By Scout Nelson
Most winter wheat has already been harvested in South Dakota, and spring wheat harvest is moving forward. Even though the wheat season is finished, post-harvest weed management remains important to ensure fewer problems next spring. Weeds that continue to grow after harvest will produce seeds, which create challenges for future crops.
Shortly after harvest, most weeds are summer annuals, but winter annual and perennial weeds may also be present. Summer and winter annual weeds can be treated with herbicides soon after harvest, ideally when they are about 2 to 4 inches tall. Taking care of them at this stage makes control more effective.
Perennial weeds, such as Canada thistle, need a different approach. These weeds should be treated later in the fall, after a light frost. This is because frost triggers perennial plants to move food and energy into their roots to survive winter.
Herbicides applied at this time also move down to the roots, helping kill the underground growth. Farmers should wait 24 to 48 hours after a frost to check plant health before spraying. If leaves are brown or dying, spraying will not work. If the leaves remain green and the daytime temperature stays near 50 degrees for several days, herbicide application can be effective.
Fall is also a good time to apply residual, or preemergence, herbicides. These herbicides work best when half to one inch of rain or snowmelt pushes them into the soil. This timing helps prevent early weeds from sprouting in the spring when fields are often too wet to spray. However, herbicide labels usually require applications to be made in October, before the soil freezes.
Photo Credit: gettyimages-ygrek
Categories: South Dakota, Crops, Wheat, Harvesting