Disease Management - Growing Organic Orchard Fruits - page 498

Symptoms. Bitter rot symptoms caused by Colletotrichum species are easy
to recognize. The first symptoms are one to many circular, light brown spots
on the fruit skins. The spots gradually enlarge to 1 or more inches in dia-
meter, with light brown outer rings and sunken, dark brown to black, saucer-
shaped centers. The centers of the spots become cream-colored with pink
spores, often arranged in concentric circles. Underneath the spots, the flesh
rots and becomes watery. Infected fruits can shrivel and mummify.
Under optimal conditions (80°F [27°C] and 80 to 100 percent humidity),
infections can occur in 5 hours. Primary infections usually occur during
warm, wet conditions in early spring, and secondary infections can occur any
time during the growing season. Common sources of inoculum are prunings
left in the orchard, mummified fruits, and fire blight cankers.
Management. Plant apple varieties that have some resistance to bitter rot
(see chapter 5 ➔ for some examples). Avoid planting 'Arkansas Black', 'Em-
pire', 'Freedom', 'Fuji', 'Golden Delicious', 'Granny Smith', and 'Nittany' in areas
with serious bitter rot problems, as these are especially susceptible.
Applying calcium as a nutritional supplement may reduce the incidence
and severity of bitter rot in some years. Practice good orchard management
and sanitation: Remove all prunings and fruit mummies from the orchard
and burn them. Keep your tree canopies open, and maintain good air move-
ment. In warm, wet areas, plan on applying fungicides from bloom through
harvest.
Entomosporium Leaf Spot
The most serious disease of saskatoons, Entomosporium leaf spot, infects the
leaves and fruit.
Symptoms. The first symptoms are small, brown spots on the leaves, which
become yellow and may drop early. Small, gray lesions form on the fruits,
which may become disfigured and crack. The disease can become serious