Biological Control of Foliage Pests
Chemical control is the primary method used for control of ornamental plant pests (Parrella 1990, Hudson et al. 1996, Hodges and Haydu 1997). However, frequent applications made to confined populations can lead to pesticide-resistant pests. Growers must also contend with phytotoxicity, labor costs associated with frequent pesticide applications, reentry periods to treated areas, importation of new pests, and the occasional loss of an effective pesticide due to health hazards or voluntary removal from the marketplace by the producer. Biological control of insects and mites has been proposed as a viable solution to these problems. Significant progress has been made by scientists throughout North American and Europe (Enkegaard 2002). However, commercial use is still limited in many sectors of the U.S. ornamental market.
Biological control programs are currently available and used for the management of twospotted spider mite, Tetranychus urticae Koch, in many ornamental production systems. Many of the remaining pest species, particularly thrips, aphids, mealybugs, and scales, still require considerable research before biological control programs can be implemented. Although many of these pests have effective natural enemy complexes outside the greenhouse, the effectiveness of a given natural enemy under greenhouse conditions may be limited or, if effective, not commercially available.
After a reviewing a number of publications and discussing this topic with my colleagues there appears to be a pattern in the successes reported. Those growers that used predatory mites or beneficial nematodes seem to have a much better success implementing biological-based pest management programs. The number one success story reported was spider mite biological control which I will discuss in more detail later. Growers that used soil inhabiting predatory mites or nematodes for fungus gnat control also reported some success although a few reported occasional failures. The use of these same predatory mites, in conjunction with N. cucumeris, for thrips management have been successful in some cases but reliability and consistency have been a problems.
The prospects for integrated programs are much more promising. Considerable progress is being made on chemical techniques that are compatible with natural enemies especially with the use of predatory mites for the management of twospotted spider mite.
Biological control programs are currently available and used for the management of twospotted spider mite, Tetranychus urticae Koch, in many ornamental production systems. Many of the remaining pest species, particularly thrips, aphids, mealybugs, and scales, still require considerable research before biological control programs can be implemented. Although many of these pests have effective natural enemy complexes outside the greenhouse, the effectiveness of a given natural enemy under greenhouse conditions may be limited or, if effective, not commercially available. The prospects for integrated programs are much more promising. Considerable progress is being made on chemical techniques that are compatible with natural enemies especially with the use of predatory mites for the management of twospotted spider mite.
Hudson et al. (1996) stated that any program designed to change pesticide use patterns in the ornamental foliage plant industry should focus on mite control as one of its major target areas. To this end, predatory mites have excellent potential for biological control of pest mites. Biological control of twospotted spider mite has been practiced in greenhouses throughout Europe for many years. As a result of the many problems and economic consequences associated with chemical mite control, research and implementation of mite control programs on ornamentals has been underway for many years (Gould and Light 1971, Boys and Burbutis 1972, Simmonds 1972, Stenseth 1976, Hamlen 1978, Hamlen 1980,Hamlen and Poole 1980, Hamlen and Lindquist 1981, Lindquist 1981, Sabelis 1981, Scopes 1985, Osborne and Petitt 1985, Field and Hoy 1986, Osborne et al.1998, Casey et al. 2003, Enkegaard 2003).
Potentially useful predatory mites for controlling T. urticae on ornamental plants are Neoseiulus (= Amblyseius) californicus (McGregor), Neoseiulus (= Amblyseius) fallacis (Garman), and Phytoseiulus persimilis Athias-Henriot . These predators are commercially available from a number of different commercial sources in many countries for the control of this pest and other mite pest species (Hunter 1997).
The ability of predatory mites to control T. urticae on various ornamental plants has been well documented (Osborne et al. 1998), whereas commercially viable programs with explicit directions for ornamental crops haven=t been detailed with the recent exception of a California study (Casey et al. 2003). Hamlen and Lindquist (1981) demonstrated that the two species (P. persimilis and Phytoseiulus macropilis [Banks]) suppress mite populations equally; no differences were noted as a result of host plant or geographic region (Ohio versus Florida). Hamlen (1978) evaluated the control of T. urticae on Dieffenbachia maculata (Lodd.) G. Don and Chamaedorea elegans Martius (parlor palms) by P. macropilis. He established damage indices to evaluate aesthetic injury. The density of T. urticae (stage of mite not indicated) needed to obtain the specified level of damage was determined experimentally for each host plant.
