Asiatic Brown Rot
European brown rot blighting new growth on peach. Photo: K. Cox, Cornell University.
An apple destroyed by brown rot infection. Photo: K. Cox, Cornell University.
Brown rot can spread by contact from an infected fruit to others in a fruit cluster. Photo: K. Cox, Cornell University.
Asiatic brown rot, caused by the fungus Monilia polystroma, is native to Japan. Unlike our native brown rot which infects primarily stone fruit, Asiatic brown rot readily infects apple and pear. Asiatic brown rot has been introduced into China and Hungary where it is affecting apple orchards. The fungus travels from place to place on infected plant material – young trees, nursery stock, and fruit. Because brown rot fruit infections can be latent (essentially invisible), people can unknowingly bring the disease into the U.S. from other countries.
Asiatic brown rot can be extremely destructive to stone fruit, including cherry, peach, nectarine, apricot and plums, but also apple and pear trees. On infected trees, brown rot kills the blossoms and new shoots, rots fruit, and cankers stems. In European apple orchards, losses of 7-36% have been recorded. The disease can also infect ornamental flowering fruit trees. If introduced to the U.S., there is a high probability that Asiatic brown rot would become established, particularly in the Northeast, and this could be of substantial concern to our apple farms that are growing varieties resistant or immune to apple scab.
Brown rot manifests on blossoms as wilting and browning of flower parts and emerging shoots. Infections on twigs and small branches, called cankers, are brown, oval and elongated, and usually sunken with a darker margin. Diseased fruit, the primary and most frequent symptom, develops soft brown spots which may enlarge and become covered in grey-brown tufts of fungal growth, covered with spores. Sometimes these tufts of spores develop in a characteristic concentric ring pattern on the fruit. All diseased plant parts may show signs of the grey-brown tufts of fungal growth. Spores travel to other plants primarily via rain and wind.
By killing blossoms and rotting fruits, the fungus can destroy or severely reduce crop yields. When weather is rainy, humid and warm, the damage may be even greater. Asiatic brown rot poses a considerable threat to stone fruit, apple and pear production if it becomes established in the U.S. Current IPM practices for apple varieties that are scab resistant may fall short of controlling Asiatic brown rot.