Why Are My Peaches Rotting on the Tree?

Identification

• Peach trees are susceptible to infection from the brown rot fungal disease caused by Monilinia fructicola or Monilinia laxa. The disease is among the most serious diseases of peach in many regions of the United States. Besides peach, the infection also strikes a number of other stone fruits including nectarines, cherry, plum and apricot. Under favorable growth conditions, crop losses are likely to be heavy.

Symptoms

• The disease is characterized by the appearance of sunken, brown cankers on infected new shoots. With disease progression, the cankers develop a gummy texture with gray to tan fungal spores within the infected areas. Cankers often girdle and kill the entire stem. The dead stem with leaves remains attached to tree. Fungus infects the ripe fruit with the appearance of small, round spots that gradually enlarge and merge to cover the entire fruit rapidly. Under optimal growth conditions, the entire fruit rots to a brown or black shriveled mass within a couple of days. The rotted fruit often remains attached to the tree and houses the overwintering fungal spores.

Favorable Conditions

• The fungal spores start to become active during late spring in temperatures of 55 to 77 degrees Fahrenheit and are spread by air and water. Late spring rains favor the development of disease. The moisture on trees coupled with warm temperature can lead to widespread infection through the tree in as little as three hours. The longer duration of wetness shortens the incubation period and causes the symptoms to appear more rapidly.

Management

• Remove and destroy all diseased fruit from trees during dormancy and prune trees to remove weak, dead or cankered areas. Thin the canopy to let light into the trees as this will help keep inner areas free from excessive moisture. Monitor trees for signs of infection immediately following blooming in order to start use of fungicides earlier. Chemical control options include the use of propiconazole, tebuconazole, myclobutanil or fenbuconazole, as suggested by the University of California Extension.