Phytoseiulus macropilis can significantly reduce T. urticae on greenhouse-grown dieffenbachia when introduced twice, 3 weeks apart, at the rate of 10 predators per infested plant with an initial T. urticae density of ca. 38 mites/leaf (Hamlen 1978, 1980). Results of similar studies using parlor palms were not as promising. Thus certain ornamentals may not be good candidates for biological control programs because it is harder to obtain a suitable level of mite control or they do not have the ability to recover quickly from or mask mite feeding damage.
Release methods and guidelines have been developed for use on vegetables to increase the probability of successfully controlling T. urticae with predatory mites. Most guidelines call for the release predators once natural infestations of spider mites are found (French et al. 1976). Sufficient predators must be released to create a predator:prey ratio of 1:10 (Markkula and Tiittanen 1976) or 1:6-1:25 (Hamlen and Lindquist 1981). Once the mite population has reached a high density, the cost of releasing adequate numbers of predatory mites can be prohibitive. In greenhouses producing ornamentals, predators are used prophylactically. Releases of approximately 7500 predators are made once a month even if no mites are present in the crop, on the assumption that the crop is likely to become infested.
Because of foliage plants offered for sale must be nearly free of insects and mites, the use of predatory mites will have its greatest acceptance on stock plantings where more damage can be tolerated. These plants are usually grown for relatively long periods of time -- 1 to 2 years for smaller plant types such as ivy and dieffenbachia. These "stock" plantings are grown very close together and produce very dense canopies. Dense canopies preclude thorough spray coverage with acaricides and, because most of the acaricides are not truly systemic, mites that do not feed on treated leaves or those that haven=t been directly contacted by the active ingredient often escape control. As a result, chronic mite problems occur in these areas and are often spread to other areas of the greenhouse when cuttings are taken for propagation. Osborne (1986) developed methods for reducing the potential for spreading these infestations on cuttings by dipping them in fluvalinate (a pyrethroid). This technique caused little or no phytotoxicity to cuttings of many plant types but it only achieved an approximate 90% reduction in T. urticae density. If predatory mites could be released in "stock" plantings to seek out high density patches of T. urticae and then suppress them, and if all cuttings could then be dipped in an effective pesticide, it is conceivable that cleaner cuttings could be produced than are currently available.
Although there are numerous constraints associated with the development and implementation of practical biological control-based pest management programs on ornamental plants, some progress is being made. Review of a specific operational program may provide a perspective useful in guiding the development and implementation of future programs. The program selected as an example is the use of P. persimilis on shade-grown palms for management of twospotted spider mites.
Nursery Production of Ornamental Palms. Production of ornamental palms comprises a significant activity of a number of nurseries in Florida. Palms are good candidates for biological control programs because the secondary pests that attack them do not develop damaging populations quickly. The primary pest of ornamental palms is the twospotted spider mite, but there are a number of secondary pests. These secondary pests include scale insects such as Florida red scale, Chrysomphalus aonidium (L.), and the false oleander scale (=magnolia white scale) Pseudoaulacaspis cockerelli (Cooley); lepidopterous pests such as the saddleback caterpillar, Sibine stimulea (Clemens), banana moth (Opogona sachari Bojer) and the io moth, Automeris io (F.); as well as snails and mealybugs. Historically, repeated applications of pesticides have been used to maintain plants essentially pest free as required fo acceptability in the market place. It is common for a grower to expend several thousand dollars per year per acre for pest control (Brynteson 1995).
