Cedar Apple-Rust Galls are a type of fungus in the genus Gymnosporangium. While they can and do cause damage to apple trees. They are not known to cause any significant damage to cedar trees, but can become unsightly if there is a large infestation. In some rare cases if there are apple trees and cedar trees within the same vicinity it may cause death to both trees. Cedar trees become infected in the summer months, and by June of the following year small green-brown, somewhat kidney-shaped galls will be present. Each gall is covered with small circular depressions, similar to the dimples on a golf ball. The following year, in damp weather the depressions sprout with orange tentacle-like projections that swell immensely (pictured).
After last nights rainy weather our cedar trees came alive with these odd looking fungal galls. The projections are gelatinous and feel very slimy to the touch. Once the rains of spring subside the galls die and may damage or kill the part of the tree it was attached to. If that is the case, my trees are doomed. They are completely infested.
My nearby apple and crabapple trees may possibly be in trouble. As the apple tree is next in line for spreading this fungus.
On susceptible crabapples and apples, tiny yellow spots appear on the leaves after infection in the spring. As the spots mature, they become yellow/orange and swollen with a red border, and develop tiny black dots in the center of the lesion. By mid-summer, small cup-like structures with tubes are visible on the undersides of mature leaf lesions. The fungus may also infect fruit and even succulent twigs of very susceptible crabapple and apple varieties.
From the slimy projections on the juniper, basidiospores are released that infect crabapples and apples. Although these spores may be carried several miles, most infections occur within a several hundred feet from the source juniper. A wet spring period of 4-6 hours at 50-75 F is sufficient for severe infection. Symptoms are described above. Two to four weeks after the tiny dots appear in the center of each spot, tubes appear on the undersides of leaf lesions. Most people only notice this stage after the tubes have split and take on a ragged appearance. Aeciospores, released from the tubes, become airborne and infect susceptible juniper hosts from midsummer into early fall.
The following spring, galls (consisting of both fungal and host plant tissues) begin to develop on the juniper. These galls continue to grow through the summer, and by fall they are full size (3/8 to 1 and 3/16 inches in diameter), greenish-brown to tan and round to kidney shaped.
In addition, golf ball-like depressions form on the gall at this time that will give rise to telial horns the following spring. The telial horns are brownish in color, but rapidly elongate and become bright orange with spring rain. Shrinking and swelling of telial horns can occur several times with intermittent rainfall. Each time the projections swell, basidiospores are released.
After the projections have released their spores, the horns collapse, dry and eventually fall off. The galls die at this point, but may remain attached to the juniper for a year or more.
In summary, the complete cycle of cedar apple rust takes 24 months to complete and requires infection of two different hosts.
This fungus is a major pest to apple orchards and can cause significant damage and make the fruit unmarketable. In some states there are ordinances that state any infected cedar tree within a mile radius of an apple orchard must be cut down. Fines are issued for those who do not comply. Remarkably the fungus does not generally damage the cedar trees, only the apple trees. Buying resistant varieties of apples, like Delicious, helps reduce risk to this damaging fungus.