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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
Anthracnose on maple
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Leaf Problems on Shade Trees

Posted by John Fulton -

Here we go again! It seems every May many area homeowners are reporting problems with their maple trees, and this year is certainly no exception. Many times the problems begin on one side of the tree, and have the symptoms of brown or dropped leaves. What could be the problem? Well, anthracnose is back again.

What's anthracnose? It's a disease caused by a fungus. It's present most years, and affects many different plants. On trees, get this, it only affects good quality shade trees. That includes maples, oaks, ash, and especially sycamores. Silver maples are not affected by anthracnose, but are affected by other leaf spot fungi (that's plural for fungus).

Anthracnose can affect three different ways on shade trees. The first way is by affecting small twigs. In this type of infection, small twigs are actually killed by the fungus. The second way is affecting buds. In bud infections, the buds are killed. The third way is infecting leaves. The leaf stage is the most common, and shows up as dead areas along the tips and edges of leaves or as dead spots between the leaf veins. As these dead areas get larger, the leaves fall to the ground.

There is no cure for anthracnose. Once the fungus has infected the tree, we just have to ride it out. We might have prevented the disease by protecting new buds and leaves before the infection, but that isn't very practical on very large trees. This would take a fungicide application covering the entire tree every 10 days or so from when leaves first expand from the buds, until nighttime temperatures stay over 65 degrees.

That leaves us with good news and bad news. First, the bad news is the infections are just starting and will get worse. There is nothing we can do but keep the trees in good growing condition (water when dry and add a little fertilizer). We can continue to have leaves infected for quite some time. The good news is that rarely is the disease a killer on established trees. Generally the worst that happens is the loss of the small twigs if that stage was infected, or having a bare tree in your yard for a few weeks. I say a few weeks because generally when leaf drop is severe, a new set of leaves comes out within 4-6 weeks.

What usually happens is it takes more energy to shoot a second set of leaves, so that is why the water and fertilizer can be important. Fertilizing at the same rate as lawns provides a pound of nitrogen per 1000 square feet. That means using about 8 pounds of a 12-12-12 or 13-13-13 product per 1000 square feet. If you are fertilizing the lawn, or flower beds or other areas, then you are providing the fertilizer for the trees. In the case of trees, you measure drip area, which is the area covered by the branches. It is easiest to square it off, so a tree having a bit over 30 foot branch spread would be 1000 square foot of drip area. Then just spread, or scatter, the fertilizer on the area covered by branches.



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