Program Development. Frequent and repeated application of pesticides for pest control on palms have, over time, become less acceptable for a variety of reasons, but most notably because of the lack of acaricides, reduced acaricide efficacy, or concern of worker safety. Efforts were undertake in 1991 by a distributor of nursery supplies to explore the possible use of P. persimilis to control twospotted spider mite on several foliage and ornamental plant species, including 9 different species of palms. These trials led to the development of a management program on palms based on releases of P. persimilis and the highly selective use of pesticides. Bacillus thruingiensis Berliner can provide effective control of the lepidopterous pests without harming P. persimilis, but use of effective short-residual pesticides , followed by reintroduction of P. persimilis, may be necessary to manage other pests effectively. A key factor in the successful development and implementation of an integrated pest management program on palms was the employment, by a distributors, of a highly qualified people to work with growers on a daily basis.
Assessment of Use. One of the primary users of P. persimilis reported expenditures of $2,000-3,000/wk to treat approximately 100,000 palm plants prior to implementation of a program using P. persimilis. Implementation of a biological control based program using predaceous mites reduced cost by 50% (Brynteson 1995). The use of pest management program base on continuing periodic releases of P. persimilis and periodical use of short-residual pesticides is being adopted by an increasing number of growers and in 1996 was the preferred program for more than 30 growers of ornamental palms (Osborne et al. 1998). Brushwein (1991) presented a cost analysis for a commercial palm grower, who used P. persimilis to manage twospotted spider mite on shade-grown royal palm liners (approximately 36,600). The data presented demonstrated a savings of $1,696. This translated into a substantial savings of approximately $0.05 for each liner, which were valued at approximately $0.75 each (almost 7%).
One palm grower is so convinced that biological control is the best way to manage mites that he has, with our help, developed his own P. persimilis rearing program. The production at this nursery has reached an astonishing one million predators a month (minimum) to a high of two million. These are all used in the nursery. For the first year of production, the palms receive no acaricide applications. During the second year and just prior to shipment, pesticides are applied only if scouting indicates the need.
Biological control of Tetranychus urticae, the twospotted spider mite, TSSM has been successful in a number of commercial ornamental crops. This success has been with the use of Phytoseiulus persimilis and Neoseiulus californicus. We have found that for the “beginner” N. californicus is often a better choice because it is much more tolerant of pesticides. If fact, one grower that was rearing his own predators had a problem with N. californicus getting into his colony of spider mites. He tried to kill the predators with pesticides but failed.
Banker plant systems are currently being used at one of Florida=s largest nurseries. This system is used to increase the number of N. californicus available for release. The grower plants corn and/or sorghum each week. Once the pants reach a height of about 12 inches they are infested with the Banks grass mite, Oligonychus pratensis (Banks). This mite does not feed on ivy or palms which are the crops being protected. The grower receives a shipment of N. californicus every other week. These predators are then released, as usual, with some of the shipment being held back to be put on the invested corn plants. These “banker” plants are then moved into the crop and the predators move off of them in search of spider mites in the crop. The plants are occasionally moved to allow better distribution of the predators. This system does an number of things: 1) It allows the grower the ability to detect problems with the health and quality of the purchased N. californicus, 2) It ensures a continuous supply of N. californicus which enables the grower to treat hot spots as needed, 3) Because the banker plants are permanent mini-rearing units in the crop, the number of predatory mites in the system greatly increases on the banker plants making the use of predatory mites more economical, 4) Attractive to additional “wild” natural enemies, and 5) Increases the efficacy of the predators. The use of a similar banker plant system for aphids has greatly increased the acceptance of biological control by ornamental growers in both Canada and Europe.
Recent work in California demonstrated that the use of P. persimilis in an integrated program can be successful and allow for the commercial production of cut roses. This program was successful for a number of reasons. There were significant inputs in terms of scouting and technical assistance from the University fo California and from Syngenta Bioline. There was a well defined scouting and sampling program. The program was established around one key pest with chemical, cultural and physical controls utilized to manage other pests. Unfortunately, a common scenario began to unfold - - Mealybugs! This is a problem that Florida and Georgia growers had already begun to experience. Successful IPM was hindered in a few of the 8 commercial nurseries by the citrus mealybug, Planococcus citri. Biological controls exist for this pest but the commercial availability is very limited. Chemical controls proved disruptive to P. persimilis. We have used N. californicus and succeeded with integrating this predator with the chemicals used to manage mealybugs.
