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Wisconsin State Horticultural Society / Annual report of the Wisconsin State Horticultural Society for the year ending July 1, 1921
Vol. LI (1921)

Roberts, R. H.
Off-year apple bearing,   pp. 72-78 PDF (1.8 MB)

Page 74

they are very vegetative, while others are unfruitful because they
are undervegetative. It is well to know which kind of unfruitful
spurs we have in our trees if we are going to make the best
decision as to the cultural practice needed.
We find this condition of spurs especially with the Wealthy.
If the spur makes a growth of about one-eighth inch or less it
forms, typically, a leaf bud; if the growth is somewhat greater
than one-eighth inch, up towards a quarter inch, it will form,
typically, a blossom bud, but such spurs seldom set fruits. If
the growth is somewhat longer, as a half to three-quarters of an
inch, such a spur will form a blossom bud. It is such spurs
which produce fruit on the trees. If the spur is longer, as an
inch or more, very many of this type of spurs have terminal leaf
buds: So we say that blossom bud formation is related to the
nutritional conditions, as shown by the length of the growth of
the spurs.
Now, the question comes, what relation has this to off-year
bearing. It occurs in this way: We find that with Wealthy, for
example, in the off-year ninety per cent or more of the spurs
grow to be of average lengths and they practically all blossom
the next year. Now, what happens to these spurs when they
blossom? They produce four, five or six blossoms and a sec-
ondary wood growth at the same time. That is, the apple blos-
som bud produces both blossoms and wood growth. We find by
measuring this new secondary growth that ninety per cent or
more of them are of the undervegetation class, so there is in
off-year trees a fluctuation from all spurs forming blossom buds
one year to none the next. So we propose that off-year bearing
is related to nutritional conditions of the trees.
The reason that only short growths form on the spur the year
it is blossoming is doubtless due to the drain upon the reserve
food in the tree for the production of blossoms. The early
growth is apparently made very largely from the reserves that
are in the tree.
Now, what is the situation in trees which are regular in bear-
ing? There are four very distinct differences in the spur
growth, spur habits, if you please, between off-year trees and
regular bearing trees. There are two that are very important,
and there are two that are not so important, as we see the situ-
ation now. Probably the most important difference in many

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