April, '21] DUSTING DISCUSSION 235 



the different aphids, red bugs and similar insects. When used against 

 fungous diseases the results have been less satisfactory, and regarding 

 the use of dust for apple scab and similar fungi, I agree perfectly with Dr. 

 Headlee in his conclusions, and have advised Michigan fruit growers to 

 "spray when you can for the apple scab, and when you cannot spray, 

 dust." 



In Michigan, many of our best fruit growers are becoming very 

 enthusiastic over dusting for apple scab. They had sprayed for years 

 with Bordeaux or lime-sulphur solution but in some seasons had russeted 

 the fruit badly with Bordeaux mixture, and had burned the leaves, 

 especial!}' in hot weather, when they had used lime-sulphur sprays. 

 For the last four years, the weather in the southern part of the State 

 has been comparatively dry during the spring and early summer and 

 they have been able to control apple scab practically as well with the 

 ordinan,^ sulphur dust as with lime-sulphur sprays. In the northern 

 part of the State, where the weather has not been as warm, and where 

 rains have been more frequent, the results have been less satisfactory. 

 We visited one forty acre orchard containing mostly Baldwin and 

 Northern Spy trees in July and again in August, 1920, which had re- 

 ceived three applications of dust. One was given when the trees were 

 in the pink; the second immediately after the fruit had set; and a 

 third two weeks later. The fruit was so badly infested with apple- 

 scab that the owner considered the crop worthless for packing and sold 

 the entire 20,000 bushels for cider. The results were not unlike those 

 secured in Michigan by Dr. Quaintance in 1916 in an experiment carried 

 on at Benton Harbor under the direction of Professor Simanton. The 

 Ben Davis and Northern Spy apples upon which dusts were used were 

 quite badly infected with scab, while the sprayed trees were practically 

 free from that disease. They also agreed with those secured by Mr. 

 Dutton of the Michigan Experiment Station in 1915. Although the 

 trees were very carefulty dusted, when the crop was harvested, it was 

 difficult to note any difference between the dusted and the check trees. 

 In 1915, the season in Michigan was very wet, there being some twenty- 

 six rainy days during t]ie month of July. Frequent rains in 1916 also 

 had much to do with the development- of apple scab upon the Benton 

 Harbor orchard reported by Dr. Quaintance. 



From the fact that dusting is a rapid method of treating the trees, a 

 large number of Michigan fruit growers with orchards of from 20 to 100 

 acres are now relying almost entirely upon their dusting machines 

 except for their dormant sprays. They have been well satisfied with the 

 results secured in dry seasons but we fear that they will not be so success- 

 ful in controlling the apple scab and other fungous diseases in wet seasons 



