Eggplant Integrated Pest Management AN ECOLOGICAL GUIDE

__________________________________________________________________________________Major Diseases of EggplantSymptoms may also appear on fruits. Infection of the fruit pedicels may cause a premature fruit drop. Onfruit, spots develop into brown to black leathery sunken area, often with dark concentric rings. Theconcentric rings contain the spores of the early blight fungus.Source and spreadThe fungus can survive in soil and in infested crop and weed residues. It may be seed-borne and carriedby wind, water, insects, workers and farm equipment. It can persist for at least one year, possibly severalyears without a host plant. The spores that land on eggplant will germinate and infect the leaves whenthey are wet. Spores can enter the leaf, stem or fruit. When infected seeds germinate, the fungus caninfect the seedling before or after emergence.Role of environmental factorsThe fungus is most active during mild to warm temperatures (24 to 28 o C) and wet weather. The diseaseis worse during the rainy season. Disease is severe on plants of poor vigor such as old transplants andtransplants that are wilted during a long period between pulling and planting. Early blight disease canalso be severe on plants stressed by a heavy fruit load, nematode attack, or low nitrogen fertility.Spores of this fungus are like plant seeds: they need water for germination. Spores of early blightgerminate on plant leaves. The spores penetrate the leaves through natural openings in the leaves ordirectly through the leaf skin when humidity is high and temperatures are between 10 and 25 o C.Generally, the higher the temperature, the quicker the infection can occur. The outside of the plant stilllooks normal but inside the leaf, the fungus starts growing and killing plant tissue. Under field conditions,leaf spots may become visible 2 or 3 days after the infection. The minimum time from first infection toproduction of new spores is about 5 to 7 days. This relative short disease cycle allows for numerouscycles when conditions are favorable.Importance - plant compensation - physiological impactThere is a loss of young plants in seedbed, plus the danger of spreading disease on transplants. Leafinfection may result in defoliation starting at the base of the plant. Early blight can lead to completedefoliation during humid weather at temperatures near 24 o C. This weakens the plant and may reduce theyield. In addition, losses may occur as a result of fruit infection.Natural enemies/antagonistsIn USA, the biocontrol agent Bacillus subtilis, sold as “Serenade” is available for control of severalpathogens including early and late blight of vegetables. It can be applied as a spray. Biocontrol productscan be found in “The BioPesticide Manual” (Copping, editor) or at several sites on the internet, forexample, www14 and www15 (see reference list in chapter 11).Management and control practicesThe best way to manage the disease is on a preventive basis. Once early blight is established in thecrop, it is very difficult to control. Inspect the crop twice a week for plants with disease symptoms.Prevention activities:• Planting season: In areas with high early blight incidence it may be advisable to plant eggplant orother solanaceous crops in the dry season when the incidence of early blight (and other leafdiseases) is lower.• Plot location: It is better not to have multiple plantings in the same area because old crops will serveas inoculum of early blight for the new plantings. Select plots surrounded by e.g. grasslands becausethey are not a host of this disease.• Resistant and tolerant varieties against early blight may be available. It would be advisable to testsome varieties to check the resistance against early blight (and other diseases and insect pests)under local conditions.• Use of disease-free seed and plant material. Presence of initial disease spores attached to seed, soilor transplants should be reduced or avoided. When transplants have leafspots or other signs ofinfection, they should not be transplanted to the field. Seed should be used only from disease-freeplants. Hot-water or chemical treatment of seed is of limited value.• Nursery beds should be distant from old plantings. It is important to use new deep soil that has gooddrainage properties for the nursery. Sterilize the soil (see section 3.10.1) to reduce soil-bornepathogens. Inspect seedlings for any sign of disease and discard and destroy any that are suspectedof infection.141Eggplant Ecological Guide