Soybean aphids: Time to scout

August 3, 2022 / Categories: Uncategorized

By David Kee, Minnesota Soybean Research & Promotion Council Director of Research

According to the latest USDA-NASS report, 66% of the Minnesota soybean crop is rated good to excellent and about 81% of the crop is in flowering (five days behind the five-year average).  It looks like certain areas may be in position to produce a decent crop.  However, reports from across the state indicate that soybean aphids are present in increasing numbers.

It is time to scout.

The foundation of a good Integrated Pest Management (IPM) program is a properly implemented scouting program.  With the development of pyrethroid resistance, using the threshold of 250 aphid per-plant and a majority of the plants infested is critical for the stewardship of our chemical resources.  Utilization of the threshold also allows the predators such as ladybugs, and a growing population of the Aphelinus certus parasitic wasp, to keep the aphid population below damaging levels.  This saves time and expense of spraying an insecticide until needed.  Some salespeople will still suggest throwing in some insecticide, usually a generic “Warrior” with your fungicide application, regardless of the scouting reports.  However, this kind of thinking can lead to the development of pesticide resistance.

Minnesota Soybean checkoff resources support several exceptional entomology projects.  Listed below is a recent article developed by Bob Koch and Bruce Potter.  We lost chlorpyrifos, but we have three relatively new insecticides (Sivanto, Transform and Sefina) labeled for use in 2022.  The Soybean IPM team has tested these products over recent years and found their performance to be as effective, if not more, as several other commercially available materials.

Over the last six years, we have seen reports of pyrethroid resistant aphids over a broad geography. If your fields require an aphid insecticide application, contact your local agronomist about development of resistance near you.  If you apply an insecticide and have failure to control the pest, eliminate the normal paths of insecticide failure (rate to low, improper application, etc.). If you need to treat the field again, choose an insecticide from a different insecticide group. In addition, contact Bob Koch or Bruce Potter, .  The University, with support from Minnesota Soybean checkoff dollars, has developed a quick laboratory assay to determine if a soybean aphid population has developed resistance to pyrethroids.  Applying pyrethroids to pyrethroid resistant aphids will not make a farmer much money and will make the aphids more resistant. As you examine the pesticide choices, remember to read the pesticide labels. 

It is essential that we all better steward our chemical tools.  While there are dozens of insecticide products labeled to control soybean aphids, there are limited groups (families) of chemicals.  To steward your chemical families, one should rotate chemistry.  Given the spread of pyrethroid resistant aphids, starting with a pyrethroid is probably not a safe bet.  However, if you start with an inexpensive pyrethroid this leaves you with neonicotinoid or one of the new products as the next most logical selection for a follow up. Following that initial pyrethroid spray with a pyrethroid mix may provide pest control, but could provide more selection pressure that results in insecticide resistance

Soybean aphid control can be a complex problem, use all your tools wisely.

Click here to learn more from the University of Minnesota..

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