Plant and Insect Diagnostic Clinic Update - September 2, 2016

News Article

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


We received several oak samples with the following problems: 

  • Pin oaks showing iron chlorosis have been reported in several counties.  See more info in the Horticulture & Home Pest News.
  • Tubakia leaf spot in oaks of the red group (pointy end leaves) has been confused for oak wilt symptoms.  See a comparison on the Clinic website and the photo below.  



We have received multiple samples from lawns. Common problems are rough blue grass (Poa trivialis) and stress conditions that can lead to diseases such Curvularia or Nigrospora blight.


Good lawn maintenance practices that promote turfgrass health can help turfgrass to fend off diseases.  For more information see

Rough bluegrass can contribute to the unsightly look of some lawns. It grows rapidly in cool, wet weather and can quickly form patches. This grass will then go dormant and turn brown as soon as hot, dry weather arrives. The grass will green up and begin to grow again as soon as cooler weather comes in the fall. In most cases, it is introduced as a contaminant when the lawn was seeded. It can remain hidden for many years until environmental conditions are optimal. Unfortunately eradicating rough grass is a hard decision as any herbicide will impact the Kentucky bluegrass too. See Purdue University's publication AY-41 for more information.


Curvularia blight in Kentucky bluegrass is commonly associated with stressed lawns. Adjusting fertility, reducing compaction, improving aeration and reducing other stresses can contribute to reducing the symptoms.



We received several tomato and pepper samples with bacterial spot disease.  Learn more about symptoms and control on the Clinic website.


Septoria leaf blight symptoms cause brown spots on the leaves that look similar to bacterial spot, but tomato fruit will remain clean (no spots will occur). For more information on this diseases visit the Clinic website.   



We received several samples of apple fruit with Sooty blotch and fly speck symptoms, and rust symptoms in both leaves and fruit.


 Leaf spot close up with fungal bodies(black dots), and Fungal bodies close up (600x magnification)
Tubakia leaf spot on oaks (red oak group; note pointy leaves). Photo credit: Lina Rodriguez Salamanca, Plant & Insect Diagnostic Clinic


Lina Rodriguez Salamanca Extension Plant Pathologist and Diagnostician (Program Specialist II)

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 North Central Plant Diagnostic Network (NCPDN) and National Plant Diagnostic Net...