Eggplant Integrated Pest Management AN ECOLOGICAL GUIDE

________________________________________________________________________________________Weed management• The continued use of the same herbicide may lead to tolerance or resistance of weeds against thatherbicide. This means such a herbicide does not control those weeds anymore. This results in abuildup of weeds, particularly perennials, which are difficult to control with herbicides. The best wayof preventing the buildup of weeds tolerant to herbicides is to regularly remove them by hand and touse several brands of herbicides after each other (do not mix them!).• Generally, the best time to apply soil herbicides is when soil is moist. Do not apply herbicides on drysoil (particularly the systemic herbicides) because they may become inactive before they can kill theweeds. Not all herbicides should be applied on soil - some are to be applied on the weeds directly.Check labels before applying.Mixing pesticides: herbicides and insecticidesMixing herbicides with insecticides are of special concern because they oftenresult in injury to crop plants. Crop injury results because of chemical reactionsbetween the insecticide and the herbicide and the effects of those chemicalson the crop. Symptoms of this injury can include stunting and yellowing.The severity of injury dependents on environmental conditions, the insecticideused, and the method of insecticide application. It seems that rain during or prior to the applicationof a mixture may increase the severity of injury.• When applying herbicides, it is recommended to spray infected spots only, not the whole field. Thiswill save on amount of pesticide and may save part of the beneficial population.Dependence upon herbicides alone seldom provides the most economical weed control.9.5.3 Biological controlWeeds, just like insects and pathogens, have natural enemies! These include insects, fungi andnematodes. Just like an eggplant can be attacked by an insect, a weed plant can also be attacked.Weeds are normal plants, but they are “weeds” because they grow where we do not want them.There is a lot of research being done on biological control agents for weeds. For example, there are fungithat live on certain weeds and can kill them in a short time. Applying a water solution containing sporesof those fungi may be a valuable alternative to chemical herbicides. For example, the fungusColletotrichum gloeosporioide has been effective in controlling northern jointvetch, a plant pest in riceand soybean crops in the USA. Unfortunately, these fungi are often specific to a particular weed speciesand unlikely to control all the major weeds present.Insects can control weeds by feeding on seeds, flowers, leaves, stems, roots, orcombinations of these, or by transmitting plant pathogens, which will infect plants.Other natural enemies of weeds include nematodes, and fish (for those weeds growingin canals, fish ponds, etc.).Although there are very interesting trial data on control of weeds with natural enemies,practical field application under various conditions is still a problem. North Americanintroductions of weed-feeding natural enemies for example, have ranged from very successful, with a99% reduction of the pest species, to complete failures, with the introduced species unable to becomeestablished in the new location. Weed-controlling fungi need a certain amount of humidity and may notwork during the dry season.Therefore, to date, only very few biological weed control agents are commercially available but this maychange in the near future (ref. www5).Related exercises from CABI Bioscience/FAO Vegetable IPM Exercise Manual:2-C.7. Mulching of plant beds: organic and inorganic mulches162Eggplant Ecological Guide