By LON TONNESON
Early alarm bells are going off in South Dakota and North Dakota over the possible development of Bt-resistant corn rootworm.
In South Dakota last year, some fields of Bt-corn near Lake Campbell, Bruce, Milbank, Baltic and Colman exhibited signs of corn rootworm damage.
South Dakota State University entomologists are trying to learn about the extent of the damage.
Key Points
• Bt-resistant corn rootworm may be in South Dakota and North Dakota.
• Evidence of damage was seen in both states last year.
• Findings should alert farmers to take steps to safeguard their corn.
“Not all problem fields are reported; therefore, it is difficult to quantify whether these are isolated instances or represent a potential broader-scale occurrence,” says Ada Szczepaniec, SDSU assistant professor and Extension entomologist. “In those fields that have been investigated, resistance to Bt hybrids has not been confirmed yet, and we will work to collect data to test this next year.”
Fields with a history of at least three years of continuous corn with the same Bt hybrid are at the greatest risk of having Bt-resistant populations of corn rootworms.
She is asking South Dakota corn growers to complete an online survey about the damage.
“The survey will take only a minute or two to complete, and it will provide us with invaluable information on the needs of corn producers in the state. Knowledge of the locations and scope of corn rootworm issues will enable us to prepare customized Extension resources based on specific needs of the corn producers in the state,” Szczepaniec says.
See www.surveymonkey.com/s/CRWinSouthDakota.
North Dakota
Janet Knodel, North Dakota State University Extension entomologist, says that last summer she visited a cornfield in northern Richland County, N.D., that appeared to have resistant corn rootworm damage.
The field had been in continuous corn for the last 10 years and had been the same Bt trait, YieldGard VT Triple (VT3) (Cry1Ab and Cry3Bb1) for about five years. Last year, it was planted to Genuity SmartStax RIB (Cry1A.105, Cry2Ab2, Cry1F, Cry3Bb1, Cry34/35Ab1) hybrid.
“It was evident that volunteer corn (a good food source for resistant corn rootworms) was a problem in the field for several years,” she wrote in the NDSU Crop and Pest Report. “Western corn rootworms were very common and outnumbered the northern corn rootworms by 10 to 1.
It was easy to observe rootworm lodging and root feeding on both the volunteer corn and Genuity SmartStax RIB corn. Other states [Illinois, Iowa and Minnesota] also have reported severe cases of rootworm damage to Bt hybrids expressing Cry3Bb1 protein. Most of these fields have been continuous corn for at least three years, and producers have relied on a single Bt trait to control corn rootworm.
“In spite of the increased numbers of western corn rootworm, lodging and lack of control with Cry3Bb1 protein, this does not confirm corn rootworm resistance to Bt hybrids in North Dakota. Resistance confirmation requires a detailed bioassay and further sampling,” she continued.
The finding, however, is an “early alarm call to wake up and start using long-term integrated pest management strategies” to prevent the development of corn rootworm resistance to Bt proteins and to preserve the Bt technology, she says.
Bugged out: Western corn rootworm adults feed on an exposed corn ear due to stunted husk leaves from drought stress.
Photos by : P. Beauzay, NDSU Extension entomology
Western corn rootworm
This article published in the January, 2013 edition of DAKOTA FARMER.
All rights reserved. Copyright Farm Progress Cos. 2013.