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Growers on lookout for grass weed escapes in wheat

Dry fall weather has limited the effectiveness of herbicides used on grass weeds in wheat fields, an OSU expert says.


For the Capital Press

Published on January 9, 2014 5:53PM

ALBANY, Ore. — An Oregon State University weed specialist recently advised Willamette Valley wheat growers to be on the lookout for grass weed escapes this spring.

“As you’re out scouting, looking at wheat fields, I would expect that we’re probably going to see some grass weed escapes,” OSU Extension weed management specialist Andy Hulting said.

Speaking to grass seed and wheat growers at an extension production meeting in Albany Jan. 7, Hulting said dry fall weather limited activation of fall-applied herbicides.

“We got the wheat planted on time for the most part this year,” Hulting said, “but some of the dry conditions after winter wheat planting may have limited the activation of some of our soil-applied herbicides.

“I know in our research trials this is happening,” he said.

“It doesn’t really matter what the herbicide product was, the issue is lack of rainfall following those applications,” Hulting said.

Controlling grass weeds in wheat is critical, Hulting said, given that even low-densities of the weeds can dramatically reduce yields.

“Four or five plants per square foot can drastically reduce winter wheat yields if you allow that grass to compete with wheat throughout the season,” Hulting said.

“Anywhere from 20 or 30 percent yield reductions from that low of a grass weed pressure underscores the importance of controlling grass weeds in our winter wheat crop,” he said.

Hulting identified several grass weeds that could be problematic in wheat this season, including ryegrass, rattail fescue, annual bluegrass, roughstalk bluegrass and annual brome species.

“I know that there are going to be some issues with some grass weed escapes on some of those pre-emergence herbicides,” Hulting said. “We need to be thinking pretty critically about getting our spring post-emergence herbicides on in a timely fashion.”

Hulting said it is important for growers to identify which grass weed species are present in a field, given that different herbicides perform better than others on certain species.

For example, Hulting identified Power Flex (from Dow AgroSciences) as “the best brome herbicide we have in Oregon right now.”

In general, Hulting said, bromes are better controlled in the fall, but, he said: “It is not too late to make an application in the spring on some of these brome species.”

Also, he said, growers should know if they are dealing with resistant biotypes of ryegrass. For example, he said, if dealing with biotypes with Group 1 resistance, “Then Power Flex and Osprey (from Bayer CropScience) are probably your best choices.”

Hulting also advised growers to be aware that herbicide options are limited in spring wheat due to crop injury concerns.

And Hulting said it is important to be aware that application timing of the different wheat herbicides vary widely. “Usually it is anywhere from weed emergence or two or three leaves,” he said. “In some cases, you can go all the way up to flag leaf, but usually you want to shut off those applications somewhere around jointing for most of these wheat products.”

Hulting also advised growers to be aware that tank mixing multiple chemistries can reduce their effectiveness.

“My theory in general on tank mixes to control weeds and disease is less is probably more,” Hulting said.

“We know that you guys want to (tank mix),” he said. “It reduces cost and time required for pest management. But think critically about how you devise your tank mixes.”

More information

Pacific Northwest Weed Management Handbook: http://pnwhandbooks.org/weed/ .


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