There have been a few reports of good sized (>12”) horseweed (marestail) putting on significant new growth after an Engenia or Xtendimax application. Though these occurrences have been relatively few they are a concern as the horseweed appears to be growing back with a vengeance.
As we go into the double crop soybean planting stretch these reports are a good reminder to apply a good burndown on horseweed prior to even Xtend soybeans emerging.
Herbicide Resistance Info
Good sized horseweed recovering from being cut by the combine in wheat harvest will likely be very hard to kill.
The two best burn down options after the combine departs the wheat field is Liberty or Gramoxone plus a metribuzin product. Both Liberty and the Gramoxone tankmix should be applied with a minimum of 15 GPA with nozzles that provide good coverage. Liberty works best when applied between 9 a.m. to about 5 p.m. Gramoxone on the other hand works a little better if applied before 9 a.m. and after 5 p.m.
So which option should be used? Depends on the situation. If there is a lot of Palmer in the field then the Gramoxone tankmix option would be the best fit. Also if the soybeans are Liberty Link then save the Liberty for in-crop to remove any recovering horseweed.
If the field is to be planted with Xtend soybean then either option would likely work well. Keep in mind I would not expect 100% control of horseweed with either option. However, they should be beat up enough that an application of Engenia or Xtendimax in-crop should control any escapes.