Leaf-spotting diseases are flourishing with all of the rain

Gail Ruhl, Sr. Plant Disease Diagnostician, Botany & Plant Pathology, Purdue University

Anthracnose has been diagnosed on a number of different shade trees this year, including sycamore, maple, oak, ash and birch. We also frequently see anthracnose on walnut and dogwood trees. Dogwood anthracnose can be quite serious due to the development of girdling trunk cankers.

Anthracnose requires cool, wet conditions for infection. Succulent new growth is most susceptible. Older leaves, drier conditions, and warm temperatures usually discourage further disease development.

Symptoms of anthracnose include brown to black leaf spots, brown to black blotches, and sometimes (as with sycamore anthracnose) stem cankers and death of entire, young leaves. Anthracnose of shade trees is usually worse in the lower or inner canopy of the tree where leaves stay moist longer.

Even though defoliation may occur, long term affects on tree health are minimal for vigorous trees. Fungicides are not usually recommended for these early anthracnose diseases of shade trees, with the exception of dogwood anthracnose (BP-48, Dogwood Anthracnose). Spring fertilization following defoliation will help trees push out a second flush of growth (HO-140, Fertilizing Woody Plant). It is also important to water these trees during periods of drought stress this summer.

For more information, refer to BP-9, Anthracnose of Shade Trees.

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Anthracnose on Ash

Anthracnose on Oak

Anthracnose on Oak

Anthracnose on Sycamore

Anthracnose on Sycamore

Anthracnose on maple

Anthracnose on maple