Cedar-apple rust is a fungal disease common to several varieties of apple, crab apple, juniper and hawthorn trees. Cedar-apple rust is usually only an aesthetic worry, but with time and repeated infection it can become a serious problem.
Symptoms on Juniper Plants and Cedar Trees
Galls, or sores, appear on a tree once the infection begins to develop. In appearance, the galls are red or reddish-brown in appearance. After a rain, the gall will send out long tendrils, orange in color and gelatinous in touch and appearance. The galls, once developed, will release spores into the air, which will infect apple trees.
Symptoms on Apple Trees
Yellow or yellowish-orange spots will begin to appear on the upper portion of the apple tree leaf once the infection has taken hold. This discoloration may include a reddish halo surrounding it, with a dark spot slowly appearing in the middle once the infection begins to mature. Once the dark spot appears, tendrils will develop on the underside of the leaf, which will release further spores in the late summer time. Fruit may also develop some discoloration. These spores cannot infect the apple tree further, instead traveling to a cedar tree via wind currents to complete its life cycle.
Apple-cedar rust is incredibly difficult to control, so prevention is key. When considering apple trees for your orchard or garden, choose rust resistant varieties. Keeping the plant healthy, well-watered during the winter months and free from injury will also keep it free from infection. Some rust resistant varieties include the Dayton, Enterprise, Freedom, Goldrush, Jonafree and Liberty apples.
On juniper plants and cedar trees, it is important to cut away galls on the tree before they develop the tendrils that send out the infectious spores. If possible, remove the branch that has developed the galls. This will prevent the fungus from spreading to apple trees, and back to the juniper at a later date to finish the life cycle of the spore. If the galls are widespread throughout the tree, removal is futile. Instead, consider fungicides. Remove the galls in the late winter if it is the best option for your tree.
Fungicides made specifically for apple rust can be applied to apple trees to prevent further spread and remove the disease from trees that are easily infected. Periodically apply fungicide during the pink stages of the bud development on the apple tree to the third cover development stage to protect new leaves and fruit.
The best fungicide to use for most apple trees is Bayleton spray. Is is particularly effective against cedar rust and powdery mildews. Due to its strength, it needs fewer applications than other, organic fungicide treatments. According to the Journal of Arboriculture, Bayleton should be applied in two sprays, one following the first 1/2 an inch of rain in May, the second one 14 to 20 days later. Apply spray both to the leaves and soil around the tree.