• Topics: Pesticide Information Office  | Florida Crop Pest Management Profiles series  |  Food Science and Human Nutrition  | Eggplant Pest Management  |  Nesheim, Olaf Norman  |  Mossler, Mark Allen 

Florida Crop/Pest Management Profile: Eggplant¹

Production Facts

• In 2000, 1,800 acres of eggplant were planted and harvested in Florida. Florida was ranked first nationally in the annual production of eggplant, with over twice the acreage of the next largest eggplant-growing state (1).

• Florida ranks first in all states with respect to eggplant production. In 1997, 85 farms in Florida had 2,314 acres in eggplant production, which was a 9 percent decrease over the acreage in 1992 (2).

• The ten-year experimental production mean for eggplant is 762 bushels per acre (3). Eggplant production in 1999-2000 totaled 1,515,000 bushels or nearly 50 million pounds (4). Yield averaged 842 bushels per acre in 1999-2000, which is over ten percent greater than the ten-year average (4). Eggplant is sold over an approximate ten-month period throughout the year, with 25 percent harvested in winter (January through March), 42 percent harvested in the spring (April through mid-July), and 33 percent harvested in the fall (mid-September through December) (4).

• In 1999-2000, the value of eggplant production in Florida was $15,180,000, which was barely one percent above the ten-year average (4). Growers received $10.02 per bushel of eggplant, which was a $1.07 increase over the ten-year average (4).

Production Regions

The southeastern part of Florida is the main region for eggplant production. In 1997, 46 percent of Florida's harvested acreage was in Palm Beach County, 17 percent was in Miami-Dade County, five percent in both Manatee and Collier counties, and four percent in both Lee and Hillsborough counties. The remainder of production (19 percent) is distributed throughout the state, mostly in the northern region (2).

Production Practices

Eggplant are normally planted in August and again in February to March in north Florida, in August to September and January to February in central Florida, and between August and February in south Florida (5).

Eggplant can be grown year-round, and are often double cropped with pepper or cucumber following eggplant harvest. The vegetable crop that follows eggplant in a double cropping production system depends upon prevailing environmental and economic factors. Growers in Florida often put eggplant in as an extra crop, and grow okra, squash, or cucumbers after the eggplant has been harvested (5). Because of the extended harvest period in Palm Beach County, double cropping with eggplant is not as common a practice in Palm Beach County as it is for pepper or tomato. A spring crop of eggplant may follow as a second crop after a fall crop of pepper or tomato.

Eggplant does best on well-drained, fertile, sandy-loam soils at a pH of 6.0-6.5. Poorly drained soils may result in slow plant growth, reduced root systems, and low yields. Eggplant requires a long, warm, frost-free growing season, usually of 14-16 weeks. Cold temperatures below 50°F injure this crop. The best temperatures are between 80°-90°F during the day, and 70°-80°F during the night; plant growth is curtailed at temperatures below 60°F. Additionally, soil temperature below 60°F restricts germination. However, most eggplant is started in the field from transplants (5).

Eggplant production practices are similar to tomato production. In the Palm Beach area, production is usually by the full-bed mulch system with seepage irrigation. The field is plowed and disced to turn under old crop residue, and then shaping the bed, fumigating, and fertilizing are done prior to plastic application. Advantages in the use of plastic include increased weed control, moisture retention, and reduced leaching of fertilizer. Water should be maintained approximately 15 to 18 inches below soil surface to ensure seepage into the root zone. Maintaining a moist environment creates a nutritional concentration gradient. This gradient allows the banded nitrogen and potassium to diffuse into the soil and replace those nutrients which are lost to the plant. Plastic mulch also helps retain nutrients by preventing leaching by natural rainfall.

Methyl bromide is often used in the full-bed mulch process. Until 1999, the chemical formulation primarily used was 98 percent methyl bromide and two percent chloropicrin. Since then, growers have been forced to use formulations with lower concentrations of methyl bromide and higher amounts of chloropicrin, due to the phase-out schedule of methyl bromide. Aside from the cost increases, this formulation change is currently not viewed as detrimental, as eggplant production areas often have high fungal infection pressure, and chloropicrin is highly effective as a fungicide (5,9).

Eggplant can be planted by direct field seeding or as transplants. Transplants are usually purchased by the grower and set by workers riding a transplanting aid. Stakes are placed in the rows when plants are 2 to 3 weeks old, and plants are "sandwiched" between two lines of plastic twine that are wrapped around each stake. This procedure is usually done by workers three to four times during the growth of the plant. Approximately 90 percent of eggplant grown in southeastern Florida is staked, either next to every plant or next to every other plant within the row. Upon maturity, eggplant acreage is usually picked once a week, and harvest may last six to eight weeks on any single plant. After the final harvest, plants may be killed with a herbicide such as paraquat or glyphosate. Some growers may remove old vegetation by mowing, without the use of herbicides. If the price that eggplant receives is still appealing at the end of the growing season, a grower may hand-cut the old vegetation and ratoon the mature plants. Stakes can be removed by a stake puller and can be sterilized by steam or methyl bromide; however, growers in the Palm Beach area often reinsert the opposite end of the stake in the ground for the second crop without sterilization (5).

