66 BITTER PIT INVESTIGATION. 



The trees were pruned on 29th July and the fruit was picked on 20th March, with the following 

 results : 



TABLE XXXVI. RESULTS or DIFFERENT METHODS OF PRUNING ON CLEOPATRA- 

 SEASON 1914-15. 



Pruning No. of Trees. Yield. Clean. Pitted. Per cent. Pitted. 



Ibs. Ibs. Ibs. 



Severe 6 2J 2* 100 



Light 6 6 li 4| 79 



Leader 6 6 2 4| 69 



Unpruned .. 6 30 16 14 



The yields are too small on which to base conclusions, but every apple on the severely pruned 

 trees was pitted. 



GENERAL SUMMARY. 



Severely pruned trees had invariably the most Pit, and at the other extreme of no pruning 

 there was comparatively little Pit. Experienced orchardists who have devoted some attention to 

 this disease have also arrived at the conclusion that when the trees are in bearing they should be left 

 alone, except to prune for regular growth and shape in order to minimise the trouble. (Figs. 47, 48, 49.) 



An equable flow of sap is more likely in a tree in which the branch system is in full harmony 

 with the root system, and this harmony of root and branch must be disturbed by heavy pruning of 

 the branches without any pruning of the roots. As the tree ages, heavy pruning is used for keeping 

 up the size of the fruit, but this end might perhaps be more safely achieved by leaving the tree alone, 

 except removing superfluous wood and thinning the fruit, at least for some years. In Report III., 

 Fig. 51, an illustration is given of very severe pruning. An old Champion tree was severely cut back, 

 almost to the stump, for regrafting, and the two branches which were left of the original tree bore 

 fruit with 92 per cent, of Pit. If the orchardist could see that the heavy pruning which is so common 

 in vigorous trees is just a milder form of the same operation, he would realize that in the one case, as 

 in the other, there is a disturbance of the equilibrium between root and branch. 



C. EXPERIMENTS WITH STOCKS. 



There is a suspicion in the mind of the orchardist that the stock might have an influence upon 

 the disease, for he reasons that since the Northern Spy stock is the one most commonly used, at least 

 in Victoria, and since the tree itself is a liable variety, therefore the disease is likely to be transmitted 

 through the stock. But this raises the whole question of the mutual influence of stock and scion, 

 and 1 have endeavoured to settle experimentally if there is any evidence of the stock influencing 

 the graft as regards Bitter Pit. Of course, to carry out such experiments thoroughly would require 

 longer time than the course of this investigation allows, but the results obtainable in four years are 

 here presented. They are discussed under the following headings : 



(1) Blight-proof stocks (including Northern Spy) with grafts each of four Pit-liable 



varieties. 



(2) Various stocks (including seedling stocks) in screen with grafts of varieties liable 



and non-liable. 



(3) Cleopatra budded and grafted on to pear stock. 



(4) Varieties on their own roots Gravenstein, Magg's Seedling, and Winter Majetin. 



(5) Reciprocal grafting of Cleopatra and Yates. 



(6) Winter Nelis and Josephine varieties of pear with grafts from badly affected to Pit-free 



trees, and vice versa. 



