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)
74 FIFTY-FIRST ANNUAL REPORT OP 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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