near doors and among new plants, are used to provide information about the presence and movement of aphids. Detect aphid feeding on plants by randomly selecting 10 plants per 1,000 square feet of greenhouse space and throughly examining the underside of leaves and growing terminals of these plants for the presence of adults and immatures. Green peach aphids often start in the growing terminal and melon aphids are often first noticed on the lowest leaves on pot plants and the population builds here before expanding to the top growth. Management Chemical. Chemicals of all classes are available for management of aphids. In recent years it has been more difficult to manage aphids, especially melon aphids. Recent insecticide registrations for aphids include: imidacloprid (Marathon), pymetrozine (Endeavor), pyriproxyfen (Distance), and neem oil (Triact). Exclude aphids from the greenhouse. Use screens with a hole size of <0.88mm to exclude adult green peach aphids and a hole size of <0.19mm to exclude adult melon aphids. Be proactive, find them first. Scout greenhouses by using sticky cards, leaf inspections or random sampling techniques. Use this information as a decision basis for timing of chemical applications. Start any control practice early, at first detection of aphid activity. Control is difficult once populations have increased to high levels. Biological Control. Several biological agents are available, including predators (i.e. Orius, Aphidoletes, syrphid fly and lacewing larvae, lady beetles, etc.), parasitoids (i.e. Aphidius, Eretmocerus, Encarsia, etc.) or pathogens (i.e. Beauveria bassiana, etc.) that can be introduced into the greenhouse to attack adult and immature aphids. |
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THRIPS Description and Biology There are several species of thrips that can be a problem in greenhouses. However the primary thrips of concern is the western flower thrips, Frankliniella occidentalis (Pergande). Western flower thrips (WFT) not only damage plants by direct feeding but also by vectoring Impatiens necrotic spot virus (INSV) and tomato spotted wilt virus (TSWV). Adult WFT are approximately 1 mm long and vary in color from yellow to dark brown. Most adult thrips are females that lay eggs into plant tissue, particularly leaves. Both the larvae and adults are very active and feed on leaves and flowers. The mature larvae drop onto the bench, or growing medium to pupate. The WFT life cycle (egg to adult) is primarily dependent on temperature. In warm greenhouses thrips may develop from egg to adult in 10 to 14 days, and they can be active throughout the year. There are many species of thrips and correct identification can only be determined by proper slide preparation. One species that is similar to WFT in color and size is Frankliniella tritici, the flower thrips, which was most common in the southeast before WFT. Flower thrips can be distinguished from WFT using a dissecting microscope and comparing the two pairs of setae (hairs) on each half of the front edge of the anterior portion of the dorsum (just behind the head). WFT setae are the same length whereas those in F. tritici are not equal in length, with the lateral-most setae being the longest. There are other species that will be encountered during the growing season. One time that is especially noticeable is during the harvest of crops near the greenhouse, especially hay, when the thrips are disturbed and migrate. The result is thousands of thrips coming into the greenhouse during a few days. In general these thrips do not establish and become pests. Other thrips common to greenhouses are: banded greenhouse thrips, greenhouse thrips, tobacco thrips and Echinothrips americanus which are all dark brown or black species. The melon thrips, onion thrips, and Florida flower thrips are small light brown to yellow species. Feeding Damage and Symptoms Western flower thrips feed on flowers and plant tissue of a wide variety of ornamentals and vegetables. Thrips feed by inserting their mouthparts and removing plant fluids. In addition, their feeding leads to macerating plant cells, resulting in spots on plant leaves or flower petals. Since affected cells are unable to expand, the plant's new growth is distorted as the remainder of the tissue expands. Feeding damage to flowers results in early maturity, bud drop, bud distortion, or flower discoloration. Leaf injury is exhibited by silvery streaking on expanded leaves. Greenish-black fecal material left by thrips feeding may also be evident on leaves. Thrips can vector plant viruses in less than 30 minutes during feeding. Detection and Sampling Scout for thrips by trapping winged adults on yellow or blue sticky cards and/or inspecting leaves and flowers for larvae and adults. Place sticky cards throughout the greenhouse, especially in areas where thrips are most likely to enter a greenhouse such as near doors, side vents, and sidewalls. Place one sticky card per 500 ft2 of greenhouse space. Additional sticky cards may be needed for plants that are highly susceptible to the viruses. Evaluate thrips feeding on plants by randomly selecting 10 plants per 1,000 ft2 of greenhouse space and thoroughly examine these plants for damage, and the presence of adults and larvae. The larvae, which are light yellow in color, are often found in feeding scars. Another method to detect thrips is to tap 3 flowers per plant over a piece of white paper and count the number of thrips on the paper. This information can be used to determine the population dynamics of thrips throughout the growing season. Management Sanitation. Remove weeds, old plant debris, and growing medium from within and around the greenhouse. Eliminate old stock plants as these are a source of thrips and viruses. Removing old flowers may reduce the number of WFT adults and eggs. Place flowers into a sealed bag or container. Exclusion. Screen greenhouse openings such as vents and sidewalls with the appropriate screen size (<0.88 mm) to exclude adult thrips from entering the greenhouse. Airflow may be obstructed with the use of screening containing small pore sizes and as a result the screened surface area must be increased to compensate for this. Check with your extension specialist about proper screen sizing. Chemical Control. The most effective insecticide for thrips control is spinosad (Conserve). In addition, there are several other insecticides including methiocarb (Mesurol), novaluron (Pedestal) and abamectin (Avid) registered for use against thrips. However, no insecticide will provide complete control of thrips. It is important to detect