Soybean Aphid Management — A Step-by-Step Guide to Control

Soybean Aphid Management — A Step-by-Step Guide to Control

July 1, 2009

Identification and Scouting

For more on soybean aphids, their life cycle and scouting for them, see a July 1 CropWatch article, It's Time to Scout for Soybean Aphids

 

Soybean Aphid Threshold = 250

In late vegetative through R5 stage soybeans the treatment threshold is 250 aphids per plant (field average) with 80% of the plants infested and populations increasing.
  1. Scouting. Begin scouting soybean fields once or twice a week in late June to early July. Check 20 to 30 plants per field. Aphids are most likely to concentrate at the very top of the plant early in the season, and will move onto stems and within the canopy as populations grow and/or the plant reaches mid to late reproductive stages. As the season progresses, aphid numbers can change rapidly (populations can double in 2-3 days).

     

  2. Economic Threshold. The current recommended threshold for late vegetative through R5 stage soybeans is 250 aphids per plant (field average) with 80% of the plants infested and populations increasing. Depending on economic conditions, this gives you about five to seven days to schedule treatment before populations reach damaging levels (if populations do not increase during these seven days, you may be able to eliminate or delay treatment). Determining if the aphid population is actively increasing requires several visits to the field. Factors favorable for aphid increase are relatively cool temps, plant stress (particularly drought), and lack of natural enemies.

     

  3. Natural Enemies. Look for the presence of aphid natural enemies such as lady beetles, minute pirate bugs, and other insect predators. Aphid "mummies" (light brown, swollen aphids) indicate the presence of parasitoids. These predators and parasitoids may keep low or moderate aphid populations in check (under 200 aphids per plant). One can often find soybean aphids by examining plants where lady beetles are observed.

     

  4. Winged Aphids. Look for the presence of winged aphids. If the majority of aphids are winged or developing wings, the aphids may soon leave the field and treatment can be avoided.

     

  5. Late Treatment. If the plants are covered with honeydew or sooty mold, or stunted, an insecticide treatment may still be of value but the optimum time of treatment is past.

     

  6. Test Strip. If fields are treated, leave an untreated test strip to compare against sprayed sections. This also provides a refuge for beneficial insects.

     

  7. Coverage. Good insecticide coverage and penetration is required for optimal control of soybean aphid, as many aphids feed on the undersides of the leaves and within the canopy. Use high water volume and pressure. Aerial application works well when high water volume is used (5 gallons of water per acres recommended).

     

  8. Insecticide Selection. Several insecticides are labeled for the soybean aphid. A list of registered insecticides, rates, preharvest intervals, and grazing restrictions can be found at http://entomology.unl.edu/instabls/soyaphid.htm. Pyrethroids have a relatively long residual. Chlorpyrifos has a fuming action, and may work well in heavy canopies or high temperatures. Dimethoate is least effective.

     

  9. Bee Safety. Spraying flowering soybean poses a threat to honey bees. Inform nearby beekeepers of treatment plans and follow precautions to minimize honey bee kills. When there is concern about honey bees, pyrethroids are the better insecticide choice.

     

  10. Not With Glyphosates. We do not generally recommend applying an insecticide at glyphosate application. In Nebraska this is usually before the aphids reach damaging levels, or are even in the field. Insecticide treatment at this time would simply rid the field of natural enemies. In addition, application methods for herbicides (e.g. lower pressures) are not optimal for good insecticide efficacy.

     

  11. Dual Treatment. If soybean rust is present and being sprayed when soybean aphid thresholds also are met, a fungicide/insecticide tank mix should be effective because application methods for both require high water pressure for adequate penetration and coverage. 

Resource

More information can be found at entomology.unl.edu or from your local UNL Extension office.

Tom Hunt, Extension Entomologist
Northeast REC Haskell Ag Lab, Concord
Keith Jarvi
Extension Educator in Dakota, Dixon and Thurston counties