NOTE: see also the update [1] to this article.
Whether due to unfavorable weather conditions or inevitable spring constraints, there are some fields where corn has emerged before the planned preemergence herbicides could be applied. Many preemergence corn herbicides can also be applied early postemergence in corn. Axiom, Balance, Define and Epic herbicides are exceptions and can only be applied prior to corn emergence. The table below lists some of the preemergence corn herbicide products that can also be applied postemergence, as well as the recommended maximum plant heights or growth stages at application. Products listed include only those that do not require specific, herbicide tolerant corn hybrids.
It is important to remember that control may be less consistent with delayed preemergence treatment compared to treatments applied closer to planting. This is primarily due to weeds germinating and emerging before exposure to the herbicides, but can also be due to other factors such as weed species present and weather conditions. Fields in which the preemergence herbicide applications were delayed a week or more after planting should be monitored to determine the actual control levels obtained. Weed control from preemergence herbicides may be acceptable, or additional control measures may be needed.
Always consult the individual herbicide labels for specific adjuvant requirements, rate adjustments, tank mix restrictions, insecticide interactions, and other precautions or comments regarding delayed preemergence and early postemergence applications.
Corn height/stage and maximum weed height/stage recommendations for preemergence herbicides that can also be applied postemergence.
| Herbicide product | Corn height/stage | Maximum weed height/stage |
|---|---|---|
| Aatrex, Atrazine | 0-12" | 1.5" |
| Bicep II MAGNUM, Bicep II Lite Magnum, Cinch ATZ, Cinch ATZ Lite |
Broadcast 0-5", Post-directed applications 5-12" corn |
before 2 leaf stage |
| Bullet, Lariat | 0-5" | before 2 leaf stage |
| Callisto | 0-30" | 5" |
| Camix | 0-5" | prior to grass emergence, broadleaves less than 3" |
| Dual II MAGNUM, Cinch | 0-40" | prior to emergence |
| Frontier, Outlook | 0-12" | prior to emergence |
| Guardsman MAX, G-Max Lite | 0-12" | 1.5" |
| Harness, Surpass, TopNotch, Degree | 0-11" | prior to emergence |
| Harness Xtra | 0-11" | before 2 leaf grass stage |
| Hornet | 0-20" | 6" |
| Degree Xtra, FulTime, Keystone, Keystone LA | 0-11" | prior to emergence |
| Lasso, MicroTech | 0-5" | prior to emergence |
| Lumax | 0-5" | less than 3" |
| Marksman | 0-8" | not listed on label |
| Prowl/Prowl H2O | 0-30" | prior to emergence |
| Python | spike | prior to emergence |
This article originally appeared on page 43 of the IC-492 (8) -- May 17, 2004 issue.
