Monilinia fructigena, and Monilia polystroma are closely related fungi, and are among those responsible for brown rot in fruit trees. They primarily cause disease in pome fruits (apples and pear) and stone fruits (apricot, plum, peach and cherry). M. fructigena is currently found in the Mediterranean basin of Africa, throughout Asia, and throughout Europe. It was discovered in Maryland in 1979 and eradicated. It has also been found twice on fruit from Mexico, but trace-backs were unable to find an infected source. In Europe, most losses are in the field (<10% to over 40%), with an additional few percent lost in storage. The greatest losses are seen in apple and plum. M. polystroma has been found in China, Japan, and parts of Europe. Neither is currently found in the U.S.

three purplish round fruit with many cream colored granular spots

Monilinia sp., brown fruit rot, peach, University of Georgia Plant Pathology, Bugwood.org

Hosts and Symptoms

Hosts of M. fructigena and M. polystroma include apple, pear, Prunus spp. (apricot, cherry, nectarine, peach, and plum), strawberry, cotoneaster, hawthorn, rhododendron, rose, tomato, and blueberry. Both fungi are favored by moist conditions (rain, fog, dew, etc.), especially at the beginning of the season. They are rarely seen in arid production areas. The fungi overwinter in mummified fruit still on the tree, as well as fallen fruit; they also survive in branch cankers.

2 black shrunken fruit with tan granular spots against green leaves

Monilinia sp., dried fruit mummies, peach, University of Georgia Plant Pathology, Bugwood.org

completely mold-covered green lumpy granular fruit

Monilinia fructicola, fruit mummy with heavy sporulation, peach. This is a related species, widespread in the U.S., Clemson University, USDA Cooperative Extension Slide Series, Bugwood.org

Spores are produced in the spring, and easily spread by wind, water, insects, birds, and humans. They do not require liquid water for spore germination. Spores may infect flowers, causing blossom blight or twig blight. Brown spots may form on flowers and twigs. Flowers may wilt and collapse, some remaining on the tree and others falling. Twigs may die as the fungus moves toward larger branches. Moist conditions with moderate temperatures cause spore production and multiple cycles of infection may occur.

twig with unformed branch or fruit

Monilinia sp., blossom blight, peach, University of Georgia Plant Pathology, Bugwood.org

Monilinia sp., blossom and twig blight, peach, University of Georgia Plant Pathology, Bugwood.org

Cankers may develop on blighted twigs or branches. They are generally elliptical (elongated circles) or spindle shaped (larger in the middle, tapered at ends). Gum may be produced at the leading edges.

twig with a few leaves

Monilinia sp., blossom blight with gum production, peach, University of Georgia Plant Pathology, Bugwood.org

If the stem is girdled, leaves beyond the canker may be blighted. Leaves on infected twigs may be dark brown and remain attached. Cankers are usually on twigs and don’t extend into previous year’s wood. Additional spores may be produced on canker surfaces. Unlike many other canker diseases, those caused by M. fructigena and M. polystroma do not continue to enlarge year after year. If the branch is not girdled, callus (wound healing) tissue will form around the canker margins. Other fungi and bacteria may invade cankers and dead shoots.

The most important disease phase is brown rot of fruit. Infections take place via cracks and wounds (including scab lesions, growth cracks, hail damage, and insect damage), as well as by fruit-to-fruit contact. Fruit may be infected at any stage of development. Infections may be inactive until conditions favor disease development. Fruit may also become infected during harvest or storage. Initial lesions are small, brown, circular, and firm. These spots rapidly expand and may rot the entire fruit.

round fruit with large blotchy spots

Monilinia sp., brown rot, before sporulation, peach, University of Georgia Plant Pathology, Bugwood.org

When the relative humidity is high and fruit are ripe or nearly ripe, tufts of cream-white to tan mycelia and spores may erupt from the skin. These often form concentric rings.

a bunch of fruit on tree with white mushy blotches

Monilinia sp., brown fruit rot, early sporulation, peach, University of Georgia Plant Pathology, Bugwood.org

Monilinia fructicola, brown fruit rot, concentric circles, peach. This is a related species, widespread in the U.S., Kevin Ong, Texas AgriLife Extension Service, Bugwood.org

Rotted fruit may drop or stay attached to the tree, eventually drying into hard shriveled mummies. Fruit in storage may rot, apples may turn brown or black. Fruit rot is common in apple, pear, and plum. Rot is less severe in apricot, nectarine, and peach. M. polystroma may colonize fruit faster than M. fructigena; it also produces a larger fungal mass, which may inhibit decomposition, and may increase the amount of inoculum the following spring. Some infected fruit show no symptoms.

Similar symptoms may be caused by other common fungi. Related fungi, Monilinia fructicola and Monilinia laxa are widespread in the U.S., their pustules are grayish-brown (as opposed to the light yellowish-brown of M. fructigena and M. polystroma). Penicillium spp. and Mucor spp. can also cause a fruit rot similar to M. fructigena.

6 fruit with blankets of cream and tan mold

Monilinia spp., brown fruit rot, apricot. M. fructigena is is the upper right and lower left. University of New South Wales, Bugwood.org

Monilinia spp., brown fruit rot, pear. M. fructigena is is the upper right and lower left. H.J. Willetts, University of New South Wales, Bugwood.org

Monilinia spp., brown fruit rot, plum. M. fructigena is is the upper right and lower left. University of New South Wales, Bugwood.org

Penicillium sp., fruit rot, apple, Gerald Holmes, California Polytechnic State University at San Luis Obispo, Bugwood.org

The main pathways of introduction to new areas are infected fruit and vegetative propagation material. USDA-APHIS conducted a host risk analysis for the contiguous U.S. based on the presence of susceptible hosts. The eastern U.S. has a high risk of pathogen establishment while they found California, Oregon, and Washington to have moderate risk of establishment. Though Alaska was not included in the analysis, the risk is probably similar to, or lower than, Washington due to lack of large orchards. However, the climate of much of Alaska is conducive to pathogen survival and spread.