Kansas State University entomologist Brian McCornack discovered soybean aphids July 11 in some of his Riley County soybean research plots. The aphids had started colonizing - feeding on the soybean plants - and to produce many young.
"That indicates they had probably been around for seven to 10 days prior to detection," said K-State Research and Extension entomologist Jeff Whitworth, who is encouraging producers to scout for the pests.
Soybean aphids were first detected in Kansas in 2002. But, most soybeans were well past the growth stages that are susceptible to soybean aphid feeding damage, Whitworth said.
"We´ve had soybean aphid migration into the state every year since then, but it was only in 2004 that environmental conditions allowed them to reach damaging population levels," he said.
Soybean aphids damage the plant by sucking juice from the phloem (veins). This can stunt plant growth, reduce pod set, and/or result in smaller seeds.
The aphids are tiny, lime-green to yellow insects with black-tipped cornicles (tailpipes). They are most commonly found on the underside of leaves of early vegetative plants but may be found on all parts of late vegetative to early reproductive plants.
Healthy aphid populations produce enough shiny, sticky honeydew to be very noticeable, and it may be covered with a black "sooty" mold. They can also transmit several viral diseases that further affect the plant.
When planning a strategy to manage soybean aphids, Whitworth said, a producer should take natural enemy populations and the weather into consideration.
Lady beetles, green lacewings, and other predators feed vigorously on these aphids. Along with aphid parasites, they help regulate these pests in most years.
High temperatures also help to slow soybean aphid reproduction, which helps the predators and parasites to keep populations in check, he said. Daytime temperatures need to exceed 97 degrees F for a few days, however, to have a negative impact on aphid populations.
Information on scouting for soybean aphids, treatment thresholds, and insecticide treatment options is available at county and district K- State Research and Extension offices, as well as on the university´s entomology Web site. Information is also available by contacting Whitworth at jwhitwor@ksu.edu or 785-532-5656 or Phil Sloderbeck at psloderb@ksu.edu.