Eggplant Integrated Pest Management AN ECOLOGICAL GUIDE

________________________________________________________________________________________Weed managementThe SeedbankTo check if there is weed seed in your soil, this exercise is a useful one. Take a portion of soilfrom the field (about half a bag full) and bring it to the ‘classroom’ or any other place near thehouse. Put the soil on a piece of plastic. Water it and leave it for several days. Keep the soil moistbut do not make mud out of it! Seed of weed will germinate in the next days and you can checkhow many weeds come up and which species they are.soilpiece of plastic9.3 Control or management?Similar to disease and insect management, weeds also must be managed. Weed management means arange of activities that support each other. Some of these activities should be done during crop growth,some even before sowing the seeds. Weed management, just like insect and disease management, is along-term activity, sometimes it needs planning for several years. Control is a short-term activity, focusedon killing or removing weeds from the field.A good weed management program is one that will control existing weeds economically and prevent abuildup of weed seed or tubers, rhizomes, etc. in the soil. Integrated weed management, like insect anddisease IPM, focuses on prevention, beginning with identification of weed species. Such a programincludes integrated use of several crop management practices which may include any of preventionpractices listed in section 9.4 below.Is 100% control of all weeds necessary?The ultimate goal of growing vegetables is to maximize profits in a sustainable way. While it is true thatcrops are able to tolerate a certain number of weeds without suffering a yield reduction, it is firstimportant to consider weed problems on an individual basis. There are some weeds for which 100%control may be desirable because they are particularly competitive, persistent, or difficult to control.Identification of weed species is therefore a first step in weed management.Weed management should also be related to growth stage. It may be necessary to go for 100% weedcontrol in the first few weeks after transplanting but when plants are fully grown, some weeds may betolerated. Such weed-free period is called the critical weed-free period, a concept explained in the boxbelow (modified from Peet, www1).Critical weed-free periodThe critical weed-free period is the minimum length of time during which the crop should bepractically weed-free to avoid a yield or quality reduction. The critical weed-free period varies withcrop, weed species and environment. The critical weed-free period concept is based on the followingobservations: At the time of field preparation and planting, the field is virtually free of weeds. Soonafter, however, weed seeds brought to the surface by field preparation start to germinate.At some point, crop seedlings and weeds are large enough to compete for light, water and nutrients.Weeds usually win this competition, marking the beginning of the critical weed-free period. Youngseedlings that have to compete with weeds for nutrients and light may form weaker plants. Weakerplants are more susceptible to pests and diseases and may eventually give lower yields. Economiclosses will occur if weeds are not controlled. The end of the critical weed-free period is generallyseveral weeks later when the crop is large enough to shade late-emerging weed seedlings or isotherwise competitive with weeds (Peet, www1).158Eggplant Ecological Guide