Plant and Insect Diagnostic Clinic Update - September 16, 2016

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.


Broadleaf Trees


Black leaf spot in elms is caused by the fungal pathogen Stegophora ulmea. This disease is favored by cool, wet weather in the spring and summer.  Black leaf spot is primarily a cosmetic issue. In severe cases, defoliation can occur. Since this disease is not typically harmful, no management measures are recommended for control. However rake up and destroy fallen leaves in the fall to possibly reduce severe infections in future years.


Several clients have been worried about maples with leaf spots or leaves yellowing and in some cases droopy leaves and defoliation. Several fungi cause leaf spots in maple.  However, they are not consider harmful to the tree. Sanitation (raking and destroying leaves in the fall) can over time reduce the foliar leaf spots on the tree. However, if you see yellowing on one side of the tree that may be an indicator of a more severe disease in maples. Check our Verticillium Wilt Resource if your maple is looking yellow and wilted. 

Coniferous Trees


We received a sample of Austrian pine confirmed with pine wilt, a disease caused by a nematode (pine wood nematode Bursaphelenchus xylophilus). This nematode is moved long distances by wood-boring beetles.  What makes this disease unique is that fungi may be involved that sometimes cause blue staining to occur in the branches. For information on pine wilt visit our Pine Wilt resource. Check our Facebook page to see a video of the nematode under microscope magnification. 



We confirmed downy mildew in basil. Downy mildew can be transmitted via seed or transplants. Therefore, when buying basil in garden stores, always inspect the plants for symptoms. Avoid overcrowding plants; basil plants can get big in the right location. Good spacing allows for air circulation reducing leaf wetness that the pathogen needs to thrive.  For more information on basil downy mildew visit Cornell University's website, "Expect and Prepare For Downy Mildew in Basil."

Mushroom Identification


We received a beautiful mushroom specimen for identification. This particular mushroom can be confused by beginner mushroom hunters for the Hen of the Woods given its shape and color. However, this specimen is, in fact, Meripilus sumstinei (black-staining polypore). See the photo below and read more at MushroomExpert.Com


Meripilus sumstinei sample, photo by Lina Rodriguez Salamanca
An exceptional specimen of the black-staining polypore mushroom, Meripilus sumstinei.


Lina Rodriguez Salamanca Extension Plant Pathologist and Diagnostician

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

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