Cabbage Integrated Pest Management : An Ecological Guide.

Weed Management9.1 Weeds: good or bad?LWeeds in a cabbage field are usually unwanted because they compete with cabbage plants forwater, nutrients, and sunlight. They may harbor insect pests and diseases or form breeding places forpest insects. In addition, the presence of weeds decreases air circulation between the plants, increasingthe humidity inside the crop. This can lead to more diseases, because many (fungal) diseases needhumidity to infect a plant. Weeds may also directly reduce profits by hindering harvest operations,lowering crop quality, and produce seed or rootstocks which infest the field and affect future crops.Weeds are normal plants, but they are “weeds” because they grow where wedo not want them.J But there can be some good points of weeds too: many weeds makegood compost, several are edible for human use or when fed to farmanimals. Weeds have consumed nutrients from the soil and these can bereturned to the soil by using weeds as mulch or as “green manure” (seesection 3.5.3.2).There are also weeds that have a medicinal use. Under certaincircumstances, weeds may have a beneficial effect in preventing soilerosion. And, very important, some flowering weeds can be food sourcesfor adult parasitoid wasps that feed on the nectar inside the flowers, andprovide shelter places for predators and other beneficial insects.Weeds can be indicators of soil fertility. Chan (Imperata cylindrica) forexample is a very common weed in Bangladesh, growing only where soilis very infertile. This gives valuable information on the status of the soil.Imperata cylindrica9.2 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 die within one year. In some casesannual weeds have several generations per year. Most areproducing a lot of seed. The seed can remain viable for manyyears in the cool depths of the soil, ready to germinate whenexposed by cultivation to light and moisture.2. Perennial weeds: those weeds that remain in the soil from oneyear to the next. They often require more than 1 year to completetheir life cycle. Typical perennial weeds have deep roots or creepingrunners which spread vigorously, or roots which can resprout fromsmall fragments left in the soil.perennial weedCabbage Ecological Guide - 2000174