•January, 1921. 



SCIENTIFIC AGRICULTURE. 



39 



Biennial Fruit Bearing in the Apple 



J. W. CROW. Ontario Agricultural College, Guelph. Canada 



Biennial bearing is not a fixed characteristic of 

 the Duchess and Wealthy varieties. It is brought 

 about by the development in one year of blossoms 

 on too large a percentage of spurs. Alternate bear- 

 ing trees commonly show in their fruiting year fruit 

 buds on from 60 to 90 per cent of their fruit spurs. 

 From 30 to 50 per cent of these would be sufficient 

 to produce a full crop. Growths on bearing Duchess 

 and Wealthy trees are of six distinct types, based 

 on their position and on the behaviour of their ter- 

 minal buds. 



(1^ Weak leaf spurs, making 1 to 2 mm. of growth 

 anmially. So long as they make only this amount of 

 growth t.iiey do not set fruit buds. 



(2l Axillary leaf spui"s, 1 to 3 mm. in length, pro- 

 duced as lateral growths on blossoming spurs. They 



rarely produce fruit buds in the season of their origin 

 but normally do .so the following year. 



(3) Weak fruit .spui-s. 3 to 4 mm. in length. They 

 blossom but seldom produce fruit. 



(4) Strong fruit spurs-, 4 to 9 mm. in length. These 

 bear nearly all the fruit. Individual spurs bear every 

 second year and rarely blossom two years in succes- 

 sion. 



(5) Extra long fruit spurs (or shoots). With 

 .some varieties shoots from 10 to 200 mm. in length- 



occasionally produce strong terminal fruit buds. 



(6) Xon-fruiting shoots of lengtlis varj-ing from 10 

 mm. up to 500 mm. or more. The majority of the 

 longer growths on a tree are of this nature. 



The percentage (from actual count) of growths fal- 

 ling in each category is as follows: — 



1. Alternate bearing tree, in on year 



2. Alternate bearing tree, in off year. . . . 



3. Annual bearing tree (Mcintosh) 



To secure annual fruiting it becomes necessarj' to normally produce fruit buds in that season will be 



stimulate the growth of the tree in the off i/ear so forced into categories 5 and 6. Spur behaviour will 



tjiat a considerable percentage of spurs which would then tabulate as follows: — 



1. Rtartin? with (on year) 



9. Stimulated (bv pruning") off year 



3. Next year (estimated) 



4. Result is annual fniiting. . 



We tihus get a tree with two sets of spurs, each set 

 of which produces fruit in alternate years. Our ex- 

 pmments show- that this result cannot be accomplished 

 by thinning of the fruit but that it can be accomplished 

 by moderate heading back of small branches in the 

 off year. Our experiments show that it can also be 

 accomplished by stimulating the growth of the tree 

 with Nitrate of Soda /" ihe off year. The Nitrate 

 requires to be applied veri- early in the spring for 

 the reason that the large ma.iority of fruit spurs have 

 a very short period of growth (from 4 to 10 days). 

 Our observations lead us to believe that 75 per cent 

 or more of the fruit spurs on Duchess and Wealthy 



have completed their growth for the season hy the 

 time the first blossoms have well set on blootning 

 trees of the same irarieties. Experiments in bud and 

 blossom removal indicate that the date given Ls cer- 

 tainly the critical period of fruit bud formation for 

 trees in their on year. Table 3 shows 79 por cent of 

 fruit bud formation from spurs disbudded before that 

 time and none whatever from spurs disbudded after 

 that time. We suspect that no treatment can be ap- 

 plied after that time whicfh will change t.he destiny 

 of buds falling in categories 1. 2. 3 and 4 on cither 

 bearing or non-bearing trees. 



