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50 Ways Farmers Can Protect Their Groundwater
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15. Know the Economic Thresholds for Weeds


Scouting for weeds keeps you on top of shifting weed pressures and makes it easier to spot-treat for weed problems. The result may be less chemical use, less risk to groundwater, and less risk that weeds will develop resistance to certain herbicides.

Scout weeds early—10 to 12 days after planting. This improves the chances of control and timely application of herbicides. Then scout periodically for four to six weeks, sampling enough areas to get an accurate count of the different weeds present throughout the field.

cucumber bur Identify and record the location of all weed species found. If a weed cannot be identified, send samples to a local or state laboratory. Record the approximate height and growth stage of both the weeds and the crop. In all sample areas, calculate the severity of the problem by counting the number of weeds per 10 feet of row for large infestations or every 100 feet of row for smaller infestations.
Draw a weed map Draw a weed map for each field early in the season. This map will be useful for monitoring changes in weed infestations from year to year. Along with weed condition reports, early soil moisture observations are important. Adequate moisture is necessary for effective weed control with most soil-applied herbicides.
ragweed After you assess a weed problem through scouting, consider the economic threshold, which compares the cost of weed control with the expected yield loss due to weeds. Economic thresholds for weeds may be most useful after some form of primary weed control has been done. Growers could then decide if additional weed management practices are economically justified.

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