Three Rivers Ag News

Caterpillars and Asian Soybean Rust

Asian Soybean Rust has officially been detected in Peach County, which means it could be anywhere and in any field. Once this rust appears, it can develop quickly with the help of a little rain and wind. This disease is of particular concern if your soybeans are between flowering and the early pod stage. Preventative fungicide is an option, but plants are generally considered safe after the R4, or full-pod, stage. When scouting, Asian Soybean Rust appears speckled on the underside of the leaf and the lesions are raised with spores present. If you are unsure, bring a leaf by the office and we can put it under the microscope to confirm. Many fungicides are labeled for ASR, so call to establish an exact recommendation.

If your soybeans were not sprayed with Dimilin, worms may be a concern, as well. There have been many problems with velvetbean caterpillars, soybean loopers, and green cloverworms in the past few weeks. When looking at caterpillars in your field, they can be identified by the number of prolegs, which are the legs toward the rear of the abdomen.

  • Velvetbean caterpillars: 4 pairs of prolegs, and will thrash when touched.
  • Green cloverworm: 3 pairs of prolegs.
  • Soybean looper: 2 pairs of prolegs and black markings.

The thresholds for these caterpillars vary, so call your extension office to establish when to spray.