As reported in the July 21st issue of Wisconsin Crop Manager, soybean aphids continue to warrant close monitoring. By mid-July fields exceeded threshold in many southern WI counties and received timely insecticide application based on populations in excess of 250 aphids per plant average.
Critical to Watch Soybean Aphids asTemperatures Cool
Eileen Cullen, Extension Entomologist,
UW Entomology Department
As reported in the July 21st issue of Wisconsin Crop Manager, soybean aphids continue to warrant close monitoring. By mid-July fields exceeded threshold in many southern WI counties and received timely
insecticide application based on populations in excess of 250 aphids per plant average. After a recent high heat
index over the weekend, temperatures are forecasted to be quite mild this next week in the 80s and even below.
Mild temperatures in the upper 70s to mid 80s are ideal for soybean aphid reproduction. Fields that are subthreshold should be watched closely for increase. In our plots at Arlington, numbers continued below threshold as of 7/22 and we are watching closely this week (counts being conducted Thursday 7/28) to detect plot increase to 250 per plant.
Dave West, crop consultant near Viroqua, WI, has noted soybean aphid morphology and distribution on plants
very similar to what Craig Grau and I are seeing at West Madison in the soybean variety aphid/virus study. 7/26, Dave reports a high proportion of soybean aphids on the older leaves compared to the newest trifoliate. Dave asked about the viability of the small, pale (nearly white) aphids on the older leaves versus healthy looking,
yellow/green soybean aphids on the newest trifoliate. I don’t have an answer at this point for why this small, pale white morph occurs (usually on the underside of older leaves) by mid-summer. (Many of us noticed this in 2003 as well). Specifically, Dave asked if the small white morph is known to represent a significant event in the soybean aphid life cycle. I’ll keep you updated if I learn otherwise, but at this point I do not know of a scientific or researched answer to this question, beyond the speculation that older leaves are of lower nutritional quality to the aphids as compared to newest trifoliate. Nonetheless, we do continue to include these soybean aphids in our counts.
Table 1 is reproduced here from the July 22nd issue of the WI DATCP WisconsinPest Bulletin http://pestbulletin.wi.gov/, an excellent link for extensive statewide pest developments throughout Wisconsin. Very similar to plots at Arlington, WI DATCP reports many fields currently just below 250 aphids/plant. Watch fields closely to determine whether existing populations increase to and beyond threshold, and to detect winged aphids dispersing into fields to start new colonies
Table 1. reprinted from the WI DATCP Pest Bulletin July 22nd, 2005.
Courtesy of Krista Lambrecht and WI DATCP Pest Survey Team.
