From the Farm: Dicamba-resistant Weeds


CENTRAL ILLINOIS (WCIA) – Just as fast as chemical companies are introducing new herbicides, weeds are finding ways to survive them. Dicamba may be losing its ability to control summer emerging weeds, such as waterhemp.

It may not a real problem for a homeowner who can pull a weed from a flower bed, but it is a problem for a farmer with thousands of acres of crops.

Illinois weed scientist Aaron Hager has found patches of waterhemp in McLean and Champaign Counties that have developed resistance.

“The difference on the resistant ones is that they do recover. If you give them sufficient time, they will flower, they will produce seed by the end of their life cycle,” Hager said. “And so they were able to do crosses in the greenhouse, do some calculations of inheritance, and so long story short, at the end of the day, what I believe our work has shown is that we can demonstrate somewhere between a 5 and 10-fold level of dicamba resistance now in that population. It’s here.”

Dicamba-resistant waterhemp isn’t just being found in Illinois. It’s being found in other states too.

“My colleague in Tennessee, Dr. Larry Steckel, is confirming that he’s has found dicamba-resistant waterhemp, I believe he said in some of the middle counties in Tennessee, as well as dicamba-resistant Palmer Amaranth in the western portion of Tennessee,” Hager said.

So what can a farmer do?

“The key point is we really don’t know what the origin of this evolved metabolic resistance is. And if we don’t know the origin, to be able to say that we have a very sound, data-driven recommendation for its management would be a bit of a stretch of the imagination,” Hager said. “So at least from a chemical standpoint, if we don’t know what caused it, it makes it kind of difficult to try to recommend something in terms of a herbicide program because when you deal with metabolic resistance, you really have no predictability. You don’t know what still works, and what doesn’t work, unless you make an application and observe the outcome.”

Grandpa may have an old weed hook you can borrow.

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