Dying Branches on Aspen
We have two mature aspens in Camp Sherman Oregon. Starting last year and continuing to this year, one of them has the leaves turn brown on a branch and then the branch dies (or at least does not produce leaves the next year). Over the last two years about a 5 foot section on one side of the tree now does not have leaves. It does not seem to have canker from what I can tell from online pictures and the leaves just dry up and do not seem to have spots. There is a black dust like stuff on the tree that rubs off. Looks like black mold. The tree gets regular water with our sprinkler that was put in a couple years ago and has grown significantly since the sprinkler addition. Thank you for any insight you have. I was not worried with two branches last year but since it continues, I am concerned for the tree.
Jefferson County Oregon
I can't say with 100% certainty, but this looks like a case of leaf scorch. If you are watering frequently but not for an extended period of time (the way you would water lawns for example) you could be creating a situation where the tree cannot form an adequate root system. Over-watering in the summer and the addition of our dry winter and Spring this last year can really contribute to leaf scorch. You can read more about leaf scorch here: http://extension.colostate.edu/docs/pubs/garden/02911.pdf
I would recommend starting a good Fall watering regime (infrequent slow and long drip) continuing into Winter (1-2x/month) and through Spring if we don't get good rain or snow. If you don't get new leaves on those branches next Spring give us a call at the Deschutes County Extension Service Plant Clinic: (5410 548-6088.