Fungus on trees is tricky to control. When noticed, it’s too late. If you had fungal problems last year, now is the time to treat. Of course, a cool, wet spring makes fungus more of a problem.
If you’re using dormant oil to control insects, many (but not all) fungicides can be mixed with dormant oil and that takes care of two problems with one spray. Read the label carefully and make sure the materials you’re using are compatible. Some come pre-mixed. Dormant oil alone won’t control plant disease.
Fungicides are most effective when the tree is dormant. Without leaves, the material can reach the areas on the tree like the buds, cankers and bark where the fungal spores are held.
Sanitation is the best way to control disease. Bag up leaves and dispose of them, eliminating a huge source of fungal spores. Branches with cankers should be removed if possible. Disinfect pruning tool between each cut so disease isn’t spread around the tree or from tree to tree.
Shot hole disease, or Coryneum Blight, is a common disease on stone fruit. This fungus attacks all stone fruit, fruiting or ornamental, commonly, peach and apricot but also cherry and plum, which means flowering cherry and flowering plum, too. Symptoms during the growing season are clearly visible on the leaf. Small purplish spots leave round holes. On peaches and apricots, you may notice small, brown, scabby spots on the fruit. The most damage occurs to the branches where cankers form. These cankers can eventually kill the branch. Sap bubbles are most likely a symptom of fungus, as most borers on stone fruit occur at ground level.
Peach Leaf Curl is a fungus of peaches and nectarines that causes a thickening and contorting of the leaf. They get twisted and reddened. The infected leaves drop early in the season. The tree may releaf but this is stressful and weakens the tree.
Sycamore blight (anthracnose) is a common disease during a cool, wet spring. This fungus kills new leaf buds causing early leaf drop, ragged looking leaves, witches broom and cankers on the branches. In severe cases the entire tree may defoliate. Cankers can girdle branches causing small branch drop. Since most sycamores are too large to spray, consider a fungicide injection. This has shown good results. London Plane, a type of sycamore, is more resistant to this disease.
Leaf spot, a leaf spot fungus may causes black spots that enlarge to eventually affect most of the leaf. It may infect twigs and in severe cases cause early defoliation. This disease can slowly weaken the tree since leaves produce the food for the tree. Leaf spot, like other fungal diseases, should be treated while the tree is dormant, because the fungal spores are held in the buds, cankers and bark.
A good offense is the best defense. If you’ve had past problems with fungus, using a fungicide along with your dormant oil will help control fungus and insects at the same time. Read the product label and use only as directed.