Postemergence crabgrass control 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.

There have been several questions about the possibility of failed preemergence herbicide applications and the likelihood of annual grass weed escapes, particularly more difficult to control weeds such as large crabgrass. Emerged large crabgrass is difficult to control in conventional systems with smooth crabgrass being even harder to control. An article in last year’s Field Crop CAT Alert noted the difference between the two crabgrass species (vol. 20. No. 8 – June 2, 2005).

Postemergence herbicides that suppress large crabgrass include: Accent Gold, Accent Gold WDG, Basis, Callisto and Steadfast. These herbicides give only fair control of this weed. Additionally, weeds must be very small to provide even fair control of this weed.

Fair control of large crabgrass and smooth crabgrass is also possible with Liberty (Liberty Resistant Corn only) or Lightning (Clearfield Corn only). The weeds should be no more than two inches tall. Glyphosate is the only postemergence herbicide that provides excellent control of large crabgrass and smooth crabgrass (Roundup Ready corn only).

For specific rates of these herbicides please refer to the 2006 Weed Control Guide for Field Crops (E-434).

New herbicide: Impact

Impact is a new postemergence herbicide in corn in the same family as Callisto. Field trials established in 2006 will provide MSU information on the efficacy of Impact on various weed species. There is currently no MSU field data on the effectiveness of Impact in Michigan. Currently, the only source of information on this herbicide is the product label. Both the maximum rate per application and per season is 0.75 fl. oz/A for Impact. The main limitation with using this herbicide is that there is an 18 month restriction when rotating to soybeans in Michigan. Risk of carryover, as with any herbicide that has soil activity, is greater under dry conditions.

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