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Despite their beauty, cherries aren't the easiest trees to grow. They grow poorly in soggy, badly drained soils, and can suffer from root rots. Another disease common to cherries is bacterial canker, which produces gummy sunken areas on branches and also infects buds and leaves. Probably the most common problem, appearing on both edible and ornamental cherries growing on the wet side of the Cascades, is a damaging fungal problem appropriately nick-named "brown rot blossom blight."
The infection begins when fungal spores attack the flower buds of the cherry or plum as they begin to open in spring. Infected flowers wilt, turn brown, and die before unfolding fully. The dying flowers resemble wads of wet tissue paper, with a grayish or brownish hue. Damaged blooms remain on the twigs after infection, and become covered with a grayish-brown fungal growth that is worsened by wet spring weather.
Once established in the bloom, the infection may spread to twigs and shoots. If the plant is a fruiting cherry, infection may not appear until after the fruit begins to ripen. Soft brownish spots on the fruit will gradually expand until the fruit is covered with gray-brown fungal spores. Twigs will also be killed. For control information and to see a picture of the problem, go on line to the WSU site http://pep.wsu.edu/hortsense A menu will list "Tree Fruit" and you select cherry, then proceed.
This is the time, just as cherry blooms, check the trees for dead looking areas and mummified fruit left from previous infections. Prune out as much of the affected and damaged parts as possible. It's easier to see them when the trees just begin bloom. Remove and destroy diseased twigs as you spot them, continuing to do this throughout the summer.
Don't compost this diseased material.
A few other good management tips can help with brown rot control. Rake and clean up under the tree during the summer to remove all fallen blossoms, leaves, and fruit. Keeping the ground raked of litter under fruit trees helps with all disease management. (rake up fallen apple leaves that show scab, for instance.) Prune trees to allow as much air circulation as possible.
We've had lots of dampness this spring, and that's not good for cherry tree health. Sunny days that dry leaves and branches will help prevent brown rot infections. The fungus organism, Monilinia fructicola, grows best when the temperature is above 40 degrees and weather is damp.
Be sure to keep high nitrogen fertilizer away from cherry trees. WSU research reports that brown rot infection can be worse if the trees are heavily fertilized with nitrogen. A cherry tree located in a lawn that received a high nitrogen application (such as a 31-0-0) could be made more susceptible to brown rot. Use a 3-1-2 ratio on your lawn.
Some trees may coexist with symptoms and continue to bloom and fruit sufficiently. But if the tree is a prominent landscape specimen with severe damage, and you choose to use fungicides, apply them at the correct time and in the correct sequence.
Spray the tree three times during the bloom period: suggested intervals are 'early, when you see red or pink showing on the buds'; one more spray when the tree is in full bloom, and a final spray after the petals have dropped.
Chemicals registered for home use include Daconil 2787, Captan, and Spectracide Immunox. Check the label carefully for all instructions and be sure that cherries are listed on the label. If the cherry has edible fruit, it's necessary to find a product listing 'fruiting cherry.'
Hortsense: Managing plant problems with Integrated Pest Management
