It turns out that hot weather is hard on crops and soybean aphids. If there is any advantage to the extreme heat gripping the state, it could be that soybean aphid populations have remained quite low as a result. Few, if any farmers have needed to treat for them so far this season.
It's been too hot for them to get established in any great numbers," says Keith Jarvi, University of Nebraska Extension educator in Dakota, Dixon and Thurston counties.
Soybean aphids lay eggs on buckthorn in the fall, and overwinter until hatching in the spring. Normally, a few aphids are observed in late June and early July. Usually, aphids are not found in fields regularly until mid-July. In Nebraska, populations tend to increase rapidly at R3 to R4 growth stages and this usually occurs in early August, Jarvi says.
"Of course, everything is two to three weeks ahead this year, so growth stage and weather may not synchronize for aphids this year, which is another reason we may not see many."
Reproduction and development is most rapid for aphids when temperatures are in the 70s through the mid-80s. The do not do well when the temperature rises to the 90s, and they begin to die when the temperature reaches 95 degrees, as it has many times this summer.
To treat for aphids, it is recommended that there be at least 200 aphids per plant across the field and the population is increasing. This normally allows for a four to five day treatment window, before populations grow to around 600 per plant.