Eggplant Integrated Pest Management AN ECOLOGICAL GUIDE

________________________________________________________________________________________Weed management9.1 Weeds: good or bad?Weeds are normal plants,but they are “weeds” because they grow where we do not want them.Weeds in an eggplant field are usually unwanted because they compete with eggplants for water,nutrients, and sunlight. They may harbor insect pests and diseases or form breeding places for pestinsects. In addition, the presence of weeds decreases air circulation between the plants, increasing thehumidity inside the crop. This can lead to more diseases, because many (fungal) diseases need humidityto infect a plant. Weeds may also directly reduce profits by hindering harvest operations, lowering cropquality, and produce seed or rootstocks which infest the field and affect future crops. But there can be some good points of weeds too: many weeds make good compost, several areedible for human use or when fed to farm animals. Weeds have consumed nutrients from the soil andthese can be returned to the soil by using weeds as mulch or as “green manure” (see section 3.8.3.2).There are also weeds that have a medicinal use. Under certain circumstances, weedsmay have a beneficial effect in preventing soil erosion. Weeds can provide shelterplaces for predators and other beneficial insects. In addition, some flowering weedscan be food sources for adult parasitoid wasps that feed on the nectar inside theflowers.Weeds can be indicators of soil fertility. Chan (Imperata cylindrica) for example is acommon weed in Bangladesh, growing only where soil is very infertile. This givesvaluable information on the status of the soil.Chan9.2 Types of weedWeeds can be classified in several ways. The most commonly used classifications are:Annual or Perennial1. Annual weeds: these are the most common weeds that germinate, flower, produce seed and diewithin one year. In some cases annual weeds have several generations peryear. Most are producing a lot of seed. The seed can remain viable for manyyears in the cool depths of the soil, ready to germinate when exposed bycultivation to light and moisture.2. Perennial weeds: those weeds that remain in the soil from one year to thenext. They often require more than 1 year to complete their life cycle. Typicalperennial weeds have deep roots or creeping runners which spreadvigorously, or roots which can resprout from small fragments left in the soil.perennial weedBroadleaf weeds or grasses1. Broadleaf weeds: germinating seedlings have two leaves. The leaves areusually wider than those of grasses. Broadleaf weeds are basically allweeds except grasses, sedges and bamboo.2. Grasses: seedlings have only one leaf. Next to grasses, other commonweeds in this group are sedges and bamboo.broadleaf weed157Eggplant Ecological Guide