Eggplant Integrated Pest Management AN ECOLOGICAL GUIDE

__________________________________________________________________________________Major Diseases of Eggplantspread throughout the plant. As they move, they damage the plant tissue which becomes filled with slimymasses of bacteria. The plant vessels are blocked and this results in the wilting of the plant. If moisture ispresent on leaves, the bacteria can enter aboveground but infection is more likely when inoculum ispresent just below the soil surface.When diseased plant parts decay, bacteria are released in great numbers into the soil where they aredisseminated in water.Diagnostic method for bacterial wiltTo distinguish bacterial wilt from other wilts, select a recently infectedplant that is not yet completely dry and dead. Take a stem cutting at soil level uptill a few cm above the soil level and place it in a glass of water abovethe glass bottom. Support the stem piece with toothpicks so that itdoesn’t slide away. If bacterial wilt is present, a milky stream flows fromthe lower cut surface of the sliver within a few minutes. This milky streamis called ooze and contains many thousands of bacteria.See photo 20, page 177.Glass jar with tomato stem piece.Milky bacterial threads flow from stem.Role of environmental factorsWet and warm soil is good for this bacterium. The wilt bacterium is sensitive to high soil pH, low soiltemperature, low soil moisture and low fertility levels. Although the bacteria are able to reproduce andcause infection over a wide temperature range, the most favorable temperature is 29 to 35 o C.Importance - plant compensationBacterial wilt is a very serious disease that can cause dying of plants in large parts of a field. Oncepresent in the field, it is very difficult to control. Usually, plants will die quickly and no compensationoccurs.Natural enemies/antagonists• The antagonist Trichoderma species may be tried, preferably in combination with compost (seesection 3.8.3.1).• In USA, a non-pathogenic strain of Pseudomonas solanacearum is available as biocontrol agent.(ref. www15)• Several other antagonistic micro-organisms have been studied against bacterial wilt, such as Bacillussp. (Silveira, 1995) and Streptomyces sp. (El-Raheem, 1995). Most of these studies were done inlaboratories so results are not yet applicable to field situations.Management and control practicesPrevention activities:• Resistant eggplant varieties have been reported. For example Arka Kesev and Arka Neelkanth fromIndia. See table in section 3.2.2. However, there are different strains of the bacterium so eggplantvarieties may give differences in actual tolerance. Set up a varietal trial to experiment.• Hot water treatment of seeds at 50 o C for 25 minutes effectively reduces the bacteria that stick toseeds. See section 3.6.1.• Eradication of weeds help reduce the bacterial wilt population.• Use healthy seedlings grown in wilt-free soil.147Eggplant Ecological Guide