Eggplant Integrated Pest Management AN ECOLOGICAL GUIDE

___________________________________________________________________________________Major Agronomic PracticesPreventing soil-borne diseases: some techniques.Preventing soil-borne diseases is not a single action, there are several factors involved. Some of themain activities include:1. Crop rotation (see section 3.17).2. Use of clean seed (see section 3.6).3. Use of disease-free planting material.4. Sanitation practices such as:• removing left-overs from previous crop,• removing weeds,• cleaning field tools.5. Increasing soil organic matter content (increasing organic matter of soil can increasemicrobial activity, which can lower population densities of soil-borne pathogens (seesection 3.8.3).6. Proper water management: mainly providing drainage to keep soil around roots frombecoming waterlogged (see section 3.14).7. Application of antagonistic fungi such as Trichoderma sp. into the soil. See section 7.10.Related exercises from CABI Bioscience/FAO Vegetable IPM Exercise Manual:3.7. Demonstration of spread of pathogens3.11. Simulating pathogen spread3.7.4 Soil sterilizationOnce the soil is infected with a pathogen, there are few options for control/management. The best is toreduce the pathogen population with structural methods like crop rotation or the use of resistant varieties.For some crops, such as tomato and eggplant, it is possible to graft a variety to a resistant rootstock.For smaller field sizes, such as nurseries, it is possible to use certain methods to sterilize soil. Suchmethods include solarization or burning (plant)materials on the soil. These and other methods aredescribed in section 3.10 on nursery management.It is dangerous to use (non-specific) chemicals for soil sterilization. Such chemicals are not alwayseffective because pathogens may live deep in the soil, or are protected inside plant left-overs, wherechemicals do not reach. In addition, residues of pesticides in the soil may cause damage to the next cropand residues may leach into (ground)water causing death of fish, problems with drinking water, andcause damage to micro-organisms in the soil and the aquatic biosystems in general.New methods, such as biofumigation, for “sterilization” (actually control of soil-borne pathogens) of largerfield sizes are being studied. Biofumigation refers to the release of certain components (so called“biocides”) by plants that can control soil-borne pests and pathogens. For example, excellentsuppression of bacterial wilt (a soil-borne disease attacking solanaceous crops like eggplant and tomato)by mustard green manures was obtained in field studies. See section 3.10.1.4 for details onbiofumigation and other options for biological soil sterilization.3.7.5 Soil pHAn important factor in soil is whether it is acid or alkaline. This is given in the form of a pH value. ThesepH values range from 1 to 14. If the pH is less than 7 it means that the soil is acid, and if it is greater than7, the soil is alkaline. Soil with a pH of around 7 is considered to be neutral.Soil pH affects the ability of the soil to release nutrients. If the pH level is too high or two low, nutrientscan get “locked up” in the soil chemistry and become unavailable to plants. A pH range of approximately6 to 7 promotes the most ready availability of plant nutrients.The soil pH can also influence plant growth by its effect on activity of beneficial micro-organisms.Bacteria that decompose soil organic matter are hindered in strong acid soils. This prevents organicmatter from breaking down, resulting in an accumulation of organic matter and the ‘lock up’ of nutrients,particularly nitrogen, that are held in the organic matter.Humus (that comes from the breakdown of organic matter such as compost) has an important function inregulating soil pH. Humus itself is neutral and can absorb acid and alkali shocks from outside.17Eggplant Ecological Guide