Update on Soybean Aphid numbers around Rochester - Keep Scouting
August 8, 2014
Lisa M. Behnken
We have been scouting several soybean fields in the area for aphids over the past three weeks. The soybean aphid numbers have been very low, most plants have very few aphids per plant, with only one or two plants at over 40 aphids/plant (counted as a positive plant using the Speed Scouting method). This is well below the economic threshold of 250 aphids per plant, 80% of plants with aphids and population increasing.
The only "hot spot" we have is in our plot area at Rochester. This location is the first place we found soybean aphids this year (always is) and the population has been increasing. These are droughty soils, and there is plenty of buckthorn nearby to provide a source of aphids for early colonization. Having said this, the population has not reached the economic threshold yet. We will continue to scout these fields for a few more weeks, targeting Monday and Tuesday and will keep you posted.
We use the speed scouting method to collect and evaluate the aphid population. We collect 30 plants randomly (as recommended) across the field and evaluate them in the lab so we can do additional counting if necessary. This method is still an approved and effective method of scouting for soybean aphids. Worksheets are available at: http://goo.gl/UC9vus.
See updated information about soybean aphids from UM Extension Entomologist, Bob Koch and IPM Specialist, Bruce Potter at http://www.extension.umn.edu/agriculture/soybean/pest/docs/soybean-aphid-scouting.pdf
Note: If seed treatments that included insecticides were used in your fields, aphid populations will be "reduced" for awhile. Our field research has shown about a 2-week delay in aphid population establishment when seed treatments with insecticides were used at planting. So, keep scouting.
|Soybean aphids found in our Rochester plots. This is the only location (of those we are scouting) with aphid numbers approaching, but NOT at, the economic threshold level.|