Corn Maturity Cutoffs For Herbicides

JACKSON, TENN.

    The maturity of our corn crop has a lot of variability do to the ongoing starts and stops in corn planting this spring. It ranges from V6 for the earliest window that corn was planted to still in the bag for corn that folks plan to plant yet on some irrigated fields. After 3 inches of rain it may well be early June before those last fields can be planted.

   From rating corn weed control trials and walking a few corn fields this spring it is very apparent that the pres that were applied to mid-April planted corn started breaking last week. That they have lasted almost 4 weeks is extraordinary after all the rain (13.5” of rain since April 19 at Jackson). These pre applications however, were not applied in vain as they have kept the weeds down until now. The corn in these fields can be cleaned up much easier as the weeds are very small. Weed in corn fields where no pre was applied have grown very large now and will be more difficult and expensive to control.

   There have been quite a few corn fields already treated most notably with Halex GT or Capreno. These herbicides like all corn herbicides work better when tankmixed with atrazine. Unfortunately, for corn that is over 12” tall that is no longer an option. Do to the limited amount of days fit to spray there are a number of corn fields where the corn is well over the 12” height that will need to be sprayed. One good substitute for atrazine on large corn to be tankmixed with some of the premixes is Status. There are other options as well like Liberty on Liberty Link hybrids or Distinct. These and other herbicides offer effective postemergence options even on large weeds, but there are cutoffs associated with all these. This serves as a reminder for cutoffs timings for several postemergence corn herbicides.

   Crop stage and/or crop height can be used to determine this and typically the label states the limits so that whichever comes first is the cutoff. Crop stage can easily be done by counting the number of collars that are fully open (ex. 4 open collars = 4 leaf), but crop height can also be used. One other thing to note is a newer product, Realm Q. This is a combination of rimsulfuron (Matrix) and mesotrione (Callisto). This product provides postemergence control of broadleaf and grass weeds, as well as residual control. The Q stands for a built-in safener, allowing for safe postemergence applications in corn. Δ

    DR. LARRY STECKEL: Extension Weed Specialist, University of Tennessee