Issue 5, June 17, 2021
May 2021 Plant Clinic Sample Summary
The Plant Clinic remains open. We are currently operating with reduced staff and are only in the lab as needed for diagnostics and other lab work. We may not be able to answer or return phone calls in a timely manner; MWF are the best days to contact us due to staffing schedules. You can also email us at plantclinic@illinois.edu.
Samples shipped via USPS, UPS, and FedEx are all arriving in a timely manner. We recommend shipping early in the week (Monday-Wednesday) and keeping the tracking number so we can trace the package if needed.
Maple samples were the most submitted hosts in the May. We also received a number of spruce, and boxwood samples. Anthracnose, especially on maple and oak trees, is showing up a lot this year. This is not surprising given the cool temperatures in spring. Needle blights and needle casts are continuing to be problematic mostly on spruce, arborvitae, and pine. I have started seeing apple scab around town.
We’ve also received a number of samples and emails about arborvitae thinning or a general decline. While we often find some sort of needle blight on these samples, the overall problem often appears to be stress. Arborvitae are often used as green fences or living screens to provide privacy and protection from wind. They grow quickly and have few major pests or problems, so they should be well-suiting for this use. Unfortunately, the are often spaced much too closely together and, as they grow, they start to shade each other which can lead to thinning and dieback. Also, when plants are crowded there is usually reduced air flow around or through them, increasing drying time from dew or rain events and favoring the development of fungal diseases. Always remember to consider the mature size of plants when installing them and space them appropriately!
Boxwood blight continues to be a concern especially in the northern part of the state. For more information about boxwood blight, please see: http://hyg.ipm.illinois.edu/article.php?id=869 and http://hyg.ipm.illinois.edu/article.php?id=1137.
May 2021 Plant Clinic Sample Summary
Host |
Pathogens and/or Pests Confirmed (C) or Suspected (S) |
| Arborvitae | Phyllosticta needle blight (C), environmental stress (S) |
| Basil | Pythium root rot (C) |
| Boxwood | Volutella blight (C), Fusarium canker (C), Boxwood leafminer (C), Boxwood psyllid (C), Boxwood spidermite (S), environmental stress (S) |
| Cedar | Pestalotiopsis needle blight (C), environmental stress (S) |
| Douglas fir | Swiss needle cast (C) |
| Eastern Redbud | Environmental stress (S), possible Verticillium wilt (S) |
| Impatiens | Pythium root rot (C) |
| Juniper | Juniper scale (C), Pestalotiopsis (C) needle blight (C) |
| Kale | Nutrient deficiency (S) |
| Lavender | Rhizoctonia root rot (C) |
| Maple | Anthracnose (C), Fungal cankers (C), Gloomy scale (S) |
| Oak | Oak twig canker (C), Fungal cankers (C), environmental stress (S) |
| Pear (ornamental) | Entomosporium leaf spot (C) |
| Spruce | Spruce spidermite (C), Rhizosphaera needle cast (C), Stigmina needle cast (C), Cytospora canker (S), environmental stress (S) |
| Strawberry | Anthracnose basal rot (C), Mycosphaerella leaf spot (C), cultural problem (S) |
| Tomato | Septoria leaf spot (C), Nutrient deficiency (S) |
| Watermelon | Rhizoctonia damping off (C) |
| White Pine | Phomopsis dieback (C), environmental stress (S) |
Author:
Diane Plewa