Eggplant is usually forced-air cooled, with cold air blown over the fruit. If eggplant is room-cooled, cooling occurs more slowly. Eggplant is not hydro-cooled because the skin is susceptible to damage if suspended in water (6). This crop is generally shipped out of Florida to other states and Canada by truck (7).

Although eggplant is a fairly hardy crop which is well suited for production in Florida, failures do occur. In 1993, early drought conditions followed by excessive moisture caused $1.08 million in eggplant damage. Damage was nearly the same in 1994 ($960,000) with hail and freezing temperatures affecting the crop (8).

Insect/Mite Management

Insect/Mite Pests

Major insect pests of eggplant include thrips, armyworms, whitefly, leafminer, aphids, tomato pinworm, and mites (5,9). However, once methyl bromide is removed from the market, other insect pests such as wireworms may increase and require the use of insecticides which are currently not used in great quantity. Some researchers postulate that eggplant production in Florida may fail due to the loss of methyl bromide (10,11,12).

Melon Thrips (Thrips palmi). Thrips are small (usually less than 2 mm in length) insects that attack a number of crops. Eggs are deposited on plant tissues, usually hatching in two weeks or more, with nymphs becoming mature in another two weeks. Females lay fertilized and unfertilized eggs, with unfertilized eggs developing into males. These insects can produce several generations in a year (13). Damage to the plant is caused by the feeding of both adults and larvae on leaves, stems, flowers, and fruit, removing sap with their rasping mouthparts. In eggplant, they are more abundant on leaves (14).

Melon thrips is present in south Florida during the entire growing season, but is most abundant between December and April (5). Each female thrips produces an average of 50 eggs, which are deposited in slits the female makes in the leaf tissue. In eggplant, infestation appears first on the older leaves (particularly near the midrib and veins) at the bottom of the plant. Populations move upward to the younger leaves as food reserves in the older leaves are exhausted. Consequently, larvae are found first on the older leaves (5). After passing through two larval instar stages in about four to five days (at 79 to 90°F), the larva drops to the ground, where it passes the prepupal and pupal stages in a soil chamber it has constructed. After three to four days, the adult emerges and seeks new host plant leaves on which to feed (15). Direct feeding damage from thrips degrades the quality of the fruit by either discoloring the calyx or causing scab formation. Leaf feeding can cause serious defoliation (5).

The relationship between early damage from thrips and eggplant yield has not been determined. However, levels of fruit damage may result in economic crop loss at a density of 1 larva per fruit (5). Melon thrips is resistant to many insecticides. In addition, the use of broad-spectrum insecticides may increase populations of melon thrips by killing its natural enemies (particularly pirate bugs of the genus Orius), which are thought to contribute to thrips management in the field (16). Use of insecticides also requires thorough spray coverage and is not effective against the protected egg and pupal stages (17).

Chemical control of thrips in south Florida includes the use of multiple applications of imidacloprid, endosulfan, methomyl, and spinosad. Other thrips control methods include the release of the native predator, Orius insidiosus, and the destruction of old host plants (5).

Silverleaf Whitefly (Bemisia argentifolii). In the past few years, this insect has become a significant pest of eggplant, cucumber, squash, succulent bean, tomato, and sweet potato in south Florida. B. argentifolii has been an economic pest of greenhouse ornamentals since 1986 (18). This pest is most abundant between December and May (5), although it may be seen over the whole season. Whitefly infestations may also result in sooty mold formation from the accumulation of honeydew on leaves (16). This fungus is more commonly seen on leaves, but can also occur on fruit, discoloring them (9). As the whitefly migrates from crop to crop throughout the year, populations commonly peak on the state's crops at the time of harvest. In south-central Florida, populations build on fall vegetables and move directly to overlapping spring crops (19,20).

Whiteflies attack over 500 species of plants, and have been observed to reproduce on at least 15 crops and 20 weed species in Florida. Females deposit eggs on the underside of leaves and are capable of laying from 50 to 400 eggs, averaging around 160. The tiny (0.2 mm long) eggs are attached by a stalk to the leaf and are smooth and whitish yellow, but turn brown just before hatching in about 5 to 7 days (16). After hatching, the nymph, called a crawler, moves a short distance. Later nymphal stages are sedentary. They pierce the plant with their mouthparts and remain in place, sucking the plant juices. These nymphs are found on the underside of the leaf and may even cover the entire surface (16). This insect goes through four instar stages, appearing thin, flat, and greenish-yellow. The pre-adult stage (pupa) has conspicuous red eyes and a convex body.

