Residual options for postemergence herbicide applications in corn
Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included
The weather this spring (there isn’t a normal spring is there?) with warm, dry weather early followed by cool, wet weather in May resulted in a number of corn acres without an herbicide application throughout the state. Weed control timing is critical to preserving yield potential and has been discussed in previous years. It is important to consider all options and make timely applications due to limitations of some herbicides. Postemergence programs without a residual herbicide applied at planting can provide excellent season-long weed control. However, important considerations that should be made include timing, herbicide resistance and management strategies. Studies conducted at MSU showed the highest yields and greatest weed control were observed where a residual herbicide was applied preemergence and followed by either glyphosate or glufosinate postemergence. See the Field Crop CAT Alert article Postemergence herbicide applications in corn – it’s all about timing from June 4, 2009.
During this time of year, it is easy to see how weeds can get away from you. It only takes a few days for weeds to germinate and grow an inch, and in good growing conditions, weeds can grow several inches within a couple of days. Now throw in some rains and your weeds jump to seven to eight inches before you can spray all your fields. The most effective weed management program will include residual herbicides either preemergence or postemergence with postemergence applications being made to three-inch weeds or smaller to avoid a yield reduction. Postemergence only programs with no residual herbicide will need multiple applications to ensure maximum weed control and yields. Preemergence herbicides can still be applied to corn if tank-mixed with a postemergence herbicide, and will provide residual weed control. There are limitations for several preemergence products if applied to emerged corn. A previous article on Delayed Preemergence Herbicides for Corn from the May 13, 2009 Field Crop CAT Alert covers many of the products, and Table 1K in 2010 Weed Control Guide for Field Crops Extension Bulletin E-434 gives the height restrictions for many common preemergence herbicides.
It is important to note that atrazine and atrazine-containing products can only be applied on corn up to 12-inches in height. Much of the corn in the state is at or near this stage, so other herbicide options will have to be utilized. There are several products that can be used alone or in combination with a non-selective herbicide such as glyphosate (Roundup Ready corn) or Ignite (Liberty Link corn) for increased control while providing residual control. The HPPD inhibiting herbicides Callisto, Impact and Laudis or Hornet WDG (ALS + growth regulator) can be used as a tank-mix partner to provide both additional postemergence and residual control of broadleaf weeds. For residual control of grass weeds, products containing metolachlor (Dual II Magnum, Cinch, Stalwart C, Parallel) can be applied up to 40-inch corn, and Prowl H20 can be applied up to 30-inch corn. As always, rainfall is needed for activation of preemergence herbicides. It is also important to remember that glyphosate can only be applied to corn up to 30-inches or 8 collars, and Ignite can only be applied to corn up to 24-inches or 7 collars, so plan your herbicide applications accordingly. For further information, see 2010 Weed Control Guide for Field Crops Extension Bulletin E-434 or consult herbicide labels.