Croton Production Guide

CFREC-A Foliage Plant Research Note RH-91-12

R.J. Henny, L.S. Osborne and A.R. Chase University of Florida, IFAS Central Florida Research and Education Center - Apopka 2807 Binion Road, Apopka, FL 32703-8504

CROTON

Crotons have been popular in tropical gardens for centuries, but only in recent years have they become popular indoor plants. Even the most popular croton cultivars commonly available in the U.S. through the early 1970s, such as Codiaeum variegatum `Bravo' experienced considerable leaf drop upon placement in an interior environment. During the last 5 to 10 years, many new varieties have been developed in Europe which tolerate low light interior conditions. There are seven croton cultivars listed in the 1991 Florida Foliage Locator (Table 1). Considerable research has been conducted under European greenhouse conditions on these cultivars, including stock production, propagation, and factors affecting growth of pot plants, but has little application in Florida, since it was conducted under light intensities and temperatures that are much lower than those found in Florida except for winter periods.

Table 1. Codiaeum variegatum cultivars listed in the 1990-91 Florida Foliage Locator

Banana		Icetone Red		Norma
Bravo		Karen			Petra
Gold Dust

PRODUCTION

Potted plant production light levels suggested for the cultivars mentioned above should be in the range of 3000 to 5000 ft-c or higher. Light levels as high as 6000 to 7000 ft-c are acceptable provided high temperatures can be controlled. These light levels can be obtained with 50 to 63%shadecloth depending on season. Excellent growth can be obtained with 3-1-2 N-P-K ratio liquid or slow-release fertilizer when applied at a rate of 1500 to 2100 lb N/A/yr (equivalent to 34 to 48 lbN/1000 ft2/yr) plus micronutrients. The lower rate is applicable to lowest light levels and the higher rate to highest light levels. Potting media used for crotons should have good aeration, but not have excessive drainage since crotons wilt rapidly if allowed to dry. Crotons tolerate 40 to 100°F without chilling or heat damage for short periods, but best growth and quality occur between 65 and 90°F.

PHYSIOLOGICAL PROBLEMS

1) Poor color development

Symptoms -

Terminal leaves are mostly green and even after they mature, color intensity is poor or uneven.

Control -

Best color develops in bright light under cooler temperatures. Therefore, it is more difficult to obtain good color in summer than other times of the year. In summer, color improvement can be obtained with higher light, cooler temperatures and sometimes reduced fertilizer levels. Development of good color during the winter is rarely a problem when proper light is provided and fertilizer rate is not excessive.

2) Faded foliage (photoxidation)

Symptoms -

Subterminal leaves become dull and grayish where flat surfaces face the sun during the hottest part of the day. This occurs primarily when plants are grown in summer in full sun or under light shade but with high temperatures.

Control -

Increase shade level or ventilate to reduce leaf temperature to reduce fading.

3) Excess fertilization

Symptoms -

Leaf blades roll and some entire leaves may twist and reduce aesthetic value of plants. Rolling is often also present when leaf size is large and color poor.

Control -

The symptom is most commonly present when plants receive excess fertilizer and are growing rapidly under low light levels. Reduce the fertilizer level and increase light intensity.

BACTERIAL PROBLEMS

Reference Pest Control Guides Here

1) Crown gall (Agrobacterium tumefaciens)

Symptoms -

Slightly swollen areas on the stems, leaf veins and even roots are initially apparent. These swollen areas enlarge and become corky. Galls may also form on the ends of cuttings or stems where cuttings have been removed. In cases of severe infection, they may enlarge and merge to create a very distorted stem or root mass.

Control -

Remove and destroy all plants found infected with the bacterium, then sterilize any cutting tools used on them. Since a fungus is also known to cause galls on croton, an accurate disease diagnosis must be made for crotons with gall symptoms.

2) Xanthomonas leaf spot (Xanthomonas campestris pv. poinsettiicola)

Symptoms -

Foliar infections on croton start as tiny pinpoint water-soaked areas which can rapidly enlarge to 1/4 inch or more. They tend to remain confined to the areas between leaf veins and are very wet and dark-brown or black appearing when well developed. On some cultivars the lesions have a bright yellow border. Most lesions also show an irregularly shaped border which is corky and especially visible on leaf undersides. All cultivars tested were shown to be susceptible to this pathogen as well as the related plants crown-of-thorns and poinsettia.