and start management strategies before thrips populations have a chance to increase to moderate or high levels. During warm weather and when populations are high, application intervals of 3 to 5 days may be needed. Rotate chemical classes of insecticides with different modes of activity to reduce the chances of thrips developing resistance. Insecticides should be applied in rotations using one chemical for 2 or 3 applications (pyrethroids only once) and then switching to another class of insecticide with a different mode of activity. Frequency of application may depend on the season. During winter and early spring, the life cycle is extended compared to spring and summer. This can influence the number of applications needed on a weekly basis. Biological Control. Several biological agents are available for managing thrips, including predators (i.e. Neoseiulus or Amblyseius spp., Orius spp. and Hypoaspis miles), and entomopathogenic fungi (i.e. Beauveria bassiana). The key to using biological control against WFT is to release natural enemies early. Releases must be initiated before thrips enter terminal or flower buds. Biological control agents will not control a large existing thrips population. |
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FUNGUS GNATS AND SHORE FLIES Description and Biology Fungus gnat adults are flies, about 1/8-inch long, with long legs and long, thread-like antennae.They resemble mosquitoes more than common flies. Fungus gnat wings are gray with a distinct, Y-shape in the vein near the tip. Adults are weak fliers, but they run rapidly on the medium surface or may remain motionless. Fungus gnat larvae live in the soil, which makes them difficult to find. Larvae resemble worm-like maggots with no legs. They are translucent gray to white in color, about 1/4 inch long, and have a shiny black head. Fungus gnats have a life cycle consisting of an egg, 4 larval, a pupa, and an adult stage. A generation can be completed on 20 to 28 days, depending on temperature. Females tend to fly around the surface of the growing medium, and live approximately 7 to 10 days. Females deposit between 100 to 200 eggs into the cracks and crevices of the growing medium. Eggs hatch into larvae in 4 to 7 days. Larval development requires from 8 to 20 days. The pupa stage lasts about 3 to 5 days. Shore flies are found under similar environmental conditions, but they are more robust and stronger fliers than fungus gnat adults are. Shore flies are shorter than fungus gnats, and are similar in size to fruit flies but they are black in color with dark eyes, wings and legs. Shore flies have approximately five, tiny whitish spots on each wing. Both the antennae and legs are short. The shore fly larvae is also a maggot and is approximately half the length of a fungus gnat larva and is fatter, being more than one-third as wide as it is long. The shore fly larval head capsule has the same whitish color as the rest of the body. Shore flies have a life cycle consisting of an egg, 3 larval, a pupa, and an adult stage. A generation can be completed in 15 to 20 days, depending on temperature. Fungus gnats and shore flies can infest a crop from either soil or algae within the greenhouse, from contaminated potting soil or transplants, or by flying short distances into the production area. Feeding Damage and Symptoms Fungus gnat larvae feed on plant roots and any organic matter in the growing medium. They tend to be found more in growing medium containing peat moss or pine bark. Their feeding on roots can create sites for fungal infections and can reduce the plants ability to take up water and nutrients from the growing medium. This may result in excessive moist conditions that may lead to more disease problems from soil-borne pathogens including Pythium spp. Tender plant stems and leaves that contact the soil surface can be fed on by the fungus gnat larvae. In contrast, neither larvae nor adult shore flies feed on plants. Damage caused by shore flies is primarily due to the excrement ("flyspecks") deposited. Detection and Scouting The best way to scout for fungus gnat adults is to use yellow sticky cards. These are similar to those used for detecting adult thrips, whitefly and leafminer in greenhouses. For fungus gnat adults, yellow sticky cards can be placed horizontally on the edge of pots or flats with the sticky side facing upward. The thread-like antennae and long legs are prominent characteristic features of adult fungus gnats stuck to sticky cards. For shorefly adults, place yellow sticky cards just above the crop canopy. To determine the presence of fungus gnat larvae insert a ¼ inch raw potato wedge or stick into the growing medium. Remove after 48 hours and count the number of fungus gnats on the potato. Management Cultural Control. Implementing proper cultural controls such as watering and fertility denies fungus gnats and shore flies the conditions necessary for development, reduces the need for pesticides, and promotes healthier plants. Shore flies can be controlled by managing algae, which is their primary food source. Both insects are more of a problem under excessive moist conditions such as during propagation. Over wet conditions can develop quickly in a greenhouse during rainy, overcast weather, especially when automatic irrigation has not been reduced. Growing medium should be stored dry, and pots and production areas must be well drained. Once regular scouting indicates that fungus gnats or shoreflies are likely to cause a problem then chemical or biological measures may be appropriately implemented. Sanitation. Remove weeds, old plant material, and old growing medium to reduce problems with fungus gnats and shoreflies. Weeds growing underneath benches can create a moist environment that is conducive for fungus gnat and shorefly development. Allow the potting medium to dry before watering also will reduce population levels. Chemical Control. Insecticides used for controlling fungus gnats can be applied as drenches to the pots (for larvae) or as sprays to foliage, pots, beds or other soil surfaces (for adults) as indicated by the label directions. Some insecticides, such as Bacillus thuringiensis israelensis, cyromazine, diflubenzuron, fenoxycarb, kinoprene, and pyriproxyfen work on the larvae stage when applied to the growing medium in pots and to the soil underneath benches. These materials do not kill adults present during application or adults that develop from pupae present. As a result, effects may seem disappointing for the first few days. Adulticides, such as the pyrethroids (i.e. bifenthrin and cyfluthrin), may be used in conjunction with products targeting the larvae. Insecticide applications for fungus gnats should be made according to pest presence and the label instructions. Sometimes this results in applications at 10 to14 day intervals. Good resistance management practices dictate that classes of insecticides be rotated, approximately every generation cycle or 3 weeks, depending on the temperature. Always follow pesticide label directions. Biological Control. Sometimes naturally-occurring, beneficial parasites or parasitoids may become established and regulate fungus gnat populations. This frequently occurs when broad spectrum pesticides are not used in the production area. Fungus gnat parasites are small, fragile wasps, much smaller than fungus gnats and may be seen walking on the surface of growing medium. Commercially available biological control agents include the soil predatory mite, Hypoaspis miles, and beneficial nematodes in the genus Steinernema. |
