PPDL Picture of the Week
May 22, 2017
Anthracnose of Shade
Trees or Wind Injury: Look Alike Symptoms Can Be Perplexing
Gail Ruhl, Senior Plant Disease Diagnostician
The cool, wet, weather
experienced periodically this spring has been ideal for the development of anthracnose
on shade trees.
Anthracnose is the common name for a type of leaf spot and canker
disease caused by certain kinds of fungi. Anthracnose diseases affect many
trees, but are particularly prevalent on ash, maple, sycamore, white oak,
walnut and dogwood. Each species of tree is infected by a different species of
fungus, thus the fungus does not spread from oak to maple or maple to ash or
ash to sycamore. A different fungal species is also responsible for dogwood anthracnose.
Symptoms will vary depending on the type of tree and the stage of
plant development at the time of infection: leaf spots or blotches; twig
dieback and wilting; and browning or death of emerging leaves are all possible.
Premature leaf drop often occurs with anthracnose diseases, however, most of
the trees infected with anthracnose usually show good resilience, and are not
permanently damaged by this early season leaf blight.
Sycamore anthracnose causes severe blighting of newly emerging
leaves and shoots, and eventually causes twig and branch cankers which distort growth. Twig and branch cankers, shoot blight, and leaf blight are
all symptoms of the fungus that causes sycamore anthracnose. Leaflet drop, as
well as dead tissue along leaf veins or at the leaf edges is a symptom for ash
anthracnose. Although defoliation may be so great that anthracnose-infected
leaflets practically carpet the walks and lawns nearby, the tree is not dying,
it simply puts out a new set of leaves. Anthracnose symptoms on maple and oak
range from leaf spots to enlarged blighted dead areas along veins and sometimes
to shoot blight.
Abiotic (noninfectious) injury from environmental factors such as excessive
winds or late frost/cold damage have also occurred this spring and may also
cause foliar symptoms similar to anthracnose on various deciduous trees.
The most appropriate course of action for established trees suffering from severe effects of anthracnose is to rake and remove fallen leaves from beneath the tree; stimulate vigorous new growth with a balanced fertilizer after the leaves open and the spring rains have stopped; water regularly during extended dry periods this summer; avoid irrigation systems that wet leaves.
Leaf Diseases BP-143-W (pdf file)