Plant and Insect Diagnostic Clinic Update – July 13, 2018

The following are highlights and updates about sample submissions from fruit, vegetables, and ornamentals, and questions recently received in the Plant and Insect Diagnostic Clinic. Visit the PIDC's Facebook page for updates and more pictures. For more information on a particular disease or insect problem listed, follow the article cited.

Plant Problem Diagnoses 

Weather has been a big factor in plant health this year and we continue to receive samples of conifers and other plants with symptoms consistent with excess water and/or heat. Examples include tomatoes with excessive advantageous roots, and conifers with newer growth browning. 

Samples with suspected herbicide exposure have also been common in the past few weeks.  Be careful when using herbicides near sensitive plants such as tomato.  Growth regulators (2,4-D, dicamba) can cause problems via drift onto plants or exposure through grass clipping mulch or manure.

Other plant problem samples and diagnoses by the PIDC since July 1:

Tomato - early blight, pythium root rot

Arborvitae - bagworm.  See the article elsewhere in this newsletter.

Cherry - cherry fruit fly

Pear - fire blight, cedar-apple rust

Honeylocust - leafhopper

Turfgrass - anthracnose


We have had several pondweed identifications in the past few weeks.  Sago pondweed, Potamogeton sp (American or Illinois Pondweed), and coontail. Managing weeds in ponds must be done carefully in order to prevent fish kill.  ISU Extension and Outreach has some great publications and videos on pond management.  


Speaking of water, all the rainfall has brought on the mosquitoes.  Be sure to check for and dump out any standing water in containers in your yard, change water in birdbaths weekly, and use repellents when outdoors.   The latest results from the ISU Medical Entomology mosquito surveillance program are online at

Zucchini - squash bugs

Humans  - American dog ticks (be sure to check for and remove any ticks when you spend time in tick habitat)

Cicada killer wasps are at their peak.  They can be quite frightening but rarely, if ever sting.  If tolerance and avoidance cannot be achieved, then the effective control is to apply insecticide dust or powder into the nest opening at night.  Cover the nest entrance with soil so you can tell if the treatment was effective.  Repeated application may be needed. 




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