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WHITEFLIES Description and Biology The greenhouse and silverleaf whiteflies are the primary whitefly pests of greenhouse crops. Banded-winged and citrus whiteflies are also found in greenhouses but usually do not reproduce and develop damaging populations. Whiteflies, when compared to other pests of ornamentals, have a long life cycle, ranging from 2.5 to 3 weeks up to 2 months under cooler conditions. Adults are moth-like and covered with white, waxy powder. Adult female whiteflies are about 1/16 of an inch in length and deposit about 50 eggs in cool environments and up to 400 eggs at higher temperatures. Consequently a whitefly population can reach very high levels in a few generations at higher temperatures. Eggs are inserted on end upon a short stalk on the underside of leaves. The eggs are whitish to light beige but darken to a dark blue or purple before hatching. The immature stages resemble miniature scale insects. They are flat and oval, glassy to opaque, light yellowish or greenish, and often provided with a fringe of wax filaments. Older immatures tend to be darker and either cream or yellow. Newly hatched immature crawlers move around on the leaf for only a few hours and then insert their mouthparts and begin to feed. The remainder of the immature development is sessile. Whiteflies feed exclusively on leaves, nearly always occurring on the undersurface. They suck juices from the plants and also excrete large quantities of honeydew in which sooty mold grows. Characters to Separate Species The pupae, or last immature, is the primary stage used to separate greenhouse whitefly (GHWF) from silverleaf whitefly (SLWF). The GHWF pupae are usually more oval-shaped with straight sides. There is a fringe of wax filaments (hair-like protrusions) along the edge, completely encircling the top surface. There may or may not be wax filaments scattered on the top of either species. The SLWF is more pointed on each end, with two setae on one end, rounded sides, and no fringe of wax filaments around the edge of the top. The adult SLWF is the smaller of the species and holds it's wings tight against the body, making it appear rod-like. The adult GHWF hold their wings roof-like over the body, with the wings held almost parallel to the leaf surface. Feeding Damage and Symptoms Whiteflies feed on more than 500 species of host plants. Greenhouse-grown ornamentals such as poinsettia, hibiscus, Gerbera daisy, lantana, verbena, garden chrysanthemum, salvia and Mandevilla are especially susceptible to whitefly damage. Whiteflies feed on plant phloem by injecting enzymes and removing the sap, reducing the vigor of the plant. Honeydew secretions from the whitefly promote the growth of sooty mold which also significantly reduces plant quality. The most obvious whitefly feeding damage symptoms are stem blanching, chlorotic spots, leaf yellowing and shedding and, at high population levels, plant death. Detection and Sampling Monitor whitefly population levels by trapping winged adults on sticky cards and inspecting leaves for the presence of feeding immatures. Strategically place yellow sticky cards throughout the greenhouse, especially near doors and among new plants to provide information about the presence and movement of whiteflies. Detect whiteflies on plants by randomly selecting 10 plants per 1,000 square feet of greenhouse space and throughly examining these plants on the underside of leaves, using a 10X hand lens, for the presence of whitefly adults, nymphs and eggs. Management Chemical Control. Insecticides are the primary method used to control whiteflies. Many compounds have been used, but the systemic Marathon (imadacloprid) has been used most frequently over the past few years. The newer chemically related compounds Flagship (thiamethoxam) and TriStar (acetamiprid) are also effective. Endeavor (pymetrozine) and the insect growth regulator (IGR) Distance (pyriproxyfen) are new chemical classes that have worked well. There are several other effective IGRs: Azatin/Ornazin/AzaDirect (azadirachtin), Enstar II (kinoprene), Pedestal (novaluron), and Talus (buprofezin). Tank mixes of orthene (acephate) with a pyrethroid are synergistic, providing better control than either alone. A few other general insecticides, aerosols and soaps or oils can also be used. The newly hatched crawlers and the adults are most susceptible to chemicals, but the waxy covering on the larger immatures makes them more difficult to reach. Resistance is a potential problem and every effort should be made to rotate chemicals and not rely on any one product or chemical class for whitefly control. Exclude whiteflies from the greenhouse. Whiteflies are very small. Screens with a hole size of <0.19mm are required to exclude adult whiteflies. Be proactive, find them first. Scout greenhouses by using sticky cards, leaf inspections or random sampling techniques. Use this information as a basis for decisions for chemical applications. Start any control practice early, when the first whiteflies are detected. Control is difficult once populations have increased to high levels. Biological Control. Several biological agents are available including predators (i.e. Orius, Delphastus, lacewing larvae, etc.), parasitoids (i.e. Eretmocerus, Encarsia, etc.) or pathogens (i.e. Beauveria bassiana, etc.). Check with suppliers on compatibility with chemicals and environmental requirements such as temperature, humidity, and daylength. Check the Cornell and Univ. of Mass. Websites for more information on whitefly biocontrol and sampling methods (http//www.hort.cornell.edu/greenhouse/pestsdis/index.html).
