Weather Extremes Are Learning Opportunities
“A single resistant gene can reduce aphid populations from thousands to hundreds,” said O’Neal.
“When two genes are combined, survivors drop from hundreds per plant to tens. What we don’t know is how this works, whether by producing a toxin or simply allowing the plant to ignore the aphids.”
While other pests such as corn rootworm have developed resistance to gene-based protection, work in the O’Neal lab is focused on preventing this from happening with the soybeanaphid.
Although single and pyramid aphid resistance is available, it is not found in many varieties. Through his website, O’Neal reports the commercial sources of soybean aphid resistant varieties (http://www.ent.iastate.edu/soybeanaphid/files/SBAresistance2012corrected.pdf).
“The limited use of the aphid-resistant genes contributes to preventing soybean aphids from becoming resistant to these genes,” O’Neal said. “By using a pyramid line, farmers are employing a strategy that can also limit soybean aphids from becoming resistant to these genes as well.”
O’Neal’s lab is exploring other tactics that may be necessary to prevent resistance from developing if more farmers use soybean aphid-resistant varieties. “With funding from the Soybean Checkoff program, we are developing Insect Resistance Management (IRM) plans for the long-term use of aphidresistant varieties. We are exploring if a refuge-in-a-bag strategy that is used for corn rootworms can be used for soybean aphids.”
What is made clear by such extreme weather years is how much is yet to be learned about crop disease. Dean Malvick, Extension plant pathologist, University of Minnesota, reported he will be keeping a close eye on phytophthora, rhizoctonia and white mold diseases of soybean. The wet spring with prolonged
planting set the stage for problems with them as well. Smaller plants in wet but warm, high organic soils are also favored by rhizoctonia. He cites cases with soybeans planted following peas in central Minnesota where half the field was killed. This year, similar conditions are much more widespread. The warm and wet field conditions in many fields also increase the risk of phytophthora rot, which is being seen in a number of fields.
The wet weather pattern may increase the risk of white mold if it continues into flowering and pod set, although hot weather during that time will tend to decrease this disease.