Plant and Insect Diagnostic Clinic Update - September 24, 2008

News Article

The following are a few of the problems received the past two weeks.

Diseases and Disorders

  • Brown leaves. This is the time of year when trees begin senescing for winter and it can be hard to determine if discolored leaves are a disease problem. We have been getting many samples in of ash with browning leaves, and I have been seeing trees all around Ames with just one or two branches exhibiting fall color. At this point we think it is probably another symptom of the stressful spring weather, and nothing to be concerned about. But if you notice one of your trees behaving strangely, note which branches are having problems and check to see that they leaf out normally in the spring. If not the tree should be evaluated for a disease problem.
  • In the past few weeks we have received samples of Diplodia tip blight in Austrian pines. This disease is one of the reasons we do not recommend Austrian Pine be planted in Iowa. Please see HHPN March 9, 2005.
  • Burr oak have also been a common sample all summer, and especially the last few weeks. Tubakia is a disease that affects the leaves. Leaves often turn brown along the veins and in vein-delimited V-shaped areas. Small brown spots are often visible on the leaves.. Please see HHPN Aug 22, 2007 explaining what we currently know about this disease.
  • We have also received many samples of burr oak with wasp galls on them. We think they are caused by a cynipid wasp, and are called the oak flake gall. They cause the leaves to be deformed, but overall pose no long term health problem for the tree. Please see our pamphlet on Insect Galls on Trees and Shrubs


  • The recent warm damp nights have been conducive for migrating masses of millipedes. See our website for more information.
  • Praying mantids, especially the large Chinese mantids are now noticeable in the southern half of the state. For more information see last year's Extension Garden Column.
  • Garden spiders and their webs of radiating lines and concentric circles are noticed in the fall of the year. These orb weaver spiders such as the banded garden spider, the yellow garden spider and the barn spider are not dangerous.

Millipede.  Photo by Diana Pounds.Millipede. Photo by Diana Pounds.

Chinese mantis on autumn snakeroot, Actaea simplex.  Photo by Julie Swanson, Master Gardener
Chinese mantis on autumn snakeroot, Actaea simplex. Photo by Julie Swanson, Master Gardener.

Banded garden spider.  Photo by Lori NelsonBanded garden spider. Photo by Lori Nelson.