Plant and Insect Diagnostic Clinic Update - July 11, 2014

The following are highlights and updates about samples and questions recently received in the Plant and Insect Diagnostic Clinic. Visit the PIDC's Facebook page to ask questions and for updates and more pictures.


It has been an interesting couple of weeks in the clinic. We have seen impatiens downy mildew, botrytis blight on peony, and raspberry cane borer.


Impatiens Downy Mildew


Impatiens downy mildew is caused by a pathogen that is similar to fungi. This disease has caused a lot of problems for growers in the past few years. Symptoms usually begin with leaves turning yellow and then they will begin to fall off until only a bare stem is left on the plant.  (Photo 1 & 3)  The white downy fungus can often be seen on the undersides of the leaves. (Photo 2) There is no effective treatment once plants are infected. All infected plants should be carefully and completely removed by bagging and placing in the trash. The spores of impatiens downy mildew can survive and spread in the soil for many years, so infected plants should not be placed in the compost. Additionally this means that Impatiens walleriana should not be planted in the same area again for many years. Only Impatiens walleriana is affected by this disease. Prevent infection by carefully inspecting plants before bringing them home, improve circulation between plants, and try to keep the leaves dry.  Although it is tough to step away from our old standby the impatiens, it is a great opportunity to try other shade loving plants.


Botrytis Blight


Botrytis blight on peony is a fungal disease. Symptoms include large dark brown spots on the leaves and young stems. The stem lesions can rot through causing the stems to fall over. Botrytis also infects the flower buds, causing them to turn brown or black and fail to open. Often a grey mold can be seen on the buds and rotted stems. As with many fungal diseases, management involves improving drainage and circulation, removing and destroying plant debris as well as choosing healthy plants.


Raspberry Cane Borer


Raspberry cane borer is a beetle larva that hollows out the canes as it feeds inside the plant. The plant then wilts above the feeding area. The borer can also infest roses and blackberries. Pruning and destroying infested canes is the recommended treatment.


Staff Changes


This week we said goodbye to Dr. Erika Salaau, our friend and plant disease diagnostician for the past three years. Erika has moved to New Bedford MA where she will be the cranberry extension assistant professor of plant pathology at the University of Massachusetts. We wish her the best of luck and know she will be a great success.


Two new diagnosticians have joined the Clinic this summer.  Ashely West and Melissa Irizarry are graduate students in Plant Pathology & Microbiology and will be sharing the plant disease diagnostic duties this summer.  Welcome aboard!



Impatiens downy mildew can rapidly defoliate plants.Impatiens downy mildew can rapidly defoliate plants. White downy fungus appears on the undersides of infected impatiens leaves.White downy fungus appears on the undersides of infected impatiens leaves. Only stems remain after an attack by impatiens downy mildew.Only stems remain after an attack by impatiens downy mildew.

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