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MEALYBUGS Description and Biology Mealybugs are scale insects and among the most serious interiorscape and greenhouse pests, especially on foliage plants and plants that are maintained in the greenhouse for long periods before shipping. There are many species of mealybugs and they, as a group, are some of the most active scale insects since most of them retain well-developed legs and are mobile throughout their life. The body is generally oval, 1-4 mm long, and usually covered with a white cottony or mealy wax coating. Many of them produce marginal filaments of wax that may be wedge-shaped or spine-like. They appear as a small spot of cotton on the leaf and may be particularly noticeable as a cottony mass when the female is laying eggs. This cottony mass helps protect the eggs laid within the wax filaments. The male and female immatures are similar, but adults are very different. Seldom-observed, the adult male is fly-like, a very weak flier, and very short lived. The female is but a larger form of the immature and may lay up to 600 eggs, usually in a cottony ovisac beneath her body. Eggs hatch in 6-14 days, and the first instars (‘crawlers’) disperse for only a short distance on the same leaf. Once they insert their mouthparts, they generally remain anchored for the duration but can move to a new site if disturbed. Some mealybugs, like the longtailed mealybug, do not lay eggs but bear their young as active crawlers. There may be as many as 8 generations of mealybugs per year indoors. In recent years there have new species of mealybugs introduced to the United States, picked up primarily in Florida and California. However, this does not mean that these are the only states where they can occur. The pink hibiscus mealybug is now in Florida and California and other new species are being identified at a all to frequent pace. Everyone should be on the lookout for mealybugs that look different and let APHIS or state authorities see them. Detection and Sampling Female mealybugs do not fly so the only way they disperse is on plant material, on people moving from one area to another, or as crawlers floating on air currents. Check plant material susceptible to infestation before it enters a growing area to make sure mealybugs are not being brought in. Mealybug may survive on empty benches for 1 to 2 months so make sure the benches are clean before bringing in new plant material. Check stems and leaves for white cottony substances on a regular basis. They start as an isolated infestation and can reach high levels if unchecked. Make sure the area is clean following removal of infested plants. Characters to Separate Species Common mealybugs include: the citrus mealybug, the madeira mealybug (Phenococcus madeirensis formally identified as the Mexican mealybug), and Pritchard’s ground mealybug in greenhouses, and the longtailed mealybug in interiorscapes. The citrus mealybug is by far the most common and widespread mealybug pest and attacks nearly every flowering species grown in the greenhouse. It has an orangish or purplish body covered with a white bloom of wax, and there is a dark line down the middle of the back. The madeira mealybug is also purplish and covered with white bloom but there are three rows of white tufts down the back. This mealybug has become extremely difficult to manage in Georgia. The longtailed mealybug has long, white filaments at the rear, and the female give birth to live young. Mealybugs found only below-ground, on the roots, are likely Pritchard’s mealybug or root mealybugs. Feeding Damage and Symptoms Citrus mealybug is the most damaging greenhouse pest, primarily because it is the most widespread. However, madeira mealybug is more difficult to manage and has a larger host range. Longtailed mealybugs are the most common mealybug in interiorscapes. Direct damage is caused by feeding of adults and immatures on host tissue and injecting toxins or plant pathogens into host plants. Mealybugs are sucking insects and secrete honeydew that falls to leaf surface below, producing a shiny sticky coating on the surface and a medium for the growth of the sooty mold fungus. The waxy cotton material is also very distracting to consumers. Feeding by mealybugs can cause leaf distortion, chlorosis of leaves or areas of leaves, premature leaf drop, dieback, and will kill plants if left unchecked. Management Chemical Control. Mealybugs have been very difficult to manage during the last few years. There are few insecticides that are effective against the madeira mealybug. Other species can be controlled with broad spectrum sprays and IGRs. It is important to know the species of mealybug before attempting to manage them. Sprays should be high volume wet sprays to penetrate the waxy coating protecting the mealybugs. Orthene, Talstar, oil, and Enstar have been the most effective against Madeira mealybug. The crawler stage is the most susceptible to chemicals but the overlapping of generations makes targeting that stage difficult. The higher the mealybug population, the more difficult it is to achieve control. Commercial growers should discard heavily infested plants rather than try to rescue them with insecticidal treatments. Keep it clean! Exclude mealybugs by purchasing plants free of mealybugs. Discard severely infested plants and prune infested tissue from remaining plants. Keep greenhouses clean of weeds which may serve as host plants. Be proactive, find them first. Scout greenhouses using random sampling techniques. Start any control practice as soon as mealybugs are detected; repeat applications to control the crawler stage. Control is extremely difficult once populations have increased to high levels. |
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SCALES Description and Biology Scales are a very diverse group containing several different species/families. The most common families of scales found on greenhouse crops are armored scales, soft scales, and mealybugs. The mealybugs are covered in another chapter in this guide so this chapter will strictly be limited to the armored and soft scales. There are several species in these two groups but the most common are: armored scale- the fern scale, cactus scale, and boisduval scale; soft scale- hemispherical scale and brown soft scale.
