Agriculture Reference
In-Depth Information
Symptoms.
Affected fruits develop dark, corky spots in the flesh just under-
neath the skin. The spots can grow to
⁄
2
inch in diameter. At about the time
1
of harvest or perhaps not until the fruits are in storage, sunken spots develop
on the fruit skins over the lesions, sometimes starting near the petal ends of
the fruits. Fruits from young trees or from vigorous, upright shoots are most
susceptible to bitter pit. With the exception of highly susceptible varieties,
older, well-managed trees bearing high and sustainable yields are quite res-
istant to the disorder.
Management.
The best control starts with good site preparation and crop
management practices. Strive for moderate vegetative growth and high, sus-
tainable yields of moderate-sized fruit. Calcium foliar sprays can help pre-
vent bitter pit. Calcium nitrate is a synthetic product made by treating lime-
stone with nitric acid. While it is used in conventional orchards as a fertilizer
and for bitter pit control, its use in certified organic production appears to
be prohibited.
For California apple growers, the University of California Extension re-
commends applying three to six sprays of calcium chloride at two-week in-
tervals beginning after bloom. Apply 12 pounds of calcium chloride in 400
gallons of water per acre, and ensure that the fruit is thoroughly covered.
Similar control programs should work in other growing areas. Be sure to ap-
ply the calcium sprays during dry weather and under conditions when the
fruit will dry rapidly, to reduce russeting. While calcium chloride is a natur-
ally occurring substance, it is prohibited by the National Organic Program
except when derived from a brine process and used to treat physiological
disorders associated with calcium uptake (e. g., bitter pit).
Dipping fruits into a 2 to 3 percent solution of calcium chloride can help
prevent bitter pit from developing in storage. Dipping the fruit can damage
it, however, and may not be acceptable to your organic certification organiz-
ation. Certified organic growers should consult with their certification agen-
cies before using postharvest calcium dips.
