Anthracnose is a fungal disease that infects ash, oak, maple, and sycamore trees growing in Minnesota. The fungus causes dead blotches on the leaves that disrupts photosynthesis and transpiration which can eventually lead to spring leaf drop. As leaves mature they become less susceptible to the pathogen. Repeat defoliation by anthracnose can reduce tree health.
Apple Scab is a fungal disease that infects apple trees causing lesions on the leaves and fruit. These lesions can also infect stems, resulting in dieback. Most apple cultivars are susceptible to scab and will require fungicidal sprays to prevent the disease. The disease rarely kills its host but causes unsightly defoliation. The pathogen overwinters primarily in infected leaves on the ground.
Cankers are dead areas of bark that are located on the trunk, branches or twigs of a tree. Cankers are caused by numerous species of fungi that infect stressed or wounded trees, killing the living bark. Characterized by discoloration, oozing sap, and sunken areas, cankers are some of the most difficult disease problems to manage.
Cedar-Hawthorn Rust as its name indicates is a disease of two urban landscape trees. The disease has two life stages, one which occurs as rust spots on foliage and fruit of hawthorn and one that creates galls on juniper. The disease can be quite devastating to the appearance and health of hawthorn and treatment on this host is necessary to prevent infection. On juniper the galls may be unsightly when the orange spores are oozing out, but otherwise they can be easily removed from the infected trees.
Cytospora Canker is an opportunistic fungus that invades the bark of twigs, branches and main stems of stressed spruce trees. The canker that forms appears as a dead, discolored, and sunken area that ranges in size from 1 inch to possibly several feet. Eventually the canker girdles the twig, branch or stem killing anything that was growing beyond it.
Rhizosphaera Needle Cast
Rhizosphaera needle cast is a foliage disease of spruce trees. It causes significant damage to trees growing outside of their native range. Older, inner needles of the branches show symptoms first. As the disease progresses, newer needles will exhibit symptoms. Infected needles first appear mottled or speckled with dull yellowish blotches. Later, the needles turn brown to purplish brown. The needles are dropped (cast) anywhere from 3 to 15 months after infection depending on the variety of spruce infected. Branches begin dying if they are defoliated in 3-4 consecutive years. Larger trees are rarely killed by Rhizosphaera needle cast, however they may become so disfigured that they lose all of their ornamental value.