Be proactive to manage weed resistance

By Matt Reese

Devastating stands of suffocating weeds, $100 per acre in weed control costs to avoid significant yield loss, and hand chopping weeds for clean fields are just some of the herbicide resistance horror stories from the southern U.S.

Ohio farmer Mark Dowden, from Champaign County, got to see these challenges first hand on a recent trip to Tennessee.

“In the south, they couldn’t kill weeds that were taller than a couple of inches tall. After being down there and seeing it, I wanted to come back and tell people, ‘Hey look, we have got to start using these residuals to control this problem in Ohio,’” Dowden said. “We’ve all got to work together on this because, even if I’m doing things right, if the guy down the road is not doing things right, it is all coming our way. It is just a matter of time. We just don’t want this problem. We have too much valuable technology out here to have these problems and I don’t want to be the guy that is causing the problem. We have a colder winter here, but winter won’t stop these problems.”

Ohio State University weed scientist Mark Loux is highlighting the importance of multiple modes of action, burndowns and residual herbicides to help address weed resistant issues in a series of meetings this week.

“We have been seeing resistance issues for years,” Loux said. “Roundup Ready corn and beans are predominantly

Mark Loux gives a presentation at the first of this week's Weed Resistance meetings.

the problem. We knew in the late 1990s that we had a lot of ALS resistance in giant ragweed and marestail. If we didn’t have Roundup Ready soybeans introduced when they were, we would have had tremendous problems with ALS resistance. We were also finding plants with multiple resistance.”

In Ohio, triazine (atrazine, simazine, and metribuzin) resistance was showing up in Ohio in 1980. ALS resistant waterhemp, ragweed, lambsquarter, marestail, and cocklebur started showing up in the late 1990s and early 2000s. In 2002, glyphosate resistant marestail was confirmed in Ohio. Marestail with both glyphosate and ALS resistance was found the following year. Since then, resistance to both types of herbicides in Ohio has been found in giant ragweed, common ragweed, waterhemp and palmer amaranth.

And, even with unprecedented weed control technology available, weed control is getting worse, instead of better in Ohio fields based on findings from Extension field surveys.

“Only 30% of the fields surveyed were weed free at end of the season in 2011,” Loux said. “With the technology we have, this number should be much higher.”

Loux offered several approaches growers can take to deal with increasingly difficult weed control scenarios, particularly resistant marestail:

• Apply burndown plus residual herbicides in late March or early April, which is applying early enough that burndown of emerged crops is not an issue.

• Apply burndown plus residual herbicides in late April or close to planting, which increases the potential for adequate control of late-emerging plants. The disadvantage of waiting this late, especially as applications are delayed into May, is increased variability in the burndown of existing crops.

• Split the pre-plant application of herbicides with a late March or early April application of glyphosate plus 2,4-D plus a low rate of residual herbicide. Follow that with a second application at the time of planting that consists of the majority of the residual herbicide plus whatever additional burndown is needed.

• While there is no perfect time for growers to apply herbicide in the spring, it is important is that they get rid of weeds before crops emerge.

“You need to diversify herbicides over seasons and within seasons. A weed free start is essential to prevent weed issues,” Loux said. “You need to react quickly when weeds start to escape. Once those patches go to seed, you could have a major problem the next year.”

It is also important to take a higher cost, proactive approach to weed management to avoid a more costly forced reaction to a herbicide resistance problem.

“If you have a proactive strategy, your costs won’t increase over time. Your costs will be higher to begin with, but they really shouldn’t change much over time,” Loux said. “If you have resistance that gets away from you, you have a yield loss and then you have increased herbicide costs in the following years to control the problem. If you are reactive instead of proactive, it will cost you more in the long run.”

The Ohio Ag Net’s Dale Minyo was covering the event as well. Listen to all of the audio highlights.

 

 

 

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