COMBATING APPLE SCAB. 37 



It is quite evident that copper-lime-arsenate dust controlled scab 

 TOore effectively than the sulfur dusts, as in three of four orchards 

 it gave a higher percentage of clean and marketable fruit. However, it 

 cannot he recommended for apples on account of the russeting of the fruit 

 and the hurning of the foliage. On the other hand, sulfur dusts neither 

 injured the foliage nor russeted the fruit. If kept covered with the sulfur 

 dust, the leaves grow normally and develop a dark green color. Sulfur 

 dust is cheap and is the 07ihj dust that has shown itself worthy of further 

 trial. It is possible that the copper-lime-arsenate dust may prove useful 

 for the pre-pink and pink applications, to be followed with sulfur dust 

 for the later applications. This combination will be tested another year. 



In the Stow^e and Marshall orchards there were no experimentally 

 sprayed plots to compare with the dusted plots, but if we may judge 

 from the results wliich these orchardists obtained on sprayed trees ad- 

 jacent to the dusted plots, the sulfur dust was equal to the sprays. 



The Effect of Apple Scab on the Vitality of the Tree. 



The most striking example of what may be expected of an unsprayed 

 Mcintosh orchard may be seen on the check plot in Knights orchard 

 (Table V, plot 1). The trees of this plot have not been sprayed with a 

 fungicide since 1920, and in 1921 and 1922 they showed approximately 

 100 per cent infection of fruit and foliage. The heavy loss of foliage in 

 1921, in spite of the fact that the trees were fed heavily, caused a very 

 light set of leaves and blossoms in the spring of 1922, and consequently 

 a greatly reduced yield of fruit. Plots 1 and 2, Table V, are located side 

 by side in the orchard. It is planned to shift the check plot in this orchard 

 from its present location to some other part of the orchard in 1923, as 

 permanent injury to the trees is feared. 



The Relation of Weather to Spraying. 



Spraying should always be done in advance of rain periods, since the 

 fungicide must be on the leaves in advance of the germination of the 

 spores. If allowed to dry thoroughly, efficient sprays do not wash off 

 sufficiently to destroy their fungicidal value. By studying the low bar- 

 ometric areas of the daily weather reports, the grower should be able to 

 predict, with some degree of accuracy, weather conditions two to three 

 •days in advance. ^ 



Burning of Apple Foliage by Sprays and Dusts. 



The foUage of some of the apple trees in the plots was badly burned 

 with lime-sulfur during 1921, while in 1922 very little injury from this 

 material was noticed. The writer believes that weather conditions were 



^ These daily reports may be obtained by addressing the United States Weather Bureau. 

 Boston, Mass. 



