Monday, July 31, 2017

Pyrethroid resistant soybean aphids: What are your control options?

Bruce Potter (Extension IPM Specialist, U of MN), Robert Koch (Extension Entomologist, U of MN), Phil Glogoza (Extension Educator – Crops, U of MN), Ian MacRae (Extension Entomologist, U of MN), and Janet Knodel (Extension Entomologist, NDSU) 

We are receiving an increasing number of reports of pyrethroid insecticide failures for soybean aphid management from northwest and central Minnesota, and northeastern North Dakota this year. However, many areas of Minnesota and North Dakota still have low, non-yield threatening aphid numbers and scouting should continue to determine when to apply insecticides. 

In this article, we review the insecticide groups used for soybean aphid control (Table 1) and discuss the potential role of and challenges associated with insecticide mixtures. 
We are all familiar with the multistate, researched-based economic threshold of 250 aphids/plant for determining when to apply insecticides for soybean aphid. Waiting until this economic threshold to apply insecticides is KEY for ensuring continued efficacy of current insecticides for soybean aphid. Using the soybean aphid economic threshold for deciding when to apply insecticides will:

  • Prevent unnecessary selection pressure for insecticide resistance; 
  • Save time by reducing the odds of a field needing a second treatment;
  • Mitigate secondary pest problems like spider mites; and perhaps most importantly
  • Reduce production expenses.

Poor insecticide resistance management of a mobile insect like soybean aphid affects not just your farm, but other farmers as well. 

Read more »

UPDATE: NW MN Soybean Aphid Scouting Summary for July 21 to 28, 2017

Soybean aphid populations continue to increase in NW Minnesota. Populations are increasing in the west central and central areas, too. More fields are being treated, HOWEVER, not every field is at threshold. 

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

Comments from his July 31 report:
"Treatment of economic threshold populations are now being made in more southerly areas and the general trend is trend is economic threshold populations developing from north to south.

"Parts of Central Minnesota are receiving insecticide applications and sentinel plots at Morris had a fairly uniform 40 aphids/plant early last week. Some fields in parts of the Minnesota River Valley are at economic threshold now.

"As of last week, there were many areas of MN, including most of the SWROC, that still had low aphid populations. Winged aphids can change that quickly.

"The next two weeks will be the critical scouting window for most areas. Remember that most aphids will often be found lower in the canopy now.

"This year, much of SW Minnesota appears to have been colonized by non-local aphids."
Bruce Potter 
UMN Extension IPM Specialist