All posts by Larry Steckel, Extension Weed Specialist

Good Time to Scout for Weeds

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Pigweed that has escaped dicamba + S-metolachlor + glyphosate on 4 to 6″ weeds followed 20 days later with dicamba + S-metolchlor + glyphosate: Montgomery County, TN. Sept 1, 2020

Some have been concerned about losing dicamba due to court or EPA rulings. Everyone should be more concerned about losing dicamba and 2,4-D to Charles Darwin’s theory. Weeds developing herbicide resistance has caused the loss of many more herbicides than anything a court or the EPA has ever done. It’s not even a close race.

This is particularly true for Palmer amaranth. The newest development is that Palmer amaranth has evolved dicamba resistance here in Tennessee. We are in the beginning stages of Palmer amaranth, yet again, becoming a major problem due to the loss of a herbicides’ utility on that weed. Continue reading

Dicamba-Resistant Palmer Amaranth in Tennessee: Stewardship Even More Important

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Picture 1. Palmer amaranth escapes after a dicamba + glyphosate application in a Gibson County cotton field.

Has Palmer amaranth evolved dicamba resistance in Tennessee?  Results from some of the greenhouse experiments this winter and spring as well as in field research this growing season would suggest that our state now has dicamba-resistant (DR) Palmer amaranth. These DR populations are established in Crockett, Gibson, Madison, Shelby, and Warren counties and likely several others. Continue reading

Strategies to Address Palmer amaranth, junglerice and goosegrass Escapes from Follow-up Applications in Xtend and Enlist Crops.

Carpet of Palmer amaranth escapes from a 0.5 lbs of dicamba + 32 ozs glyphosate + S-metolachlor: Pic taken 20 DAA: S-metolachlor was only herbicide that looked to be working in this field.

Calls continue from some folks frustrated with goosegrass, junglerice and Palmer amaranth escapes after a dicamba + glyphosate application. A large reason for the frustration is the follow-up applications have often provided less control than hoped. Timing is the cause for some of these poor weed control issues. Herbicide resistance is another cause. Continue reading

Concerns About Poor Palmer Amaranth Control with Dicamba

Palmer Amaranth Escaping 2 Applications of Engenia + Roundup PM. Crockett County TN. Pic taken 14 Days after 2nd Application

Calls continue to come in on concerns about poor Palmer amaranth control after a dicamba application. More than a few have reported that Palmer amaranth has survived multiple dicamba + glyphosate applications (Example above). Continue reading

UT Weed Tour Cancelled

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Dear Colleagues

The University of Tennessee Weed Tour has been cancelled.  Due to the covid-19 virus no large groups are allowed to visit a University research station.  Since we cannot have an in-person tour, we plan to post some short videos on the UT Crops News Blog highlighting some of the more interesting research from this summer.


Larry Steckel

Corn Maturity Cutoffs for Herbicides

Due to little time and very few good spray days some corn fields have yet to have their lay-by application. Corn is putting on a new leaf every 3 days with all the heat and water. Therefore time is short before it will be too mature to apply any herbicide safely over the top.

The most asked question “is how large can corn be before glyphosate could potentially cause injury”? The glyphosate label states it can be applied up through the V8 corn growth stage. My experience has been if glyphosate is applied to corn larger than that it can at times cause ears to be barren.  This phenomena is difficult to predict ahead of time as it can vary due to maturity of the corn at application, hybrid and weather. Continue reading