Cabbage Integrated Pest Management : An Ecological Guide.

Weed Managementcompost or it may be plastic sheets. A thick layer of mulch(5 cm or more) controls 90% of weeds. The mulch preventssunlight from reaching the ground. Germination of weed seedis reduced because most weed need light for germination.Even when some seed germinates, young seedlings die whenthey do not get sufficient light. In addition, a layer of mulchhelps to retain the moisture in the soil during dry periods.When organic mulch is used, it gradually rots into the soilgiving off nutrients and helping to improve the soil structure.See also section 3.5.3.· Increase planting density to shade weeds: When the crop is sown or transplanted densely, thecanopy will close quickly. Shade will prevent many weeds from germinating. In a dense crop however,chances for disease infection are higher because the humidity inside the canopy can be high.Another problem is that if weeds germinate anyway, they will be difficult to control at tight spacing.· Compost manures to reduce weed seed: animal manures may still contains weed seed.· Using cover crops to smother weeds is another widely used cultural practice. Cover crops can eitherbe planted ahead of the vegetable crop, or they can be seeded at the same time the crop is plantedto form a living mulch under the crop as it develops. Grasses, or legumes such as soybeans grownin narrow rows quickly form a complete cover, outcompeting weeds. See section 3.5.3.2 on covercrops.· Relay cropping: this means sowing seeds for the next crop before the standing crop is harvested. InBangladesh for example, common relay crops are Aman rice and Khesari (pea grass). The Khesariseeds are broadcast a week before the Aman harvest. This does not provide enough time for weedsto grow.· Weeds, and especially annual weeds, should be prevented from producing seed. When this is doneat regularly, the “store” of weed seed populations in the soil will be reduced gradually every year thatthe field is cultivated. If pulled weeds have gone to seeds, do not use them as mulch because theseeds may be spread. Instead, put them on a compost pile away from the field. If the compost isprepared properly, weed seeds are killed during the heating process of composting. See section3.5.3.1 on compost.Botanical weed control….!?Grasses, such as sorghum-sudan grass, grown as cover crops to provide weed control, may alsohave another effect. For example, when sorghum-sudangrass decomposes in the soil, a chemical isreleased that suppresses weed germination. JSome vegetables may also be sensitive to these residues, however. L(Peet, www8).9.5 How to control weedsOnce there are weeds in the field, and weed control is considered economically justified, there are manyways to get rid of them. A number of options is listed below (Peet, www6; www8; www7; www9 andwww20).177 Cabbage Ecological Guide - 2000