COMBATING APPLE SCAB. 



SPRAYIN(i AND DUSTING EXPERIMENTS IN WVl?^' WITH 

 SUMMARY OF THREE YP]ARS' RESULTS. 



By William L. Doran and A. Vixcext Osmux. 

 IXTKODUCTION. 



Scab has long been a disease to reckon with in the apple orchards of Massachu- 

 setts, but not until the advent and extensive planting of the Mcintosh, a variety 

 particularh^ susceptible to attack by the scab fungus, did it become a menace of 

 large proportions. As more and more of the Mcintosh orchards came into bearing, 

 an increasing number of growers experienced difficulty in controlling the disease 

 and losses became so large as to seriously threaten the orchard industry. Finally, 

 in 1920, appeal was made to the Station by the growers, and in the fall of that year 

 the Station entered into a cooperative agreement vnih the Nashoba Fruit Pro- 

 ducers' Association vmder wliich experiments on the control of scab were planned 

 and undertaken by the Department of Botany. 



The results of the spraying and dusting experiments of the first two seasons 

 already have been reported by Krout (1) (2).- The present report is on the work 

 of 1923, together ^vith such references to the work in ^Massachusetts in 1922 and 

 1921 as will assist in making points clear. The results of the three years' experi- 

 ments are summarized in Table III (page 17). Other references in tliis report 

 are for the most part to spraying and dusting experiments conducted within the 

 last two years, especially in the northeastern states. 



The general objectives of the investigations in 1923 were to secvu'e more light 

 on the follo\\ing questions in regard to the control of apple scab: 



1. What is the effect of the addition to the spray schedule of a prepink apph- 

 cation? 



2. How does dry lime-sulfur compare with licjuid hme-sulfur in fungicidal effi- 

 ciency? 



3. What is the ratio of dry lime-sulfur to water, at which this fungicide is de- 

 pendable? 



4. What is the effect of the addition of calcium caseinate spreader to the fungicide 

 when applied as a dust and as a spray? 



5. How does a spray schedule consisting of lime-sulfur throughout the season 

 compare with a schedule in which Bordeaux mixture is substituted for the applica- 

 tion or applications before flowering? 



6. How does Atomic Sulphur compare \Nith dry and liquid lime-sulfur for the 

 control of scab? 



7. Does the addition of lime or of calcium caseinate to the combination lime- 

 sulfur-lead arsenate spray improve the mixture? 



S. For the control of apple scab, what is the fungicidal efficiency of sulfur dust? 

 What is the effect of substituting a copper-lime-arsenic dust for "the prepink and 

 l)ink apfjlications? 



The rainy summer of 1922 was especially suitable for the experimental work, 

 because of the abundant infection on unsprayed trees. The summer of 1923 was 

 much drier; there was a rainfall of only 7.29 inches in Msiy, June and July, as 

 compared with 20.14 inches in the same period in 1922. This naturally resulted in 

 less infection, but there was sufficient infection on unsprayed trees in every case 

 but one to justify the drawing of conclusions as to the relative values of the several 

 treatments applied. 



1 The experiiiients here descriVjed were conducted in the orchards of Harry L. Knights of Littleton, H. L. 

 Frost of J-ittlcton, Stephen W .Sabine of Groton, and A. N. Stowe of Hudson. The superintendents of these 

 orchards are Roy C. Wilbur of the Frost Farm, John J. Collins of the Stowp Farm, and J. W. Ames of the 

 Knights Farm. Acknowledgment is due these men for placing their orchards at the disposal of the Experi- 

 ment Station, and for cooperating in the investigations. Acknowledgment is also due to the Nashoba P'ruit 

 Producers' Association for tlieir cooperation. 



- Numbers in parentnesis refer to literature cited, see page 13. 



