A number of different trees are affected by anthracnose diseases. These fungal diseases can cause severe leaf blighting and deformation, but in many cases damage to plant health is not severe. However, with sycamore anthracnose and dogwood anthracnose, the fungus regularly moves back into stem tissue and causes more significant problems. Following are profiles of some of the more common anthracnose diseases of landscape trees.
Anthracnose diseases are generally not severe on maple, but can cause considerable unsightliness from brownish leaf blotches and some leaf drop when moist weather conditions make the disease particularly severe. Extensive development of stem infections is not common on maples, as it is with sycamore anthracnose and dogwood anthracnose.
The most common symptoms include brownish discoloration along veins, varying from discrete spots to irregular patches of discoloration bordered by veins. Spore masses of the fungus can sometimes be found on lower leaf surfaces along veins during extended moist conditions. The fungus spreads in spring from previously infected tissue to new growth. Where fungicides are used, applications must be started at bud break and continued during early leaf development.
This anthracnose disease is primarily a leaf blighting and blotching disease of white ash and, to a lesser extent, green ash. Small twig cankers do occur and the fungus overwinters on these twig lesions, but little damage occurs from this phase of the disease. In wet, cool, spring conditions, leaves and sometimes shoots first develop water soaked area. They later develop large tan-colored blotches and leaflet distortion.
Considerable leaf drop occurs, especially from lower areas of the canopy. Though this causes concern when leaves litter the ground in late spring, damage to overall plant health is not generally severe and plants typically re-leaf. As leaves mature they tend to become more resistant to infection. Fungicide applications, if warranted, should be made at bud break, with several repeat applications early in the season.
White oaks are the most susceptible of many oak species to this leaf blotching disease. Twig infections occur but are not significant except as sources of overwintering fungal inoculum from year to year. Leaves and shoots are infected during cool, wet spring conditions causing leaf blotches that often are strictly delimited by leaf veins. Eventually, lesions become a papery tan color and some leaf shriveling occurs. Multiple cycles of infection can occur. As leaves near maturity, lesion size lessens, and once leaves mature they become fully resistant by early to mid summer. Fungicides are generally not recommended.