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Thinking Strategically about Soybean Aphids

University of Minnesota Extension, Stearns County News
July 8, 2015         
           
Source:  Dan Martens, Extension Educator
University of Minnesota Extension
Stearns, Benton & Morrison Counties

 

Thinking Strategically about Soybean Aphids
By Dan Martens, University of Minnesota Extension

FOLEY, Minn. (07/02/2015) — During discussion about small grains north of Kimball on June 23, Phil Glogoza, Extension Regional Educator for pest management talked about finding dead soybean aphids there were dull orange to gray in color. He said these aphids died from fungal infections due to frequent rains and warm weather. He advised following scouting and treatment threshold guidelines carefully.

Spraying too early kills predator insects that have a good chance of keeping soybean aphids under control and increases the chance of needing a second spray. Responsible use of insecticides is important for care of predator insect populations, pollinators, potential profits, soil and water resources, and agriculture’s stewardship credibility.

The following discussion was provided by Robert Koch, U of M Extension Entomologist for Soybeans. It was posted on the Minnesota Crop News Website on June 18. Aphid levels are well below thresholds yet. And these guidelines should continue to serve us well through the growing season. Here is Koch’s discussion…

“Soybean aphids can now be found in soybean fields in various areas of Minnesota. However, there is no need to panic. The percentage of plants infested and number of aphids per plant are still low (far below economic levels). Furthermore, aphid predators, such as lady beetles, have been observed feeding on soybean aphids in some fields.  As we get into late June (and early July), you may want to begin checking soybean fields for aphids. (Tracking trends and patterns in fields is helpful.)

Early in the season, pay particular attention to fields in areas with abundant buckthorn, smaller fields with wooded borders, and/or early-planted fields. At this time of year, soybean aphids will typically be found on the new growth. Also, the presence of lady beetles or ants on soybean plants is often an indicator of the presence of early-season aphid colonies.

Last year, Bruce Potter and I (Koch) created a guide for soybean aphid scouting in Minnesota (http://z.umn.edu/soybeanaphidscouting). Here’s a summary of some key points on aphid scouting and management that you should keep in mind throughout this growing season.

  1. Scouting requires getting into the field and estimating aphid numbers on plants.
  2. Aphid populations can vary from field to field, so each field being managed should be scouted.
  3. Estimate aphids from a representative number of plants spread throughout the field.
  4. Aphid counts should include winged and wingless aphids, but don’t count dead aphids or aphid look-alikes.
  5. Infested fields should be scouted on a regular basis (about weekly). Rapidly growing populations may need to be scouted more frequently.
  6. Scouting should continue until R6.5 (pods and leaves begin to yellow), regardless of calendar date.
  7. Through R5 (seeds developing, but pod cavity not filled), use the economic threshold of an average of 250 aphids per plant AND aphids on more than 80% of plants AND aphid populations increasing.
  8. Yield loss can occur into early R6 (pod cavity filled by seed). At this stage consider insecticide application if aphid populations are high and plants are experiencing other stress.
  9. Fields should be scouted after application of a foliar insecticide to monitor for resurgence of the aphid population or outbreak of a secondary pest.

Again, the soybean aphid infestations that I have seen and heard of this year are currently far below economic levels. It is too early to tell what will become of these infestations as the season progresses. However, if you implement a regular scouting program, you can stay abreast of the infestations in your fields.”

Thanks, Robert.
Calendar Note: Friday July 10 - Summer Field Day at West Central Research Center at Morris. Registration 7:30 a.m. Three tour choices run at 8 a.m. and 9:15 a.m. plus special tours. Do Internet search for “Summer Field Day 2015 at WCROC Morris MN” or call County Extension Office for info.
 

Contacts

Daniel Martens
Extension Educator, Ag Production Systems
(320) 968-5077
marte011@umn.edu
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