Published in the
Contra Costa Times on
Q. How can I prevent brown rot from ruining
my peaches and nectarines this year?
A. We have had so much rain this year that
brown rot is going to be a big problem for many backyard
orchards. Brown rot, (Monilinia spp.), are very destructive fungi, that can destroy
more than 50% of the fruit from peaches, pears, apples, nectarines and plums
prior to harvest.
The first visible symptom is
the shriveling of blossoms. Often droplets of clear-amber sap appear where the
infected twig attaches to the stem. If weather remain wet and humid, gray
fungal masses may appear on the dead blossoms. Infected twigs have
cankers with brown margins that appear on the surface. Twig lesions apparently
do not produce spores
Young
fruit is not usually susceptible to brown rot unless it is damaged in some way,
giving the spores access to the interior of the
fruit. Once the fruit ripens and becomes soft, it is more easily infected,
especially under warm, moist and humid conditions. In severe infections, an
entire crop of fruit can be destroyed in just a few days. If the fruit is
infected, small soft brown circles appear, gradually spreading over the entire
surface. The fruit eventually shrivels up (becomes mummified) and is covered by
a grayish coat of spores.
Monilinia spp. overwinters on mummified fruit fallen to the ground or
remaining in the tree. In spring, ascospores are
released from the fallen mummies at the same time as the trees bloom, the
primary source of infection.
The
first line of defense is to meticulously pick up all fallen fruit from the
ground and from the tree. Bag and remove from your yard; compost only if you
have a hot compost pile. In the dormant season, prune off all cankered
twigs.
By
April your tree have bloomed. If mummified fruits were
in your yard the blossoms are likely to be infected. Prune off any infected
blossoms, carefully removing the twigs from the garden. Several fungicides are
registered for use on peaches and nectarines. For currently
registered products and for more information on brown rot, look under peaches
on the UC IPM Web site at http://www.ipm.ucdavis.edu/PMG.