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Angie Peltier

Angie Peltier
Former Extension Educator, Commercial Agriculture

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Hill and Furrow

Current topics about crop production in Western Illinois, including field crops research at the NWIARDC in Monmouth.
Figure. Japanese beetle; notice the iridescent metallic green head, the copper colored wings and the white tufts of hair along the sides and posterior. The tufts of hair or setae help in distinguishing the Japanese beetle from look alikes.
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Japanese beetles have emerged - now what?

Posted by Angie Peltier - Insects

Japanese beetle trapping. I work with personnel from the Illinois Natural History Survey to gauge insect population size and arrival either from out of state or emergence from the soil. This is accomplished through the use of pheromone traps. One insect that is of interest to corn and soybean producers in Illinois is the Japanese beetle (Figure). A pheromone trap was established at the Northwestern Illinois Agricultural Research and Demonstration Center (NWIARDC) to gauge when Japanese beetle adults begin emerging from the soil to feed and mate in 2013. Checking the trap this morning, I found that THEY HAD EMERGED. There were a half an inch of beetles piled in the bottom of the trap (Figure).

Japanese beetle identification. Japanese beetles are oval-shaped and have an iridescent metallic sheen. They have a green head and thorax and copper colored outer wings with a green stripe down the center. There are also five white 'racing stripes' along each side of the beetle under the wings towards the posterior end, and two on the rear end. These are actually small white tufts of hair called setae (Figure). There are several Japanese beetle look-alikes, but the Japanese beetle can be distinguished by these white tufts of hair. Matt Montgomery, former University of Illinois Small Farms Local Foods Educator, wrote a detailed article in 2012 describing the differences between Japanese beetles and look-alikes.

Economic thresholds vary by crop. Economic thresholds and control recommendations may be vastly different in a home garden setting than for a cash grain operation. Rhonda Ferree, Horticulture Extension Educator, has summarized information on the Japanese beetle paying special attention to helping homeowners combat this pest on a blog called Japanese Beetle News.

Damage on corn and soybean plants can be alarming, particularly if individual leaves are in tatters. Often-times the beetles tend congregate on field edges, and so damage occurs on the edge of the field. Scouting more than just the outside edge of the field should help to inform decisions on whether to consider an insecticide spray. Just observing the outer edges of the field may over-estimate beetle density throughout the field.

Ms. Kelly Estes and Dr. Mike Gray of the University of Illinois have summarized information about the Japanese beetle on field crops in a fact sheet on the U of I's IPM website. For soybean, treatment recommendations depend upon the growth stage of the plants. Thresholds for treatment are 30% defoliation before bloom and 20% defoliation between bloom and pod-fill.

It may be difficult to train the eye to estimate defoliation, but a photo from Dr. Marlin Rice of Iowa State University, may help with visualizing the differences among the different levels of defoliation. One way to help train the eye is to imagine taking all of the holes in the leaf/leaflet and condensing them into one area. You can then more easily estimate how much is gone by relating this 'image' to the total leaf area. This is a skill that takes practice.

Corn recommendations are a little bit more straight forward. Consider using an insecticide if during silking if you have 1) three or more beetles per ear and 2) silks are clipped shorter than ½ inch and 3) pollination is less than 50% completed.

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Thank you for informing the public that the Japanese Beetles have emerged in this area. This will help in preparing for the season. Keep up the good work that you do Angie.
by Diana Dugan on Tuesday 6/25/2013

Thanks for keeping us up-to-date on all of the new research and findings so that we neither overuse nor under-apply our pesticides, fungicides, fertilizers, etc. Your on-target articles are very helpful and timely.
by Japanese Beetle on Monday 6/23/2014