Overlapping Residual for Optimizing Weed Control

Spring has sprung and the warm days seem to be here to stay. Along with the warmer weather, we have recently received some very nice rains across our territory. These rains have helped our spring crops take off growing and our wheat to recover some from the later freezing nights we had a couple weeks ago.

Unfortunately, with rain and warmer soil temperatures also comes the germination and emergence of annual weeds. Crabgrass and pigweeds can be found in fields throughout Central Kansas this week. Pigweeds can grow as much as an inch per day, so that 1-inch pigweed can be a 6-inch pigweed within a week and have over 30 growing points. Pigweeds and grasses compete with our crops for moisture, sunlight, and nutrients and can be detrimental to yield. If you wait until you can see the weeds down the field, it is often too late for complete control.

Residual herbicides help control weeds by preventing germination and emergence. At this time in the weed life cycle, it only has one growing point and is easily controlled. After emergence, weeds can quickly put on multiple growing points, making them much harder to control.

Many residual herbicides can control weeds for about 14-21 days after application and incorporation by a rain/watering event. While it is hard to want to spray a “clean field”, the best weed management strategy is to plan another residual herbicide application just inside of that 21-day window. This overlapping of residual products will help prevent a lapse in coverage that would allow pesky weeds to emerge. The main goal of overlapping residuals is to help prevent weed emergence until the crop can reach canopy stage.

We have residual products available for corn, soybeans, and grain sorghum. While the products are different, the plan is basically the same:

• Apply 1^st Residual Product right before or immediately following planting
• Apply 2^nd Residual Product 14-21 days Post Plant, typically just before canopy of the crop
• Crop Canopy should help with weed suppression after the next 14-21 days
• If a hail event should remove crop canopy, some residual products may be applied later in the growing season, check labels carefully for details

Eric Hanson, Winfield United Agronomist, states  “Round 2 of herbicide residual application is here. When timing post-emerge applications in corn, the ideal circumstances is when weeds are small for best efficacy, but also when the corn plants are small for a variety of physiological and crop safety reasons.  This also means that when we make an application, we have a longer period until the crop shades the ground.  For that reason, it is important we talk about using overlapping residuals in our corn program just like we do in our soybean program to make the same sound recommendation. There are many herbicides on the market today that are labeled for post-emerge residual in corn utilizing several different modes of action.  It is important to match the herbicide with the weed species that you fight late season in each field, keeping in mind the emergence patterns that each species tends to exhibit. If you get hail damage that reduces the canopy, you will be glad to have that extra layer of protection in place. Your GBC agronomist can help you choose the program that is most beneficial.”

For more information on the best herbicide program for your operation, speak to your Great Bend Co-op Agronomist.