Plant and Insect Diagnostic Clinic Update - November 13, 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.




We received clinic samples with seasonal needle drop in conifers, and other conifer and turf grass maladies.


Even though season needle drop may look scary, do not worry! This is a natural process in conifers that occurs every 2 or 3 years, for more information see our article on seasonal needle loss


We have diagnosed both Diplodia Tip Blight in pine and Arborvitae Needle Blight in the clinic this month. Diplodia tip blight is a fungal disease that causes tip die-back and browning needles. For more information see our article on Diplodia Tip Blight and Canker. 


Arborvitae Needle Blight is caused by a fungus, Phyllosticta thujaewhich usually only infects trees that are experiencing some degree of stress. Identifying stressors and reduce them if possible to help the tree.  See the photos below.


Powdery mildew and rust have become problems in lawns. Powdery mildew is caused by the fungus Erysiphe graminis. Fungal spore production and infection of leaves are favored by cool, humid, cloudy periods. The disease can be more severe in turf heavily fertilized with nitrogen or shaded with trees or shrubs. If the powdery mildew is severe, alternative shade-adapted ground covers or a mix of shade tolerant turf varieties may be planted in shady locations. For additional information visit the Clinic website.


Turfgrass Rust is caused by the fungus Puccinia coronata. See pictures on our Facebook page. Lack of or excess water or nutrients and other stresses are conducive to rust diseases. Water infrequently and early in the day to avoid standing water and moisture in the evening. Mow regularly and remove clippings to reduce the number of the pathogens present in the lawn. If the problem persists, consider replanting with turf grass varieties resistant to rust, or at least use a blend of a cultivar with resistance.


To manage both turf diseases, selective pruning of trees or ornamental shrubs that will allow good penetration of sunlight and increase air circulation in turf canopy will help reduce the severity of both diseases. The grass should be mowed relatively high and water as needed to avoid drought stress.


Arborvitae needle blight kills the smaller twigs.Arborvitae needle blight kills the smaller twigs.

Sign of arborvitae needle blight on arborvitae needles.

Sign of arborvitae needle blight on arborvitae needles.


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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