With the unusually cool weather interspersed with heavy rain, some corn has emerged without receiving a residual herbicide application.
Here in the central part of the state, we have some emerged corn that appears yellow and cold stressed. We would suggest waiting a few days until air temperatures are warmer and the corn has greened a bit before applying herbicides to reduce the potential for herbicide injury.
For Roundup Ready corn, the potential for injury from glyphosate is minimal even with the cold stress. However, for many residual herbicide applications, a few days of warmer day and night time temperatures will ensure better corn tolerance.
For the maximum corn and weed size for delayed preemergence corn herbicides, see Table 2.2-12 in the Penn State Agronomy Guide. Here is a quick summary of what is allowed for selected PRE products. Balance Flexx and Corvus contain a safener and can be applied up to early POST (V2 growth stage) to corn. Other herbicides such as Bicep II Magnum, Cinch ATZ, Dual II Magnum, etc. can be applied to corn up to 5 inches tall. Acetochlor-containing products such as Degree (Xtra), Harness (Xtra), FulTime, Keystone, and SureStart can be applied to corn up to 11 inches tall. Herbicides including Atrazine, Lumax, Lexar, Guardsman Max, and Realm Q can be applied to corn up to 12 inches tall (20 inches tall for Resolve Q). And finally, Prowl H2O, Halex GT, and Warrant can be applied to 30 inch tall corn or less.
Keep in mind, when tank-mixing with other pesticides, to follow the most restrictive product label. Refer to the most recent herbicide label for use guidelines and additional information—
Crop Data Management Systems (CDMS)
Source : psu.edu