The female scale is wingless and is only mobile during the crawler stage just after egg hatch. The crawlers will move a short distance from where they hatch and begin to feed by inserting their proboscis into the plant tissue until it is in the vascular system. Once they start to feed they will remain in that spot for the rest of their life. The male is different from the female in the third immature stage. At this time, they will form a long slender pupal case which is usually white. This is the most noticeable scale on a plant because it is white in color and stands out from the surrounding green plant. The winged male will emerge from this case, only lives for a few days, and spends it's short life looking for females to mate.
Armored scale is covered by a waxy shell that is separate from the body. They secrete wax and incorporating the cast skins at molt into the shell. The insect is flat, close to the plant surface, and often oyster-shell shaped. The female loses its legs and is separate from the wax shell that covers and protects it. Eggs are laid under the shell and each female may produce from 30 to 200 eggs. There can be 8 or more generations per year in the greenhouse.
Soft scales are not covered by a separate wax shell but the wax cover is actually part of the scale body. If wax is present it is tightly bound to the body of the female and it can not be separated from the body. The female soft scale body maybe almost flat in the early stages to spherical and turtle-shell shaped as mature females. Females may either reproduce sexually or asexually and may lay eggs or give birth to live young. Soft scale may lay as many as a 1,000 eggs. Characters to Separate Species Flip a mature scale over, if there is a separate soft body beneath the wax shell, it is an armored scale. If there no distinction between the shell and the body, just a plump mass, it is a soft scale. The armored scales are often specific to particular plant group or species. The oyster-shell shaped (flat with one end more narrow than the other) scale are only found on specific species (i.e. fern scale). The boisduval, cactus, and oleander scale are circular or oval in shape (more like the soft scale), but when turned over, the body is separate from the shell. The soft scales are circular to oval and may form a bump or turtle-shell shaped. The hemispherical scale is shiny brown in color and mature individuals are noticeably convex or hemispherical in side view. Ridges on the dorsum of the shell often form the letter 'H'. The soft brown scale is flatter and leathery. It is yellowish-green to yellowish-brown and often mottled with brown spots. Species identification of scales requires preparation of specimens on microscope slides so they can be viewed under a microscope. Feeding Damage and Symptoms The primary damage from scale is a general weakening of the plants, soft scale produces honeydew making the leaf surface sticky and serves as a medium for fungal growth called sooty mold. Armored scale feeding often results in chlorotic spots where feeding occurs. The presence of scale is a distraction, reducing the esthetic quality of the plant. Heavy infestations can distort and kill small plants. New growth is often distorted from scale feeding. Heavy feeding will result in dead stems and leaf drop. Detection and Sampling Scales do not fly so most infestations originated from infested plant materials that are brought into the greenhouse. Plants must be inspected to find an infestation. You must inspect plants for live scale infestations. Look for suspicious looking bumps that might be on the plant stems or leaves. Armored scale are usually first detected by the white pupal cases of the adult scale that are very noticeable on the leaves. Soft scales are often first noticed by the shinny sticky honeydew found on leaves produced by the scale feeding above. Ants feed on the honeydew so the presence of ants on a plant may indicate that a sucking insect is present and close inspection is needed. If you smash a soft scale with your fingernail a drop of liquid will come from the bump. Scale may feed on stems or the underside of leaves so detection requires looking under leaves and into the canopy of plants. Management Chemical Control. The crawler stage is the most susceptible to pesticides and repeat applications are needed for control. Several insecticides are registered for scale control and it will probably take different compounds for soft and armored scale. Sevin has been the most common compound used against soft scale. Oils have been used for all scale species. Cultural Control. Scales cause more damage on stressed plants, so keep plants healthy. Inspect plants that come into the greenhouses for scale insects. They can not fly and must come into the greenhouse on plants. Biological Control. Scale insects live a sessile life so they are vulnerable to natural enemies. However, the wax cover helps protect them. Natural enemies include lady beetles, microscopic wasps, predatory mites, and lacewing larvae. The crawlers are also the easiest prey for predators and can fall prey to numerous species. Natural enemies, specific to scale insects, are available from biological control supply companies. |
