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APPLE SCAB SITUATION 



Vfhatever we may say about the present season, this much at least is 

 true* It's different. From the apple grower's standpoint, the season is 

 characterized by late bud developipent, early scab development, and day after 

 day of wrong kind of weather for spraying. Below normal temperatures in April 

 delayed fruit buds to an almost unprecedented degree. Bud development has 

 been lagging approximately two weeks behind 194E, This spring vihen Mcintosh 

 buds had reached the Delayed Dormant stage we were reminded that on the same 

 date in 1942 the buds were in the Pink stage. Fruit buds, being very sensi- 

 tive to temperature, refuse to open up until the weather is reasonably warm, 



V/hile the apple buds were biding their time, the apple scab in the 

 old leaves on the ground was steadily developing. At the Pre-Pink stage of 

 bud development there were about as many mature spores in the old leaves as 

 we normally find at blossoming time, Vfe may safely say that a larger per- 

 centage of scab spores were either mature or already released by the time 

 the blossoms were ready to open than has been the case in all the years 

 we've been fighting scab in Massachusetts, Careful studies of old leaves 

 from various sections of the state, made by 0, C. Boyd on May 19, revealed 

 the interesting fact that a mere 10 to 20^o of the scab spores still remained 

 in the old leaves. This represents an unusual spore discharge - not from 

 the standpoint of the calendar, but of bud development. 



Spray Message for Massachusetts Fpuit Growers (No. 8), issued May 19, 

 carried this timely suggestion: "If apple trees came into bloom before the 

 Pink spray could be completed, it is advisable to finish that spray with sul- 

 fur alone, Apple varieties subject to scab and cedar rust need protection 

 throughout the blossom period, particularly if v/et v;eather threatens. Either 

 a sulfur dust or a wettable sulfur spray may be used, but lead arsenate should 

 be omitted. The protection from the Pink spray can be expected to last only 

 five or six days at most, Vifhere apple scab infection occurred on May 10 to 

 12, the new scab spots should begin to show up around May 24," 



Apple leaves were hot held back by cool weather to the same extent 

 as apple buds. As a result, there is more leaf area in evidence on Mcintosh 

 spurs at blossoming time than in a normal season, Baldwin trees, on the other 

 hand, always show a considerable leaf area at blossoming time. This year there 

 is much less difference in the leaf area on Mcintosh and Baldwin spurs. 

 Following is a siommRry of the scab situation in Amherst, prepared by 0. Ct Boyd* 



Date when scab opots 

 may be expected to 

 appear on leaves 



? (May 21.22) 



May 24-26 



May 31- June 2 

 ? " (June l-3j 

 ? (June 3-4) 



