Cultural Weed Management
Crop rotation should be an integral component of a weed management program. Crop rotation allows the use of different types of herbicides on the same field in different years. This can prevent the buildup of problem weeds and help to keep the overall weed population at lower levels. More important, crop rotation and proper selection and rotation of herbicides are key components in a strategy to avoid evolution of weed resistance to herbicides. Some soybean herbicides may persist long enough to damage certain rotational crops. Before using any herbicide, check the rotational restrictions.
Crop competition is an effective but often underused weed control tool. The basic strategy is to follow practices that result in rapid soybean growth and canopy closure so as to provide maximum shading of weeds. Soybeans should lap in the row middles as soon as possible and certainly before blooming begins. Planting in narrow rows is the most effective means of achieving rapid canopy closure. Other practices that enhance crop competition with weeds include good seedbed preparation, use of high-quality seed, proper variety selection, early-season disease and nematode management, proper fertilization and liming, and early planting.
Soybeans obviously can be grown without cultivation. Cultivation, however, is an effective and economical way to supplement control achieved with herbicides. Applying herbicides in a band over the row and cultivating the row middles can substantially reduce weed control costs. In fields with a light weed infestation, cultivation alone may be sufficient. Cultivation should be shallow (1 to 2 inches) to avoid damaging crop roots and to avoid breaking through any residual herbicide layer and bringing up untreated soil and weed seed. To be effective, shallow cultivation must be done while the weeds are small. Weed control is the only benefit received from cultivation except where special soil problems such as crusting or poor drainage exist.