Plant and Insect Diagnostic Clinic Update - June 26, 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.




Roseslug sawfly damage to roses has been apparent the past few weeks.  Sawflies look like caterpillars but are actually the larva of a wasp.  The damage on samples that we have seen is old damage and just cosmetic.  There is only one generation of roseslug sawflies per year so the damage you see is what you get.  The roses will be just fine!


Fishing spiders have been on the move the past week!  They are a large noticeable type of spider and a bit intimidating especially for those who are not fans of spiders.  Luckily fishing spiders are completely harmless.




With all the rain, diseases are flourishing!


The clinic has received several of oak samples. It seems this is a harsh year for oaks. We received samples that were positive for Bur oak blight and Tubakia leaf spot.


We also received samples of oak trees suffering iron deficiency and oak decline.  Multiple factors can contribute to oak decline including environmental stress such drought, frost, diseases and pests. For more information visit the USDA Forest Service resource on oak decline.


Elm black leaf spot and anthracnose. These two diseases are common fungal diseases of elm leaves. Anthracnose tends to be worse in years with wet spring weather. Anthracnose is caused by several fungal pathogens and is primarily a cosmetic disease.  It causes leaves to look unsightly and sometimes drop. Raking and removing fallen leaves can reduce the pathogen numbers.  See the photo below.


We received several apple, crabapple and pear samples with symptoms of fire blight and bacterial blast. Symptoms may include blossom blight, wilting and browning of shoot tips (shaped like a shepherd’s crook), and stem cankers. It is important to confirm the disease as other abiotic factors can cause similar symptoms. Once confirmed, manage fire blight by thoroughly pruning infected limbs (blighted shoots and cankered limbs) as soon as symptoms are detected and before extensive necrosis develops. Sterilize pruning tools between every cut with alcohol or household bleach. Read more about pruning in ISU Extension & Outreach pamphlet PM0780, available online.  Prune infected branches well below the infected area.  For more information about fire blight, please visit the Plant & Insect Diagnostic Clinic website


Cedar apple rust. Bright orange lesions on the leaf surface are characteristic of this disease. For more information visit the Horticulture and Home Pest Newsletter from May 10, 2006


Common samples inlcude solanaceous vegetables (potatoes and tomatoes) with herbicide injury. For more information read the article "Chemical injury in vegetables."


With all the rain and moisture mushrooms and slime molds are also thriving. Our curiosity of the week is a slime mold commonly known as "dog vomit slime mold." This is a Myxomycete (not a true fungus) that grows on mulch.  For more interesting facts see the University of Wisconsin Botany website.    



Elm anthracnose

Elm anthracnose


Slime mold Fuligo septica known as “dog vomit slime mold”

Slime mold Fuligo septica known as “dog vomit slime mold.”


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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