Farmers Concerned About Bt-Resistant Corn Rootworm

Farmers Concerned About Bt-Resistant Corn Rootworm

Iowa growers are experiencing more problems trying to control rootworm with certain Bt traits in corn hybrids.

During the past several years, controlling corn rootworm has become more of a challenge for an increasing number of Iowa farmers. Populations of Bt-resistant corn rootworm have been found in the state, and more and more farmers are finding that corn hybrids which have genetic trait protection to guard against this yield-robbing pest are failing to provide control. More than half of farmers in a recent survey are concerned that the pest will become a major problem here, according to the 2013 Iowa Farm and Rural Life Poll.

ROOTWORM RESISTANCE: Iowa farmers are well aware that populations of Bt-resistant corn rootworm have been found in the state, and more than half are concerned the pest will become a major problem here, according to the 2013 Iowa Farm and Rural Life Poll.

"We asked this question in our poll because we wanted to better understand farmers' perspectives on the threat of Bt-resistant corn rootworms and various management practices," says J. Gordon Arbuckle Jr., a sociologist with Iowa State University Extension and Outreach. Arbuckle co-directs the annual poll with Paul Lasley, also an ISU Extension sociologist.

The questions were developed in partnership with the ISU Department of Entomology. Only farmers who planted corn, soybeans or other row crops in 2012 were asked these questions. The survey data were collected in February and March of 2013.

Controlling corn rootworm has become more of a challenge
"Corn rootworm is becoming a more prominent issue for Iowa corn growers. We've seen performance problems with Bt traits in corn hybrids in continuous cornfields since 2009," says Erin Hodgson, an ISU Extension entomologist and a member of the research team. Bt corn has been genetically modified to express genes from Bacillus thuringiensis or Bt. Farmers plant this type of corn to prevent corn root injury by larvae of the western corn rootworm in the Midwest. However, western corn rootworm populations that have evolved resistance to these transgenic technologies have been found in Iowa and other Corn Belt states.


Of the farmers responding to the 2013 Iowa Farm and Rural Life Poll, 69% indicated they are aware that populations of Bt-resistant corn rootworm have been found in Iowa. And 53% are concerned that Bt-resistant corn rootworm would become a major problem in the state, Arbuckle says.

Thirty-eight percent of the farmers said they had changed their approach to rootworm management during the past five years, and 77% of those who planned to plant corn in 2013 reported they would use a rootworm-resistant corn variety.

Two-thirds say farmers comply with refuge requirements
One method for maintaining rootworm susceptibility to Bt toxins is to establish "refuge" areas of corn plants that do not express Bt genes. If farmers do not follow the refuge recommendations, rootworms can rapidly evolve resistance to Bt.

"We asked farmers whether other farmers in their area generally comply with refuge requirements," says Arbuckle, "and 63% reported that farmers in their area comply, 7% indicated that they don't comply, and 31% indicated they didn't know." He adds, "We also asked farmers whether they had used particular practices to reduce the risk of corn rootworm larvae damage to corn plants, and how effective the practices were."

In the survey, 93% of farmers said they rotated corn and soybeans, and 86% planted rootworm-resistant corn. These two most commonly used strategies for preventing injury to corn by rootworm larvae were also rated as either effective or very effective by more than 80% of farmers, notes Arbuckle.


"The single most effective thing farmers can do to manage corn rootworm is to rotate away from corn. Planting soybeans, alfalfa or any other crop will starve corn rootworm larvae," says ISU entomologist Erin Hodgson. "We strongly encourage farmers to assess root injury in every cornfield, every year. Looking for rootworm feeding is an important step in evaluating Bt efficacy."

About the Iowa Farm & Rural Life Poll:
1,209 farmers participated in the 2013 Farm Poll and on average they were 65 years old. Because the farm poll is a panel survey, in which the same farmers participate in multiple years, participants are somewhat older on average than the general farmer population. Of the farmers responding, 52% earned more than half of their income from farming, while an additional 17% earned between 26% and 50% of their household income from the farm operation.

In addition to Bt-resistant corn rootworm, the 2013 Iowa Farm & Rural Life Poll asked for farmers' opinions on climate change, rented land, herbicide resistant weeds and soil health and compaction.

The 2013 Iowa Farm and Rural Life Poll summary report (PM 3061) and previous Iowa Farm and Rural Life Poll summary and topical reports are available to download from the ISU Extension Online Store and Extension Sociology. Conducted every year since 1982, the Iowa Farm & Rural Life Poll is the longest-running survey of its kind in the nation. ISU Extension, the Iowa Ag & Home Economics Experiment Station, Iowa Department of Agriculture & Land Stewardship, and the Iowa Agricultural Statistics Service are all partners in the farm poll effort.

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