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John Fulton


John Fulton
Former County Extension Director



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In The Backyard

Horticulture columns and tips done on a timely basis

Tree Leaf Diseases Accelerate

Posted by John Fulton -

As mentioned last week, fungal leaf diseases were present. They are now making their presence felt with a vengeance. These diseases infected trees and shrubs earlier, and they have continued to develop rapidly. Adding insult to injury, we had the extremely high winds affecting the tender leaf tissue, especially on maple trees. Some trees are now to the point of being, well, leafless.

Anthracnose is the number one fungal disease of good quality shade trees, and apple scab is starting to hit apples and crabapples. To give a brief overview, these diseases are preventable but not curable. They are seldom life threatening to the tree or shrub, but they can make things look rather unsightly. Many shade trees losing a large percentage of their leaves will often set another set of leaves within four to six weeks. Apples and crabapples are less likely to set another set of leaves, but it sometimes happens.

Anthracnose has different stages depending on the time of infection. There is a bud stage, where buds are killed as they begin to open. Next is a leaf stage, which affects only leaves. This stage is the one we are commonly seeing, and it infects leaves and gradually consumes the leaf. And the other stage is the twig stage which affects smaller twigs on trees and shrubs. This is one reason why sycamore trees tend to have so many small branches break. The infection leaves a brittle scar on the branch which makes it susceptible to breakage. There is actually a specific anthracnose disease for each shade tree. This means sycamore anthracnose, maple anthracnose, and so on.

As I mentioned, once infection has occurred it can't be cured. The prevention part needs to begin with a regular spray program similar to production apples. This means starting when the leaves are just out of the bud in the early spring. The same kind of timing applies to ornamental trees. The main harm caused is the loss of food produced by the lost leaves, and the loss of energy to set another set of leaves. Fertilizer application at the lawn rate, to supply a pound of nitrogen per 1,000 square foot broadcast, will help the tree as much as anything.


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