Brown rot is a minor disease on apples from the United States. It is caused by the fungus Monilinia fructicola, and if discovered on apples, it’s normally connected with nearby infected stone fruits that are more vulnerable to the illness. The brown rot fungus survives the winter inside dead fruit or regions of dead timber, called cankers. In spring, the fungus produces spores, which are spread by rain and wind. The spores can infect the blossoms and young fruit on stone fruit trees, but apple infection generally occurs when the spores enter through through breaks in the skin of maturing fruit. This fungus can be controlled with fungicide sprays and dirt around the infected trees.
The most common fungicide spray for apple juice rots is captan. Captan is a contact fungicide that stays on the surface of the apple and stops energy production in the fungus. It has low toxicity at normal levels and rapidly degrades in water. Apply a fine spray that covers the fruit, leaves, and branches. Heavier sprays will not increase or prolong the effectiveness since, even if dry, captan’s half-life on fruit is significantly less than 13 days and it easily washes off with rain. Captan sprays can begin 10 days after petals have fallen and continue in 10-day periods through May, then at 14 day intervals throughout August.
Captan can also used in conjunction with thiophanate-methyl for more comprehensive protection. Thiophanate-methyl is a xylem-mobile fungicide that penetrates into the apple tree and travels through the tree liquid-transport system. Similar to captan, apply a fine spray that covers the fruit, leaves, and branches. Thiophanate-methyl travels upwards from the apple tree, so it’s necessary to adequately cover the lower portions of the tree. This spray can begin 10 days after petals have fallen and continue at 10 day periods during May, then at 14 day periods during August.
Dilute solutions of copper fungicide mixed with liquid lime-sulfur can help to control infection, but does not completely eradicate brown decay. Sulfur products do not control apple rots and high levels of copper will harm the fruit. Many sulfur and copper products are not labeled for use after petal fall, when most of the brown rot in apples occurs. Though approved for use in organic apple production, these fungicides have to be combined with careful sanitary measures.
Other spray options exist for stone fruit trees, however they’re not all approved for use on apples. Use sanitary controls, alongside these sprays, to boost their effectiveness. Infected fruit can remain on the tree and will harbor the fungus until the following calendar year. Remove all infected branches and fruit with cankers in the tree, then bury or burn them to isolate and destroy the fungus. Do not allow dropped apples to remain under the tree since injuries suffered in the autumn can allow infection. After you have picked the apples, block the development of brown decay by rapidly storing the apples in a refrigerator.