By Eric P. Prostko
Over the last few years, the attention of most weed scientists has been devoted to the management of herbicide-resistant Palmer amaranth. We had to or U.S growers could have been in serious trouble.
Since more field corn is projected to be planted this year, it might be a good time to review management options for one of the most problematic weeds that corn growers can have. I am talking about the morningglories.
There are numerous species of morningglory that can be found including bigroot, cypressvine, ivyleaf, palmleaf, pitted, purple, red, sharppod, smallflower, and tall.
Before discussing control strategies, I want to make it very clear that morningglory control will always be a challenge for southeastern field corn growers. Why?
There is no herbicide on the market that will provide season-long control of morningglory.
The region's climate favors late-season emergence of morningglory plants as the crop matures and the canopy dries down. For the extreme SE, that could be as early as June!
No field corn weed control system would be complete without the inclusion of atrazine. If I was King, I would make every corn grower (except those dealing with atrazine resistance or vegetable rotations) use a preemergence application of Atrazine 4L @ 1 qt/A followed by an additional 1.5 qt/A in combination with whatever POST herbicide is needed or preferred. The only downside to atrazine is that is does not last as long in the wet, warm and humid Southern climate and in soils where it has been used repeatedly. Please follow all labeled directions for atrazine use rates in your state.
Other postemergence herbicides that can be used for morningglory control with any type of corn hybrid include Aim®, ET®, Clarity, Status, and 2,4-D. Liberty (LL corn hybrids) has always been more effective than glyphosate for morningglory control. However, split applications of glyphosate can be effective if applied when morningglory plants are small and not running into the next county!! Post-directed applications of Evik can be effective for morningglory control as well. For those fields that get out-of-hand, some growers have had success using a harvest-aid such as Aim®. Aim applied at that time will not remove large weeds from a field but will dessicate the plants enough to facilitate harvesting.
Enlist corn hybrids will be available that will permit higher rates and wider application windows of 2,4-D to be used. Enlist Duo will be a combination of glyphosate + 2,4-D choline for use in all Enlist cropping systems. This technology may prove useful in the war on both morningglories and pigweed. Time will tell.
Lastly, growers may want to consider harvesting corn early in fields with a known morningglory problem. In this situation, drying costs will be increased but you may be able to get the corn out of the field before the morningglory makes combining a nightmare.
Morningglory may be the bane of many a corn growers existence. The use of maximum labeled rates of atrazine, timely postemergence applications, harvest-aids, and early-harvesting will be crucial for optimum control programs. Unfortunately, morningglory control in SE field corn will never be easy! As always, good weed hunting!
Prostko is a weed specialist with the University of Georgia Cooperative Extension.