We experienced similar problems on hibiscus with silverleaf whitefly and the mealybug, Phenacoccus madeirensis Green . In early 1984-86 mites and aphids were the major pests that most hibiscus growers were concerned with. Growers were beginning to complain that the current acaricides were not working and they perceived a major problem on the horizon. They were able to manage all the other pests with a combination of chemical and cultural controls.
Growers began to purchase P. persimilis to control the twospotted spider mite. Bacterial diseases were managed by switching from overhead watering to the use of irrigation systems that significantly reduced wetting the leaves. Aphids, if present, were managed with spot treatments of various materials. The program was working well until we noted whiteflies. Releases of Encarsia formosa were made thinking we were dealing with greenhouse whiteflies. It soon became obvious that something was WRONG! Samples were sent to USDA whitefly specialist and it was determined that were had Bemisia tabaci or what is now called the silverleaf whitefly. Since November 1986, this new pest and its invasion have changed how we manage pests in greenhouses. The silver leaf whitefly negatively impacted all of the IPM programs we had developed for mites.
A few years ago, the same grower developed significant problems with resistant spider mites and was forced to entertain the idea of using predatory mites again. He made releases of natural enemies for mites, whiteflies and aphids. Whitefly and mite control was excellent. In this case he used N. californicus for the mites. Aphid control worked well until the average greenhouse temperatures exceeded 90 EF. We noted populations of very small but reproductive aphids that were not being attacked by the parasitoids. The problem became so severe that the grower abandoned the program. It addition to his inability to control the aphids, the grower also felt that managing 3 pest species at one time with biological controls was too difficult and expensive. We are now managing the pests of this crop by releasing N. californicus and treating with Marathon with spot treatments of Conserve and Bacillus thruingiensis to control caterpillars. So far the results are excellent.
The biology and biological control of the broad mite Polypphagotarsonemus latus (Banks) is poorly known. Until recently, pesticides have been the only control method used (see Gerson 1992). Since 1989, broad mite damage at The Land, EPCOT Center, has been very effectively controlled by making inundative releases of Neoseiulus barkeri (Hughes) (Petitt 1993), which has been released for biological control of thrips (Bonde 1989). About 1-2 ml of bran containing an average of 10-30 N. barkeri were placed weekly on each pepper plant (Capsicum annuum Linnaeus), though fewer predators may be sufficient as indicated by cage experiments. Control failures in pepper were observed in late October of 1989-1991, causing reversion to treatments of elemental sulfur for mite control. Reproductive diapause of the predator that was induced at the insectary in the northern United States or during shipment was suspected as the cause of the failure of the predatory mites. Neoseiulus barkeri reared at The Land, EPCOT Center did not show any diapause and weekly releases controlled broad mites on pepper successfully throughout 1992 and 1993. Reproductive diapause has been studied in Neoseiulus (=Amblyseius) cucumeris (Oudemans) (see Morewood and Gilkeson 1991). Laboratory tests showed that an adult female N. barkeri consumed a mean of 26 adult female broad mites in 24 h. Consequences of this high predation rate were seen in cage experiments in which 20 adult female N. barkeri released per plant reduced the broad mite population from 230 per leaf to 16 mites per leaf in one week and to 0.3 mites per leaf in two weeks. Unfortunately, the colony at The Land, EPCOT Center was lost and this species is not available in the United States. Work is currently underway evaluating N. californicus and N. cucumeris to control this pest and the results look very promising.
FUNGUS GNATS AND SHORE FLIES
Growers are utilizing both nematodes Steinernema feltiae (= bibionis) (Filipjev) (when available) (Lindquist et al. 1994) and the predatory mite Hypoaspis miles (Berlese) (Gillespie and Quiring 1990) for the management of Bradysia spp. (fungus gnats). Testimonials from growers indicate that both achieve adequate control. The problem faced by most growers is that control options for Scatella stagnalis (Fallen) (shore flies) are inadequate and populations of this pest reach economically damaging levels. Biological control options do exist for this pest but they are not commercially available. In the past growers have also experienced problems with the availability and quality of these nematodes from certain suppliers which has resulted in failures and/or erratic results. Growers must learn how to evaluate the quality of the beneficial nematodes if they are going to use them.
