Jeff Wessel, farm manager of the J. F. Richards Demonstration and Research Farm at Joliet Junior College, reported the first soybean aphids of the season in Illinois on May 29. He found as many as 40 aphids on one V2-V3 stage soybean plant. He found various numbers of aphids and ants on other plants in the planting-date study that was planted on April 9. Jeff indicated that a natural area on the Joliet Junior College campus has a significant number of buckthorn plants, the overwintering host for soybean aphids. Obviously, soybean aphids have left their overwintering hosts in the area to colonize these early-planted soybeans. In the three years during which soybean aphids have been found in the spring in Illinois, Jeff's report is the earliest report of soybean aphids on seedling soybeans.
David Voegtlin, research entomologist with the Illinois Natural History Survey, reported finding the first winged soybean aphid adults in Illinois this season on April 23. Dave and his coworkers had been watching soybean aphids on Rhamnus cathartica, a buckthorn species, and had found hundreds of aphids on some of the small plants. However, there were no soybeans in the vicinity, so the aphids' movement to their secondary host had not commenced at the time.
You might recall that the scientific literature suggests that populations of soybean aphids develop more readily when temperatures are cool. Thus far this spring, our temperatures certainly have been cool, so soybean aphids may be off to a fast start. It's also important to remember that yield losses usually are more significant when soybean aphids colonize seedling soybeans than when they colonize older plants.
This early sighting of soybean aphids serves as a heads-up for everyone scouting soybeans right now. During the past few years, David Voegtlin and his co-workers have established and operated a set of suction traps (currently at nine locations) designed to sample the air for flying aphids. Dave and his team have had limited success capturing winged soybean aphids during the spring movement from buckthorn to soybeans. He has speculated that the number of aphids flying in the spring is relatively small compared with the larger flights that occur later in the summer. Nonetheless, you should check out information about the Soybean Aphid Suction Trap Network. At the time I wrote this article, no data for 2003 had been posted. However, Dave and his coworkers are looking through the samples collected thus far this spring and will report their findings soon.
Again, just keep your eyes open for soybean aphid colonies on seedling soybeans. Because soybean aphids were not very prevalent in 2002, neither were some of their predators, most notably the multicolored Asian lady beetle. Consequently, if soybean aphids become established this spring and few predators are around, their densities could increase rapidly. We'll keep you posted as we learn more from around Illinois and from neighboring states.--Kevin Steffey