Plant and Insect Diagnostic Clinic Update - June 9, 2017

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. For more information on a particular disease or insect problem listed, follow the article cited.

symptoms of hops downy mildew
Symptoms of hops downy mildew



Below the summary of diseases that have been diagnosed at the PIDC since our last update

Broadleaf Trees

Birch-suspected iron deficiency  
Crabapple- Scab 
Willow, Cytospora canker 


Coniferous Trees

Signs of Pseudopernospora humili
Signs of Pseudopernospora humili

Yew- Cryptocline needle blight
Arborvitae- Phyllosticta needle blight


White mold in pepper, see our updated article “White mold, with a focus on vegetables

Tomato early blight, stay tuned for our update version of the publication “Tomato Diseases and Disorders”

Fruit (small and tree fruit, including hops)

Strawberry leaf spot
Hops downy mildew
Hops Fusarium crown root
Peach leaf curl



Adult viburnum crown borer.

We receive a sample of viburnum crown borer (also called the viburnum clearwing), Synanthedon viburni, earlier this year which I kept in order to see the moths emerge. Viburnum crown borers are a clearwing moth so they look and behave a bit like wasps. This insect is not terribly common, but when it gets into a viburnum hedge it can cause a lot of damage.

Management options include pruning out and destroying any dead branches, cutting as low to the crown as possible to remove  the caterpillars.Insecticides applied at the base of the plant before caterpillars bore into the branches can reduce problems. Timing is difficult as insecticides should be applied in early June. 


We also received a horned oak gall caused by the cynipid wasp Callirhytis cornigera.  These large woody galls occur on oak trees.  They can cause some branch tip dieback and their weight can leave trees more prone to breaking branches during snow and ice storms.  

Horned oak gall
Horned oak gall.

Unfortunately there are no controls for insect galls on trees except to prune out and destroy them. Remember that oaks should only be pruned in the winter or they can become infected with oak wilt. Some individual trees seem particularly prone to horned oak calls and will have almost every branch affected, in these cases pruning is not feasible.


Our online article about Powderpost Beetles was extensively revised and rewritten with input from Dr. Eugene Wengert, Emeritus Extension Specialist, Wood Products, University of Wisconsin-Madison. The conclusion remains the same: first determine the extent of the powderpost beetle infestation and if it is active and then decide to repair or replace the damaged wood or contact a pest management professional for treatment options. See the revised article on our website at






Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Yard and Garden, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on June 9, 2017. The information contained within may not be the most current and accurate depending on when it is accessed.