Agriculture Reference
In-Depth Information
Thinning, Crop by Crop
While the general principles of thinning apply to most stone fruit and pome
fruit crops, the specific methods vary slightly from crop to crop. We cover
these specifics in the following sections.
Apples
In pome crops, if a flower receives abundant, compatible pollen and weather
conditions are favorable, many seeds form. The presence of these seeds stim-
ulates growth, causing a large and uniformly shaped fruit. If a flower receives
only a fraction of the pollen that it requires, only a few seeds form in the
fruit. Fruits that have a small number of seeds are typically small and often
misshapen. Some of these fruits fall naturally during June drop. Those that
remain continue to compete for nutrients, reducing the size of well-formed
fruits on the same tree.
Handthinning. In apples, the centermost blossom is called the “king” blossom.
King blossoms usually open first in a cluster and produce the largest fruits.
When hand or pole thinning, try to target the smaller surrounding fruits;
ideally, you want to leave one apple on every other spur. Spurs that do not
have apples are more likely to develop fruit buds for next year's crop. As
mentioned above, however, keep the larger fruits when possible and leave 6
to 12 fruits for every 48 inches of fruiting wood.
Chemical thinning. Growers in conventional apple orchards have applied
chemical sprays during and shortly after bloom for many years to cause
some of the flowers and fruits to fall. For a long while, the materials of choice
were carbaryl insecticide, usually combined with synthetic plant growth reg-
ulators like naphthalene acetic acid (NAA). None of these materials can be
used in certified organic orchards.
Using synthetic chemicals is an extremely effective and relatively inex-
pensive way to thin fruits. Not only are the chemicals effective, but they can
 
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