Under experimental rearing conditions, whiteflies developed significantly faster on eggplant than on tomato, sweet potato, cucumber, or succulent bean. Adults can live 24 days on eggplant, and egg to adult survival is 89 percent. Females reared on eggplant laid an average of 224 eggs, two to three times the average laid by females on other crops. The highest numbers of eggs were laid between 3 and 12 days after emergence (21).

At transplant, soil application of imidacloprid is preferred and provides excellent control for approximately two months. Florida growers also use endosulfan for whiteflies. Those who scout (about 50 percent of growers) apply endosulfan based on the scouting reports, and growers who do not scout apply it on a routine basis, every 2 to 3 weeks (5). Generally, imidacloprid is preferred by growers over endosulfan, permethrin, and methomyl because it affects beneficial insects less than the other compounds (9). Abamectin in combination with pyrethrins/rotenone has been shown to reduce whitefly populations (22).

Armyworms (Spodoptera spp.) Beet and occasionally southern armyworms are minor pests of eggplant that may occur throughout the growing season. Populations in Florida peak from June through September (23). Adult beet armyworm moths lay a mass of 50 to 75 eggs covered with fuzzy brown or light-colored scales. Newly hatched larvae aggregate on the underside of the foliage, where they scrape away everything but the clear cuticle, giving the leaf a "window pane" look. They also spin a loose webbing. Older larvae disperse, and may enter the fruits of crop. When full-sized, they reach 1 to 1.5 inches in length. Generation time is about 25 to 35 days, depending on temperature (16). Southern armyworm larvae feed on a number of weed species such as pigweed (Amaranthus spp.) from which they move to a wide range of crop plants. The adults feed on flower nectar. Growers use endosulfan, B.t., spinosad, and methomyl for the management of armyworms in Florida (5).

American Serpentine Leafminer (Liriomyza trifolii). These insects are present throughout the growing season, and have a very broad host range including eggplant, celery, spinach, lettuce, melons, cucumber, pumpkin, okra, tomato, pepper, potato, and carrot (24). The adult is a tiny black and yellow fly which deposits eggs within leaf tissue that hatch within a few days. The larva is yellow, 3 mm long, and feeds within the leaf, where it forms a serpentine mine. Mature larvae generally emerge from inside the leaf and drop to the soil where they pupate. Egg to adult life cycle is less than three weeks under optimum conditions, thus many generations may occur within a year (25). Young plants are most susceptible to damage. Parasitic wasps manage leafminers well, but are often killed by spraying non-selective insecticides. This decrease in natural enemies may lead to a large outbreak of leafminers. As Florida growers are aware of this problem, and outbreaks are rare, perhaps only a few growers experience problems with leafminers (5).

Aphids (Myzus persicae, Aphis gossypii, Macrosiphum euphorbiae). Aphids are a minor pest that normally appear at the end of the season when growers are not actively spraying (5). Aphids feed by injecting their sharp hollow mouthparts into plant tissue and sucking out phloem exudate. Female aphids reproduce asexually, giving birth to live young that develop rapidly. Under conducive conditions, adults remain sedentary, continuing to give birth to more asexually reproducing adults. When populations become crowded, winged, sexually-reproductive forms are produced that disperse, and may spread plant viruses (16). Aphids that occur on eggplant in Florida include Myzus persicae, Aphis gossypii, and Macrosiphum euphorbiae. The latter is very susceptible to a fungus in Florida and doesn't thrive under natural conditions (9).

Aphids have a number of natural enemies, including ladybird beetles, aphid lions, hover flies, and parasitic wasps. If these natural enemies are present in sufficient numbers before aphid populations expand, they can keep aphids under control. If foliar sprays are needed to manage aphids, thorough coverage of all the plant surfaces is essential, as aphids tend to prefer the underside of leaves. Because aphids do not lay eggs, a life stage often protected from insecticides, a single, well-delivered spray will often kill all aphids on a crop until winged individuals migrate (16). Growers in south Florida use mostly imidacloprid against aphids, but some endosulfan and methomyl use has been reported (5).

Mites (Polyphagotarsonemus latus, Tetranychus urticae). The broad mite, Polyphagotarsonemus latus, is a major pest of eggplant. Additionally, the twospotted spider mite, Tetranychus urticae, is a potential problem (9). Broad mites are cosmopolitan in distribution. They feed by piercing plant cells and sucking the sap that leaks from the wound (26). Photosynthesis is reduced, and water balance is affected. Additionally, some of the terminal leaves and flower buds develop deformed. Blooms abort, leaves become discolored and thickened, and young foliage or fruit are often malformed and rust-colored (27). The life cycle from egg to adult lasts 4 to 6 days. Eggs are oval, approximately 0.7 mm long, and hatch in 2 to 3 days (28). The larvae feed for 1 to 3 days, and then go into the resting pupal stage (26). Adults are very small (1.5 mm) and difficult to see without a hand lens. Females may live as long as 10 days and lay an average of 2 to 5 eggs per day (20 to 50 eggs per female). Unfertilized eggs develop into males (26). The broad mite may be dispersed by climbing onto the legs and bodies of adult whiteflies.

