Concerns about herbicide resistance are growing in Iowa, as weeds such as waterhemp are showing resistance to multiple herbicide groups.

The 2017 Iowa Farm and Rural Life Poll surveyed Iowa farmers to ask them if they have herbicide-resistant weeds in their fields, to learn about perspectives on the manageability of major weeds and to measure their level of concern about herbicide resistance.

Several questions asked about weed management had previously been asked in 2013, allowing for comparisons between years.

The poll found 22% of respondents believed they had weeds that were resistant to PPO inhibitor herbicides in their fields, up substantially from 3% in 2013. And 12% believed they had weeds that were resistant to HPPD inhibitor herbicides, compared to 4% in 2013.

Farmers were also asked if they had changed their weed management program due to concern about herbicide-resistant weeds. A larger number of respondents had, with 77% acknowledging a change, up from 52% in 2013. Many farmers sought assistance with weed control, as the percentage of farmers who develop their own herbicide programs dropped from 45% in 2013 to 36% in 2017.

Farmers changing strategies
“Farmers are changing their weed management approaches due to worries about herbicide resistance,” says J. Arbuckle, ISU Extension sociologist and director of the Farm Poll survey. “And one of the strategies seems to be more reliance on others for herbicide program development.”

The poll also asked questions about the manageability of major weeds. A majority (more than 50%) of farmers indicated waterhemp (80%), marestail and horseweed (52%), and giant ragweed (51%) had become more difficult to control or had become resistant to herbicides.

Lambsquarter was listed by 46% of respondents as easy to control, while 45% said it has become more difficult to control. Common ragweed was the only weed listed by most farmers (55%) as easy to control.

The poll also found that 54% of farmers are not familiar with Palmer amaranth. Seven percent claimed it was easily controlled, while 23% said it had become more difficult to control and 16% listed it as herbicide-resistant.

“Palmer amaranth is a highly invasive weed that has evolved herbicide resistance in other states, so it’s important that farmers be able to identify and eradicate it,” Arbuckle said. “The finding that most respondents were not familiar with the weed means that more intensive awareness-raising efforts are needed.”

Speed of resistance
Several survey questions measured farmer concern about herbicide-resistant weeds. Nearly 80% agreed that they were concerned about the spread of herbicide-resistant weeds from other regions of the United States and, locally, other counties. Also, 77% agreed they were concerned about spread of weeds from neighboring farms.

 “Most Iowa farmers are concerned about the potential spread of herbicide-resistant weeds, and many are changing their strategies due to that concern,” Arbuckle says. “The survey results show that more outreach is needed, particularly on identification and management of Palmer amaranth.

Recent research shows that non-herbicide weed management approaches, such as extended rotations and cover crops, can also be effective weed suppression techniques.

The Iowa Farm and Rural Life Poll has been in existence since 1982, surveying Iowa farmers on issues of importance to agricultural stakeholders. It is the longest-running survey of its kind in the nation.

Source: Iowa State University