66 BITTER PIT INVESTIGATION. 



lightest yield, in which sulphate of potash and .sulphate of ammonia had been used ; and in Western 

 Australia the lowest percentage occurred with sulphate of iron applied at the rate of one Ib. per tree. 



In Western Australia the use of fertilizers had a tendency to increase the amount of Pit rather 

 than to reduce it, but in New South Wales, South Australia.'and Victoria, where the fertilizers used 

 increased the yield, the tendency was to reduce the amount of Pit below that of the unmanured plots. 



The presence of nitrogenous manure in excessive quantities in proportion, that is, to the other 

 nutritive constituents of the soil, would tend to produce Pit. The rapid growth induced by the undue 

 accumulation of soluble nutritive substances in the pulp-cells, the walls of which are imperfectly 

 thickened and exceedingly stretched, would render them liable to rupture. 



PRUNING EXPERIMENTS. 



Since pruning is one of the most important means of controlling this disease, it has received special 

 attention. 



In conducting pruning experiments extending over a series of years it is necessary to adopt some 

 definite method whereby the varying results obtained may be compared and contrasted according to 

 the respective systems followed. These methods have already been clearly explained, and illustrations 

 have been given of spur-pruned and lateral-pruned trees. 



The best results in checking the disease have followed up leader or light pruning, and these are 

 the methods recommended for practice. 



CAUSE AND CONTROL OF BITTER PIT. 



In seeking for the cause of this disease, we are at the same time endeavouring to discover how to 

 prevent it, for by removing or counteracting the cause the effect will not be produced. Even although 

 the cause is discovered, it is not always possible to get rid of it, and then we seek to minimize its effects. 

 According to the nature of the cause or the supposed cause, so will be the nature of the remedial 

 measures. 



In France the insect origin of this disease is generally accepted, and accordingly the measures 

 recommended are those calculated to destroy injurious insects. But we have found that the disease is 

 produced even when insects are excluded, as in the case of apples grown inside calico bags, so that 

 the special disease of Bitter Pit does not originate in this way. 



In America it is sometimes mistaken for a disease caused by a fungus, and spraying with fungicides 

 is resorted to, but the "Bitter Rot" for which it is mistaken is quite a different disease, and all attempts 

 to associate a fungus with Bitter Pit have failed. If we cannot always decide definitely what the cause 

 of a disease is, it is important to know what it is not, in order to avoid the application of useless remedies. 

 Bitter Pit is due neither to insects nor fungi, nor even to bacteria, and therefore it is not parasitic in its 

 origin. 



In Australia it has been frankly confessed that the cause was unknown and that it required 

 investigation. 



The result of this investigation goes to show that the primary cause of the trouble is the extra 

 pressure of the sap in the outermost layer of pulp-cells to begin with, causing them to burst and collapse, 

 together with the rupture of the vascular network associated with them. A large number of well- 

 established facts have been brought forward to support this view, which has suggested the best known 

 means of reducing the amount of Pit in the orchard, and these remedies are supported by experimental 

 evidence. 



The cause having been considered, the control of the disease may now be attempted from a rational 

 standpoint. 





