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What is it?
Brown rot is a plant disease which occurs in peach and nectarine trees. Two closely realted fungi contribute the the formation and propogation of brown rot. Monillinia laxa and M. fructicol are the two harmful fungi and in addition to peaches and nectarines they can attack any and all stone fruits causing damage that can be quite extensive. Once the peaches, nectarines and other stone fruits have been infected with either Monillinia laxa or M. Fructicol the fruits must be destroyed and are inedible, which can greatly lessen the productivity of a harvest.
What does it look like?
Peach and nectarine tree brown rot initially shows up in the form of wilting young leaves and blossoms. After the wilting process has begun in fungally infected portions of the stone fruit trees, the leaves and blossoms then begin to decay and will turn brown. Typically this occurs during the first two weeks of the bloom period in the growing season. Peach and nectarine fruits will have brown spots on the young fruits. Spots can enlarge to cover the entire fruit, or may remain just one localized spot. The spots are brown, squishy and may get covered in a grayish mold as spores present. Additionally, as the season progresses stone fruit trees may show further signs of infection and damage as they begin to defoliate and gray spores and clumps appear on the flowers. These masses of gray material are spores. Along with the spread of spores, peach and nectarine trees may develop sunken lesions on the fruit tree bark, trunk and twigs. Extensive twig die-off may occur as the fungal infection becomes more severe, and as the growing season lengthens the lesions may begin to ooze a sticky, oozy material.
How does it manifest?
Spores emerge in the spring after over wintering in lesions and rotted fruit. The rotted fruit which has overwintered is known as a mummy in the singular form. Clusters of rotted stone fruites are known as mummies. The spores are either splashed through rain and water or even wind that blows them from the infected mummies onto healthy peach and nectarine tree parts. Additionally, ooze from the lesions will begin seeping again once spring temperatures heat up and this infected fungal sap can spread onto previously healthy sections of the tree. The brown rot disease spreads especially quickly in moist, damp and warm temperatures and is easily splashed about as spores and sap during periods of heavy rainfall.
What can you do about it?
Once you see signs of infection with fungal brown rot in your peach and nectarine trees you will want to spray any uninfected blossoms on the stone fruit trees with a chlorothalonin or triforine containing fungicide. Repeat the application again approximately ten days after the first application. This method usually helps prevent further infection from spreading to uninfected blooms. You should then remove any infected fruits, mummies, twigs, and areas of bark which show lesions. Often you can prune out the infected cakerous lesions rather than having to cut off an entire limb. However, be sure that you have sprayed first so that any spores you stir up in your pruning and removal efforts are not spread to uninfected areas of the tree. After harvest be sure to clean all debris and check again for fallen fruits which could turn into mummies harboring the fungus. Often previously hidden lesions will be easier to see once the harvest has been had, and the tree begins fall defoliation. Prune out any existing cankers and then in the spring be sure to treat the peach and nectarine trees, as well as surrounding foliage in case you missed any overwintering areas of fungal spores.
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