Brown rot of apricots and other stone fruits (plums, peaches, prunes, cherries, and nectarines) can be a serious problem for Central Coast gardeners. Brown rot is caused by a fungus which can attack all parts of the tree. Buds, twigs, and fruit are the primary infection sites, however. The fungus survives the winter in diseased fruit called “mummies,” which remain on the tree or on the ground under the tree. The fungus also survives in bud and twig cankers on the tree. Fruit spurs and twigs are often killed by the fungus. As the trees defoliate, the evidence of brown rot can be seen as gray-green dried up fruit still hanging in the tree, and as buds and twigs which have balls and drops of gum hanging from them.
To reduce brown rot, you should remove the diseased fruit from the tree and from the soil under and around the tree. When you prune in late December or January, prune out all (or as many as you can without destroying the tree) the diseased spurs and twigs. The diseased fruit and wood should be removed from the area. Put them in the green waste can and let waste management take them to their composting site. DO NOT keep this diseased material in your yard as it can be a source of fungal spores come spring. Next, when the tree begins to bloom in spring, i.e., the first buds swell to the “red bud” stage, the tree should be sprayed. The tree should be sprayed every 7-10 days until bloom is completed. The bloom period may last several weeks, so be prepared for 4 to 8 spray treatments. The blooms are the primary infection site for brown rot spores in the spring. So, if sprays are carefully and thoroughly applied, the incidence of brown rot should be greatly reduced. If there is a rain during the bloom period, a spray should be applied as soon after the rain as possible. If the above cleanup and spray program is carefully done, you should reduce brown rot incidence to a minimum.