April, 1910.] Bitter Pit of the Apple. 



BITTER PIT OF THE APPLE. 



D.. McAlpine, Vegetable Pathologist. 



This disease has hitherto baffled all our efforts to control it, chiefly be- 

 -cause its exact cause is not known. It is not, as has sometimes been errone- 

 ously stated, peculiar to Australia, for it is well-known in Europe, America, 

 and South Africa. There is neither insect nor fungus concerned in it, and 

 although bacteria have been suspected, careful in\estigation has failed to 

 prove any such connexion. It is found in quite a number of varieties of 

 apples, as well as pears and quinces, and occurs on low-lying as well as on 

 elevated ground. 



The spotting of the fruit results from the bursting and breaking down 

 ■of cells here and there, owing to too great pressure from wdthin. This 

 pressure is believed to be due to excesisive transpiration during the day, fol- 

 lowed bv its sudden cessation during the night, even although the root action 

 is still vigorous from the warmth retained in the soil. It is a disease, 

 therefore, which is due to phvsiological causes and the final result is 

 brought about by the abnormal flow and sudden checking of the sap, at the 

 time when the fruit is forming. How this is to be prevented or controlled 

 is the problem to be solved. It is highly probable that the method of 

 pruning, the mode of cultivation, the nature of the manuring, as well as 

 the stocks used mav all help to contribute to the result. The latest pro- 

 nouncement on this disease has been made to me in a letter dated i6th 

 September, 1909, from Professor Farmer, M.A., D.Sc, F.R.S., of the 

 Imperial College of Science and Technology, London, in which he remarks, 

 " I had some apples sent me to ascertain whether the disea^ was due to 

 fungal or bacterial action. I came to the conclusion that there was no 

 such infection, but that the disease is physiological, i.e.. intrin.sically due 

 to pathological death of tissues. But it seemed to me to be useless to con- 

 tinue the inquirv when we could not try experiments, which in m\ view, 

 alone were likelv to lead to the full elucidation of the trouble." 



As regards manuring, I have tried the effect of various manures for a 

 number of vears and while hone ha\^ proved perfectly satisfactory, it has 

 generally been found that a complete manure aggravates the disease. Ex- 

 periments were conducted at Killara during 1906-7, with the Bismarck 

 variety which is very liable. Each dressing was applied in August, 1906, 

 two trees being used in each case, and the fruit was picked from the trees 

 in March, 1907, with the results shown in the following table: — 



^, , ,. rr. Per cent. 



Plot. Manure per Tree. Sound. 



; lbs. Concentrated Superphosphate ... ... \ 



; lbs. Sulphate of Ammonia ... ... ... - 13 



lb. Potash Chloride ... ... ... ... j 



lbs. Potash Chloride ... ... ... ... ••• 13 



3. 10 lbs. Gypsum ... ... ... ... ... ... 23 



4. Check ' ... ... ... ... ... ... ..- 32 



/ li lbs. Potash Chloride ... ... ... ... \ 



•''• \ 10 lbs. Gypsum ... ... ... ... ... ( 



6. 4 lbs. Kainit ... ... ... ... ... •■■ 39 



7. 4 lbs. Dissolved Bones ... ... ... ... .•■ 45 



8. 20 lbs. Lime ... •■■ •■• ••■ ■•• ••• 36 



The manure containing nitrogen, phosphoric acid and potash, as well as 

 that consisting of potash only, yielded the highest percentage of "pit," 

 while dissolved bones applied at the rate of 4 lbs. per tree produced the 

 lowest. It gave 45 per cent, clean as compared with only 32 per cent, on 

 the unmanured trees, but such a small improvement shows that further 



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