How to Get the Most Out of Herbicide Applications

Herbicides remain critical to controlling weeds and protecting yield, so it’s important to manage herbicides to ensure they remain as effective as possible.

In order to protect the efficacy of your herbicides, there are a number of factors to consider.

• Know the weeds you are trying to control. “Knowing what weeds are most problematic will help you select the right herbicide,” says Bill Johnson, Ph.D., professor of weed science at Purdue University. “Once you know what weed you’re trying to control, you can use resources such as weed response tables and weed control guides, available through universities and companies, to make the best decisions.”
• For post-emergence herbicides, scout your fields. It’s true that computer models and extension guides can provide threshold levels and help farmers with herbicide application decisions. However, this only works if they know what weeds are in their field through scouting. “For most farmers, walking over the fields and noting the weeds present is probably good enough, but scouting from the pickup truck won’t do it,” says Alan York, Ph.D., professor of crop science at North Carolina State University.
• Apply post-emergence herbicides at the proper time. “Few farmers spray too early. Treating weeds when they are smaller and easier to kill can prevent early season competition with crops and has ramifications for resistance management,” says York. “You should start scouting fields no later than 14 days after planting. The weeds may not be ready to treat that early, but early scouting can prevent having to catch up later.”

Time of day can also impact how well herbicides work. For example, some weeds have leaves that fold up during the low light conditions, making coverage challenging.

Check the label requirements for statements that say there could be reduced activity for the herbicide late in the day or in the early morning.

• Follow label requirements to make sure you use the proper application techniques. York notes having the sprayer calibrated, applying the right volume per acre and using suitable nozzles are important. “Following label instructions is probably the most important thing you can do,” says Johnson. “The instructions are given to make sure the herbicides work to the best of their abilities, and given the cost of herbicides, it just makes sense to follow the label directions.”
• Monitor the weather. Some factors may be out of farmers’ control but still greatly affect the efficacy of herbicides. Weather is the most notable of these factors, but there are ways farmers can manage their herbicide use that consider the impact of weather on efficacy. For example, soil-applied herbicides require rainfall to activate, but too much rainfall will dilute the herbicide or wash it away entirely.

Herbicides account for a significant investment and are an important tool to protect your yield. Giving those herbicides the best chance to remain effective only makes sense. Following label instructions will help you do that.