January, ip?i 



BETTER FRUIT 



Off- Year Apple Bearing 



Page 5 



BIENNIAL bearing of apples is so 

 common in the eastern part of the 

 United States that this condition is 

 generally accepted as being a fixed tree 

 habit. It is believed, however, in view 

 of observations of fruiting conditions 

 in typical orchards and of the results 

 of experimental trials that off-year 

 bearing is due to nutritional conditions 

 and that it is consequently subject to 

 modification. This present discussion 

 deals with these observations. It is 

 taken as significant that several vari- 

 eties in a number of states which are 

 ordinarily biennial in habit, were reg- 

 ular in bearing when proper growth 

 conditions were secured. 



Because of its economic importance 

 any discussion of the off-year problem 

 in the East should deal primarily with 

 methods of relief. The interest of Pa- 

 cific Coast growers doubtless lies more 

 in the matter of prevention. Whatever 

 the viewpoint, a review of the under- 

 lying principles, insofar as they have 

 been developed, should be given as a 

 basis for an appreciation of the sugges- 

 tions as to control measures. 



The present discussion is based upon 

 information collected in the East. It 

 is recognized that the amount of growth 

 in the average eastern orchard is much 

 below that of western ones. Data from 

 experimental plats show that eastern 

 trees have an average terminal growth 

 of four to ten inches. What appear to 

 be comparable experiments on the Pa- 

 cific Coast, as at Hood River, show plat 

 averages of nearly double this length. 



This difference in growth conditions 

 is offered as an explanation of the ap- 

 parent differences in the tendency to 

 irregular bearing in the two sections, 

 rather than being an argument that the 

 conditions are different and that the 

 suggestions based upon eastern data 

 have no bearing outside of the East. If 

 a similar growth was obtained similar 

 results would follow in both localities. 

 When viewed from the standpoint of 

 the relation # of growth to fruitfulness, 

 there is no apparent lack of application 

 of the results secured. Observations 

 made by the horticultural department 

 of the Oregon Experiment Station show 

 that the relations between growth con- 

 ditions and blossom bud formation are 

 very similar to those which have been 

 found to prevail in the East. It is 

 hoped that the observations may be ex- 

 tended to the orchards of the western 

 coast soon, especially in view of the 

 off-year tendencies of Newtown and 

 Spitzenberg. 



A popular theory regarding biennial 

 bearing is that this condition is due to 

 the over production of fruit. This is 

 not necessarily true as many biennially 

 bearing orchards produce light crops, 

 even though they bear only every other 

 year. The theory is not without foun- 

 dation, however, as an off-year is quite 

 sure to follow an extreme production 

 of blossoms, which is usually accom- 

 panied by a heavy yield of fruit. This 

 is because spurs do not regularly blos- 



By R. H. Roberts, Wisconsin Experiment Station 



som two years in succession even 

 though no fruit was matured the first 

 year. As a rule, if all the spurs blos- 

 som one season, they all miss the next. 

 It is rare that an old bearing tree ma- 

 tures fruits on many more than one- 

 half of its spurs during any one season. 

 In such cases the fruits are generally 

 small and of poor quality. A full crop 

 can result with a third of the spurs 

 blossoming. In fact there is an inverse 

 ratio between the number of spurs 

 blossoming and the number fruiting; 

 the more there are that blossom the 

 lower the percentage of fruits set. The 

 result is that older trees produce their 

 crop on a minority of the spurs even 



the leaf or blossom bud was formed, 

 not the current season's growth. 



From the standpoint of fruitfulness 

 the spurs may be classified as non-blos- 

 soming, blossoming and not fruiting, 

 or blossoming and fruiting. The vege- 

 tative or non-blossoming spurs may be 

 again separated into two classes, short 

 and long spurs. Thus there are four 

 classes of spurs. In the case of 

 Wealthy these have average lengths as 

 follows: 



Class 1. 

 Vs inch. 



Class 2. Blossoming (not fruiting)— 

 %c inch. 