Aphids are major pests on a number of greenhouse-grown food and ornamental crops. Myzus persicae (Sulzer) and Aphis gossypii Glover are the primary pests and are the targets of both chemical and biological control programs. Samples of aphids in greenhouses in central Florida reveal that M. persicae is commonly parasitized by the braconid wasp Diaeretiella rapae (McIntosh) and A. gossypii by the braconid Lysiphlebus testaceipes (Cresson). The encyrtid hyperparasitoid Aphidencyrtus aphidivorus (Mayr) develops on both of these braconid parasitoids and apparently limits their ability to suppress aphid populations. Aphidencyrtus aphidivorus will attack the primary parasitoid larva either while the aphid is still alive or after the mummy is formed (Sullivan 1988). Because of the potential for disruption by hyperparasitoids, the utility of parasitoids for aphid control in Florida greenhouses is questionable. The use of commercially available parasitoids has also met with poor results. One problem that has ccurred in recent years is that Aphidius colemani Viereck will only parasitize A. gossypii that are of normal size. However, under the same conditions of light, temperature, host plant quality and possibly fertility levels, this aphid produces very small adults that escape parasitism. On hibiscus plants grown under greenhouse conditions during most of the year, if aphid populations are high, aphids are too small for parasitism by A. colemani. Secondly, temperatures regularly exceed 85 EF in Florida greenhouses which may limit the ability of this parasitoid to maintain control of A. gossypii.
Predators from many taxonomic groups have also been proposed for use in greenhouses. These include various species of Coccinellidae, Syrphidae, and Chrysopidae. The green lacewing species, Chrysoperla (= Chrysopa) rufilabris (Burmeister) is being used to manage M. persicae on eggplant (Solanum melongea Linnaeus), tomatoes (Lycopersicon esculentum Linnaeus), and peppers and both the aphid A. gossypii and the whitefly Bemisia argentifolii Bellows and Perring (= strain B of Bemisia tabaci [Gennadius]) on cucumbers (Cucumis sativus Linnaeus) at The Land, EPCOT Center. However, the cost of the lacewings is quite high and there is very little reproduction in the greenhouse.
The predatory gall midge Aphidoletes aphidimyza (Rondani) has given good control of aphids in many northern greenhouses. However, little success has been obtained with this predator in Florida. There has been little research conducted on other predatory insects in greenhouses.
Various fungi have been proposed as candidates for managing aphid pests. One species, Verticillium lecanii (Zimmerman) Viégas, was commercially formulated and used for M. persicae control in Europe. The most critical environmental factors affecting V. lecanii=s efficacy are the need for high humidity and cooler temperatures. Maximum infection occurred only when free water was present. Control in experiments with V. lecanii was not consistent in the southern U.S.A. because of variation in humidity (Oetting and Gardner 1984). The discovery of a strain of V. lecanii that could germinate at lower humidities would be beneficial because V. lecanii is very effective in controlling M. persicae and other aphids when an epizootic occurs (Etzel and Petitt 1992). Other fungi have caused mortality to aphids under some conditions but their value in commercial situations has not been demonstrated. Because of the rate at which aphids reproduce as well as molt from one stage to another, it is possible that better infection rates may be obtained if fungal preparations are applied at three-day intervals.
Other natural enemies are being evaluated for control of aphid pests of foliage plants. These include the coccinellid, Diomus terminatus, which is often found in protected environments feeding on aphids and the parasitoids, Aphelinus gossypii Timberlake and Aphelinus sp., which show some promise for management A. gossypii when used in conjunction with D. terminatus, but none of these natural enemies is commercially available. The pink spotted lady beetle, Coleomegilla maculata, has also been used for aphid control with some success but the company that produced them has just stopped production.
