The most troublesome weed for most corn growers in North Alabama is the annual morningglory. The backbone of our morning-glory weed control program is atrazine, but often atrazine alone will not provide full-season control of morningglory.
If the corn plant does not shade the ground early and sunlight reaches the soil, this triggers late-season weed emergence and growth, and full-season control using only atrazine is especially diminished.
Some important points to consider in morning-glory control in corn are:
The maximum use rate of atrazine (4 lbs. of active ingredient per gallon) is 2.5 quarts per acre. Use one quart per acre with a burndown herbicide, if needed, preemergence (PRE) and follow approximately 28 days later (while the weeds are small and the corn height allows for good coverage) with 1.5 quarts per acre of atrazine along with your contact herbicide (Roundup or Liberty) depending on the herbicide traits in your corn. DO NOT apply these on conventional corn.
Apply an additional residual herbicide such as Callisto, Capreno, Corvus, Laudis or Halex GT, to improve and extend your weed control with your postemergence atrazine application. Halex GT is a premix of glyphosate, Dual and Callisto and should only be applied to corn with the Roundup Ready trait.
If your corn has the Liberty-Link trait, Liberty is generally more effective on morningglory than glyphosate.
Corn herbicides when applied at labeled rates and corn growth stages do not have a negative impact on corn yield. Read the label for tank-mix combinations, addition of adjuvants, rotational restrictions, etc.
Status (a combination of diflufnzopyr + dicamba) can be applied over-the-top of corn from 4-36 inches tall or V10.
Consider using a harvest-aid on spots where morningglories are a problem. Although, Aim is the most effective herbicide to use on morningglories, it will not completely remove them from a field, however, it will desiccate the vines enough to improve harvest. Unfortunately, Aim has no effect on smallflower morningglory.