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Weeds becoming Resistant to Toxic Chemical Programs

Commentary: The conventional toxic chemical herbicides are becoming less effective, are destroying the soil and causing other issues. Manufacturers recommending using multiple herbicides per application and more applications each year.

Press Release from DuPont: farmers using more complex programs to control resistant weeds

Herbicide-resistant weeds remain a top concern for corn and soybean growers. According to a survey conducted by DuPont Crop Protection at the 2015 Farm Progress Show in Decatur, Ill., more farmers are scouting fields, keeping field records and adding multiple herbicide modes of action to spray tanks to combat herbicide resistance and control yield-robbing weeds.

Though most of the growers surveyed said they are taking action against resistance, they're still concerned resistant weeds will cut yields and profits. Among the more than 1,200 survey respondents, 85 percent said they worry about controlling resistant weeds on their farms. Most said they rotate and/or tank-mix herbicides to address the problem.

Though awareness of resistant weeds was high and most industry experts recommend rotating herbicide modes of action (MOA) used on a crop in a given season, survey respondents were only moderately knowledgeable about the specific herbicide MOA being used on their fields. Less than half (48 percent) said they could name the herbicide MOA used on their farms, although another 26 percent said they had the information on file. Only 42 percent of growers said they tank-mix herbicides with multiple MOA.

Jeff Carpenter, corn and soybean herbicide portfolio manager, DuPont Crop Protection, said he's encouraged by increasing farmer awareness of the resistant weed problem. "Growers understand the implications increasing populations of resistant weeds can have on their operations and are becoming more proactive by applying a full range of tools to fight resistance."

While herbicide application is just one element of a comprehensive herbicide resistance management program, using herbicides strategically can play a significant role in avoiding resistance development, said Carpenter. "Starting with clean fields is a smart way to start the new growing season. Applying a burndown plus residual herbicide program eliminates emerging weeds and keeps new weeds from developing before planting. A solid herbicide program also minimizes the weed seed bank that can create problems for years, despite crop rotation and other cultural practices to control weed pressure."

The DuPont Crop Protection survey follows publication of results from an on-farm study by the University of Illinois and the USDA Agricultural Research Service, which showed that simply rotating herbicide MOA instead of mixing herbicides in the tank significantly increases frequency of herbicide resistance.

Among the 105 farms in that study, farmers who used multiple herbicides per application in tank mixtures were less likely to have herbicide-resistant weed populations than those who simply rotated herbicides from season to season. When an average of 2.5 MOA per application were used, fields were 83 times less likely to have resistant weed populations, compared to growers using 1.5 MOA per application.

"As more growers use multiple herbicide modes of action, we hope to see further progress in fighting resistant weeds," said Carpenter. "To make it easier to achieve more complex tank mixes with less mixing and measuring, we have collaborated with growers to develop a number of herbicides with two, three or more modes of action, each designed to address specific regional weed concerns. We are working together to help increase crop production to feed the growing world population."

For effective herbicide resistance management, Carpenter recommends employing an integrated pest management strategy that includes these steps:

• Know what weeds are in fields and keep scouting records.

• Incorporate residual herbicides into the weed-control program.

• Use herbicides that contain more than one mode of action.

• Consider multiple herbicide applications in a season, starting with a strong preemergence herbicide program.

• Layer residual herbicide products across multiple applications, such as burndown, at planting, preemergence and postemergence.

By DuPont November 10, 2015

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