While reviewing the University of Illinois Plant Clinic Newsletter, it became clear that this season has really been about diseases, starting with the usual and expected diseases that come along with the cooler temperatures and rains of spring. Plant diseases continued as our rains continued well into June. That set up diseases to be with us the rest of the summer. More infection earlier and longer allowed much heavier disease pressure in our vegetables, fruit trees and ornamental plants.
It did not seem to matter whether or not we had disease-resistant or susceptible plants. The degree of infection was greater on open pollinated or heritage varieties of vegetables, but even the disease-resistant varieties showed infection. Gardeners who made treatments had the challenge of timing between the rains and that added disease pressure. Most gardeners end up with mixed results. It is always easier to look back and realize starting treatments earlier or having done them more often would have provided better results.
Diane Plewa, Plant Diagnostic Outreach Specialist at the University of Illinois Plant Clinic, shared some insights:
"Rhizoctonia, Pythium, and Phytophthora are common fungal and fungal-like root pathogens that were even more prevalent this year. Pythium and Phytophthora cause damping off and root rots and are favored by cool, wet weather, of which we had plenty. These pathogens were observed on woody and herbaceous ornamental plants, fruits, vegetables, and field crops. Rhizoctonia is most famous for causing Brown Patch and Yellow Patch in turfgrass. This year, we saw a lot of those diseases, and we saw Rhizoctonia affecting ornamentals such bachelor's buttons and coneflowers. In addition, fungal foliar spots were everywhere this year. Forty-one of 400 woody tree samples were confirmed with anthracnose, a common leaf spot caused by various fungi. While we normally see anthracnose in spring, we saw more samples with it this year and we were finding it later into the season. For most trees, this disease is not considered a serious problem. However, in sycamore and dogwood trees, anthracnose can pose a threat to the overall health of the tree. Anthracnose also was found on herbaceous ornamentals, including Hosta and English ivy".
Plewa also noted the struggle ornamentals faced this year:
"We saw a large number of stress issues in woody plants. Fungal cankers, nutrient chlorosis in deciduous trees, and tip blights in conifers were the most common stress-related issues seen in 2015. Many trees are still suffering the effects of the two summers of drought back-to-back a few years ago, and the recent harsh winters and excessively wet spring have caused substantial amounts of stress to both newly-established and mature trees…. Both pine and spruce trees are affected with needle blights, which also are considered stress diseases. Diplodia and Dothistroma fungal diseases on pine needles were very common this year. Also common were Rhizospaera and Stigmina, two fungi which affect spruce needles." For more on the University of Illinois Plant Clinic fungi report, visit http://hyg.ipm.illinois.edu/article.php?id=762
While not a direct comparison to the many specimens the Plant Clinic saw, local Master Gardeners also have logged many more calls and office visits this season on foliar diseases on deciduous and evergreen plants.
About the author: Richard Hentschel’s expertise extends across several subject areas with specialties in lawn care, fruit tree production, woody ornamentals, and home and community gardening. During his 45-year career in horticulture and agriculture, Hentschel became a well-known and respected expert for commercial and homeowner audiences, industry organizations, and media. He retired from University of Illinois Extension in April 2022 with nearly 30 years of service as a Horticulture Specialist and Educator in northern Illinois.