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Aphids return

Aphids have been spotted In the northern soybean belt. Soybean growers are urged to get out there and scout the fields. Entomologists recommend scouting at least once a week if weather conditions are ripe for infestation or if aphids are already present. Multiple field visits over critical soybean development stages of flowering and pod set are necessary to determine whether a soybean aphid population is increasing, says Eileen Cullen, University of Wisconsin–Madison Extension entomologist.

Cullen notes that growers should scout between 20 to 30 plants throughout the field. The threshold to warrant insecticidal treatment is when 80% of soybean plants (in the R1 to R5 stage) in a field are infested with an average 250 aphids/plant.

Several universities have good Web sites that growers can check for aphid updates, and several are participating in the suction trap network that is monitoring aphid movement in a six-state area. These 21-ft.-high traps help researchers monitor winged aphids as they fly to buckthorn plants in the fall. Soybean aphids overwinter on this common shrub. From each overwintered egg on buckthorn in early spring, a wingless female aphid hatches and then gives live birth to wingless female aphid nymphs. In late spring, winged soybean aphid females are produced that leave the buckthorn in search of soybeans, Cullen says. She adds that last year’s suction trap catch in Illinois was the highest catch since the suction trap network was established four years ago.

Finally, another tool available to growers is the Web site, hosted by the USDA. Although it is primarily devoted to Asian soybean rust, it features frequent discussions and state reports on foliar pests, including Septoria, brown spot, spider mites . . . and the soybean aphid.

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