Weed identification is the key to an effective corn weed management program. Incorrect identification of problem weeds can mean the difference between profit and loss. Although a weed’s life cycle, including its method(s) of reproduction, is the most important identifying characteristic, it is sometimes necessary to know the exact species before selecting weed management measures.
Corn growers should make a weed inventory to aid in the selection of weed control programs. By tailoring control programs to fit the problems in each field, growers can minimize weed control costs while maximizing yields and profits. An inventory can be made by scouting fields two or three times during the year and recording the types (such as broadleaf annuals or annual grasses) of weeds present in each field.
The first observation should be made by the time corn is 3 or 4 inches tall. These early-season observations reveal how effective preplant or preemergence herbicides, if used, have been and suggest the possible need for cultivation or for postemergence herbicide applications. A second look at the fields in midsummer (before the corn is waist high) can provide information on the overall effectiveness of weed control practices and provide clues on how the program might be adjusted in future years. This also is a good time to record the types and numbers of weeds present and to map the location of special problem areas in the field. Additional notes on weed types and numbers can be taken at harvest to complete the weed inventory.