Friday, August 11, 2017

UPDATE: NW MN Soybean Aphid Scouting Summary for July 31 to August 8, 2017

Soybean aphid populations continue to increase in west and south central Minnesota, though we are approaching a time when growth stage, day length and natural controls in those fields are likely to lead to declining populations soon. More fields have been treated, BUT not every field is at threshold and scouting to determine treatment needs is highly recommended. 

Also, be sure to follow up treatment by scouting to determine control success. Some of the fields we have scouted in NW MN show lots of dead aphids. HOWEVER, it is not uncommon to see plants where aphids survived, numbering into the 100's on some of those plants. These are fields most likely treated with a Pyrethroid - Organophosphate premix.

Where we have treated research plots with chlorpyrifos, kill has been very good. The only aphids in those sites have been winged, migrating aphids in the tops of plants. Their numbers and their babies have remained low in number and time should be on our side in those locations.

Reports for southern MN can be found at Southwest Minnesota IPM Stuff Newsletter

Comments from his August 10 report:

"Aphid treatment continues and has expanded to some new areas. Fields in the southern part of the state that have higher aphid populations are related to planting date and moisture. The earlier planted, wetter parts of the state as well as some of the extremely dry areas have lower aphid populations. Remember, there are always exceptions."

Bruce Potter 
UMN Extension IPM Specialist


Be sure to scout a field and determine if threshold populations are present and require treatment. Issues related to pyrethroid-resistance emphasize the need to treat only when infestations are justified to prevent yield loss. Avoid unnecessary treatments to reduce the chance of finding surviving, resistant aphids and help preserve our insecticide tools for the future. 

Before making any treatment decisions, be sure to read:


We remind everyone to base treatment decisions on the threshold of 250 aphids per plant, 80% incidence and increasing populations. 

We are observing parasitic aphid activity, fungal infections of aphid colonies, and increasing numbers of predators in surveyed fields. These are all good developments that can help slow aphid population growth. In addition, the northern fields are beginning to produce winged aphids. this can produce some out-migration that can be good for infested fields but contribute to new infestations elsewhere.

The MN survey map illustrates where aphid numbers were assessed last week. Each pie chart represents a production field that was scouted. Fields are selected randomly. Scouts estimate populations on each plant sampled, placing a tally mark in the estimated # of aphid / plant range.The pie chart indicates the % plants observed within a range. Any pie charts that begin to show orange and red indicate those fields had plants with aphids into the 100's. The more red, the greater the percent plants with large infestations of aphids.This map was updated Tuesday (8/8/17).