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What is anthracnose?

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Anthracnose is a fungal disease that attacks trees during cool, wet springs. Evidence of the disease appears each year, but it is much more damaging in especially rainy weather. The name sounds a little intimidating, but the disease is not normally fatal. Consider this information.

The fungal disease attacks a number of trees in northern Utah, but those most affected include maple, sycamore, oak and ash.

Anthracnose first appears on the leaves along the veins. It looks like small water-soaked lesions, and the veins turn black on the underside. The fungus can also attack areas between the veins. Severely infected leaves eventually fall from the tree.

Serious infestations can also infect twigs and branches. As the disease moves down the leaves, it attacks the twigs, causing them to become discolored. When damage has been continuous over time, the disease can move through the tree and kill small branches. However, this is not common.

Anthracnose spreads and thrives in wet conditions and spends the winter months hiding in fallen leaves and dead twigs. In the spring it is spread by rainfall and wind. It can also be spread by regular over irrigation.

Normally, control measures are not needed for anthracnose. Since the disease requires moisture to move and cause damage, the trees usually recover, and new leaves fill in. The tree may look sparse for a few weeks, but most look better by mid-July.

The best way to reduce damage from anthracnose is to clean up leaves as they drop, particularly in the fall. It is important to also remove and destroy or dispose of any dead or diseased twigs and limbs.

Fungicides should be applied in the spring. They work best if put on before the disease spreads and causes damage. Unfortunately, it can be anyone’s guess which year the spray will be needed. If you have ash, oak, sycamore or maple trees, ask your local nursery or garden center which fungicides are registered for this disease, and be prepared.

Be patient with trees suffering with anthracnose. Although they look straggly now, new leaves should reappear and fill in soon.

Posted on 8 Jul 2005

Jerry Goodspeed
County Director, Horticulture Agent, Weber County

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