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Window for early weed management shrinking

weed management

Many weed seeds will have begun to emerge by the time planting occurs.

While a wet start to the growing season may bring disease pressure, weeds will pose their own challenge in 2022.

The rain seen in much of the Midwest was a welcome sight to many as they looked to break out of a drought pattern. However, that rain has forced planting windows to tighten and with that, management windows to shrink.

Many weed seeds will have begun to emerge by the time planting occurs and are at a higher stage of growth than originally planned for, wrote Mark Loux, professor of weed management at Ohio State University in an article on delayed planting. Sprayers aren’t likely to keep up with planters, however, as farmers are likely to stay focused on getting the crop in the ground, leading to additional pressure. That means leaning more heavily on post-emergence herbicide mixtures such as glyphosate.

“Maximum rates of glyphosate can be required for control of large giant ragweed, especially if they have developed some resistance,” Loux said. “Increasing spray volume can improve the effectiveness of a herbicide into a taller, denser weed and crop canopy, especially for contact herbicides.”

Soybeans, meanwhile, have less time to develop a canopy, which would normally act as a weed preventative. That means in fields with higher pressure, it may require a different strategy. There are fewer post-emerge options for soybeans, so Loux suggests applying herbicide as soon as possible.

If fields stay wet and producers are considering a switch from corn to soybeans, look at the herbicides used in the field last year. If it was previously a corn field, the herbicide may linger and cause issues for the soybean crop. Any longer delays may result in more prevent plant acres, which will require another change.

“Have a plan for those fields since allowing weeds to survive will result in a dramatic increase in weed pressure for future years,” according to Iowa State extension.

The wet weather does give hope to herbicides being more effective, however, as a rain shortly after application will activate the product.

“As long as we get that rain after the ground is planted, it will help us a lot,” said Jay Fisher an agronomist with Nutrien Ag Solutions. “If the rain turns off like last year, we might be worried, but with the herbicides we have now, I’m not worried.”

If the window runs out for a pre-emerge application, it may make a post-emerge application less effective. If there are any excessive issues remaining, Fisher said to do some extra scouting before applying a second round.

“If the post-emergence herbicide application fails to control the weeds, check the stem for boring insects,” he said. “In the last few years we have noticed that stem borers can occasionally be the cause of herbicide failures because they may interfere with herbicide translocation in the plant.”

While there has been talk of herbicide supply issues, Fisher said he doesn’t expect it to be a major issue in his area.

“So far, so good on our end,” Meyers said. “We’ve been getting what we needed. We had to switch around a few herbicides, but as far as the ones we need, we have a pretty good supply. If you planned ahead and bought your product ahead, you should be in good shape.”

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