Disease Management - Growing Organic Orchard Fruits - page 499

under wet or humid conditions, and infections often develop following spring
and early summer rains. The pathogen overwinters on infected twigs and
fallen leaves.
Management. Some of the varieties described in chapter 5 ➔ demonstrate
at least partial resistance to the fungus. Careful site selection and prepara-
tion, resistant varieties, good sanitation, proper plant spacing, and pruning to
maintain good air movement go a long way toward managing Entomospori-
um leaf spot. The management practices described for Fabraea leaf spot will
also control this disease (see page 349 ➔ ) . Avoid sprinkler irrigation.
Bitter Pit
Bitter pit is a poorly understood physiological disorder (no pathogen is in-
volved) that produces disease-like symptoms on apple fruits. It is caused by
imbalances in mineral nutrients in the fruit. Although it is sometimes blamed
on calcium deficiency, the absolute amount of calcium in the soil is not usu-
ally the cause. Excessive amounts of potassium and magnesium contribute
to bitter pit, as does low soil pH, excessive nitrogen fertilization, excessive
pruning, and excessive irrigation. Practices that result in very large fruit, in-
cluding thinning fruit too early and overthinning, contribute to bitter pit.
Listed in the box below are highly susceptible varieties. Apple varieties
that are less susceptible to bitter pit include 'Fuji', 'Gala', 'Golden Delicious',
'Haralson', 'Lobo', 'McIntosh', 'Red Gravenstein', 'Rome Beauty', 'Spartan',
'Stonetosh', and 'Winesap'.
APPLE VARIETIES THAT ARE HIGHLY
SUSCEPTIBLE TO BITTER PIT
Baldwin