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Tuesday, July 3, 2007 04:05 am

Beetle mania

They’re back and they’re on the attack!

Untitled Document Japanese beetles have invaded our gardens again. The first beetles were noticed around June 15 in the Springfield area, and the phone at the offices of the University of Illinois Extension Sangamon-Menard has been ringing off the hook ever since. These half-inch metallic green beetles with coppery wing covers wreak havoc on the beauty of many of the plants in our yards. Adult Japanese beetles feed on the upper leaf surfaces of more than 300 species of plants. Some of their favorite landscape plants include linden, apple, birch, and willow trees; rosebushes; grapevines; and raspberries and other brambles. The beetles prefer to feed on warm, sunny days and will seek out foliage that has been previously damaged by other Japanese beetles. The beetles tend to fly to a new host about every three days and can fly as far as a mile and a half to find a new host. It appears that Japanese beetles will be numerous this year. Sufficient rainfall last fall and shallow ground freezing over the winter allowed larvae to thrive. Phil Nixon, an entomologist specialist with the extension service, says that Japanese beetle grubs need about 11 inches of precipitation in summer and fall to develop properly. Most of the grubs do not tunnel deeper than 11 inches in the ground. A deep ground freeze lasting for two to three weeks would kill more of the grubs. The most common question in connection with the beetles is “How do I get rid of them?” Unfortunately, because the Japanese beetle is an introduced species, it does not have any natural enemies to help keep the population in check. Early removal of beetles by hand is effective on most plants. For the best control, hand removal needs to be started when the beetles are first noticed. In the late afternoon and evening, disturb the beetles while holding a bucket of soapy water or rubbing alcohol under the infested foliage. The beetles will fold their legs and drop into the bucket. This should be done every day or two during the first couple of weeks after the beetles emerge. Early control can reduce subsequent damage. Although a little labor-intensive this can be great free entertainment for the whole family.
Another control option is to protect your plants with the use of netting. Some options include spun-bound polyester row covers, shadecloth with a high light transmittance, and even window screening. Chemical controls are an option but it is usually neither practical nor economical to protect all attacked plants in the landscape. Heavily infested ornamental plants may be sprayed with carbaryl (sold as Sevin) or cyfluthrin (sold as Tempo or Bayer Advanced Garden Insect Killer). Always read and follow label directions for the safe use of chemicals. Make a note of which trees become heavily infested this year so that you can plan pest control next year. Imidacloprid (sold as Merit) is a systemic insecticide. Soil applications of this chemical require about two months to move through the tree and provide control, so you should apply in April for June control. (Applying the chemical now would not be practical for this year.) So what about the beetle traps that can collect gallons of beetles each day? Beetle traps contain a pheromone attractant to lure male beetles and a floral lure to attract females. Nixon says that “research shows that beetles are attracted from a considerable distance to areas near the traps but then switch their seeking behavior to food plants, resulting in heavier plant damage near traps.” This is why we don’t recommend traps except in unusual situations.
The beetles will remain in large numbers for about six weeks and start to dwindle around mid-August. For more information and to view photos of the pesky beetle, go to the University of Illinois’ fact sheet on the Japanese beetle:
For more information about the University of Illinois Extension’s Sangamon-Menard unit, go to
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