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Western Bean Cutworm Flight Picking Up

Jul 21, 2014

Christian Krupke and John Obermeyer

  • Moth counts increasing this week.
  • Egg laying and egg hatch is occurring.
  • Scout for egg masses and hatched larvae ASAP in high-risk fields.

The western bean cutworm (WBC) trapping season continues, view the general increase in numbers from previous weeks (“Western Bean Cutworm Adult Pheromone Trap Report”). Not too surprising that many counts are surging – last week’s warm temperatures along with rains helped pupae finish off development and emerge from the soil. Evidently, the extremely cold winter did not put a huge dent in populations. Currently, clear nights with light breezes are absolutely perfect for moth flight, mate-finding and egg-laying.

A large percentage of this year’s eggs will be laid over the next 2 weeks. Use this year’s trap catches (see following trap report) and recent history as your guide for prioritizing scouting areas. As you view the trap report, notice the variability of moth captures, even within close proximity of each other. Although the relationship between trap catches and damage is not particularly strong (i.e., high trap counts does not mean high damage), traps are a good timing mechanism and presence/absence indicator. When they spike suddenly, it’s time to scout. A larger number should be prioritized for scouting over a smaller one. But that’s about as far as we can take trap counts in assessing damage potential. Areas/fields with damage last year will likely be at most risk this year, but damage will spread to adjacent counties to the south and east of the state’s northwestern “hot zone” for WBC.

Many Bt corn hybrids offer excellent control of WBC and will not require scouting for foliar insecticide treatment. However, some Bt hybrids do not offer any protection, as well as specialty corn, e.g., popcorn, high-oil, etc. Scouting is straightforward - a matter of walking fields and looking for egg masses, generally laid on the top surface of the plant’s upper, most upright leaves. Concentrate your efforts on pre-tassel corn, this growth stage is preferred by female moths as the young larvae initially feed on pollen. If 5% or more of plants surveyed have egg masses, treatment is advised. If needed, early insecticide applications are better than late ones – pyrethroid insecticides will offer enough residual activity in most cases for a few days of killing the tiny newly hatched larvae as they travel on their way into the plant’s whorl or leaf axils. They are very easily killed at that early stage, but once they get inside the whorl/ear of the plant they cannot be contacted with insecticides, so get them early. Happy Scouting!

Source : purdue.edu