Question
I live in Southern Alberta , Canada and my question is....
The leaves on my poplars are turning black and then brown and falling off.Could the Powdery Mildew that has affected my Caragana hedge also be affecting the poplars?

Answer
Ilona:
The reference I have here doesn't indicate powdery mildew occurring on Caragana, despite the fact that PM has a very wide host range.  If you do suspect PM, best to get it confirmed through your local agricultural office or inquire at your local nursery/garden center about getting a microscopic exam.  

One of the symptoms of PM infection is premature defoliation.  Here in this part of the world, PM is mostly cosmetic, not having a major impact on overall health of the tree or shrub, but climate can greatly influence this. Since may of the fungi that cause problems on leaves have the ability to survive on dead leaves on the soil during the winter, raking up and destruction of the leaves before spring arrives is very helpful in reducing disease incidence during that growing season.

Steve