Control -

Eliminate all stock plants which have Xanthomonas leaf spot. The disease is very difficult to control unless plants are produced without overhead watering or exposure to rainfall. Bactericides such as copper containing compounds may be somewhat effective if used on a preventative and regular basis.

FUNGAL PROBLEMS

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1) Anthracnose (Colletotrichum sp. or Glomerella cingulata)

Symptoms -

Spots form on all ages of leaves and are initially water-soaked, becoming tan with age. Tiny black fungal fruiting bodies sometimes form in the dead tissue of the spot and may appear in concentric rings.

Control -

Avoid wet foliage since this is necessary for infection and spread of spores. This is especially crucial during mist propagation.

2) Stem gall and canker (Kutilakesa pironii)

Symptoms -

Symptoms caused by this fungal pathogen are very similar to those described for crown gall. Diagnosis of this gall symptom must be made by a plant pathologist to assure accurate control methods are chosen.

Control -

Cultural controls are the same as listed for the crown gall.

INSECT AND RELATED PROBLEMS

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The major arthropod pests of croton include mealybugs, mites, scales, and thrips. Mealybug, mite, and scale infestations are typically the result of bringing infested plant material into the greenhouse. Thrips have the ability to fly and thus invade the greenhouse from weeds and other infested plants outside. In the control section for each pest a few of the many registered and effective pesticides will be listed. For a complete listing, please consult the references at the end of this report.

1) Fungus gnats

Symptoms -

Fungus gnats are small black flies (1/8 inch long) and are frequently observed running around the soil surface or on leaves and often confused for Shore flies (see later section). The adults have long bead-like antennae and their legs hang down as they fly. These insects are very weak fliers and appear to "flit" around randomly. The larvae are small legless "worms" with black heads and clear bodies that inhabit the soil. The larvae spin webs on the soil surface which resemble spider webs. Damage is caused by larvae feeding on roots, root hairs, leaves in contact with the soil and lower stem tissues. Feeding damage may predispose plants to disease and they are often found in close association with diseased plants or cuttings (See Shore flies). Adults do not cause any direct damage, but are responsible for many consumer complaints to growers. Adults emerge and fly around in retail shops, homes, or offices and are therefore a nuisance. For further information please consult Extension Entomology Report #74. (Management of fungus gnats in greenhouse ornamentals).

Control -

Reduce the amount of water applied to each pot where possible. Avoid algae growth on walkways, benches, and cooling pads. Soil drenches or soil-surface sprays are effective at controlling the larvae. Nematodes that seek out insects in the soil are sold commercially and have been shown to control these pests without causing any negative effects to the host plants. Adults are very sensitive to most chemicals.

2) Mealybugs

Symptoms -

Mealybugs appear as white cottony masses in leaf axils, on the lower surfaces of leaves and on the roots. Honeydew and sooty mold are often present, and infested plants become stunted and, with severe infestations, plant parts begin to die.

Control -

Systemic materials are preferred. Control of root mealybugs is accomplished with soil drenches with an insecticide. When pesticides are applied to the soil, care must be taken to assure that the pots have good drainage and that no saucers are attached, or phytotoxicity may result.

3) Mites (Broad mite and false spider mites)

Symptoms -

Mites are very small and go unnoticed until plants become severely damaged. Broad mites cause foliar necrosis of the vegetative shoot apex. Initial symptoms of injury show new leaves cupped downward, puckered, stunted and have serrated margins. Broad mite eggs are covered with many tubercles which give them the appearance of being jeweled. False spider mites (Brevipalpus spp.) are red in color and sedentary. Eggs are bright red and oval-shaped and are laid on both surfaces of leaves. Initial infestations are indicated by faint brown, scruffy flecks, later becoming bronze or reddish in color. Basal leaf areas are affected, vegetative shoot apexes maybe killed, and severe leaf drop may occur.

Control -

The critical point in any control program is thorough coverage with the pesticide. The best control program is to minimize the possibility of introducing mites into the growing area on infested plant material.

4) Mites (Two-spotted spider mites)

Symptoms -

Two-spotted spider mites are the major arthropod pest of crotons. They are very small and go unnoticed until plants become severely damaged. Damaged foliage begins to turn yellow or become speckled due to the feeding of mites. This discoloration is difficult to see in some varieties of croton because of the yellow appearance of healthy leaves. Often the presence of this pest is overlooked because the cast skins and webbing produced by this mite are confused for dust on undersides of leaves. Mites have round pale yellow to reddish eggs deposited on the under surfaces of leaves; nymphs and adults have two dark patches on either side of their bodies.

