PUTNAM COUNTY — Fall is nearly upon us and harvest is around the corner. Now is a good time for farmers to evaluate the effectiveness of their weed control programs. While the corn and soybean fields are rapidly maturing, weeds above the crop canopies and are a good indicator of future problems.

Farmers that consistently use effective weed control programs year after year have the least amount of weed problems. Some weed species can produce 100,000-500,000 seeds per plant, so even one year of poor control can result in serious weed issues in years ahead.

When weeds are present at harvest time, farmers need to ask several key questions. Did I use the wrong herbicide or management program? Did unusual weather interfere with the success of the program? Have these weeds become resistant to the herbicides used?

Some of the most troublesome weeds to control in agronomic crops such as marestail and giant ragweed can be found in soybean fields throughout our area. This is a result of several factors including complex biology, weed resistance to commonly used herbicides like glyphosate, the ability of weed seeds to germinate throughout the growing season, and a lack of soil applied pre-emergent herbicides that provide residual control after planting.

Also on the radar for local soybean growers is waterhemp, a new weed in our area that is similar to pigweed but lacks hairs on the stem. Waterhemp has created major problems in many soybean fields across the county because plants are commonly resistant to herbicides used in weed control programs.

Farmers needing to control marestail, giant ragweed, and waterhemp are encouraged to use a burndown program with a mix of herbicides with different modes of action, a pre-emergent herbicide with soil residual activity, followed by removing any waterhemp plants that are not killed by this program. Following a zero tolerance for waterhemp will pay off significantly in the future. Go to the following website for identification and more information on waterhemp: https://www.extension.purdue.edu/ extmedia/bp/gwc-13.pdf.

Farmers will continue to battle weeds in their fields. Waterhemp is a new concern and may require farmers to change their weed management program. Farmers have the best chance to battle these troublesome weeds when they grow corn since they have a wider variety of products that are effective, especially against broadleaf weeds.

For additional information visit the OSU Weed Management site at http://u.osu.edu/ osuweeds/ , or contact the Putnam County Extension office at 419-523-6294, by email at Scheckelhoff.11@osu.edu or stop in at 1206 East Second Street in Ottawa. You can also find us on Facebook by searching for OSU Extension Putnam County.