Corn planting is winding down in Tennessee. A good bit of the early April-planted corn will need to be sprayed post shortly.
Wet weather in the forecast will likely make for a narrow window to get these fields sprayed timely. As a result, there is likely to be some good size Palmer amaranth up in some corn fields by the time we can get back into spray.
A common question is how large a pigweed will the popular layby premixes Halex GT, Capreno and Realm Q control? All three of those herbicides are a bleaching-based herbicide premix. The bleaching herbicide in Capreno is Laudis. The bleaching herbicide in Halex GT and Realm Q is Callisto. Those herbicides can effectively control Palmer up to 4 inches tall, depending upon rate.
When Palmer becomes larger than that, a tank-mix partner is needed for consistent control. The most commonly used tank-mix partner is atrazine. When atrazine is tank-mixed in with one of the herbicide premixes mentioned above, considerably larger Palmer can be controlled. However, atrazine can only be used on corn up to 12” tall.
What about large Palmer in corn that is taller than 12”?
One good option is Halex GT + Status in up to 30-inch tall or 8-leaf corn or Capreno + Diflexx on corn up to 7-leaf. Status may be applied at rates as high as 5 to 10 ounces per acre in corn that is 4 to 36 inches tall.
In our research, 4 ounces per acre of Status added to either Halex GT at 4 pints per acre or 3 ounces per acre of Capreno has been very consistent controlling large Palmer amaranth over the past three years.
Realm Q is another option because it can be applied to corn up to 7-leaf or 20 inches tall, whichever comes first. We evaluated Realm Q at 4 ounces per acre plus Status at 4 ounces per acre on large Palmer amaranth and have found that it provides less consistent Palmer control than the tank-mixes previously discussed.
Realm Q has less Callisto in it than the 4-pint Halex GT rate and this is likely the reason. This can in most cases be offset if the Status rate is bumped up to 6 ounces per acre.
Some have inquired about making their own tank-mix utilizing the bleaching herbicide Impact or Armezon (common name topramezone) instead of the premixes listed above. In our research we have seen good results with Impact or Armezon when tank-mixed with herbicides Dual Mag and either atrazine or Status.
If the field has a good deal of grass weeds in it, adding glyphosate will help.
If Palmer amaranth is 4 inches tall or more, be sure to go with the maximum use rate of 1 ounces per acre of Impact or Armezon.
The cutoff for Halex GT is 8-leaf corn and the cut off for Capreno is 5-leaf corn. On corn past these cutoffs, Impact or Armezon + Status would be a good choice on corn up to 36 inches tall. It is not ideal to have to remove pigweed in corn this large as yield loss from competition has already occurred, but some will be left with few other options in some fields.