APPLE POWDERY MILDEW AND ITS CONTROL. 13 



proportional to the sulphur content of the spray mixture employed. 

 If the first spraying is delayed until the apples are an inch or more 

 in diameter and a spray mixture containing a relatively large amount 

 of sulphur is used, a heavy shedding of fruit and foliage may be 

 expected to follow. The leaves that fall are turgid and green and 

 look in all respects fresh and normal. In bad cases the foliage 

 shedding may be so severe as to leave the trees bare. The fruit that 

 drops is also normal in appearance and may amount to 50 per cent 

 of the crop. The loss of foliage is usually more than replaced by 

 the vigorous production of new, extra-large leaves. Spraying with 

 very weak mixtures brings about an increased foliage growth with- 

 out causing leaf dropping. It is therefore evident that this unusual 

 foliage production is not a reaction to any leaf pruning caused by 

 spraying. 



It might seem that the increased foliage growth is only the normal 

 production of new growth to be expected as a result of the mildew 

 control. That this, however, is not the case and that sulphur spray- 

 ing has an actual stimulating effect seems to be a clearly established 

 fact. Plate V, figure 1, shows two twigs from a tree that was not 

 sprayed until considerable growth had been made. The first leaves 

 that came out in the spring, those at the bases of the twigs, were of 

 fair size. Gradually, as the new leaves appeared, they became more 

 and more infected with mildew, and when the twigs had grown to 

 the length indicated by the letter T in the figures, the leaves were 

 small, distorted, and badly diseased. Very little more growth could 

 have been expected. At that time the tree was sprayed with a mix- 

 ture made by dissolving sulphur in carbon disulphid and emulsify- 

 ing this solution with ammonia soap. Such a spray leaves a very 

 fine coating of sulphur all over the foliage. Almost immediately 

 growth was resumed and conspicuously large leaves were sent out. 

 The photograph reproduced as Plate V, figure 1, was taken some 

 time after the spraying was done, and no spray had been applied 

 meantime. In other words, the extra growth of leaves took place 

 after the spray was applied and their large size was not due to 

 killing any mildew that was on them or to preventing infection, 

 because they were not out at the time the spraying was done, and 

 therefore they received none of the application. Thus, it seems 

 evident that the spraying itself stimulated a new growth of foliage. 



One type of fruit injury that may result from sulphur spraying is 

 shown in Plate VI, figure 1. A strong dosage of iron-sulphid mix- 

 ture was applied after the fruit had become partly grown. Shortly 

 after the application was made there were several days of very hot 

 weather, and on the exposed sides of the fruit, where the hot sun had 



