Inconsistent Control With Burndown Herbicides

Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

There are a lot of fields that have been sprayed with a burndown and the control was not as good as expected. It is not uncommon for early season burndown applications to be erratic, but this season seems worse than others. The most common complaints have been with grass control, henbit, and chickweed. A few observations from my experiences: glyphosate is good on most of these species, but is not great. Glyphosate often provides good to excellent control of grasses if the rate is adequate (at least 0.75 lbs acid equivalent) and the plants are growing. However, annual ryegrass (aka Italian ryegrass) is hard to kill with glyphosate and requires close to a 2X rate if spraying in early spring. The addition of a triazine will significantly reduce the control of annual ryegrass. I often see only fair control of henbit with glyphosate. The addition of a triazine herbicide like atrazine or simazine will help. That is the tough choice, adding a triazine may help with some species, but can reduce the control of other species. You have to determine what weeds you have and which are going to be the most difficult to control and decide.

As far as paraquat, adding a triazine for the burndown before corn almost always improves control. However, grass control of annual ryegrass or grass cover crops will probably not be acceptable due to significant regrowth.

 

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