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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

Anthracnose Disease

Posted by John Fulton -

A lot has happened in a week with our trees. The maples continue to show increasing leaf drop. Sycamores have been hit with a vengeance, and leaves have been falling like rain for the last week. Other good quality hardwoods, such as ash, are also showing symptoms.

The symptoms are dead material between the leaf veins, along the leaf edges, or dead tips of leaves. There are also times when the disease affects buds and twigs. In the leaf stage, the disease only affects leaves currently out. If damage to leaves results in enough dropped leaves, the tree will shoot another set within four to six weeks. All we're out is the energy the tree spent in pushing out another set of leaves. Of course, we also had a freeze that caused the loss of leaves on many trees. What I'm getting at is trees have spent quite a bit of energy already this year. We need to do what we can to replace nutrients and keep moisture available.

Moisture will be needed to with keep those affected trees in a vigorous growing condition. Usual watering rates are an inch a week, and rainfall can supply part or all of that. Fertilizer applied to lawn area or trees is the other part of the equation. Fertilizer should be applied at the lawn rate (supply one pound each of nitrogen, phosphorus, and potassium per 1000 square foot of drip area), if you haven't fertilized the lawn area around the trees. This would translate to about 10 pounds of 10-10-10 fertilizer or eight pounds of 12-12-12 or 13-13-13 per 1000 square feet.

Anthracnose is usually the first leaf spot fungus to affect trees each spring. That means the others can't be far behind. One the more common ones is apple scab. This disease affects apples and crabapples in much the same way as anthracnose does the shade trees. It starts as spots on leaves between the veins of the leaves, and ends with leaves dropping at a rapid rate. This is the reason for so many "naked" crabapple trees late in the summer. Traditional spray programs for production apples (used on the apples or crabapples) should prevent the problem. Samples of apple scab have been coming in for a week now, so expect some acceleration of the disease on susceptible varieties.

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