Weed Control in Field Crops

Clean, seed, proper seedbed preparation, good rotations, and sound soil management practices are prime requisites for controlling weeds in crops. They will eliminate many annual weeds and prevent infestation by most perennial weeds. Chemicals are valuable supplements to these practices. However, if we rely on 2,4-D or other chemicals, we at least partially neglect the standard practices. Consequently, weeds resistant to chemicals are allowed to spread. Once weeds become established, special practices are needed to eliminate them. These practices include the use of special cultivation, competitive crops, and chemicals in addition to the old reliable practices already mentioned. One application of any one method seldom eliminates all perennial weeds. Even though they are eliminated, new weeds come from seeds in the soil. Some of these seeds remain viable for as long as 20 years and many years of diligent work are required to eradicate them. Numerous tillage and chemical methods that will control weeds in crops are available. In fact, it is possible to eliminate some of the most persistent perennial noxious weeds while growing crops if the proper combination of crops, cultivation, and chemicals is used. For detailed information on the control or elimination of any of South Dakota\u27s noxious weeds, refer to the circular that discusses the specific weed. If chemicals are to be used in the weed program, it is important to remember that chemicals cause more damage to crops when applied at certain stages than at others. This is particularly true when rates of application required to control perennial weeds are used. If the most tolerant stage of the crop does not occur when the weeds are in the most susceptible stage of growth, there are two choices-risk injuring the crop to get good weed control or get poor weed control with less chance of injuring the crop. Good weed control usually pays off in the long run. The maximum rate of chemical application that can be used on crops without much risk of reducing the yield is discussed on the following pages. Many annual weeds are killed with lower rates; consequently, the rate of application will frequently be lower than the maximums mentioned. On the other hand, many perennials will require higher rates than the safe rates mentioned. As a result one may have to use a more tolerant crop or risk injuring the crop if he wishes to eliminate the weed