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.
Below the summary of diseases that have been diagnosed at the PIDC since our last update
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)
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.
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 https://hortnews.extension.iastate.edu/powderpost-beetles.