Winter weather!

• 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.