Diversity key to herbicide weed management, fighting resistance

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WOOSTER, Ohio — Weed resistance to herbicides has been a concern among crop farmers since about 1998, but the fact that it’s no longer new is no reason to become complacent.

Grain farmers in Ohio and certain parts of Pennsylvania are in an ongoing battle against herbicide resistance and the spread of stubborn weeds like marestail and ragweed.

“It’s not new and it’s not as likely to surprise you,” said Bill Curran, weed extension specialist for Penn State. “Farmers become kind of complacent and maybe think that it won’t happen to them.”

They may be right, at least for now. But Curran and Mark Loux, who is weed specialist for Ohio State University Extension, say farmers are doing themselves and their neighboring farms a great service by conquering weed resistance before it starts.

Battling weeds

This past year saw an increase in marestail in soybeans in both states, and Ohio saw an increase in giant ragweed, Loux said. Marestail is now an issue in most of Ohio, except the far east and southeast. For Pennsylvania, it’s mostly an issue in the southeast, where most of the state’s soybeans are grown.

Both types of weeds can put a serious dent in yield. In fields where marestail is well established, farmers can lose as much as 30-50 percent of their soybean yield, Loux said. The weed is much more costly to treat once established.

Lack of diversity

Weed resistance can occur for several reasons, but “basically it’s a lack of diversification in weed management programs,” Loux said.

For many producers, it’s the result of using glyphosate year after year, and now certain weeds are no longer being killed.

Curran and Loux said soybean growers can conquer many resistant weeds by applying glyphosate (Roundup), as well as 2, 4-D. However, soybeans are not currently resistant to the 2, 4-D, so it must be applied well before the beans are planted.

During wet seasons like we experienced this past spring, applying the 2, 4-D in advance can be difficult or impossible.

“They (growers) were in a hurry and they were late and behind” and didn’t apply all the herbicides they had intended, Curran said.

New technology

There could be hope on the way in the form of 2, 4-D resistant soybeans, which would allow the 2, 4-D to be applied post planting, but they’re not expected to hit the market for another four years.

Linking up. Another option today is to use LibertyLink soybeans in combination with Ignite herbicide. This well-known duo is supported by Loux and Curran, and the many growers who find it successful.

According to Stine Seeds, which markets LibertyLink beans, the combination is high-yielding and controls more than 120 broadleaf weeds and grasses, including ALS- and glyphosate-resistant weeds. Moreover, there is no documented weed resistance to Ignite worldwide.

“Liberty beans is just one viable option right now,” said Phil Huffman, who farms about 2,800 acres of corn and soybeans near Dayton.

Even though Liberty works well, he still changes his modes of action in each field each year, to prevent new resistance into the future.

His advice to other producers is “don’t keep trying to do the same thing and expecting different results. We’ve got to change our chemistries.”

If farmers are unwilling to change their own chemistries, the chemistry of the weeds will eventually change for them.

“I think some of those (older) chemistries, I think we’ve ruined them for many, many years,” he said.” They are a genetic part of the plant now.”

Crop rotation

It may be old school, but another thing that works is crop rotation. Planting cover crops such as wheat, rye and hay can make a big difference.

“Any time that you rotate crops, it’s going to benefit your weed management,” Curran said, but “they’ve got to be able to make money doing it.”

Some farmers may only be set up to handle soybeans or corn, while others have been able to use the same equipment to plant cover crops, and find markets for the grain and foliage of those same crops.

Loux and Curran agree the biggest thing is getting producers to do things today that will prevent resistance, while preserving the use of proven herbicides.

Spending some extra money upfront on a new system can save a lot more money down the road, “but that’s a bit of a hard sell,” Curran said.

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