Plant Diseases/Black spots on Corkscrew Willow leaves
I noticed today that both of my Corkscrew Willows have black spots all over the leaves. I imagine it is probably fungal. They are both a couple years old and approx 12' tall. How do I treat this?
These are leaf spots caused by a fungus disease. I would not be concerned with these. Most leaf spots show up late in the year when the trees are beginning to shut down for the winter. These cause no real health problem to the tree. The best way to cut down on the number of these leaf spots is to rake up and remove from the site the fallen leaves. This will remove the fungus spores and reduce the amount of spots next year.
If you want to treat the spots you will need to wait until next sprain as the leaves bud out. Then next spring spray the new foliage with a fungicide for leaf spots. Spraying with a fungicide after the spots show up will not control the spots. The fungicide is a preventive and will keep the fungi from infecting the leaf.
Spraying three times at two-week intervals with a copper fungicide (Hi-Yield Copper Fungicide, Ferti-lome Black Spot %26 Powdery Mildew Control) or mancozeb (Bonide Mancozeb Flowable, Southern Ag Dithane M-45, or Dragon Mancozeb Disease Control) starting when the leaves begin to unfurl in spring will provide control. Spray until all the leaves have fully expanded usually about three applications will work. Read and follow all directions on the label.