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LEPIDOPTEROUS LARVAE (CATERPILLARS or WORMS) Description and Biology Lepidopterous larvae are the immature stage of moths or butterflies. There are many different kinds of caterpillars that feed on ornamental plants in the greenhouse but the most common are beet armyworms, cabbage loopers, corn earworms, leafrollers and leaftiers. Most of these pests are the young of moths which means they either came into the crops as larvae on plants or the adult moth flew into the greenhouse at night. Caterpillars are often green but different species have different colors and patterns. All have a distinctive head, 3 pairs of true legs (with a claw at the end), and usually 5 pairs of prolegs which includes a pair on the posterior end. These prolegs are not true legs and have hooks (called crochets) around the end of each proleg. This row of crochets may be a complete ring or only partial. Caterpillars may be specific to certain hosts of ornamentals (ei. the Florida fern caterpillar only feeds on ferns); others have a broad host range. Once the larvae are mature they spin a cocoon and become a pupa or resting stage. The adult emerges from the pupa. Total development time will vary depending upon the temperature and species, but during the summer will range to a little over 2 weeks to 7 or 8 weeks. In the cooler season with shorter days, development is much longer and may even extend over the winter and emerge in the spring. Characters to Separate Species There are several characteristics that are used to separate species including: host species, location of feeding, boring, leaf rolling, size, color patterns, pairs of prolegs, pattern of crochets, location of setae, and behavior. You should obtain a simple key or collection of pictures of common pests. The NC State Univ Coop Ext Serv. AG-136 bulletin titled: “Insect and Related Pests of Flowers and Foliage Plants,” Edited by James R. Baker contains an excellent key to the common lepidopterous larvae found on southeastern ornamentals. This key contains line drawings of the major pests and information on most of the species. Beet armyworm eggs are laid in masses on the underside of leaves, young larvae are pale green and feed in groups, especially in growing tips. The older larvae are green to almost black with stripes along each side and a black spot on the side above the second pair of legs and feed on new leaves. They have five pairs of abdominal prolegs. Cabbage looper eggs are laid singly and when the larvae are small they are whitish with a black head. As the larvae grow they become light green with two dorsal stripes and two wider lateral stripes. These larvae are called loopers because they only have prolegs on the 5th, 6th, and 9th abdominal segments and thus move in a looping fashion. The corn earworm lays eggs singly scattered on the foliage, the small larvae feed on new growth that has not fully opened hiding in the rolled tissue, and the older larvae feed on expanded leaves, flowers, and fruit. They have five pairs of abdominal prolegs like the beet armyworm. Late stage larvae leave the plant and pupate in the soil. The imported cabbageworm is a velvety green caterpillar with a faint, narrow, yellow stripe down the length of the back. They feed on kale and cabbage, including the ornamental varieties. The larvae have five pairs of abdominal prolegs. Feeding Damage and Symptoms Beet Armyworm larvae web foliage together and feed within this shelter. Older larvae scatter and may feed on foliage, flowers, and buds often boring into the buds. Cabbage looper larvae have a distinctive feeding habit. They reach out holding only with the hind legs and feed in an arc leaving an arc-shaped hole. Corn earworm larvae feed on all exposed plant parts, including buds and flowers, and may defoliate the plant. Imported cabbageworms feed extensively on the foliage giving it a ragged appearance. None of the caterpillar adults, whether moths or butterflies, damage plants in any way. Detection and Sampling In general, caterpillars are detected by either their feeding damage or by their excrement or droppings on leaves or under plants on the bench. Larvae are often on the underside of leaves making detection difficult. The young larvae often skeletonize leaves, feeding on one epidermal layer leaving a window or clear area on the leaf. Larger larvae feed on the leaf, taking chunks out of the leaf, which leaves large voids. Feeding may be on the edge of the leaf or on the leaf surface leaving large holes. Larvae will also feed on flowers and burrow into stems, buds and flowers. Some caterpillars will distort the shape of the leaf by tying leaves together with silk or rolling portions of the leaf to make protective areas to hide. Management Chemical. There are several insecticides available for the management of caterpillars. The young larvae are the most susceptible, but they are often protected in webbed areas on the leaf and on the undersides of leaves. Older larvae may be more exposed to chemical sprays but they are less susceptible. The best results will be obtained by detecting infestations early and controlling them before they get larger. Early infestations may be spotty and a spot spray may be adequate. Exclude butterflies and moths. The first defense against caterpillars is to exclude the adults from entering the greenhouse. Opening the sides of greenhouse or leaving doors open at night increases the chance of infestation. A light at night increases the chance of attracting moths. If openings to the greenhouse are used for ventilation, these openings should be screened to prevent pests from entering. Biological Control. There are several parasites of lepidopterous larvae but the most common natural control used is Bacillus thuringiensis, commonly called B.t. |
