Tree and Shrub Diseases in SE Michigan – Part 3: Anthracnose

January 24th, 2018

Continuing with our common tree diseases series, one of the most common fungal diseases are anthracnose, which can infect ash, oak, maple, and sycamore trees, as well as other tree species. The fungus causes dead blotches on the leaves that disrupt photosynthesis and transpiration with can eventually lead up to spring leaf drop. As leaves mature, they become less susceptible to the pathogen. Repeat defoliation by anthracnose can directly impact the tree’s overall health and it is important to stop this disease before it begins to spread.anthracnose-leaf-tree-disease-safaritree

The life cycle of this particular fungus is noticeable to the naked eye. In the late fall and early spring months, black pimple like bumps will develop on infected leaves from the previous year. Spores are then released and blown by wind or even splashed by rain to nearby trees, causing the spread of the fungus rapidly. The primary infections produce secondary spores which
diseased-pineneedles-safaritreeaffect other leaves and fruit. The secondary infections of this disease can and will continue throughout the growing season during wet periods of time.

The next more common tree disease is the Rhizosphaera Needle Cast, which is a foliage disease of spruce trees. This disease can cause significant damage to trees growing outside of their native range. Older, inner needles show symptoms first, and as the disease progresses, newer needles will begin showing symptoms as well. Infected needles first appear mottled or speckled with dull yellowish blotches, and as the disease progresses, the needles will begin to turn brown to purplish brown. The needles then drop (cast) anywhere from 3 to 15 months after the infection has occurred and also depends on the type of spruce species infected. Branches begin dying if they are defoliated in 3-4 consecutive years, though larger trees rarely die and succumb to this disease, however they may become so disfigured that they lose all of their ornamental value.


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