Plant and Insect Diagnostic Clinic Update - July 16, 2008


  • The Japanese beetle has been the "hot" pest of the week. They were 2 weeks late in appearing and calls and reports were sporadic until the middle of the week of July 7. By the end of the week there was a steady stream of calls. The known distribution of Japanese beetle grew to 28 counties this week with the addition of Benton County to the list. See the map below (and as always, please continue to report infestations in counties where JB has not been previously reported). See the Iowa Insect Information Note for more information. Small numbers of beetles on a few small plants can be controlled by handpicking. Larger infestation may require insecticide sprays to keep leaves, flowers and fruit on the plants. Nearly all garden and ornamental insecticides will control JB. Good choices include Sevin, permethrin, cyfluthrin and esfenvalerate. Read and follow label directions.
  • Bagworms have hatched and are defoliating trees in much of southern Iowa. Check now for small caterpillar-containing bags and spray if numbers are too great to remove by hand. The microbial insecticide Bacillus thuringiensis is a good choice for managing small to half-grown caterpillars. See the Horticulture and Home Pest News from June 20, 2007.

Other recent calls and samples include:

  • Redheaded Ash Borer in firewood See photo below.

Diseases and Disorders

Several samples of Austrian pine with Dothistroma needle blight have come into the clinic. This is a common disease of Austrian pine and is one of the reasons we do not recommend planting this tree. It is too late this year for treatment, but diseased trees can be treated with fungicides in the spring. Please see an article with pictures in the Feb. 8, 2006 HHPN.

The clinic has continued to receive many samples of conifers, especially spruce, with stress symptoms. The samples have shown no signs of disease or insect problems, but the needles are browning and/or falling off. Please see the July 14, 2008 Yard & Garden Column about the wet spring and effect it has had on conifers.

Japanese beetle distribution in IowaJapanese beetle distribution in Iowa


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