|Ohio Farm News
By Seve Bartels
This last summer we scouted soybeans for soybean rust each week up through October 10. Fortunately we did not find any rust. It did, however, get to Kentucky again this year and a month earlier than in 2005.
As we looked for rust, we also monitored aphid population. We found none to speak of until August 25. The population increased every week thereafter until it reached a high of more than 550 per plant on September 24 in our sentinel plot. The population declined after that as the winged aphid left the soybeans to overwinter in buckthorn.
Ron Hammond, an Ohio State research entomologist with the Ohio Agricultural Research and Development Center is predicting high population numbers based on recent observations of high adult numbers and increased egg laying on buckthorn - the overwintering host.
Hammond found large numbers of winged aphids as well as unwinged individuals. The significance of these finds are that the soybean aphid is still following the sequence that will in all likelihood lead to larger densities and economic problems next year. Our colleagues from northern states are seeing the same thing.
“It seems we are right on schedule with our population cycle” Hammond said.
The soybean aphid, a sapsucker relatively new to Ohio, can devastate soybean fields with its voracious appetite if in high enough numbers. Since its discovery in 2001, researchers have annually tracked and accurately predicted its population pattern: high in odd-numbered years, low in even-numbered years.
Hammond said that the level of soybean aphid populations may be tied to the population of the multicolored Asian ladybeetle, a known predator. Put simply, when soybean aphid numbers are low - as they were this growing season - ladybeetle numbers are also low, and when soybean aphid numbers are high, the ladybeetle makes its appearance.
There were low levels of the ladybeetle this year. That’s why the soybean aphid is overwintering in high numbers. Expect the multicolored Asian ladybeetle to be in high numbers next year in response to high soybean aphids in the field.
Some management recommendations include: (1) Plant early and then scout fields on a regular basis; (2) Treat with foliar insecticides when aphids reach their threshold of 250 aphids per plant. Avoid seed treatments. Although they’re effective on very early populations, they do not maintain their efficacy later in the season when aphids reach higher populations and begin their heavy feeding; (3) Practice skip-row planting, a technique that prevents spray machinery from damaging plants, thereby potentially reducing yields.
This farm news was published in the Oct. 18, 2006 issue of Farm World, serving Indiana, Ohio, Illinois, Kentucky, Michigan and Tennessee.