Growers in Florida apply endosulfan to manage the broad mite. Some studies have shown synthetic pyrethroids to be ineffective against mites (29) and resistance by the twospotted spider mite to many insecticides has been reported (30).

Tomato Pinworm (Keiferia lycopersicella). The tomato pinworm, a small moth larva, is a serious pest in warmer climates. It is common in Florida tomato-producing regions along the coast south of Tampa and Ft. Pierce. The egg to adult development time averages 67 days, but may be as short as 28 days. Eggs are laid singly or in two's or three's on the host-plant foliage. First instar larvae spin a silk tent before tunneling into the leaf where they make a blotch-like mine. Third and fourth instar stages feed from within folded or rolled portions of the leaf, or may enter the stem, and pupation occurs in the soil. Adults emerge in two to four weeks. Seven or eight generations of pinworm may occur in some seasons (31).

Damage results from the larvae feeding on leaves, stems, and fruit. The initial injury is not readily noticeable and appears as a small leaf mine. Later injury comes from leaf folding by the older larvae. Leaf folding often hinders the effectiveness of insecticides against this pest. Other damage results from pathogenic infections (31).

Pinworms are often seen on eggplant when growers use non-selective insecticides for management of whitefly that reduce beneficial organism populations. This pest is seen only in the winter and spring (9,32). Generally, spinosad is used for pinworm management.

Chemical Control

Methyl bromide/chloropicrin fumigation has historically been used as the main method of insect control in the production of Florida eggplant. Growers currently rely on this fumigant within the full-bed, plastic mulch production system. However, pest problems not eliminated by methyl bromide fumigation do exist. Reported insecticide application in 2000 was 3,500 pounds of active ingredient on 96 percent of Florida's eggplant acreage. The 2000 survey results reflect higher use of certain insecticides (imidacloprid, endosulfan, Bacillus thuringiensis, esfenvalerate, spinosad, or methomyl) rather than others (carbaryl, oxamyl, permethrin, or pyrethrins/rotenone) (1).

Methyl Bromide. In 1998, Florida growers applied a total of 241,000 pounds active ingredient of methyl bromide to eggplant crops. They treated 64 percent of eggplant acreage at an average rate of 170 pounds active ingredient per acre. Only one application is made during the year (10). Methyl bromide is applied as a liquid from tractor drawn chisels or shanks six to eight inches deep in the soil. Because of its high vapor pressure, it volatilizes rapidly and will move through the soil by mass flow followed by diffusion. Immediately after injection and bed formation, a polyethylene cover (plastic mulch) is applied. This plastic mulch serves to reduce the loss of methyl bromide to the atmosphere as it vaporizes, and has other aforementioned horticultural benefits.

A model developed in Florida to evaluate the impact on the production of the state's vegetables as a result of the loss of methyl bromide has suggested that eggplant production will cease completely in Florida without methyl bromide because without the fumigant, eggplant will no longer be economically feasible to grow. Nevertheless, the authors state that future research on possible substitutes may invalidate these conclusions (11).

Alternatives to Methyl Bromide

Several chemical alternatives are being evaluated for use in crops once methyl bromide is off the market. Many are ineffective or have problems with implementation. Tillam® is labeled only for tomato. Telone® with chloropicrin has been looked at for several years as an alternative, and provides control for nematodes and disease, but not for weeds (9).

Researchers evaluating alternatives have concluded that it will not be possible to replace methyl bromide with one cultural tactic, but rather a combination of tactics, which will vary according to the crop. The same is true of chemical alternatives. The fumigant cannot be replaced with a single chemical, but rather a combination of fumigants and non-fumigants. Specifically, the mix of fumigants (such as 1,3-dichloropropene and chloropicrin) with an additional herbicide treatment is thought to give the best yield response for crops such as tomato and strawberry in Florida (12).

Research on non-chemical alternatives to methyl bromide is for the most part still in the preliminary stage. Although many alternative management practices are currently under evaluation, including the use of cover crops, organic amendments, biological control agents, crop rotation, hot water/steam treatment, paper and plastic mulch, pest resistant crop varieties, solarization, natural product pesticides, supplemental fertilization, and fallowing, several have already been determined to be impractical under Florida conditions. For example, steam/hot water treatment is too costly, flooding can only be used by certain growers, and soil solarization is not only less effective on well-drained, sandy soils, but the hottest part of the year in Florida experiences heavy rainfall, resulting in water accumulation above the plastic that impedes soil heating (2,9,50,60).

