Brown rot is a serious disease of fruits and almonds caused by the fungi Monolinia fructicola and Monolinia laxa. The fruits most susceptible to the fungus are:
However, apples and pears are infected with brown rot on occasion.
The fungus grows and multiplies rapidly in wet weather, entering plants through wounds. It survives the winter in twigs and dry, shriveled pieces of fruit called mummies.
- Small, elliptical cankers on twigs, generally oozing.
- Gray, fuzzy masses of spores on branches or flowers.
- Brown, wet spots on blossoms.
- Blossom drop.
- Brown or gray fuzz on fruit.
- Mummified fruit.
Cankered twigs should be pruned out during the summer.
Blossoms can be treated for brown rot starting when the first pink shows in the unopened bud. Treatment should continue through the spring if the weather is wet. Fungicides are typically used, but organic growers can spray with sulfur or copper. Spraying with organic milk also shows promise at this point in time.
Fruit that is visibly affected with brown rot must be destroyed to prevent the spread of the disease. Fungicides can be applied to the unaffected fruit as soon as it begins to ripen.
The first step in preventing brown rot is to remove potential vectors of the disease:
- Destroy wild plums growing near the orchard.
- Water trees at the base so that the leaves do not get wet.
- Control insect pests.
- Pick up all fruit laying on the ground under the trees.
Proper pruning is also an important part of preventing brown rot. If air and light can reach all parts of the canopy, fungal diseases will have a hard time gaining a foothold.