What's Hot at the PPDL on
June 29, 2016
Anthracnose of Shade Trees
Gail Ruhl, Senior Plant Disease Diagnostician, Department of Botany &
Plant Pathology, Purdue University
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,
including ash, maple, sycamore, white oak, walnut, birch, elm 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 are especially severe in years with cool, wet spring weather. The
symptoms will vary depending on the type of tree and the stage of leaf
development at the time of infection: leaf spots or blotches; twig dieback and
wilting; and browning or death of emerging leaves are possible symptoms for
certain tree species. 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.
Symptoms of sycamore anthracnose are prevalent this year.
Sycamore anthracnose causes severe blighting of newly emerging leaves and
shoots (Figs 1,2). Twig and branch cankers, shoot blight, leaf blight (Fig 3)
and leaf drop 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 are
symptoms for ash anthracnose (Fig 4). Although defoliation may be so great that
anthracnose-infected leaves practically carpet the walks and lawns nearby,
healthy trees will leaf out again in a few weeks time. Defoliation early in the
year does not affect overall tree health since trees have plenty of time to
produce new leaves to supply the energy reserves necessary to survive the
winter.
Anthracnose symptoms on maple and oak (figs 5,6) range from leaf
spots to enlarged blighted dead areas along veins and sometimes, with oak, to
shoot blight.
Anthracnose infected trees need to grow more actively than they normally
would in mid-summer to replace lost leaves. Thus, cultural practices that
include maintaining a balanced fertilization program and watering during drought
stress periods are important for the active growth required in the current
season and for the regeneration of carbohydrate reserves In preparation for the
dormant season. For additional management suggestions for other leaf spot
diseases please refer to the following Purdue publication:
Leaf Diseases
BP-143-W (pdf file)