Telone® (1,3-dichloropropene) is a leading candidate for an alternative, but because of current worker protection standards and setback restrictions, growers must deal with it differently than methyl bromide. The recommendation is for it to be broadcast over the whole field with no covering. This broadcast treatment method is not always efficacious yet. Metam sodium (Vapam®) may also become an alternative. Squash growers use this chemical as a soil treatment in fields without plastic, but it does not yield consistent results. Further research may establish better methods of application (9).

Endosulfan (Phaser®/Thiodan®). Endosulfan is a cyclodiene chlorinated hydrocarbon insecticide and miticide that acts as a contact poison and is effective against a range of pests, including aphids, blister beetles, Colorado potato beetle, flea beetles, and whiteflies (38). The median price of endosulfan is $15.02 per pound of active ingredient, and the approximate cost per labeled application (1.0 lb ai/A) is $15.02 per acre (38,39). Endosulfan may be applied up to one day before harvest (preharvest interval or PHI= 1 day), and the restricted entry interval (REI) under the Worker Protection Standard is 24 hours. No more than two applications may be made per acre per year, with a maximum of 1.0 pounds of active ingredient per acre each year.

In 2000, Florida growers applied an average of 0.63 pounds of endosulfan per acre per application to 42 percent of their eggplant acreage, an average of 2.2 times. Total usage was 1,100 pounds of active ingredient (1).

Bacillus Thuringiensis. The biopesticide Bacillus thuringiensis (B.t.) is an important management tool for Florida eggplant growers who use it yearly to manage caterpillars (beet and fall armyworms, cabbage looper, cutworms and others). The median price of B.t. is $158.12 per pound of active ingredient (54). B.t. may be applied up to the day of harvest (PHI= 0 day), and the REI is 4 hours.

In 2000, approximately 400 acres (22 percent) of Florida-grown eggplant were treated with B.t. an average of 13 times per crop (1).

Alternative Chemicals

In addition to those reported as being used, there are also other insecticides available such as azinphos-methyl, acetamiprid (Assail®), azadirachtin, bifenthrin (Capture®), pymetrozine (Fulfill®), pyriproxyfen (Knack®), tebufenozide (Confirm®), thiamethoxam (Platinum®), and zeta-cypermethrin (Fury®). There are also some biorational pesticides registered for use in Florida eggplant (kaolin, harpin protein). A pheromone disruption compound exists for tomato pinworm. Additionally, insecticidal soap and oil are applied by growers to target all insects in general. These products are applied at the beginning of the season, and are applied every 2-3 weeks until something stronger is needed (5). One study showed mineral oil, with sufficient coverage, to be persistent and highly toxic to all whitefly stages, but also toxic to some stages of beneficial arthropods. The same study showed that surfactants such as insecticidal soap, household detergents, and plant extracts containing sugar esters were effective against whitefly nymphs, although less effective against other stages (40).

Cultural Control

The one cultural practice reported by eggplant growers in Florida is that of removing host plants (either crop or weed) from the fields.

Biological Control

The only biological control reported by extension personnel was that of releasing pirate bugs (Orius insidiosus) for thrips management. Beauveria bassiana has been recently registered for use as a biological insecticide

Disease Management

Disease Pathogens

There are not many disease problems on eggplant in Florida, but a few are significant (9). The warm, moist climate in the state contributes to the disease problems that do have the opportunity to become established.

Phytophthora Blight (Phytophthora capsici). Phytophthora blight occurs sporadically in Florida, but during weather favorable to the fungus, the disease can spread rapidly, causing serious losses to eggplant (41). Phytophthora infestations are more prevalent in the winter, but outbreaks can occur anytime (42). During February to April 1998, Florida experienced a severe epidemic of this fungus that affected a number of vegetable crops. Disease incidence in eggplant ranged from 16 to 25 percent (43).

Phytophthora causes seed rot and seedling blight (damping-off) in many solanaceous crops such as eggplant, pepper, and tomato. In eggplant, the entire plant may be susceptible to the disease, but fruit rot is the primary symptom. This disease begins as a round, dark brown area on the fruit, which can occur at any stage of maturity. A light tan area quickly expands around the initial lesion. A white to gray colored fungal growth may appear during wet, humid times, beginning on the more mature part of the lesion. The concentric patterns and dark fruiting structures indicative of Phomopsis rot are lacking in Phytophthora fruit rot (41).

Phytophthora capsici can survive in and on both seeds and plant debris in the soil because of its thick walled spores (oospores). The fungus may also be spread by wind and water in the form of sporangia, microscopic fungal strands (hyphae), in infected transplants, and on contaminated soil and equipment. Diseases caused by this organism are most abundant during warm, wet weather (80-90°F), and in the lowest parts of fields that are often water logged. Signs of the disease may occur three to four days after infection, and entire fields may be rapidly infected (41,44).

