Brown Rot Blossom and Twig Blight

Young blossom spurs and associated leaves collapse to form shoot blight. Gum exudes at base of infected flowers. Cankers on blighted twigs have tan centers with dark margins. Gray brown spore masses form on diseased flower parts and twig cankers under high humidity.

Monilinia fructicola overwinters on mummified fruit that either fall to the ground in late fall or early winter, or remain in the trees. In spring, apothecia form on mummies that are on the ground; these apothecia release ascospores at the same time as the trees bloom. Ascospores serve as primary inoculum for brown rot in many orchards. Mummies in the trees as well as those on the ground may also produce conidia, which may serve as the primary source of inoculum in some years. Twig lesions apparently do not produce spores.

Although all flower parts except the sepals are susceptible to infection by M. fructicola, only infection of the stamens leads to the development of blossom and twig blight.

Bloom sprays to reduce blossom and twig blight help minimize loss to ripe fruit rot at harvest. Removal of fruit remaining on trees soon after harvest and before they become mummies may help prevent reinfection of blossoms the following bloom.

Make a treatment at 20 to 40% bloom and again at 80 to 100% bloom on susceptible varieties or if heavy rainfall and other conditions are occurring that result in high susceptibility to infection. Early season varieties, especially the low-chilling ones, only need a single spray.

Aerial applications are generally not as effective as properly applied ground sprays but may be necessary when the orchard floor is wet. To help recduce development of resistance to fungicides, be sure to rotate chemicals that have different mode of action Group numbers.