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SLUGS AND SNAILS Description and Biology Snails and slugs move by gliding along on a muscular "foot." This muscle constantly secretes mucus, which later dries to form the silvery "slime trail" that signals the presence of these pests. Snails and slugs are most active at night and on cloudy or foggy days. On sunny days they seek hiding places out of the heat and sun; often the only clues to their presence are their silvery trails and plant damage. Slugs and snails are very bothersome pests in the landscape and can be just as troublesome in the greenhouse. There are several species of slugs and snails that frequent greenhouses. The most noteworthy species that has been the subject of quarantines of pot plants is the brown garden snail (Helix aspersa) which is probably most common in California. In Florida three species of slugs are very destructive garden and greenhouse pests: gray garden slug (Deroceras reticulatum), spotted garden slug (Limax maximus), and the tawny garden slug (Limax flavus). Both slugs and snails are members of the mollusk phylum and are similar in structure and biology, except snails have an external spiral shell. Slugs are easily recognized by their soft, unsegmented bodies, dorsally covered completely or in part by a tough leathery skin (mantle). The head has a pair of upper tentacles bearing eyes, and a pair of shorter olfactory ones. Snails have a spiral shell which protects them from changes in temperature and enables them to tolerate warmer and drier conditions. Most native species are solitary in habit and do little or no damage. The introduced slugs and snails are usually gregarious and may cause serious damage as they build up large populations. As slugs mature, they become functional males and then true hermaphrodites. Older slugs are females. Slugs commonly cross fertilize and may have elaborate courtship dances. They lay gelatinous eggs in clusters of 20 to 30 on the soil in concealed and moist places. Eggs are round to oval, usually colorless, and hatch in 10 to 21 days. When they hatch young slugs are active, crawl and feed if the temperature and humidity conditions are right. When the temperature rises, slugs crawl down to their hiding places on the soil surface to rest and absorb water through their skin. With the fall in temperature, they become active and begin to forage. The ideal temperature is about 65°F. Adults live more than one year. Feeding Damage and Symptoms Slugs and snails feed on a variety of living plants as well as on decaying plant matter. The feeding injury is similar to chewing insects. They chew irregular holes with smooth edges. The feeding is usually at night so it may be hard to find them feeding on the plant. On wet and humid days they will feed during the daylight hours. They also chew fruit and young plant bark. Young seedlings are often completely destroyed. A telltale sign of slug feeding is the slime trail left on the surface of plants. This is a good way to quickly differentiate between slug and insect feeding. Detection and Sampling Slugs and snails can be detected by the presence of irregular holes in leaves and the slime trails left from their movement over surfaces. They like to hide under boards and flower pots and if you lift and look under pots on greenhouse benches you can usually find them hiding during the day. Also, look under loose boards and any other item they might hide under in the growing area. You can trap slugs and snails by placing a board that has pieces of wood attached to the underside such that it is elevated off of the surface slightly so the pest can easily crawl under the board. Beer has also been used to attract slugs and snails. Management Chemical Control. There are two chemicals that are commonly used against slugs and snails: metaldehyde and methiocarb. Commercial metaldehyde baits are available which can be used in greenhouses. Baits are most effective during moist conditions. Irrigate prior to application to promote activity and place baits in areas that are the wettest. Methiocarb is applied as a foliar spray. A bait recently registered in some areas is iron phosphate (Sluggo or Escar-Go). Cultural Control. Barriers are the most common cultural control. Barriers, made out of copper flashing and screens, have been used to keep slugs and snails out of planting areas. Copper barriers are effective because it is thought that copper reacts with the slime these pests secrete, causing a flow of electricity. Copper is a repellent to snails and slugs. Bands of thin copper sheet around tree trunks prevent snails from climbing. Lines of lime and copper sulphate are also repellent and can be used to prevent migration into an area. In addition, Bordeaux mixture (copper sulfate and hydrated lime mixture), dry ashes, and diatomaceous earth have been used. Snails and slugs do not like dry surfaces. Continuous lines of saw-dust and ashes have been used as barriers. However they are only effective as long as they are dry. Biological Control. There are many natural enemies of slugs and snails, including ground beetles, pathogens, snakes, toads, turtles, and birds but there are few, if any, commercially available natural enemies marketed for this use. Birds have been used in commercial greenhouse to reduce slugs and snails |
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Commercial Foliage and Woody Ornamental Arthropod Pest Management an EDIS PUBLICATION |
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PEST MANAGEMENT STRATEGIES FOR INSECTS AND MITES IN COMMERCIAL GREENHOUSE PRODUCTION Ronald D. Oetting Department of Entomology CAES/Griffin Campus Broad spectrum insecticides have been the traditional management strategy used in greenhouse production. These compounds are effective for most pests but are also harmful to beneficial natural enemies. New strategies incorporate compounds that are compatible with natural enemies. These compounds have a narrow spectrum of pest activity and/or leave a minimal residual allowing natural enemies to help manage pests. In the following table the general insecticides are considered harmful to many natural enemies, the compatible insecticides can be used with natural enemies in a management program. The natural enemies are representatives of what is commercially available.