Mealybugs are important pests of ornamental plants grown in protected culture or maintained in interior landscapes, such as hotel lobbies, malls or restaurants. Since the horticulture industry has lost the use of such systemic pesticides as aldicarb and oxamyl, mealybugs and scales have become more difficult to control. Growers now have an increased interest in biological alternatives and these insects are good candidates for biological control. There are many parasitoids, predators, and fungal diseases which attack mealybugs. Biological strategies have not been used widely for mealybugs, but some parasitoid and predator combinations have been successful (Copland et al. 1985). A group of five encyrtid parasitoids rapidly suppressed citrus mealybug, Planococcus citri (Risso), on greenhouse citrus (Summy et al. 1986) and maintained this pest at reduced densities. Copland and Varley (1987) were able to manipulate the greenhouse environment, principally the temperature, to favor predators and parasitoids of mealybugs.
Almost all attempts to control these pests in commercial settings have resulted in less than acceptable control. The primary reason is the improper identification of the pest mealybugs. There is a complex of mealybugs that cause significant problems. One of these, the long-tailed mealybug (P. longispinus), is a poor host for the parasitoids which are commonly available for mealybugs, i.e., Leptomastix dactylopii Howard, Leptomastidea abnormis (Girault) or Anagyrus pseudococci (Girault) (Copland et al. 1985). The mealybug destroyer, Cryptolaemus montrouzieri Mulsant (Coccinellidae), is useful against most mealybugs. However, the densities needed for establishment and oviposition of this predator are probably too high to be acceptable on most ornamental plants. Also, the large size of the adults and the resemblance of the larvae to mealybugs is objectionable to some, especially if plants are in hotels or restaurants.
The use of the green lacewings Chrysoperla carnea (Stephens) and C. rufilabris has also met with erratic results. The use of eggs has often resulted in failure; however, the use of 2nd instar or larger larvae has been more successful.
Long-tailed mealybugs are often attacked by the parasitoid Anagyrus fusciventris (Girault), and the predatory beetle, C. montrouzieri. Control does occur naturally in Florida, but it usually is too late to prevent damage. This parasitoid however, is not commercially available and the predator is not acceptable to many growers because of its cost, limited availability and objectionable appearance to customers. We are currently evaluating another ladybird beetle that is much smaller than C. montrouzieri. This beetle, Diomus austrinus, feeds on most of the important mealybug species.
Whiteflies are a major pest of many ornamentals but only an occasional problem on foliage plants. The action threshold for control is very low because as few as 5 nymphs on a leaf can result in significant chlorosis and damage to newly developed leaves on such plants as Aphelandra squarrosa Nees, Hedera helix Linnaeus (Osborne et al. 1990, Osborne unpublished data). On plants that do not exhibit this “hyper-sensitivity” to whitefly infestations, biological control with Encarsia tranvena (Timberlake) and Eretmocerus eremicus Rose and Zolnerowich are and option but they are seldom utilized. A number of studies have been conducted to develop IPM programs on poinsettia with E. eremicus. Initial results were good but the program was not economically feasible. More recent work has demonstrated the utility of integrating chemical and biological controls to make whitefly management more economical (Van Driesche et al. 2001).
Banana moth (O. sachari) can devastate potted ornamental plants in both nurseries and interior-landscapes (Peña et al. 1990 ). Most pesticides able to control this pests have been removed from the market. Applications of the entomogenous nematodes, S. feltiae, and Heterorhabditis bacteriophora (= heliothidis) Poinar, to the site of infestation resulted in 58-100% reduction of larval numbers (Peña et al. 1990). Nematodes, when available, are currently used by many growers that utilize predatory mites to manage T. urticae on palms. Most foliar-feeding Lepidoptera are controlled with frequent, preventative applications of Bacillus thruingiensis Berliner subsp. kurstaki.
Florida red scale (Chrysomphalus aonidium) is effectively controlled by the by the internal gregarious aphelinid parasitic wasp Aphytis holoxanthus DeBach. This parasitoid is commonly found in commercial palm production facilities in Florida, where it decimates Florida Red scale populations. Unfortunately, this parasitoid is not commercially available and by the time it moves into a crop naturally, the scales have developed a damaging population.
