Eggplant Integrated Pest Management AN ECOLOGICAL GUIDE

___________________________________________________________________________________Major Agronomic PracticesA compost pile can be of any size as long as it is easy to handle: it will shrink considerably whiledecomposing. A common recommendation is a pile measuring at least 1 meter in each direction (high,wide and long). A smaller pile will not generate or retain enough heat to effectively kill any harmfulpathogens present.It takes about 3 to 4 months for decomposition to be complete, depending on the climate (the warmer,the quicker) and the contents of the pile (the softer and finer the pieces of the material, the quicker).Compost is ready to use when the pile no longer heats when turned, and the material looks dark andcrumbly.Compost should be sufficiently mature before it is applied. If the original hard parts are still there, thecompost is not mature. The breakdown of immature compost and directly incorporated materials will usenutrients in the soil, which no longer become available for the crop. In addition, immature compost maystill contain pathogens and weed seed. By adding immature compost to the field, you may actually adddiseases and weeds….! (refs: www17; www18; www19)Disease control with compostAn additional benefit of using compost is that it can reduce disease problems for plants. This is beingstudied for several years now because it offers an opportunity to further reduce fungicide use.Pathologists describe two different types of disease suppression in compost and soil.1. General suppression is due to many different micro-organisms in the compost that either competewith pathogens for nutrients and/or produce certain substances (called antibiotics) that reduce pathogensurvival and growth. Thus an active population of micro-organisms in the soil or compost outcompetespathogens and will often prevent disease.This type of suppression is effective on those pathogens that have small propagule (e.g. spores) size.Small spores do not contain many nutrients so for germination they need an external energy (carbon)source. Examples of this mechanism are suppression of damping-off and root rot diseases caused byPythium species and Phytophthora species.2. Specific suppression, on the other hand, is usually explained by one or a few organisms. They exerthyperparasitism on the pathogen or induce systemic resistance in the plant to specific pathogens, muchlike a vaccination. With specific suppression, the causal agent can be clearly transferred from one soil toanother. Pathogens such as Rhizoctonia solani and Sclerotium rolfsii are examples where specificsuppression may work but general suppression does not work. This is because these organisms havelarge propagules (e.g. spores) that are less reliant on external energy and nutrients and thus lesssusceptible to microbial competition. Specific hyperparasites such as the fungi Trichoderma andGliocladium species will colonize the propagules and reduce disease potential (ref. www20).Other biocontrol agents (or antagonists, also see section 7.10) that colonize composts include bacterialike Bacillus, Enterobacter, Flavobacterium balusstinum, and Pseudomonas; actinomycetes likeStreptomyces. These antagonists may appear naturally in compost. In some cases, antagonistic fungi orbacteria are added to the compost just after the hot phase, when the compost is cooling down. There arenot many micro-organisms present inside the compost at that moment. When antagonists are added atthat time, they can quickly build up their populations and this will result in compost with good diseasesuppressing quality. See box below.Compost quality plays a role in the degree of disease suppression and the length of suppressive activity.Some general observations:• Composts that are allowed to mature are more suppressive than piles used straight after the hotphase.• Compost piles that are in the open (so exposed to naturally occurring micro-organisms), andespecially those located near trees, are more suppressive than compost piles sheltered by a roof.25Eggplant Ecological Guide