Phytophthora blight can be very serious, especially when there has been a damp, moist winter. These weather conditions can produce high infection rates. In fields near Boca Raton, there have been up to 75 percent infection rates. This disease is one of the most destructive, and there are few control measures. Fumigation provides some measure of control. Some growers try not to plant on land that was previously cropped in pepper. However, this practice may be difficult for growers that plant only pepper and eggplant. Rotation is not always practical if a grower has invested so much in their equipment that they must continue to plant only high-value crops (42). Resistance or insensitivity to mefenoxam has been reported for other Phytophthora species, and has been demonstrated in the laboratory for P. capsici (41). Chemical control of Phytophthora is difficult due to the rapid rate of development of the disease, especially under optimal weather conditions. In Florida in 1993, field-testing found many isolates that varied in sensitivity to mefenoxam (43,44).

Verticillium Wilt (Verticllium dahliae). Verticillium is a soil-borne organism that can survive in the soil for many years. The wilt disease caused by this organism progresses slowly on eggplant. Eventually, plant vigor is affected and stunting occurs. The lower foliage will exhibit slight yellowing while the entire plant becomes progressively more wilted until death occurs. There may be slight vascular discoloration when lower stems are slit lengthwise. Browning is much less than with bacterial wilt, and the pith is not affected (45).

Without methyl bromide for fumigation, verticillium wilt may become a serious problem. Eggplant is very susceptible to this pathogen. Because growers have been planting on raised, fumigated beds, verticillium wilt has not been a production problem. If eggplant is grown on open ground without plastic, this disease is likely to become an issue (42).

Phomopsis Blight (Phomopsis vexans). Another disease of major importance to eggplant production in Florida is Phomopsis blight. It occurs on fruit and occasionally on leaves or stems. The disease is difficult to manage because the slippery skin of the fruit does not allow good adhesion of sprays (46). However, there are several resistant varieties (42).

Seedlings infected with Phomopsis blight exhibit dark brown lesions that turn gray in the center just above the soil line. Eventually these lesions girdle the stem and kill the plant. On older plants, round or oval spots develop on the leaf and stem, which enlarge and become more irregular. Infection of foliage is less important than fruit infection. This pathogen forms indentations on the fruit. Fungal fruiting bodies form in concentric circles inside the fruit, reducing the grade of the eggplant (45).

Alternaria Leaf Spot (Alternaria cucumerina). In southwest Florida (Naples and Immokalee), there is a problem with Alternaria leaf spot. To manage this fungus, the crop must be sprayed prophylactically as part of a routine program. This disease occurs more often in late winter and early spring (42). It is reported to be a major disease, occurring every year.

The fungus can survive on or in crop debris, especially debris on the soil surface, where wind can readily disperse spores. Volunteer cucurbit plants and weeds may also serve as reservoirs of infection. Wind is the main dispersal agent for spores, but rain splash and mechanical transmission are also important in the spread of this disease. While spore release from plants occurs mostly under dry conditions, spores require moisture to germinate and enter the leaf tissue. The optimum temperature for infection is 68°F. Within three to twelve days from spore penetration, the next group of spores is released. Disease development is most rapid when nighttime temperatures are close to the optimum (47). Growers use maneb for leaf spot management (5).

Bacterial Disease. The largest concern with regard to bacterial diseases is that of bacterial soft rot. Although this is generally a post-harvest disease, it may be observed in the field. Growers in Florida use copper-based products for bacterial diseases (5).

Chemical Control

Methyl bromide/chloropicrin fumigation has historically been used as the method of disease control in the production of eggplant. Growers currently rely on this method to control soil-borne fungal diseases and the use of methyl bromide as well as its alternatives have been discussed previously. However, disease problems not eliminated by methyl bromide fumigation do exist. In 2000, Florida growers reported fungicide use totaling 15,300 pounds of active ingredient for control of eggplant diseases. During the decade of the 1990's, between 70 and 98 percent of eggplant acreage has been treated with fungicides each year, with total annual usage ranging from 10,600 to 25,600 pounds of active ingredient. The fungicides most commonly applied are maneb, sulfur, and copper hydroxide. These three materials comprised over 97 percent of the fungicides applied to eggplant in 2000 (1,2,5,7,33-37).

Maneb. Maneb is by far the principal fungicide used in Florida eggplant production. Maneb is a carbamate foliar fungicide that is applied to many vegetable and fruit crops. It is used in the management of blotches, blights, spots, and rots (48). The median price of maneb is $3.67 per pound of active ingredient, and the approximate cost per labeled application (1.6 lb ai/A) is $5.87 per acre (39,45). A maximum of 11.2 pounds of active ingredient can be applied per crop. The PHI is 5 days and the REI is 24 hours.

In 2000, Florida growers applied an average of 1.1 pounds of maneb per acre to 86 percent of their eggplant acreage between 4 and 6 times. Total usage was 8,000 pounds of active ingredient (1).

