Two Spotted Spider Mites in Soybeans

By Ed Corrigan

I have taken a number of calls the last couple of weeks regarding Spider mites in soybeans. High temperatures with dry conditions the last few weeks has moved the mites from the dead grass on field borders into the fields. I wanted to send out a message to assist you with some talking points to consider as you find infested fields in your area.

• High temperatures (above 80 degrees with evening temps above 65) amplify the reproduction process, the lack of moisture for the soybeans will increase the damage caused by spider mites.
• Rains during high temperatures will allow the soybeans to grow and recover some from the damage, however the spider mites pressure will not reduce until the temperatures cool.
• Treatment is warranted if the spider mites are moving to the top of the soybean plants in spots in the field and the forecast is for continued heat.
• Gravel road dust can increase the pH on the soybean leaf and increase the spider mite reproduction.

Control:

• Applications of Dimethoate or Lorsban should be at 1 pint per acre. The VERY dry conditions usually favors the Lorsban over Dimethoate for spider mite control in my opinion. (vapor pressure of Dimethoate is reduced in low humidity situations). Also, the Dimethoate does not control hard shelled insects as well as Lorsban . The one pint rate has much better control of eggs.
• Coverage is critical, with the bottom side of the leaf as the target for control. 15 to 20 gal per acre by ground with high pressure (50 to 75 psi) necessary for coverage. 2 gal per acre by air or more.
• Buffer the water to a pH of 5.0 or lower to not allow the organophosphate insecticides to degrade in the spray tank. Buffering is also important to reduce the pH on the soybean leaf surface to extend the control for the eggs.
• Brandt products that can buffer the water: ( I like the first 2 products because they provide nutrition for plant recovery) You get more for your $ of buffering. Yield trials of the first 2 products, when added to spider mite treatments, measured 3 to 9 bu. per acre more yield when compared to insecticides by themselves in previous outbreaks. (Note: Do not use Manniplex Bean if glyphosate is in mix!!!)
  
  • BRANDT Smart Trio
  • Manniplex Bean (used to be Nutrition Plus)
  • Prolec
  • Indicate 5
• The applications should hold out the spider mites for 14 days or when good coverage is achieved.
  

  
  Note: in regards to spraying fungicides on soybeans in conjunction with spider mite treatments. It is ok to apply both together if the soybeans growth stage is R3 or more mature. If the soybean is less than R3 stage, I would consider applying the insecticide for mites if needed and then fly on the fungicide at R3 or later. (in 2005, I applied a number of fields at R1 with fungicide and insecticide for mites and the beans looked great for about 2 weeks, then the spider mites flared due to the increased nutrition provided by the fungicide stimulation. The R1 application timing of fungicide did not increase the yield! Fungicide is needed for increasing yields at pod fill time (R3 to R5).

Call with questions!
Ed