Plant and Insect Diagnostic Clinic Update - August 24, 2011

The following are highlights and updates about samples and questions recently received in the Plant & Insect Diagnostic Clinic:


We continue to see some blue spruces with Rhizosphaera needle cast and root damage symptoms caused by excessive soil moisture in previous years. B.O.B. is also showing up on bur oaks, for more information about this relatively new disease please see this previous article.

We’ve also received samples with summer patch, cucumber anthracnose, raspberry leaf spot.


The first report of the loose gray webs of the fall webworm caterpillars came this week from Des Moines. Populations of fall webworms vary greatly from place to place and from year to year. It's still too early to know, but there is nothing to suggest the pest will be common this fall. As always, control of fall webworms is not warranted on established, otherwise healthy trees. And spraying the foliage does not kill the caterpillars that remain inside the webs. More online at the Plant & Insect Diagnostic Clinic website.  See the photo below.

Tivon Feeley, Forest Health Program Leader for the Iowa Department of Natural Resources, shared the photo below of one of our more beautiful, large caterpillars in Iowa. The imperial moth caterpillar feeds on foliage from a wide variety of trees, including basswood, birch, cedar, elm, hickory, honeylocust, maple, oak, sycamore, walnut and even pine. The caterpillars are not numerous enough to be a pest or to threaten the health and vigor on the trees. The caterpillars go unnoticed until the end of the summer when the fully-grown larvae descend from the trees to pupate in underground burrows. For more about this caterpillar, see BugGuide.

Fall webworm on walnut tree, it's most common of numerous hosts.

Fall webworm on walnut tree, it's most common of numerous hosts.

Imperial moth caterpillar.  The horns and hairs are decorative and not harmful.Imperial moth caterpillar. The horns and hairs are decorative and not harmful.


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