Copper Hydroxide. Copper hydroxide is an inorganic foliar fungicide that is applied to many vegetable and fruit crops. It is used in the management of blotches, blights, spots, and scabs (48). The median price of copper hydroxide is $2.22 per pound of active ingredient, and the approximate cost per application is $1.67 per acre (37,39). The maximum application rate is 2 pounds of active ingredient per acre. The PHI and REI are both 48 hours (4).

In 2000, Florida growers applied an average of 0.80 pounds of active ingredient per acre of copper hydroxide per application to seven percent of their eggplant acreage. Average number of applications was five times. Total usage was 500 pounds of active ingredient (1).

Alternative Chemicals

Based on surveys and information obtained from extension personnel, other fungicides that have been used for eggplant production include copper sulfate and chlorothalonil. Other fungicides registered for Florida eggplant production in 2002 include acibenzolar (Actigard®), azoxystrobin (Abound®), copper octanoate, and trifloxystrobin (Flint®). Peroxyacetic acid has also been registered for post-harvest fungus control. Zoxamide (Gavel®) and mefenoxam (Ridomil Gold®) were also registered for use on eggplant but products which contain these active ingredients were not available in 2002 in Florida.

Cultural Control

Planting in well-drained soils and avoiding planting in fields with large amounts of decomposed plant debris are recommended as cultural controls for damping-off. Most research on alternative controls for disease has been done on tomato, and growers are likely to adapt those findings to eggplant. Tomato was the first crop to be grown under full-bed mulch culture; consequently, progress in tomato pest management will likely be applied to related crops (42).

Management practices for Phytophthora in transplant production areas include the use of pathogen-free and fungicide-treated seeds and sterile potting media. Flats, plug trays, benches, seeding equipment, and plant house structures should be disinfected using a sodium hypochlorite solution or other disinfectant. Steam sterilization of flats and plug trays may also be useful. Transplant trays with infected plants should be removed immediately from production sites. Workers should disinfest their hands after contact with infected plants. Planting sites should be well drained and free of low-lying areas. The drainage area of the field should be kept free of weeds and volunteer crop plants, particularly those in the solanaceous and cucurbitaceous groups. If practical, and disease incidence is low and plants are dry, infected fruit and plants with roots should be rogued and destroyed to prevent the spread of spores (41,44). Alternatively, pulling all infected plants, and subsequent drying and burning rather than discing is recommended.

'Florida Market' and 'Florida Beauty' varieties are resistant to the "tip over" stage of seedling Phomopsis blight. However these strains are still susceptible to leaf and stem blight and fruit rot stages of this disease (45).

Biological Control

Gliocladium virens has recently been registered for soil-borne fungus control.

Nematode Management

Nematode Pests

Nematodes are small microscopic unsegmented worms that live in the soil and attack the roots of plants. Nematode problems in eggplant are similar to those in tomato and pepper, where root damage leads to reduced rooting volume and reduced water and nutrient uptake. Several different species of nematode attack eggplant. The root-knot nematode is prevalent in sand, muck and rock based soils, such as those found in many Florida counties. Stubby root nematode is found in sand and muck soils, and sting nematode is present in sandy soils (49). Since growers have used methyl bromide, nematodes have not been considered serious pests on eggplant (5).

Root-knot Nematode (Meloidogyne spp.). Root-knot nematodes enter the host plant as second stage juveniles and settle within the root to establish a feeding site. At the feeding site, secretions from the nematode cause the surrounding plant cells to enlarge and multiply, producing the characteristic galls associated with root-knot attack. The female develops within the root, living for as long as several months, and laying hundreds to several thousand eggs that are released into the soil. Low temperatures or dry soil conditions may slow the hatching of eggs (50,51). Root deformation results in symptoms that include stunting, wilting, chlorosis, and yield loss. Additionally, the gall tissue is more susceptible to secondary infections such as root rot (50).

Stubby-root Nematodes (Trichodorus spp.). Stubby-root nematodes feed externally on the root surface and remain in the soil throughout their life cycle. The primary effect on roots from the nematode's feeding is cessation of root growth at the root tip. Their feeding may also cause abnormal growth of lateral roots. In combination with the lack of root tip growth, the result can be a short, stubby root system with swollen root branches. Populations of this pest build up quickly in the presence of a suitable host and decrease quickly when a host is no longer available (52,53).

Sting Nematode (Belonolaimus spp.). These nematodes are also ectoparasites, like stubby-root nematodes, remaining outside the plant root and feeding superficially at or near the root tip by penetrating the root with a long stylet. Affected root tips turn yellow and later necrotic, with cavities forming and the root tip swelling slightly. Damage from feeding inhibits root elongation and causes roots to form tight mats and appear swollen, resulting in a stubby or coarse root appearance. Under severe infestations, new root growth is killed in a way that resembles fertilizer salt burn (50,52-54).