,-If S fe e wer _%*££, Blossomin 8 < f ™ting spurs) 



Vegetative (short spurs) — 



spurs blossom a higher percentage set 

 fruit, and an equal or better crop of 

 fruit may result. In practice, an ideal 

 would be to have from a third to two- 

 third blossoming each season. 



Although thinning has been frequent- 

 ly advanced as a remedy for the off- 

 year, it has given results in but few 

 cases. The reason lies apparently in 

 the fact that commercial thinning is 

 done too late to affect blossom bud 

 formation. Either the blossom buds 

 are already formed for the next season 

 or it is too late to modify the condi- 

 tions determining their differentiation. 

 Blossom buds can be distinguished from 

 leaf buds as early as late June or early 

 July. Removal of the blossoms before 

 the fruits normally set in experimental 

 tests has given successive blossoming. 

 Early frost injury to the blossoms may 

 likewise cause repeated blossoming of 

 the same spurs. 



Little more will be said of bearing 

 although fruit production is the result 

 desired. At present, interest centers 

 about conditions of blossom bud for- 

 mation, including spur habits as well 

 as growth conditions of both the spurs 

 and longer growths or branches. 



Blossom bud formation is related to 

 nutritional conditions. This seems to 

 apply equally well to individual spurs 

 or to trees as a whole. The principal 

 measure used to show the relation of 

 growth conditions to fruiting has been 

 that of spur length. The part measured 

 was the "previous season's growth," 

 that is, the growth that was made when 



ire 1. Fruit Spur Habits of Off-year Trees. 



A. The growth during the blossoming sea- 

 son consists of a "cluster base" and a "sec- 

 ondary shoot." This latter docs not regularly 

 form a blossom bud. 



B. In the off-year a vegetative growth is 

 made which usually forms a blossom bud. 

 This gives a biennial growth cycle of the in- 

 dividual spurs. 



Class 4. Vegetative (long spurs)— 

 % inch or over. 



These relations of spur length to 

 fruitfulness vary with the tree, variety, 

 and season, but the main point is that 

 such a relation clearly exists between 

 growth (as measured by length) and 

 fruitfulness. The medium length spurs 

 are fruitful while the shorter and long- 

 er spurs are either unfruitful or less 

 fruitful than the former. The fact of 

 economic importance is that the fruit- 

 fulness of the older bearing trees ap- 

 pears to vary with the relative per- 

 centages of spurs of the different classes 

 which are present. 



The length of the spurs is of course 

 not the cause of blossom buds forming 

 but is only a correlated condition. 

 Other characters such as the number of 

 leaves on a spur, or better the leaf area 

 of each spur, would show similar re- 

 lationships. In fact the leaf area would 

 probably show the closest correlations 

 because of its function as a manufac- 

 turer of the type of foods which are 

 known to be necessary in relative 

 abundance before blossom buds are 

 formed. At any rate, we can begin 

 to appreciate more clearly that fruit- 

 fulness is a definite condition resulting 

 from what appear to be rather definite 

 conditions of nutrition and also that it 

 seems possible to arrive at fair judg- 

 ments of these conditions from external 

 growth relationships. 



An off-year is seen to be definitely re- 

 lated to the growth when we make a 

 study of their fruit spur habits. An 

 apple blossom bud produces two kinds 

 of growth; the blossoms and a second- 

 ary wood growth which generally 

 forms a vegetative bud, Fig. 1, A. This 

 secondary growth seems to function 

 much as a separate spur and in growth 

 measurements made, it has been consid- 

 ered as such. That is, when measuring 

 the blossom spur growth, from the 

 standpoint of bud formation, only the 

 secondary growth, from the cluster base 

 out, was considered. Willi biennially 

 bearing Wealthy trees it was found that 

 in I lie on-year over 90 per cent of the 

 secondary growths were less than one- 

 eighth of an inch long or over 90 per 

 < cnl of the growths were of class one. 

 This very logically results in an off- 

 year. During the off-year when no 



