Larger than usual soybean aphid populations have been reported by a crop consultant in Adair, Boyle and Lincoln counties in central Kentucky. In addition, aphids in our sentinel plot in Shelby County have increased significantly.
Throughout the season we have seen small numbers of soybean aphids over most of the Kentucky soybean production area, but we have not seen populations of any importance.
But, we are likely to see increasing soybean populations in late-maturing beans. This is largely due (in my opinion) to reduced heat during this late summer early fall time, allowing for greater reproduction by the aphids.
These larger soybean aphid populations are most likely to occur in the production area that lies between I-65 and I-75. This is borne out by historic observations. Again it is likely the result of cooler temperatures as compared to the far western part of the state.
It is unlikely, but not impossible, that these populations will eventually require insecticidal treatment. The threshold for soybean aphid remains: 250 or more aphids per plant, on 80 percent of the plants, with an increasing population (two measurements required), in any vegetative stage through the reproductive stage R5.
Beans in R6 or later would need many more aphids per plant to warrant control and payback is unlikely.
In addition to these plot and field counts, the aphid suction trap in Lexington, Ky., and in Dixon Springs, Ill., have both caught soybean aphids, though only a few.
Suction traps in Princeton, Ky., and Portageville, Mo., have not yet captured any soybean aphids.
Suction trap captures for the remainder of the year are unlikely to have relevance to the 2008 infestation. These aphids have already begun the reverse migration back to their over-wintering host. They are therefore moving out of beans.
Producers and consultants should remain on the lookout in late-maturing beans.