20 BULLETIN 712, U. S. DEPABTMENT OF AGRICULTURE. 



The iinsprayed trees were located adjacent to the sprayed trees 

 and all were of the same age and size, and except for the spraying 

 all were treated alike ; yet those in plat 9, where the mildew had been 

 most effectively controlled by spraying with lime-sulphur solution, 

 produced an average of 83 per cent more fruit than the checks, and 

 other sprayed trees also yielded greatly increased crops. 



INJURY TO FRUIT AND FOLIAGE. 



Only a small amount of foliage injury was usually found accom- 

 • panying the fruit sj^otting. The foliage injury generally developed 

 so soon after the application of the sprays as to indicate that it was 

 induced by the wet sprays. However, hot, burning sunlight undoubt- 

 edly increased foliage injury as well as fruit spotting. The addition 

 of lead arsenate to the sodium-sulphur sprays also resulted in in- 

 creased injury and demonstrated the incompatibility of these spray 

 materials. 



The general appearance of the fruit injury or sulphur sunburn 

 was the same in all plats. (PL II, fig. 7.) The injury was 

 confined to apples exposed to the direct rays of the hot midday or 

 early afternoon sun. The injured area was of a reddish brown color, 

 usually sharply marked but of irregular outline, and soon became 

 depressed. The affected skin became wrinkled, hard, and leathery, 

 often scurfing off' or becoming traversed by cracks which extended 

 deep into the flesh of the apple. The injury most often appeared in 

 the calyx region, probably due to the collection there of much of the 

 spray material. Deposits of spray material usually were clearly 

 discernible over the injured areas. 



The conditions under which this fruit injury occurred were identi- 

 cal in each of the three years of the experiment, i. e., it followed the 

 advent of hot, burning sunlight, and only those fruits which were ex- 

 posed to the direct rays of the sun at the hottest part of the day were 

 affected. The burning was generally more severe where the sulphur 

 was applied in its free state. This fact, together with the delay in the 

 appearance of the injury until after the occurrence of hot, burning 

 sunlight, indicates that the burning of the fruit is not the result of 

 any caustic action of the various sulphids at the time the fruit was 

 wetted. The exact manner in which sulphur sunburn takes place has 

 not been demonstrated. 



During the course of the spraying experiments several of the trees 

 developed the " collar-rot " disease, and others suffered severely from 

 drought at certain periods. In such cases, where the vitality of the 

 tree was reduced, the spray injury, especially the foliage injury, was 

 much increased. 



In view of the recent revival of dusting for fungous-disease control 

 in certain sections of the United States, the question arises as to what 



