Plant and Insect Diagnostic Clinic Update - August 7, 2015

The following are highlights and updates about samples and questions recently received in the Plant and Insect Diagnostic Clinic. Visit the PIDC's Facebook page to ask questions and for updates and more pictures.




It's been a busy two weeks in the Clinic with multiple samples to be tested for bur oak blight, oak wilt and tomato diseases.


Bur Oak Blight (B.O.B.) causes premature browningof leaves and  is caused by the fungus Tubakia iowensis. Typical symptoms include browning of leaf veins, wedge-shaped lesions on leaves, and early defoliation. For more information about B.O.B. please see the Horticulture and Home Pest News from February 9, 2011 or the USDA Forest Service.


If you are considering having an oak tree tested for Oak Wilt please follow the sampling guidelines online.  Samples must be refrigerated to improve our chances of recovering the pathogen.  Resources:  ISU;  USDA Forest Service


Tomato foliar diseases are a common nuisance for home gardeners and commercial growers.  See the Horticulture & Home Pest Newsletter article from July 25, 2014 for information on tomato disease prevention.




Many, many more inquiries of strawberry root weevils were received over the past two weeks.  Strawberry root weevils are accidental invaders from outdoors. The practical control is to vacuum them up as they appear and discard.  See the photo below and our online article.


Magnolia Scale crawlers have emerged and NOW is the time to be applying contact insecticides to infested trees.  Contact insecticides such as insecticidal soap and horticultural oil will reduce the population of scales for next year, and help the tree recover some of the vigor lost this year from heavy, honeydew-producing populations.  See the previous issue and the August 28, 2008 Horticulture & Home Pest Newsletter.  Control recommendations are included on the Clinic website > Insects > Magnolia Scale.


Corn Rootworm Beetles (photo below) are on the move out of corn fields and into home gardens, already.  Rootworms develop on the roots of corn plants in fields that are not GMO or insecticide protected. After laying eggs in the field in the late summer, the beetles get a wanderlust and migrate out of the corn fields and become a pest in the garden where they nibble on succulent flower petals.  Beetles are often found long distances from the closest corn fields. There is no easy answer for stopping this damage. See our online article at Clinic > Insects > Rootworms for suggestions. 



The distinctive "light-bulb shape" of strawberry root weevils is apparent even in their usual bottom-up pose.

The distinctive "light-bulb shape" of strawberry root weevils is apparent even in their usual bottom-up pose.


The pale-green northern corn rootworm feeds on garden flower petals in the fall.

The pale-green northern corn rootworm feeds on garden flower petals in the fall.


Lina Rodriguez Salamanca Extension Plant Pathologist and Diagnostician

Dr. Lina Rodriguez-Salamanca is a diagnostician and extension plant pathologist with the Iowa State University Plant and Insect Diagnostic Clinic  (, a member of the National Plant Diagnostic Network (NPDN, ...

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