If indications from fall trappings in the Midwest are proven correct, growers may see minimal soybean aphid pressure this growing season, according to soybean experts at Pioneer Hi-Bred, a DuPont business.

"Soybean aphids tend to be more prominent during odd years," says Leon Streit, Pioneer senior research scientist. "However, although we are in an even-year growing season, Pioneer suggests growers continue to monitor fields regularly. There still may be areas that have a spike in soybean aphids."

Soybean aphids migrate in the fall to buckthorn, the overwintering host. According to the USDA integrated pest management Web site, suction traps in fall 2007 recorded low numbers of winged soybean aphids migrating. This indicates a year of low pressure.

While soybean aphid pressure may prove minimal this year, Pioneer suggests growers continue to scout fields for any indication of the pest. Aphids are small and yellow with distinct black cornicles ("tailpipes"). At only one-sixteenth inches long (the size of a pinhead or smaller), they cannot be distinguished from other aphids with the naked eye. It is the only aphid in North America known to extensively colonize in soybean fields.

"Aphids have natural enemies that help reduce populations," says John Soper, senior research director for Pioneer. "However, if a grower has 250 aphids per soybean plant, an insecticide treatment is recommended."
Based on ratings, growers should scout fields planted to varieties with a below-average resistance rating first and with greater frequency than fields planted to varieties with average, above-average or exceptional resistance scores," says Streit.

According to screening and characterization studies, aphids will reproduce faster on varieties with average or below-average resistance ratings than on varieties with above-average or exceptional resistance ratings.

If scouting results indicate a need for insecticide treatment and a grower is unable to make applications immediately, varieties with lower ratings should be prioritized for earliest treatment with an insect control product.

To aid in monitoring this pest, a number of state university Web sites and the USDA track the movement of aphids. Growers can monitor sites such as USDA Public Pipe Site (select soybean aphid in the upper right-hand corner drop-down menu) and begin scouting when aphids appear in their area.