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Weed Control With Tillage
Soybean is a poor competitor with weeds when cool soil temperatures cause slow germination and reduced early season growth, but are good competitors in warmer soils when seed germination and seedling growth are rapid. Control of early weeds is one of the most critical components of a profitable soybean production system. Weed control during the first 2 to 4 weeks of the growing season is essential to maximize yield. Good cultural practices such as through seedbed preparation, adequate soil fertility, choice of a well-adapted variety, use of good quality, high germination seed free of weed seeds all contribute to a soybean crop which will compete with weeds. Finish seedbed preparation immediately prior to planting the crop to kill germinating weeds.
A rotary hoe or harrow can be used in both wide row and narrow row soybean to control emerging weeds. These tillage tools can be used to control weed seedlings after planting but before soybean emerges or after emergence when soybean is in the 1 to 2 trifoliolate leaf stage. Avoid using the harrow or rotary hoe when soybean seedlings are just emerging (cracking stage). The rotary hoe is an effective and economical weed control method when the ground is not trashy, lumpy or wet and weeds are emerging (not more than 0.25 inch tall). If little or no precipitation has occurred to activate preemergence herbicides, a rotary hoe or harrow may eliminate early flushes of weed seedlings and partially activate the herbicide to control subsequent flushes of weeds. Cultivation is most effective when soybean is slightly wilted during the warm part of the day. Cultivated at this time, soybean is less susceptible to breakage and the disturbed weeds will die quickly.
Many herbicides are available for weed control in soybean. Most are currently labeled for tank mixing with other herbicides for broad spectrum weed control. A number of commercial herbicide mixtures also are available for use in soybean.
An economical chemical weed control program involves a number of strategies and steps. These include (1) Identify weed species present as seedlings, older plants or potential weeds based on previous weed infestation problems. (2) Evaluate soil type, texture and organic matter content of each field to help in determining rates of soil applied herbicides. (3) Inspect, adjust and calibrate all herbicide applicators or banding equipment to insure accurate herbicide application and even distribution. (4) Read and follow label carefully when using herbicides for weed control.
Soybean is susceptible to injury from 2,4-D, MCPA, dicamba (Banvel), or picloram (Tordon) therefore, non-labeled herbicide drift into soybean fields should be avoided. Refer to NDSU Ext. Circular W-253, "Agricultural Weed Control Guide," for current information on herbicide rates, mixtures and use. Always read and follow label directions when using pesticides.
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