Page 1 6 



BETTER FRUIT 



August 



The Orchard Ladder of Quality must bear 



the name "Northwest." Thousands are sold 

 on their merits. Ask your dealer to let you 



, . [ «a/-J/-|c»r If your dealer does not carry our ladder in stock, 



oCC OLil L/dUUCl . write us direct for prices. 



No crushed fruit if you use the Barnett Fruit Picking Pail. 



PRICE $2.00 



Information on our Orchard Supplies will be gladly given on request. 



N. W. Fence & Supply Co. 



Station A 



Portland, Oregon 



Bitter Pit; It's Cause and Control 



By Professor D. McAlpine in the Fruit World, Department of Agriculture, Melbourne, Australia 



[Editor's Note. — The disease Bitter Pit, so 

 called in Australia, is generally known through- 

 out the Northwest as Core Rot, being the same 

 trouble. Very little has been done in the 

 Northwest to get at the cause of this trouble, 

 and not much in the way of investigation for 

 control. The Australian Government, in con- 

 nection with the fruit districts of Australia, 

 appropriated £10,000, or $50,000, for ten years' 

 research work. The work was extended an- 

 other year at an additional cost. This has 

 been published in four large volumes. The 

 research work done in Australia has been the 

 most complete, the most thorough and efficient 

 of any campaign waged for the solution and 

 cause of any disease or pest. The Editor of 

 Better Fruit has been in constant correspond- 

 ence with Professor D. McAlpine and has re- 

 ceived one of each of his four Progress Reports. 

 Conditions under which the trouble occurs in 

 the Northwest are seemingly very similar, and 

 the suggestions of control as outlined by Mr. 

 McAlpine, where practiced in the Northwest, in 

 the opinion of the Editor have been effective in 

 reducing Bitter Pit or Core Rot to a minimum. 

 This article is of course a brief summary of 

 the principal features in the cause and control, 

 as worked out by Professor McAlpine and his 

 assistants, and as before stated is the most 

 thorough campaign ever put up for the solu- 

 tion of any pest and its control. Therefore the 

 Editor believes every fruit grower in the North- 

 west who is troubled with Bitter Pit or Core 

 Rot will find this article not only very instruc- 

 tive but very valuable.] 



WHEREVER apples are grown on 

 a commercial scale this disease 

 is more or less prevalent. In 

 Australia there are some valuable ex- 

 port varieties, such as Cleopatra, which 

 are so susceptible that they have been 

 cut down and replaced by other varie- 

 ties. In the United States of America 

 the Baldwin variety is so subject to 

 attack that the disease is actually 

 known as "Baldwin spot." In a recent 

 American publication it is stated that, 

 "Unless a remedy for this trouble is to 

 be found, the indications are that Bald- 

 wins will sooner or later need to be 

 replaced by some other variety of the 

 same season and quality which is not 

 affected by the spot." There is conse- 

 quently a keen desire on the part of 

 growers to know the cause of the dis- 

 ease, in order, if possible, to devise 

 measures for its prevention or mitiga- 

 tion. By this means alone may certain 

 valuable varieties be retained under 

 cultivation. 



In my previous report I have offered 

 alternative views as to the cause of 

 bitter pit, viz.: (a) Concentration of 

 cell sap in the tissues of the apple and 



consequent local death of the parts, 

 (b) Over-pressure of water in the tis- 

 sues, leading to local rupture and sub- 

 sequent death of the parts. 



The first explanation was indicated 

 by certain of my observations. The 

 brown flecks of the pit, when exam- 

 ined, always contained less water than 

 the surrounding healthy tissue, and it 

 appeared possible that the concentra- 

 tion of the cell sap involved in loss of 

 water might have reached a point 

 where the acids, tannins and other con- 

 stituents acted injuriously upon the 

 living protoplasm, causing its death. 

 The sap concentration theory of the 

 disease also received support from its 

 point of occurrence on the apple pit 

 generally appears in the first instance 

 on the upper half of the fruit and 

 toward the "eye" end. As the openings 

 in the skin of the fruit are much more 

 numerous toward the "eye" end than 

 on the basal portions, the larger num- 

 ber of openings at the "eye" end would 

 obviously allow more active transpira- 

 tion, and consequently might render 

 easier an undue concentration of the 

 cell sap, leading to development of 

 the pit. 



The further investigations which I 

 have subsequently been able to make 

 into the occurrence of pit lead me to 

 abandon an undue concentration of the 

 cell sap as the probable cause of the 

 disease. I am of opinion that over- 

 pressure of water in the tissues, leading 

 to local rupture and subsequent death 

 of the parts, furnishes the most prob- 

 able explanation of bitter pit. Histo- 

 logical examination of the tissues of the 

 apple, and the results of field experi- 

 ments, pruning tests and climatological 

 observations concur in supporting the 

 view that over-pressure of water is the 

 real cause. The diminished supply of 

 water in the flecks of bitter pit is the 

 result of cell rupture and death of the 

 parts — not its cause. 



The following observations support 

 this view: (1) When the apple fruit is 

 mostly confined to the main upright 

 branches and produced on fruit-spurs, 

 the bitter pit is usually increased. Un- 

 der these conditions the strong flow of 



sap might reasonably be supposed to 

 burst the thin walls of the pulp cells 

 and produce the effect. (2) In a young 

 and vigorous growing tree, bearing 

 only a few apples of rank growth, all 

 the fruit is often pitted. The rank 

 growth will cause rapid tension of the 

 cell wall, and this may reach the break- 

 ing point when the pressure is dis- 

 tributed only through a few apples. 

 (3) When a tree in full bearing, has 

 only a light crop, and the apples are 

 comparatively large, then the tendency 

 to bitter pit is greater. The fewer 

 apples in this instance would get a 

 larger proportion of sap, as evidenced 

 by their larger size. Instances have 

 already been given where Cleopatra 

 trees only showed bitter pit in the 

 clusters of fruit at the tips of the 

 branches, and the larger apple in the 

 center of the cluster was invariably the 

 worst. Superabundance of sap is asso- 

 ciated with the overgrown apple and 

 the development of pit. (4) When the 

 fruit of a susceptible variety is picked 

 and graded, it is found, as a rule, that 

 the larger the fruit the more liable it 

 is to pit. Thus, in the produce of 39 

 Cleopatra trees, while apples two 

 inches in diameter had only one per 

 cent of pit, those three and one-quarter 

 inches in diameter had 61 per cent of 

 pit. The greater growth in the larger 

 apple relatively to the smaller would 

 tend to distend the pulp cells and ulti- 

 mately burst them. (5) When the 

 strong flow of sap is checked by cinc- 

 turing it is found that the pit is re- 

 duced. This favors the view that the 

 over-pressure of the sap in a variety 

 unable to withstand the strain may be 

 exciting the cause. Root pruning is a 

 well-known means of checking the 

 growth and inducing fruitfulness, but 

 owing to the danger in our variable 

 climate of root-pruned trees suffering 

 from a diminished water supply at a 

 critical period of their growth, no satis- 

 factory experiments were carried out. 

 (6) Irrigation experiments bear out the 

 view that over-watering is a sure means 

 of producing pit. When apple trees are 

 heavily watered, and particularly late 

 in the season when the fruit is ap- 



