Corn weed management

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It's hard to keep corn growers looking long-range about weed control programs when cutting corners in the short term is so enticing. Using multiple herbicides with different modes of action is definitely the answer to keeping weed control options viable.

"Our main effort is identifying the weed problems in fields properly and then using multiple modes of action herbicides against the predominant weed species in the field," said Jon Silsby, manager, crop consultant, TH Agri Chemicals in Union City, Mich. "The most cost-effective approach is requiring a little time and management."

Glyphosate weed resistance has to be addressed, according to Silsby and also Tom Nash, Bayer CropScience technical sales consultant for southern Illinois.

"Growers in southern Illinois don't say we have weed resistance. People just say that some weeds are getting harder to control with glyphosate, and, therefore, we've got to do something different," Nash explained.

In Silsby's portion of Michigan, growers are more accepting that weed resistance can quickly occur and that glyphosate resistance is inevitable. "I would say that 90 percent of the farmers assume it is going to get here, but they also look at their checkbook and wish they could just control weeds with a couple shots of cheap glyphosate," he said.

Glyhosate-resistant weeds are "pretty isolated in this area, but they are going to increase, just like previous weed resistance," Silsby said. Triazine-resistant lambsquarters and ALS-resistant weeds have been a major problem in the area. "Today, we don't go to the field without something that will control triazine-resistant lambsquarters," he added.

Nash noted, "Integrated weed management principles kind of go by the wayside when glyphosate is so low priced. I think if glyphosate cost more like $12 per acre then we'd see better stewardship of the product and more agronomically-correct weed control programs."

Although Monsanto has encouraged pre-emergence herbicide use with Roundup Ready corn followed by a Roundup application (glyphosate), too many pre-emergence herbicides have allowed glyphosate-tolerant weeds to escape, and the Roundup application has not cleaned up these fields. Some of the typical hard-to-control weeds are ragweed, Palmer amaranth and waterhemp.

Both Nash and Silsby report growers in the two distinctly different areas of the country are aware of the competitiveness of early season weeds and grasses reducing yield potential of corn by taking moisture and soil nutrients away from the crop.

Most growers want to invest only in what is necessary for a pre-emerge herbicide, which accounts for the extensive use of low rates of older products containing metolachor or acetachlor active ingredients. Of course, more high-powered pre-emerge weed control provided by such products as Corvus and Balance Flexx is also available for different regions of the country, and is beginning to be used more extensively.

"A light rate of a pre herbicide will hold 90 percent of the weeds off, and then we can turn around and follow up with Laudis or a glyphosate and Laudis tankmix in Roundup Ready corn," noted Silsby. "We can count on coming back almost exactly three weeks later and spraying the Laudis because it has some residual control. It allows us to go out there when the weeds are small and the corn is small so that we kill weeds easier and with less stress to the corn."

Nash explained that the safener used in Laudis is the reason for lower crop stress, and he further explained that the residual from Laudis keeps new weeds from emerging while the corn plant has time to shade the row middles. Laudis provides up to two weeks of residual control for grasses and four weeks for broadleaf weeds. The control of more than 65 grass and broadleaf weeds is also why Laudis has caught on as the post alternative or glyphosate tankmix partner. Laudis can be used on conventional, LibertyLink and Roundup Ready corn.

For more information regarding Bayer CropScience products including Laudis, readers can contact Tom Nash at

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