What causes this powdery white coating on my shrubs?
We have a border of Siberian peashrub around our lot, and many summers (including this one) it gets a powdery white coating on the leaves and sometimes they die off. Is there a way to treat this?
St. Louis County Minnesota
It sounds like powdery mildew. See http://www.extension.umn.edu/garden/yard-garden/trees-shrubs/powdery-mildew/ for information on it. If you do decide to spray, make sure to do it early. It will not work if you wait until the fungus is advanced.
Powdery mildew is unsightly but will not seriously harm your shrubs. In fact, Caragana arborescensis is so tough it is listed as an invasive species in Minnesota. See http://www.dnr.state.mn.us/invasives/terrestrialplants/woody/siberianpeashrub.htmlfor more information.