BY BRAD HAIRE
Farm Press Editorial Staff
HERBICIDE SEASON IS winding down for a lot of Georgia cotton
farmers, and the timeliness of the applications they’ve made will reveal how much hand weeding they’ll be needing, or if they’ll have a
crop worth harvesting.
Stanley Culpepper, University of Georgia Extension weed specialist, conducted a test to see how important a timely first postemer-gence herbicide application can be for the control of Palmer amaranth in cotton. He compared an auxin-based system (dicamba or
2,4-D) and a Liberty-based system on a test site at the Sunbelt Ag
Expo Farm at Moultrie, Ga., located in the southwest part of the state.
“If executed timely, both systems work well to manage Palmer amaranth in Georgia,” he says.
For both systems, he planted cotton into weed-free plots, and for
his pre-emergence residual herbicides he applied a combination of
Warrant plus Direx at-planting. He then came back and treated part
of the test with a timely Post 1 herbicide application, hitting the aux-
in-tolerant technology with Roundup plus the auxin and the Liberty
tolerant-technology with Liberty. This was before the tallest Palmer
amaranths in that part of the trial reached three inches, or about 15
days after planting. It is important to remember that the weed can
grow one to three inches a day in the Southeast during late-season.
For the test, one part of Culpepper’s trial purposely didn’t receive
a timely less-than-three-inch pigweed Post 1 application of either
auxin or Liberty, and the cotton didn’t get a first post application of
either herbicides until eight days after the cotton that did get the
timely first applications. For both the timely and untimely systems, a
sequential POST application was made two weeks after the first application.
In short, both the timely auxin and timely Liberty systems looked
great by mid-July, with cotton growing strong and weed-free.
On the other hand, the untimely, eight-days-late auxin system by
mid-July was infested with a few large pigweeds, translating into a
real-world, on-farm cost, Culpepper says, of about $15 per acre for
hand weeding that would be needed to eliminate the weed from the
field. The untimely, eight-days-late Liberty system was dominated
by pigweeds. It might cost more than $100 per acre to hand weed
out the escapes, “meaning it would’ve been, in the real world, a challenge to harvest,” he says.
“Timely applications are the critical link to success with all cotton
weed control systems. In this experiment, not being timely reduced
our control with each technology, but much more so in the Liberty
system compared to the auxin system. We are working desperately
to figure out approaches to improve the Liberty system, because
there are many areas across Georgia where auxin herbicides should
not be used because of adjacent crops being extremely sensitive to
auxin herbicides,” Culpepper says.
Generally speaking, weed control with the auxin system in 2017
“was a great success, partly because of good technology, but also
because of amazing growing conditions that enhanced herbicide
control. Less control, especially with auxin herbicides, should be expected in 2018 if drier conditions occur,” he says.
If Georgia cotton production is to remain viable, he believes
growers must continue to walk the path they’ve blazed over the last
decade to get the edge on herbicide resistance in the state — they
can’t slide back into old bad habits.
It is critical, Culpepper says, to continue to (1) start clean, with
no weeds at planting; ( 2) apply a tank mix of two residual pre-emer-
8 days too late made an
in cotton trial
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