COMBATING APPLE SCAB. 



SPRAYINd AND DUSTJN(^ EXPERIMENTS IN 11)2:'. ^ WITH 

 SI MiAIARY OF THREE YEARS' RESULTS. 



Ry William L. Doran and A. Vincent Osmun. 

 IXTRODUCTION. 



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 

 particularly 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 expei'ienced 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 with the Nashoba Fruit Pro- 

 ducers' Association under which 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 with 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 this report 

 are for the most part to si)raying and dusting experiments conducted within the 

 last two years, especially in the northeastern states. 



The general objectives of the investigations in 1923 were to secure more light 

 on the follo^^^ng 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 liquid lime-sulfur in fungicidal effi- 

 ciency? 



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

 pendable? 



4. What is the effect of the addition of calcium caseinate si)reader 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 apphcations before flowering? 



6. How does Atomic Sulphur compare with 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? 



8. 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 

 pink applications? 



The rainy summer of 1922 was especiallj^ suital^le 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 May, 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 justif.y the drawing of conclusions as to the relative values of the several 

 treatments applied. 



' The experiments here described were conducted in the orchards of Harry L. Knights of Littleton, H. L. 

 Frost of Littleton, 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 Stowe Farm, and J. W. Ames of the 

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

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

 Producers' Association for their cooperation. 



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



I 