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LIST OF SELECTED INSECTICIDE TRADE NAMES
Chemical Class, Toxicity, and Re-Entrv Intervals (REI) Generic Name (Trade name) - Chemical Class - Toxicity Category - REI abamectin (Avid) - Glycoside - III - 12 hours acephate (Orthene TTO, 1300 Orthene TR) - Organophosphate - III - 24 hours acetamiprid (TriStar) - Chloronicotinyl - III - 24 hours azadirachtin (BioNeem, Azatin, Ornazin) - Botanical (Insect Growth Reg.) - III - 4 or 12 hrs Bacillus thuringiensis (B.t.) (Agree, Attack, Dipel, Javelin, Xentari)-Microbial-IV-4 hours Bacillus thuringiensis (B.t.) strain for fungus gnats (Gnatrol) - Microbial - IV - 4 hours Beauveria bassiana (Naturalis T&0, BotaniGard) - Microbial - IV - 4 or 12 hours bifenthrin (Talstar T&O, Attain TR) - Pyrethroid - II - 12 hours bifenozate (Floramite) - Carbazate - III - 12 hours buprofezin (Talus) - IGR - III - 12 hours carbaryl (Carbaryl, Sevin) - Carbamate - III - 12 hours chlorpyrifos (Chlorpyrifos, DuraGuard, Dursban) - Organophosphate - II - 12 hours chlorfenapyr (Pylon) - Pyrrole - III - 12 hours cinnamaldehyde (Cinnamite) - botanical oil - IV - 12 hours clofentezine (Ovation) - tetrazine - III - 12 hours cyfluthrin (Decathlon) - Pyrethroid - III - 12 hours cyromazine (Citation) - Triazine/Insect Growth Regulator - III - 12 hours diazinon (Diazinon, Knox Out) - Organophosphate - II - 12 hours dicofol (Kelthane, Dicofol) - Chlorinated Hydrocarbon - II - 12 hours dienochlor (Pentac) - Chlorinated Hydrocarbon - III - 12 hours diflubenzuron (Adept) - Benzoylurea/Insect Growth Regulator - III - 12 hours dinotefuran (Safari) - Neonicotinoid - III - 12 hours endosulfan (Endosulfan, Phaser,Thiogard) - Chlorinated Hydrocarbon - I - 24 hours etoxazole (TetraSan) - 2,4-diphenyloxazoline derivative (IGR) - III - 12 hours fenbutatin-oxide (Vendex) - Organotin - I - 48 hours fenoxycarb (Precision, Preclude TR) - Insect Growth Regulator - IV - 12 hours fenpropathrin (Tame) - Pyrethroid - I - 24 hours fenpyroximate (Akari) - Pyridazinone - - 12 hours fluvalinate (Mavrik) - Pyrethroid - 11 - 12 hours hexythiazox (Hexygon) - Thiazolidinone - III - 12 hours imidacloprid (Marathon) - Neonicotinoidl - III - 12 hours iron phosphate (Sluggo or Escar-Go) - Miscellaneous bait - s Kinoprene (Enstar II) - Insect Growth Regulator - III - 4 hrs lambda-cyhalothrin (Scimitar) - Pyrethroid - II - 24 hours malathion (Malathion, Cythion) - Organophosphate - III - 12 hours metaldehyde (Metaldehyde Granules, SlugGeta, Deadline) - Miscellaneous - III - 12 hours methiocarb (Mesurol, Mesurol Pro) - Carbamate - II - 24 hours naled (Dibrom) - Organophosphate - II - 24 hours neem oil (Triact) - Plant Derivative oil - IV - 4 hours nicotine (Nicotine) - Plant Derivative - I - (Fumigant) novaluron (Pedestal) - IGR - III - 12 hours oils (Sunspray Ultrafine, Saf-T-Side) - Miscellaneous - IV - 4 hours permethrin (Astro, Ambush) - Pyrethroid - III - 12 hours d-phenothrin (Pestroy, Sumithrin) - Pyrethroid - IV - 12 hours pyrethrin (Pyrenone, Pyrethrum, Pyreth-It, X-Clude) - Plant Derivative - III - 12 hours pymetrozine (Endeavor) - Pyridine azomethine - III - 12 hours pyridaben (Sanmite) - Pyrdazinone - III - 12 hours pyriproxyfen (Distance, Pyrigro) - Pyridene/IGR - III - 12 hours resmethrin (Resmethrin, SBP-1382) - Pyrethroid - III - 12 hours soaps (Insecticidal Soap, M-Pede) - Miscellaneous - IV - 12 hours spinosad (Conserve) - Miscellaneous - IV - 4 hours Steinernema species (BioVector, Millenium, Scanmask) - Nematode - IV sulfotepp (Plantfume 103) - Organophosphate - I - (classified as fumigant) Sulfur (Sulfur F, Kumulus DF) - Inorganic - IV - 24 hrs tefubenozide (Confirm) - IGR - IV - 4 hrs thiamethoxam (Flagship) - Neonicotinoid - III - 12 hours
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(IRAC Mode of Action Classification) In the above listing of pesticides we list the chemical class of the compounds listed. This has been the standard used in rotating pesticides in pest management for resistance management. It has been discovered that there is cross resistance among some of the chemical classes because they have the same or similar mode of actions. Therefore there has been a shift to using mode of action rather than chemical class to establish rotations of insecticides and miticides where possible. The following is a list of mode of actions of the common pesticides used in the management of insects and mites established by the IRAC. For resistance management avoid exclusive repeated use of pesticides from the same chemical, class or better yet, mode of action and chemicals subgroup [ie. (A2)].
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