Disease Management - Growing Organic Orchard Fruits - page 509

Closely monitor your trees for signs of peach scab. If a tree shows infections
one year, expect more serious problems the next year. Fungicides effectively
control peach scab. Begin sulfur applications at petal fall, and continue every
10 to 14 days until at least 40 days before harvest. Do not apply sulfur
products to apricots.
Plum Leaf Scald
A bacterial disease common in the southeastern United States, plum leaf
scald is caused by the bacterium Xylella fastidiosa , the same pathogen that
causes phony peach disease. The bacterium infects many other woody plants
and is spread by glassy-winged sharpshooter and other small, wedge-shaped
insects called leafhoppers that feed on sap in the plants' xylem. These insects
attack an extremely broad range of host plants across the southeastern Un-
ited States and into Texas. Infected trees can also infect other trees through
naturally occurring root grafts.
Symptoms. Infected trees are smaller and appear leafier than normal due to
abnormally short internodes on current-season shoots. The trees bloom earli-
er in the spring and drop their leaves later in fall than healthy trees. Infected
plum leaves look scorched or scalded, although these symptoms do not ap-
pear in peach trees. Although the disease does not kill the trees, it makes
them more susceptible to other diseases and shortens their life spans. Fruit
size, quality, and yields are reduced.
Management. Avoid planting your trees next to an infected orchard. Infec-
ted trees cannot be cured, and you should remove them as quickly as pos-
sible to reduce the likelihood of infecting nearby trees. Scout your orchard
and remove infected trees before starting summer pruning. Keep nitrogen
fertilization moderate and avoid heavy pruning that stimulates the lush fo-
liage that attracts leafhoppers. Remove all wild and escaped plums, cherries,
and peaches in and around your orchard.