Plant Disease Clinic 2019
BY BRETT ARENZ
Business was brisk in the Plant Disease Clinic in 2019, particularly in the second half of the year. A likely contributing factor was the large amount of precipitation that was experienced by the state. Officially Minnesota had its wettest water year on record with over 41 inches, which is a full 10 inches over the average amount we typically see. Frequent and abundant rain is especially associated with fungal diseases. One of the most common types of samples submitted to the clinic are oak trees, with the primary testing request being for the disease oak wilt. However, there are many “look-a-like” fungal diseases that can cause similar symptoms such as anthracnose, bur oak blight, and Tubakia leaf spot, as well as insect issues such as two-lined chestnut borer. The wet conditions this year were quite conducive to these foliar fungal diseases in particular, which resulted in many oaks with tattered and brown leaves by the end of the summer (and oak samples in the clinic being tested for oak wilt).
On the subject of oak wilt, the PDC hosted a diagnostic workshop in August specifically targeted to this disease. Attendees came from several states where oak wilt seems to be an emerging issue and represented both state (DNR) and federal (Forest Service) agencies. They had the opportunity to learn techniques for isolating the pathogen from wood samples, identify it in culture, and also see symptoms from some of the look-a-like diseases, pests, and physiological issues. PDC diagnostician, Jennifer Flynn, put in a large amount of work preparing materials for this workshop, ensuring a good experience for the attendees.
Aside from the record precipitation, the other interesting weather event of 2019 was the polar vortex induced extreme cold that occurred in late January. This also resulted in the University as a whole being shut down for a couple of days, a rare occurrence. When Spring finally did arrive in May, the clinic received several samples of hardwood trees that had odd symptoms. According to the submitters, the trees had flushed new leaves but rapidly wilted after this. The maple variety Autumn Blaze seemed to be particularly affected. For the most part, no pathogens were found on these samples, and our working hypothesis is that the root systems of some of these trees may have been damaged by the extreme cold, resulting in the unusual symptoms in the Spring.