Welcome to January! We have just recorded several of the coldest nights of 2013. An overnight low of minus 3.60 Fahrenheit was recorded Jan. 22 at the Northern Illinois Agronomy Research Center (NIARC). The cold temperatures cause discomfort for many of us, and present challenges to those who raise livestock or work outside. But is there a silver lining for farmers? Can the cold weather benefit farmers by decreasing survivability of insect pests? Winter insect mortality is affected by a number of variables including:
• Temperature fluctuations.
• Snow cover (insulating effect.)
• Overwinter stage of insect (adult, pupa, egg.)
• Overwintering site of insect (above ground, soil-borne.)
Let’s look at two corn insect pests and attempt to prognosticate. Corn flea beetles are small, shiny, black beetles, approximately 1/16-inch long that remove leaf tissue of corn as they feed leaving long scratch marks. More importantly, corn flea beetles are the primary vector of Stewart’s wilt bacterial disease. Stewart’s wilt is an economically important disease of sweet corn hybrids and seed corn inbreds that are not resistant to it. This insect pest is rarely an issue with commercial hybrids. The corn flea beetle overwinters as an adult in the soil or in crop debris. We predict the probable survivability of this insect based on averaging the monthly temperatures of December, January and February. An average temperature of 270 Fahrenheit or lower would suggest little chance for damage from this insect or the diseases that it vectors. An average temperature of 330 Fahrenheit or above suggests the likelihood for this insect to survive, and Stewart’s Wilt to be present is high. We have currently experienced a warm December (32.80 F.) with a considerable cooling to date in January (23.50 F. through Jan. 24). February temperatures will be needed before we can determine the likelihood of this insect pest in 2013.
We can provide a more definitive answer with the Western corn rootworm beetle. This insect, considered the most economic damaging to corn on an annual basis, is currently overwintering in our soils as an egg. A corn rootworm survival study was conducted by Mike Gray and Jon Tollefson at Iowa State University during the winters of 1983-85. That study examined the influence of different tillage methods and winter weather on rootworm egg survival. To aid our memories, the winter of 1983-84 was characterized by below normal snowfall and temperatures. The recorded temperature for December was approximately 15 degrees colder than average. The study indicated corn rootworm egg survival was affected by tillage during a severe winter. Egg survivorship was reduced by about 63-75 percent in plots that had been mold-board plowed during the fall. However, there was no significant reduction in egg survivorship in plots that were no tilled or chisel plowed. During the more moderate 1984-85 winter, mortality seems to be negligible; there were no significant differences among the four tillage methods. From this study, unless corn fields were moldboard plowed, and the remainder of our winter experiences below normal temperatures without snow cover, I would not expect a significant increase in rootworm mortality.
Recently Mike Gray, University of Illinois entomologist, shared the following insights and 2012 research results with the Western corn rootworm beetle. On-farm research in the early 1990s revealed that 26 of 58 producers’ continuous cornfields had root injury at or above the economic injury index. Recently published research indicates that for every one node of roots pruned by corn rootworms, a 15 percent yield loss may occur. Producers currently have three Bt proteins offer protection against corn rootworm larval injury: mCry3A, Cry34/35Ab1, and Cry3Bb1. Field level resistance has been confirmed to the Cry3Bb1 protein in some areas of northeast Iowa and northwest Illinois.
At the NIARC in 2012, yield reductions were very severe when only a soil insecticide was used on certain non-Bt hybrids. The comparative poor performance of soil applied insecticides was likely due to the very dry conditions. The 2012 entomology research conducted by the University of Illinois can be accessed at the on-Target website. http://ipm.illinois.edu/ontarget/.
Make the most of your educational opportunities; we will be in the fields before you know it!
Russ Higgins is from the University of Illinois Extension, Northern Illinois Agronomy Research Center.