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Anthracnose diseases affect a wide variety of shade trees and are common each spring in Kansas. Ash, cottonwood, elm, oak, maple, sycamore, black walnut and other trees are susceptible to injury from this disease. Actually, anthracnose is a general term that describes several different diseases caused by many species of fungi.

Many of these diseases develop in the spring and may have similar leaf symptoms, but the common thread to all anthracnose diseases is the fact that the fungi which cause them produce similar, cup-like fruiting structures called acervuli.

These fungi also are host specific, meaning the fungus which causes anthracnose on maple will not cause injury to black walnut or other ornamental plants.

Symptoms of anthracnose vary considerably. Certain anthracnose diseases result in branch dieback and extensive blighting of leaves, while others cause small circular lesions on the leaves and fruit. Anthracnose diseases may result in premature defoliation. Often damage to the trees appears severe; however, these diseases rarely kill trees. In fact, most shade trees in vigorous condition recover rapidly from anthracnose infections. Specific anthracnose diseases and their symptoms are:

Ash Anthracnose

This disease, incited by Gloeosporium aridum, is common in Kansas, although it seldom causes severe damage to trees. The fungus attacks the leaves, expanding shoots, and occasionally, small twigs. Early spring infection results in shoot and leaf distortion. Irregular brown blotches or spots develop on leaves; these spots commonly are associated with leaf veins or margins. In severe cases, twig and shoot blight can occur. Anthracnose infections may continue through early summer if the weather remains cool and moist.

Figure 1.   Ash anthracnose

Marssonina Leaf Spot of Poplars

Marssonina leaf spot can be found on most native poplars, including eastern cottonwood. Small black to purple spots appear on leaves in the spring. Individual lesions are small, but they may coalesce to cause irregular dead patches on the leaves.

During wet weather, a buff-colored gelatinous matrix containing fungal spores may be observed oozing from leaf lesions. Severe leaf infections during wet years may cause premature defoliation, but the disease generally is not a significant problem in Kansas, except on certain eastern cottonwood clones and hybrid poplars.

Elm Black Spot

Black spot, caused by the fungus Stegophora ulmea, is sometimes called anthracnose. Symptoms of black spot first appear as small whitish flecks on the upper surface of the leaf in early spring. Eventually, the lesion expands and develops a black, uneven crust-like surface. Numerous spots may form on the same leaf. Heavily infected leaves turn yellow and drop prematurely. Defoliation may be extensive during wet summers. Although the disease is unsightly, it seldom causes extensive damage to the tree.

Figure 2. Black spot of elm.

Maple Anthracnose

Anthracnose, caused by Discula spp., is a common springtime problem on maple, especially in eastern Kansas. Red to black spots or blotches form on leaves, particularly during wet, cool spring weather. Typically, the spots are formed on or near leaf veins and progress along the veins towards the petiole or stem. The disease also may cause twisting, crinkling, or other leaf malformations. Premature defoliation resulting from anthracnose is common in some years, although the disease does not kill the trees or cause permanent damage.

Anthracnose is often confused with leaf damage resulting from adverse environmental conditions. Young developing leaves are sensitive to freezing temperatures, high winds, or other sudden weather changes. Affected leaves develop water-soaked, irregular lesions, tattering of leaf margins, or leaf distortion.

This "spring scorch" malady is restricted to leaves exposed at the time adverse conditions occurred and does not cause serious injury to the tree. Summer scorch, associated with hot, dry summer conditions and inadequate soil moisture, causes a scorching or browning of the leaf margins rather than browning along the veins as with anthracnose.

Anthracnose is often confused with leaf damage resulting from adverse environmental conditions. Young developing leaves are sensitive to freezing temperatures, high winds, or other sudden weather changes. Affected leaves develop water-soaked, irregular lesions, tattering of leaf margins, or leaf distortion.

This "spring scorch" malady is restricted to leaves exposed at the time adverse conditions occurred and does not cause serious injury to the tree. Summer scorch, associated with hot, dry summer conditions and inadequate soil moisture, causes a scorching or browning of the leaf margins rather than browning along the veins as with anthracnose.

Figure 3. Maple anthracnose

Oak Anthracnose

This disease is most serious on white and bur oaks. Individual trees can be severely damaged from repeated infection by the fungus Gnomonia quercina. Individual leaves develop irregular brown, dead areas and may be slightly cupped or distorted. The fungus also attacks and kills leaf buds and new shoots. Repeated attacks will cause a stunted, brooming effect to diseased branches.

Figure 4.   Oak anthrancose

Sycamore Anthracnose

Sycamore anthracnose, caused by the fungus Apiognomonia veneta is the probably the most striking of the anthracnose diseases because of the spectacular defoliation can occur. More than 90% of the new shoot growth can be girdled and killed by the fungus in wet springs. Nevertheless, damage is restricted to the new shoot growth in spring and most trees fully recover by mid-summer.

The anthracnose fungus can infect and kill small twigs and dormant buds in late fall after leaf drop. The dead buds dry and shrivel and the twigs may break off the tree. Small black fruiting structures of the fungus, called acervuli, may dot the blighted tissue. Buds also may be damaged by fungal infection before shoot expansion begins in early spring. As tree dormancy is broken, further infection occurs on expanding shoots resulting in a rapid wilting.

Leaves that do fully expand may develop elongated tan to brown lesions parallel with the midrib and veins. This symptom is relatively rare in Kansas.

The combination of bud, shoot and leaf blighting can result in an almost complete death of new growth in early May. In fact, many homeowners mistakenly believe that their sycamore trees have been killed. Nevertheless, sycamores have a remarkable ability to recover from severe anthracnose infection. A new set of shoots and leaves begin to develop in late May and by mid-June, most trees have fully recovered. Damage is less severe on the regrowth because temperatures are usually too warm for high infection levels.

During the summer, the tree seals off twig cankers with a layer tissue called callus. This prevents further canker expansion. Nevertheless, the quiescent fungus may continue to survive in twig cankers and serve as inoculum source for fall and spring infections.

Although sycamore anthracnose rarely kills, it can cause tree damage. Repeated killing of young twigs results in abnormal branching and gives the tree a ragged appearance. Furthermore the disease can exacerbate the problem of twig and branch breakage and cleanup that is common to the tree.

Figure 5. Sycamore anthracnose
bud and shoot blight.

Figure 6. Leaf blight phase of sycamore anthracnose.

Figure 7. Sycamore anthracnose twig canker.