Ornamental Pear trees have been recently under attack from a hard to treat fungus known as Trellis rust. Originally from Europe, Trellis rust or European Pear Rust is caused by the rust fungus Gymnosporangium sabinae. The disease may present a serious health threat to members of the Pyrus species, including both ornamental and fruit pear types. Ornamental Pear trees have been popular trees planted for decades noted for their fast growth rate, tolerance of urban conditions, fairly compact shape and white blooms that appear in early spring. Unfortunately, hundreds of trees have been noted dying in Rockville Center and the disease has been spreading to the Nassau and Suffolk County areas of Long Island. The fungus has spread from the mid-western states to upstate New York and Connecticut over the past several years and seems to be getting progressively worse. According to horticulturists, part of the problem is that the trees have been over-planted, resulting in a rapid spreading of the disease.
Symptoms to look out for are yellow-orange leaf spots (see photograph), which develop into spores in late summer. The spores can be spread to other host plants by wind or to the roots if the trees are close enough together. The secondary host during the winter months is juniper, allowing the fungus to survive when the pear trees drop their leaves; hence, continuing the cycle in the spring.
If you spot damage on your tree, remove and destroy the infected leaves to prevent spores from spreading. If caught early enough, systemic and spray fungicides can be applied to inhibit the spread of the disease. Best preventive measures are to be alert in monitoring your trees, and when in doubt, call a tree professional.