Question
Aspen Leaf Disease
We have several Aspens which last year developed a black, dry looking condition on the leaves. It progressed until all the leaves were black and began falling off well before Autumn. We observed the disease move from tree to tree, some as much as 50' apart, over the summer. Now in April (Western Washington) the first sign of this disease is appearing on one of the trees again. The leaves are not fully developed yet. There is no visible insect infestation. Local 'nursery and plant experts' cannot identify it. A couple of these folks suggested various fungicides, which were applied liberally last spring and summer, but had little or no effect. Can you help?
AnswerHi Doug:
There are a few leaf spot possibilities that are all fungal in nature. The one I am thinking about is called leaf and shoot blight and is caused by the fungus Venturia. I do not know how tall your tree is, but if you intend to manage this disease with a fungicide, you will need to cover the entire tree with your spray solution and you will need to make your first application as soon as the buds start to swell. You may need to spray multiple times also. If you spray right now, the affected leaves will not get better. So, right now is probably too late to do much good. Most homeowners don't have the appropriate equipment to reach to the top of a big tree. Most of the leaf disease of trees don't have a significant overall impact on the health of an established tree, plus it becomes quite expensive to spray several times, so I tell folks to rake up the leaves and burn (if allowed),bury or bag for the garbage collector to pick up. This needs to be done late winter- before spring gets here. The fallen leaves on the ground and on the tree can be a source for the same disease the following growing season.Foliar disease tend to be worst during wet/rainy spring periods and slow down when things dry down during the summertime.
Spraying a large tree is for those who want a "specimen tree" and are willing to invest in it. Otherwise, do the raking, keep it watered well during hot dry conditions, and fertilize according to a soil test. And more important, avoid damaging the bark with things like string trimmers and lawnmowers- these are a death warrant!
Hope this information helps!
Steve