False oleander scale ( Pseudoaulacaspis cockerelli), is much more problematic. This scale attacks many important ornamentals plants and is considered the most important diaspidid scale pest of ornamentals in Florida (Dekle 1976). Few natural enemies are found in association with this scale. If this scale is not managed by culling infested plants and aggressive pesticide intervention, it will establish persistent and economically damaging populations. Many of the pesticides currently available for use on ornamental plants have limited activity against this species.
Although many species of soft scales (Coccidae) attack foliage plants (Hamon and Williams 1984), there has been very little effort at utilizing natural enemies to control them. Hamlen (1975) evaluated the impact of pesticides on the parasitoid Encyrtus infelix Embelton, which attacks hemispherical scale [Saissetia coffeae (Walker)]. Although his data demonstrated the feasibility of integrating pesticides with this natural enemy nothing was ever implemented in commercial nurseries.
Biological control of thrips control remains a significant hurdle in this crop as well as in most of the other crops. There are a number of pest species that attack foliage plants, but all of them are being controlled chemically at this time. Western flower thrips, Frankliniella occidentalis, has been managed in some situations with a combination of predatory mites (N. cucumeris and Hypoaspis miles), Orius spp. and insect pathogenic fungi (Beauveria bassiana). There is a significant amount of research being conducted worldwide to develop more reliable management systems for this serious pest. One predatory mite, Typhlodromips montdorensis (Schicha)is showing promise in other countries (Enkegaard 2002) but the USDA has refused to issue a permit to allow its importation into the United States.
Snails and slugs can feed on the ornamental plants and their presence can create problems because movement of plants infested with certain snails and slugs is prohibited. In such cases, infestations must be controlled completely or the infested plants can not be shipped. Sprays of effective molluscicides can disrupt biological control of T. urticae with predatory mites. The use of baits has less potential to disrupt arthropod biological control programs, but some baits deteriorate very quickly and acceptable control is difficult to achieve. New formulations are now available that last longer and appear to be gaining acceptance.
Because we lack the knowledge and tools to use biological control manage many of the pests found attacking foliage plants, the best we can do at this point is integrate those agents that we do have with selective use of pesticides. The prospects for developing integrated programs have greatly increased since the late 1990's. Compounds are now being registered that have narrower spectra of activity. Such activity reduces the potential to disrupt beneficial insects and predatory mites. For example, use of imidacloprid in ivy and hibiscus crops offers long term control of most Homoptera such as aphids, mealybugs and whiteflies with acceptable suppression of scales and Echinothrips americanus Morgan, a foliar feeding thrips. In combination with imidacloprid, bi-weekly releases of N. californicus are used to manage both T. urticae and broad mites on the crop. This program has been used successfully for a few years. In an attempt to increase the number of predatory mites and reduce costs a couple growers are now using the banker plant system reported on earlier.
LIMITING FACTORS IN THE DEVELOPMENT OF BIOLOGICAL CONTROL PROGRAMS
There are many factors limiting the implementation of biological control programs for pests of ornamental plants. Many of these factors have been detailed in other publications (Osborne et al. 1994) and haven=t changed significantly. Another important limiting factor is the lack of scouts and good scouting programs. With very few exceptions (see Parrella et al. 1989, Casey et al. 2003) there has been very little research conducted on sampling and or monitoring for pests, an important area that has been largely overlooked.
Currently in many commercial greenhouses in Florida, there is a critical need to integrate biological control agents with existing cultural and chemical controls. There are a number of forces creating this need but it appears that the major one is the need to preserve the current pesticides that are safe, effective and registered. These materials have to be considered a valuable resource and managed appropriately. Development of resistance to these pesticides would be of utmost concern. The use of biological controls during specific phases in the production of ornamental plants will slow the development of resistance in some of the target pests.
Although there are many obstacles, use of biological control for pests of ornamentals is a viable technique that must receive additional funding and research so that it can be integrated with other methods for managing pests of ornamentals.
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