Virginia Soybeans: Insect Pests and Fungicide Choices

Ernst Undesser
By Chris Drake, Virgina Cooperative Extension August 20, 2013

I would like to address some very key issues that I seem to be getting the most calls about in the last few days. That is soybean insects and fungicide choices. We have over 34,000 acres of soybeans in the county this year, surpassing cotton acreage for the first time in a few years.

The question I get is “should I spray a fungicide and if so, what product do I use?” The next question that usually follows is “what is the moth count, when should I spray for worms?”

Soybeans have been shown to respond well to fungicide applications in a year where conditions produce heavy disease pressure. There are some years where a fungicide application will not pay for itself. This year we have obviously had far more rainfall than normal for this area.

Full season beans have lush, dense canopies that create moist, humid environments ripe for disease development. This may be a year to strongly consider a fungicide application at R3-R5 stage in your soybeans. Dr. Phipps’s research has shown that a strobilurin fungicide or strobilurin/triazole premix shows the best results over many trials.

The following list is the top performing products based upon trial work at TAREC.

  • Headline (pyraclostrobin)
  • Quadris (azoxystrobin)
  • Stratego YLD (trifloxystrobin + prothioconazole)
  • Priaxor (pyraclostrobin + fluxapyroxad)
  • Quilt Xcel (azoxystrobin + propiconazole)
  • Quadris Top (azoxystrobin + difenconazole)

As far as insects go for soybeans, the moth counts and worm pressure have been variable. I have swept many fields without finding threshold while there are reports of corn earworm threshold being reached in other areas just to our south and northwest. Basically, if you are at threshold (about 1-2 worms per 15 sweeps) a pyrethroid at the highest labeled rate should do the trick.

If you are at two to three times threshold or have other worm species (beet armyworm, fall armyworm, tobacco budworm) you need to use a non pyrethroid like Belt, Steward, Prevathon, or Besiege. Please scout and treat fields accordingly using sound IPM guidelines.

Also, be aware of stinkbug and kudzu populations when making worm sprays to make sure you choose a product or combination of ingredients to control the insect complex in YOUR field, not the neighbor’s.

Ernst Undesser
By Chris Drake, Virgina Cooperative Extension August 20, 2013

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