A quick start to planting in many parts of the United States and Canada this spring will likely increase the need for a quick start to weed control, according to Greg Dahl, Weed Science Society of America president (pictured above.)
“When conditions are in place for early spring field work and planting, the conditions are also in place for early weed growth,” Dahl said. “Prioritizing weed control efforts early, ahead of the weeds, helps the crop start better and makes time management easier to achieve the desired result.”
Early weed control helps boost efficiency and sustainability by requiring fewer resources to manage weeds. “Weeds are nearly always easier to control when they are smaller,” Dahl said. “Within weed-crop competition, mostly the first plant out of the ground wins, and the weeds that emerge before the crop emerges greatly reduce crop yields and could also reduce crop quality.”
If timed right, pre-emergent herbicides help to control weeds before they emerge. Post-emergence herbicide applications help to control weeds after they emerge, particularly if weeds are still small.
“When weeds get larger, you may need to conduct a two-pass herbicide control program that controls initial growing points with the first application, and subsequent growing points with the second application,” Dahl said. “However, if you get behind, it is hard to play catch up, and you may not get the results you want.”
Large weeds difficult
Larger weeds often are more tolerant to later herbicide applications and can survive, compete with the crop, and produce seeds, he adds. Along with early weed management, multiple control methods help ensure success and reduce the risk that herbicide resistance could develop.
“Weeds that are adapted to various climates and regions can be very competitive and difficult to control with herbicides alone,” Dahl said. “Weeds that are highly competitive include kochia, wild mustard, Palmer amaranth, waterhemp, cocklebur, and wild —just to name a few. With the occurrence of weed resistance to glyphosate and other herbicides, it is critical that weed control begins early and needs to be followed with additional treatments as necessary.”
Nonchemical tactics implemented early in the growing season are also important for attaining maximum herbicide effectiveness. “Any agronomic practice that gives the crop an advantage will take pressure off herbicide performance,” says Sarah Lancaster, Ph.D., Kansas State University assistant professor and Extension specialist. “Simple strategies include planting crops in appropriate soil conditions and at ideal seeding rates.”
Growers might consider establishing cover crops later in 2024 for the 2025 crop.
“Cover crops are another practice that suppresses weeds, resulting in a less dense and slower growing population of troublesome weeds, like waterhemp, Palmer amaranth, and kochia,” Lancaster said. “But, the time for planting cover crops that will benefit a summer cash crop has passed for 2024 in most U.S. regions.”
Another important herbicide-resistance management tool that is most feasible for almost anyone to implement is to apply multiple effective herbicides with postemergence and residual activity. Look to state Extension personnel or other trusted advisors to recommend herbicide combinations that will be most effective for the weeds in your field.
