Monilinia fructicola (Wint.) Honey
Monilinia laxa (Aderh. & Ruhl.) Honey
authored by T.J. Burr in consultation with J.D. Gilpatrick and M. Szkolnik.
Brown rot (BR) can be extremely devastating to crops of cherries, peaches, plums, prunes, nectarines, and apricots. Under favorable conditions fruit set is reduced, twigs become cankered, and mature fruit may be completely rotted.
The BR fungi can overwinter in dried infected fruit called mummies (Fig. 1 ) or in infected twigs. In the winter BR mummies may remain hanging in the trees or be scattered on the orchard floor.
The fungus resumes growth in the spring, providing inoculum for blossom infections. Two types of spores may be produced: the sexual ascospores and the asexual conidia. Ascospores are only produced on mummies which have fallen to the ground and are at least partially covered with soil. Conidia are produced in abundance on mummies and infected twigs and may be spread by wind and rain.
Infections during bloom (Fig. 2) cause blossoms to turn brown, wither, and drop. Under wet conditions, a powdery mass of conidia develop on infected blossoms. The blossoms may also become gummy in appearance. Blossom infections not only reduce fruit set, but increase the inoculum available for fruit infections.
Twig infections occur when blossom or fruit infections continue to develop and extend down the stem into the twigs (Fig. 3). During wet weather the fungus may sporulate on infected twigs and may also girdle and kill them.
Generally, immature stone fruits are resistant to brown rot infections. Prunes, however, may become infected early in their development. These quiescent infections may remain in a latent state and not become apparent until the fruit matures and then rapidly rots.
All stone fruits become increasingly susceptible to BR as they ripen. Fruit infections appear as soft brown spots which rapidly expand and produce a tan powdery mass of conidia (Fig. 4). Fruit infections may spread rapidly, particularly if environmental conditions are favorable and fruits are touching one another. Wet weather with temperatures ranging from 15.5-21° C (60-70° F) favor disease development. Fruit cracking, bird pecks, hail damage and insect feeding increase the potential for BR development.
During wet seasons when favorable temperatures prevail, brown rot can be difficult to control. A grower with a small orchard may wish to remove mummies and infected twigs and either burn them or bury them deep in the soil.
Chemical sprays should be applied just prior to and during bloom to control blossom and twig infections and, as fruit ripen, to control fruit rot. Refer to your local recommendations for the cultural practices and fungicides recommended in your area.