April in Review: What Came Through the Clinic Doors

During April at the C. Wayne Ellett Plant and Pest Diagnostic Clinic (https://ppdc.osu.edu/home), the most frequently recorded problems observed in conifer trees were needle blights and needle casts. Phyllosticta needle blight on arborvitae was a recurring diagnosis and is commonly associated with underlying environmental stress rather than acting as a primary, aggressive pathogen. Phyllosticta species affecting arborvitae, most commonly Phyllosticta thujae, are widely described as opportunistic or secondary pathogens that become established after events that weaken host defenses. Reported predisposing stress factors include winter injury, drought stress, soil moisture extremes, transplant shock, excessive or improper pruning, crowding, and poor air circulation within dense or sheared canopies. As a result, management recommendations focus on alleviating stress factors such as improving watering practices, correcting soil moisture issues, reducing canopy density to improve airflow, and avoiding pruning during wet conditions.Rhizosphaera needle cast  was diagnosed on Norway spruce, Stigmina needle cast on Norway spruce and Colorado. A pine sample showed a coinfection of Dothistroma needle blight and Diplodia tip blight.

 Phyllosticta fruiting bodies and Phyllosticta spores under the microscope

The pests most frequently identified as causing damage on boxwood are leafminers, psyllids, and mites. As a side note, the boxwood samples submitted were generally small in size. For accurate diagnosis, it is important to submit at least 5–10 twigs or material that is representative of the symptoms observed. Always place the material in a zip-sealed bag before shipping it to the Clinic.

The circular lesions are old leafminer damage, while the white stippling is caused by boxwood mites

In the fruit category, strawberry samples were diagnosed with anthracnose. We also received an apple sample exhibiting powdery mildew along with spray injury, and a pear sample affected by Pseudomonas blossom blast. Rainy conditions and low temperatures, particularly frost events during bloom, can increase the incidence of blossom infections.

​

Characteristic symptoms of Pseudomonas Blossom blast, a bacterial infection favored by rain and low temperatures

In the vegetable category, Pythium spp. was diagnosed in several hydroponic leafy green samples, Pantoea bacterial blight was diagnosed on garlic, and Fusarium wilt  was diagnosed on tomato.

Lettuce  plants with roots showing brown discoloration caused by Pythium spp. infection

For cut flowers we observed cyclamen mites on snapdragon and ranunculus. The ranunculus plants were also affected by bacterial blight (Xanthomonas spp.)

Distorted snapdragon leaves infested with cyclamen mites

April Summary Table

​