Leave No Weed Behind in Resistance Fight

Last summer, Johnny Dodson got down on one knee and proposed that I join his spot-spray weed crew.
Herbicide-resistant waterhemp has become a major challenge in many parts of the Midwest -- especially in soybeans. The initial post-emergence application of herbicide should be made before waterhemp exceeds 5 inches in height. This spring, that spray window had already closed by late May in this Illinois soybean field. (DTN photo by Pamela Smith)
All right, so the gallant gesture was actually an effort to get me up and into one of the bucket seats on the toolbar, mounted on the front of his tractor (when did that distance become such a leap?). Dodson was so desperate to tackle herbicide-resistant pigweed on his Halls, Tenn., farm that he dusted off his old four-person spot sprayer and put it to use after decades of disuse.
When I showed up at his farm, I had such a fit of nostalgia that I volunteered to go a few rounds. Back when I was on the home farm wearing bellbottoms and Aerosmith was rocking "Walk This Way" into my transistor radio ear bud, we chopped weeds the old-fashioned way with a hoe or corn knife. Contraptions such as bean buggies came along to spoil my younger siblings -- they got all the good stuff. Some farmers purchased self-propelled gadgets such as the Weber Weeder. Eventually, rope wick applicators came along to wipe up the weed messes. Roundup Ready technology showed up and made all these tools obsolete -- for a while.
When I called Dodson this past weekend to ask if he was going to be spot-spraying fields this summer, I could hear the frustration. "We have pigweed in fields that has already gone to seed -- after three burndown applications in some fields," he said. "In the Roundup Ready cotton system, we don't have many options except hand weeding."
Dodson adopted a no-weed-left-behind policy a few years back. Bouncing through the cotton field on the sprayer last summer reminded me of one of those "Shout it out" laundry commercials. Each crew member was armed with a magic wand and we squirted doses of herbicide on Palmer amaranth and wild cotton (velvetleaf) that was visible above the cotton.
One pigweed is too many, Dodson said. "The problem this year is we didn't get the rains we needed to get the residuals activated. You can use all the right products, but timeliness is so critical.
"There is no one-size-fits-all herbicide program. You have to write a prescription for every farm and every field," he said. Neighboring fields that might not contain the same herbicide-tolerant trait must also be considered.
Far too many of my Midwest farmer friends still believe the weed-resistance plight of the South is a distant threat. In a recent DTN reader poll regarding weed resistance, 42% of the respondents said they do not have weed resistance on their farm. Only 27% said they had weed resistance confirmed on their farm -- another 29% suspect problems due to reduced effectiveness of certain herbicides.
In my home state of Illinois, 62% of those answering the DTN survey believe their farm has no weed resistance. Yet, in Illinois, almost all waterhemp populations have developed resistance to ALS-inhibiting herbicides. In total, Illinois waterhemp populations have evolved resistance to five herbicide families, and waterhemp plants and populations demonstrating multiple-herbicide resistance are becoming increasingly common.
We didn't have ideal rainfall activation conditions in central Illinois this spring and many of the fields I've been walking are chock full of waterhemp. University of Illinois weed scientist Aaron Hager told DTN that even with dry weather, growers who put down a residual should see some suppression.
"It's important to get out there and look," Hager said in a phone interview. "You need to pull the trigger on post treatment sooner rather than later -- do not delay the first post application to wait for another flush of waterhemp."
Hager recommended scouting fields to assess control five to 10 days after a post-emergence application. Scouting will allow you to determine if any timely rescue management practices could be made.
"If plants treated with a second post treatment survive, hand roguing may be in your future," Hager said.
No sweat -- a quick Google search this morning turned up a bean buggy for sale (http://www.google.com/…). I have a transistor radio you can borrow, and hallelujah, Aerosmith may have some new material because the band is going on tour again this summer.
What goes around comes around -- if you don't believe the proverb, just check the weeds in your field.
For more information on identifying herbicide-resistant weeds, view this video from the University of Tennessee: http://www.youtube.com/…


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