Control -

5) Scales

Symptoms -

Infested plants become weakened or stunted and begin to die. Scales can be found feeding on leaves, petioles, or stems. They are usually distinct from the plant material on which they are feeding. Their shape (round to oval), size (pinpoint to 2mm long), and color (light to dark-brown) are quite variable and many scales are hard to distinguish from the plant material on which they are feeding.

Control -

See Mealybugs

6) Shore flies

Symptoms -

Shore flies are small black flies (1/8 inch long) and are frequently observed sitting on the tips of leaves or on the soil surface feeding on algae. The adults have very short antennae. These insects are very strong fliers and exhibit very directed flight (straight between 2 points). The larvae inhabit the soil and are small legless "worms" with clear bodies and no obvious heads. No known damage is caused by larvae. This insect is believed to feed only on algae. Adults do not cause any direct damage, but may be responsible for spreading plant pathogens, reducing value by defecating on the leaves (small black to green spots) and for many consumer complaints to growers. Adults emerge and fly around in retail shops, homes, or offices and are therefore a nuisance.

Control -

Reduce the amount of water applied to each pot where possible. Avoid algae growth on walkways, benches, and cooling pads on which they feed. Chemicals are not believed to be very effective in the control of this pest.

7) Thrips (Western flower thrips and Banded greenhouse thrips)

Symptoms -

Thrips are small (less than 1/20 inch long), thin insects. Adult thrips can be identified by a long fringe of hair around the margins of both pairs of wings. Color varies between species with western and other flower thrips being yellow to light brown and banded greenhouse thrips and a few other thrips that feed mainly on leaves being dark brown to black. Feeding takes place with rasping type mouth parts. Infested leaves become curled or distorted, with silver-gray scars or calloused areas where feeding has occurred. Thrips can transmit the tomato spotted wilt virus to many different ornamentals. Any unusual symptoms should be investigated.

Control -

Many materials are registered and effective at controlling thrips.

8) Whiteflies

Symptoms -

Infested leaves often have small yellow spots where adults or immature whiteflies have fed. When populations become dense the leaves become yellowed and lower leaves are covered with black sooty mold. The immature stages of the sweetpotato whitefly are small scale-like insects and can be found on the undersides of infested leaves.

Control -

Many materials are registered and effective at controlling whiteflies. To minimize additional resistance problems, one of the above insecticides should be applied two times per week throughout one life cycle (3 weeks) to control an established infestation. Monitor the population to determine if the particular insecticide being applied is reducing whitefly numbers. Some populations may be resistant to one or more of these insecticides. If the infestation persists, use another compound for the above list following the same schedule. Do not apply tank mixes as they may enhance resistance. If low numbers of whiteflies persist, apply one of the above insecticides once per week for 3 weeks, then switch insecticides. Undersides of leaves must be covered thoroughly to achieve satisfactory control. For additional information on this pest, please consult Plant Protection Pointer #73. (Sweetpotato whitefly on ornamental plants).

Pesticides should be applied according to label directions.

Regardless of the pesticide or mixture of pesticides used, it is
strongly recommended that the effects be evaluated on a few
plants, under your particular conditions before treating all plants.

Mention of a commercial or proprietary product in this paper
does not constitute a recommendation by the authors,
nor does it imply registration under FIFRA as amended.

Reference Pest Control Guides Here

REFERENCES

1. Chase, A.R. 1990. Phytotoxicity of bactericides and fungicides on some ornamentals -1990 Update. Nursery Digest 24(5):11.

2. Price, J.F., D.E. Short and L.S. Osborne. 1989. Management of fungus gnats in greenhouse ornamentals. Extension Entomology Report #74.

3. Short, D.E., L.S. Osborne and R.W. Henley. 1984. Phytotoxicity of insecticides and miticides to foliage and woody ornamental plants. Extension Entomology Report #57.

4. Short, D.E., L.S. Osborne and R.W. Henley. 1989. 1989-90 Insect and related arthropod management guide for commercial foliage plants in Florida. Extension Entomology Report #53.

5. Short, D.E., J.F. Price and L.S. Osborne. 1989. Sweetpotato whitefly on ornamental plants. Extension Entomology Report #73.

6. Simone, G.W. and A.R. Chase. 1989. Disease control pesticides for foliage production- (Revision 4, February 1989). Plant Protection Pointer Extension Plant Pathology PPP#30. (Also in Foliage Digest 12(9):1-8).