Corn Rootworm Beetle
| Vol. 1 No. 2 | August 26, 1999 |
Corn Rootworm Beetle: Is Silk Clipping Damaging?
Bill Hutchison, Dept. of Entomology, University of Minnesota, St. Paul, Minn.
Northern and western corn rootworm beetle adults have been emerging the past 2 weeks and fairly abundant in many areas of southern Minnesota. They are also attracted to fresh silking corn. Since most of our fresh silking corn this time of year is sweet corn, it is common to see 4-5 beetles per ear, actively chewing down fresh silks. Beetles can easily chew off 1 or more inches of silk tissue. The primary concern is complete pollination, and thus complete kernel fill in the ear. The answer of course lies in the timing of the silk feeding damage relative to the time it takes for pollen to move down the silk tubes. I have not done the necessary research (nor presently know of others who have) to completely tease this out. However, our casual observations over the past 10 years in Minnesota has indicated that it must take a very heavy and early (i.e., very 1st silk) infestation of beetles to have a significant effect on pollination. This concern is most easily discussed with the following two production situations:
a) Conventional growers: sweet corn already being treated for ECB and/or CEW (with any of the labeled insecticides) will not have a problem with silk clipping by rootworm beetles; these insecticides will control the beetles. Also, by controlling the beetles this year, this will greatly minimize new egg-lay by the beetles this fall in the treated field. Thus, rootworm soil insecticide would not be needed the following year, in that field.
b) Fresh-market growers: those who may still be using products such as Seven SLR-Plus, will also get good control Seven (1 or 1.5 qt/ac). (We also use Seven for this purpose in our sweet corn research plots as needed, that we have purposely left untreated for ECB/CEW).
c) Organic-Certified Growers: those who may still be using Dipel (or other Bt products) for ECB/CEW control; Bt products will not control rootworm beetles, and thus can be at most risk. Options here would be Rotenone, Sabadilla or Pyrethrins, where labeled, and approved by the Certification Program.
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Last Revised August 22, 2002.
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