There's no one surefire way to control weeds on every farm. Yet all farmers can follow a few basic tenets to help protect corn and soybean crops from yield-robbing weed pressure, according to Midwestern weed specialists.
Most weed control advice can be condensed into “know thy enemy, scout thy enemy, destroy thy enemy,” says Aaron Hager, University of Illinois Extension weed scientist. “There is no substitute for knowing what weeds you have, what size they are and which management practices work best to control them before yield loss occurs.”
Bob Hartzler, Iowa State University Extension weed management specialist, agrees that timely scouting is essential to preventing yield loss, particularly early in the season. An all-too-common mistake is to allow weeds to grow too large before attempting to control them, he says.
“Plan on controlling weeds early, in case things don't go as intended,” advises Hartzler. “Build in a safety net to account for possible delays.”
Early weed control is vital, but so are several other practices that could help manage weeds before they start to reduce yields. Here are 10 tips that Hager and Hartzler give on how to avoid yield loss from weed competition:
“Number one, know what weeds are the biggest problem in each field,” says Hartzler, “then target those weeds for control.”
Farmers should scout both before and after weed control efforts, advises Hager. “There's a long period between spray applications and harvest,” he explains. “Scouting after a weed control practice could help prevent many potential problems that might ultimately hurt yields.”
Farmers should be ready to modify their weed control system to account for problem weeds and fields. “Develop your management program based on scouting information,” advises Hartzler. “A total post program might be okay in a field with low weed pressure, but consider a pre-emergence herbicide followed by a postemergence application where you have moderate to high weed pressure.”
Farmers who rely on only one herbicide every year shouldn't expect it to remain effective indefinitely, says Hager. “Resistant biotypes are always a potential threat. If cultivation or some other non-chemical weed control tool fits into your program, use it.”
All the information you need to know about how to use herbicides is contained on product labels, says Hager. Many mistakes can be avoided by checking the label to determine proper tankmixes, rates, timing and restrictions. The label also provides information on safe handling procedures and the potential for crop injury, environmental problems and drift, he adds.
“Try to give the crop an even start with the weeds,” says Hartzler. “Conclude your final seedbed preparations as close to planting as possible. In no-till, use a burndown fairly close to planting or use an early preplant herbicide to suppress weeds.”
Your planter should be calibrated to provide uniform planting depth and even seed spacing, which ensure a uniform stand, says Hartzler. He adds that crops that develop a uniform canopy early will compete better with weeds, and proper planting depth will reduce the potential for crop injury with many pre-emergence herbicides.
“Soybeans can usually coexist with weeds without yield loss about four to five weeks, compared to three weeks or so for corn,” says Hager. “Farmers should strive to stop weeds before they reach 2-4 in. tall in corn and 4-6 in. tall in soybeans.”
Crop injury often results when fields are sprayed too soon after a light frost or cold, wet conditions, says Hager. He advises waiting for corn and soybean plants to recover from environmental stress before spraying. He also cautions that spraying when the crop is stressed by drought or summer heat can also lead to crop injury.
“If you are questioning whether it's too windy to spray, it probably is,” says Hager. “Be cautious when you decide to spray on windy days, and be cognizant of what's around. Also, follow good cleaning procedures between sprays.”
If you see a nonperformance issue, document it immediately and map the place where it occurred, advises Hager. He adds that keeping good records of weed problems in each field will pay off when deciding what changes to make next year. Also, if you see a new weed species or an odd-looking weed, find a reliable expert to help identify it.