Growers are planning their herbicide programs to control pesky weeds in their corn and soybean fields. Weed control products are an important part of weed management and without them, many of our crop fields would erode away if we had to use tillage. Therefore, herbicides are part of sustaining our land production resource.

Flooded fields on the Missouri River bottom may have an abundant supply of weed seed which may have been dropped by floodwaters or as water receded, weeds grew and produced seed. Growers who are facing those situations should use full rates of herbicide products for effective control of weeds.

Also, with weather delaying corn and soybean planting last year, growers who used a herbicide which has a 10-month rotational guideline, should consider planting those fields last this spring. Later planting will allow products to degrade and reduce chance of carryover and injury to the following crops.

As spring begins, early spring weeds such as marestail begins growing. This weed should be controlled before planting soybeans. Once soybeans are planted, marestail is difficult to control and will compete and reduce soybean yields. An herbicide that burns leaf area then a photosynthetic inhibitor works well as a management strategy to control this plant.

Also, consider using multiple modes of herbicide action to control weeds. One strategy is to use pre-emergence herbicides in combination with post-emergence weed control. Also, one should consider two effective modes of action, not just one when planning an effective herbicide program.

Post-emergence weed control products are more effective on small weeds than large weeds. Always consider weed size and height when controlling weeds post-emergence and apply herbicides in a timely fashion.

For more information, contact Wayne Flanary, Field Specialist in Agronomy, University of Missouri Extension at 816-279-1691.