Japanese Beetles and Silk Clipping: New Research on an Old Foe

On June 18, Robert Bellm, Commercial Agriculture Educator, observed Japanese beetles in Madison County, Illinois. Overall this season, I’ve received very few reports regarding this insect. With corn now rapidly growing into the late-whorl stage in many areas of the state, attention will soon begin to focus on protecting the pollination process from insect injury (silk clipping). Recently, some research was published concerning the effect that silk clipping by Japanese beetles had on the yield of corn. The research was conducted by researchers with the University of Tennessee and the University of Missouri from 2010 through 2012. The citation for their journal article is as follows:

Steckel, Sandy, S.D. Stewart, and K.V. Tindall. 2013. Effects of Japanese beetle (Coleoptera: Scarabaeidae) and silk clipping in field corn. Journal of Economic Entomology 106(5): 2048-2054. DOI: http://dx.doi.org/10.1603/EC13042

During this multi-year study, the researchers manually clipped silks as well as caged Japanese beetles on ears. Hybrids used in their investigation included DeKalb DKC 64-83 VT Triple Pro (2010-11) and DKC 67-88 VT Triple Pro (2012). Key findings from this research are outlined below:

  • “Manually clipping silks multiple times daily appeared to simulate the effects of sustained Japanese beetle feeding in our studies.” – page 2052, Steckel et al. (2013)
  • …. “the number of kernels and kernel weight per ear were reduced in the test where silks were clipped three times per day the first 5 d of silking.” – page 2052, Steckel et al. (2013)
  • “The number of kernels was also reduced when four or eight Japanese beetles were caged on ears at the Missouri location, and kernel weight per ear was reduced when eight beetles were caged per ear.” – page 2052, Steckel et al. (2013).
  • “Total kernel weight was reduced by 32.4% at the Missouri location for the ears where eight beetles were caged on them, but there was no significant reduction in total kernel weight for the same treatment at the Tennessee location. The dramatic reduction in total kernel weight at the Missouri location may have resulted from other environmental stressors. The Tennessee location had a good pollination and yield environment, whereas the Missouri location had a stressful one.” – page 2052, Steckel et al. (2013)

Summary Comments from Steckel et al. (2013)

  • “It appears from our research that protecting silks from clipping during the first 5 d of silking is critical for realizing optimum yield potential. However, the sensitive window may be longer in stressful environments.” – page 2052
  • “Some states recommend treating for Japanese beetle when three Japanese beetles per ear are found, silks are clipped to < 13 mm, and pollination is < 50% complete, and that recommendation appears to be adequate.” page 2048

In the coming weeks as the corn crop moves through the silking and pollination period, I encourage producers to scout their fields for this perennial insect pest and consider the economic threshold (referenced above) prior to making a treatment decision. Also, Japanese beetles tend to concentrate their numbers along field margins. Densities within field interiors may be far lower. These factors are important considerations before any rescue treatment is applied.

Mike Gray