The recent frosty weather has resulted in the need for some corn fields to be replanted. Some of those fields may have already been treated with a PRE application of atrazine. Since it is likely that these fields will have to be re-tilled, there have been some questions on what to do next. Here are a few comments to consider:
1. Field corn is extremely tolerant of atrazine so crop injury should not be a concern.
2. The maximum amount of atrazine that can be legally be applied in a field when both PRE and POST applications are used is 2.5 lbs ai/A (i.e. 2.5 qts of 4L).
3. Atrazine could be used again PRE on the replant but that would limit the amount that could be applied POST.
4. In those fields that have already been treated with atrazine and are tilled/replanted, I would suggest that growers switch to another PRE herbicide such as Dual II Magnum 7.64EC (16-21 oz/A) or Warrant 3ME (48 oz/A). This way, growers can use an additional 1.5 qts/A of atrazine in their POST application of glyphosate or other favorite and remain within the label restrictions.
5. When using these chloracetamide herbicides in field corn, it is also a good idea to make sure that there are no potential hybrid sensitivity issues (really not that common). Generally, this information can be obtained from the seed companies.
Dekalb: No specific ratings for amide tolerance?
Mycogen: Field corn hybrids rated for careful management (i.e. limit overlap and high rates) include the following: MY90R27RA, MY13K77RA, CNX157144S3, F2F499, and TMF86H77RA.