Eggplant Integrated Pest Management AN ECOLOGICAL GUIDE

__________________________________________________________________________________Major Diseases of Eggplanthard black, irregularly shaped bodies called sclerotia form on the surface or in the pith of the stem; theyare diagnostic for the disease.Sclerotia are the resting structures of the fungus. They are actually a very dense mass of hyphae (fungus“threads”). The fungus can survive adverse conditions through sclerotia. Sclerotia range from 2 to 10 mmin length and tend to be about 2 to 3 times longer than thick. They are white to pinkish inside. After theinfection has apparently dried up, the line of demarcation between healthy and diseased tissue is verysharp. Often the diseased tissue is a light, straw color.Source and spreadThe fungus survives as sclerotia in the soil and may survive up to 7 years in dry soil. However, if the soilis maintained warm and moist, tiny spore carrying structures (called apothecia) start to grow on thesclerotia. These produce enormous numbers of spores that are blown about and cause infections. Oncethe fungus is established it continues vegetative growth as long as there is sufficient moisture.Sclerotia may be carried with seed or transmitted with soil (e.g. attached to transplants) from field to field.Role of environmental factorsThis disease is dependent on high moisture and cool temperatures. That is why this disease is morecommon in higher altitude areas of the tropics. It is infectious over a wide temperature range (10 - 30 o C),but requires high moisture to germinate and infect.Importance - plant compensation - physiological impactPlants of all growth stages are susceptible. The disease is important because a number of fruit bearingplants may be killed and the fungus can survive several years in the soil. Seldomly, all plants in a fieldare affected.Natural enemies/antagonists• Trichoderma virens (formerly Gliocladium virens) is a beneficial fungus that can reduce Sclerotiniastem rot. Trichoderma is naturally present in soils all over the world. It is available for field applicationin some countries such as Thailand and USA. More details on Trichoderma in section 7.10.1.• The biocontrol organism Coniothyrium minitans is commercially available in the USA for control ofSclerotinia sclerotiorum and S. minor.• Another biocontrol agent is Bacillus subtilis, available in Thailand for control of several soil-bornepathogens including Rhizoctonia solani, Fusarium sp., Alternaria sp., Sclerotinia, Verticillium,Streptomyces scabies. It can be applied as a suspension for seed treatment, soil drench, dip, andaddition to nutrient solutions.More information on commercially available biocontrol products can be found in “The BioPesticideManual” and on several internet sites such as www14 and www15 (see reference list in chapter 11).Management and control practicesThe control of this disease, as with many soil-borne diseases, requires a continuous good managementprogram all year:• Rotation with non-susceptible crops (beets, onion, spinach, peanuts, corn, and grasses) have beenreported to lower disease incidence.• Flooding of the field for 23 to 45 days (which can be done in areas where vegetables are grown inrotation with paddy rice) lowers disease incidence.• Deep plowing will bury the sclerotia. Without light they cannot germinate and cause infection.• Sanitation: All infected plant parts should be removed and destroyed from the field as they appear onplants. At the end of the season, plants and plant left-overs should be removed and destroyedpromptly. The soil should be kept free from weeds as these might harbor the fungus. Immature oruncomposted livestock manure and plant mulches should not be used because this may still containliving fungus.• Soil disinfection: Solarization of the soil is a good option to reduce disease incidence (see section3.10.1.2). This may even be a good practice if stem rot is not a problem since other diseases andpests are also controlled.• Moisture control: Removing lower leaves from the plants will help to keep the plant dry and this mayprevent infection through the leaf tips that touch the ground. For the same, planting at a wide plantspacing, and low plant density help reduce disease development. Furrow rather than overheadirrigation also helps to keep plants dryer.153Eggplant Ecological Guide