Chemical Control

Methyl bromide/chloropicrin fumigation has historically been used as the method of nematode control in eggplant production. Growers currently rely on this method to control nematodes and the use of methyl bromide as well as its alternatives have been discussed previously. No use of any nematicide has been reported for eggplant production in Florida. However, oxamyl (Vydate®), 1,3-dichloropropene (Telone®), and fenamiphos (Nemacur®) may be used for this crop (49).

Cultural Control

Crop rotations may be useful in managing nematode infestations. Eggplant yields can be improved following castor, sesame, or American jointvetch in comparison to yields following okra or fallow (55,56). However, some tropical rotation crops reduced only certain species of nematodes (57).

Weed Management

The most common weeds found in eggplant production in Florida are nightshade (Solanum spp.), eclipta (Eclipta alba), goosegrass (Eleusine indica), crabgrass (Digitaria spp.), bermudagrass (Cynodon dactylon), yellow nutsedge (Cyperus esculentus), pigweed (Amaranthus spp.) and morningglory (Ipomoea spp.) (9,58,59). Methyl bromide is the current weed control agent in raised bed production (8). However, with the loss of this material, weeds will be emerging through the plastic mulch and planting holes in the mulch (60). Non-selective herbicides are used to manage weeds such as eclipta and nightshade in row middles. However, selective herbicides must be used in the raised beds so that crop plants will not be injured. Selective pre-plant herbicides may be used prior to setting transplants and selective post-emergent herbicides are used for over-the-top weed control once the plants have been set.

Chemical Control

Reported herbicide application in 2000 was 500 pounds of active ingredient on 29 percent of Florida's eggplant acreage (all paraquat). During the last ten years, between 13 and 59 percent of Florida eggplant acreage has been treated with herbicides each year, with total annual usage ranging from 100 to 1,800 pounds of active ingredient (33-37).

Paraquat (Gramoxone®). This non-selective herbicide is used for total vegetation control and plant dessication. In 2000, Florida growers applied an average of 0.56 pounds of active ingredient per application to 29 percent of their eggplant acreage, an average of 1.8 times. At a cost of $12.07 per pound (39), a labeled application (0.47 lb ai/A) of paraquat would cost $5.67 per acre. The REI for paraquat is 48 hours.

Alternative Chemicals

Based on surveys and information obtained from extension personnel, other non-selective herbicides labeled for use include glyphosate (Roundup®), pelargonic acid (Scythe®), and diquat. Selective herbicides labeled for eggplant include trifluralin, napropamide (Devrinol®), sethoxydim (Poast®), clethodim (Select®), and bensulide (Prefar®).

Cultural Control

Methods of cultural control include using plastic mulches, planting grass in row middles, or planting cover crops during the off-season. Cover crops can be used to manage populations of undesirable plants. Mechanical weed control includes turning the weeds under by cultivation using a disk or plow to reduce weed infestation during the off-season or while the crop is growing

Key Contacts

• Michael Aerts is the assistant director of the Environmental and Pest Management Division of the Florida Fruit and Vegetable Association. He facilitates communication between commodity groups and regulatory agencies. Mr. Aerts can be reached at: FFVA, 4401 E. Colonial Drive, Box 140155, Orlando, FL 32814, (407) 894-1351, maerts@ffva.com.

• Mark Mossler is a pesticide information specialist for the Food Science and Human Nutrition Department s Pesticide Information Office at the University of Florida s Institute of Food and Agricultural Sciences. He is responsible for providing pesticide information to the public and governmental agencies. Mr. Mossler can be reached at UF/IFAS PIO, Box 110710, Gainesville, FL 32611, (352) 392-4721, mamossler@mail.ifas.ufl.edu.

Acknowledgements

The following individuals served as reviewers and/or provided information used in the eggplant profile:

• John Capinera, Professor and Chair, Department of Entomology and Nematology, Gainesville;

• Jeffrey Jones (Jeff), Professor, Deptartment of Plant Pathology, Gainesville;

• Kenneth Pernezny, Professor of Plant Pathology Department, University of Florida, Everglades Research and Education center, Belle Glade;

• David Schuster, Professor Dept of Entomology and Nematology, Gulft Coast Research and Education Center - Bradenton;

• Dakshina Seal (Dak), Assistant Scientist, Pest Management Tropical Research and Education Center - Homestead;

• Kenneth Shuler (Ken), Extension Agent IV, Vegetables, Palm Beach County-District V, West Palm Beach;

• William Stall (Bill), Professor and Assistant Chair, Deptartment of Weed Science Horticultural Sciences, Gainesville.

Support for Florida's Crop/Pest Management Profile project and this publication was provided by Pest Management Centers the USDA.

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The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other extension publications, contact your county Cooperative Extension service.

U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Millie Ferrer, Interim Dean.

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