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ACCOUNTiriG FC'R THE APPLE SCAB SITUATION 



Apple Scab has caused a great deal more trouble than most growers expected 

 considering the relatively light carryover of the Scab fungus and the character 

 of the weather. By studying the rain dates (with temperature and duration of wet 

 periods) and the dust and spray dates during the growth period from delayed dormant 

 unx.il one to two weeks after petalfall, it is not difficult to account for primary 

 and secondary'- infections that occurred in certain orchards. 



Below is a list of Scab infection periods for Amherst, rath the tree develop- 

 ment stages and the dates when the infections showed up as Scab spots. 



No. 

 1 

 2 

 3 

 h 

 5 

 6 

 7 

 8 



9 

 10 



Rain Date 

 Apr. 20 

 V30-5;/l 

 May 9-10 

 May 17-18 

 May 19-20 

 May 2ii-26 

 Hay 29-30 

 June 1-2 

 June 3 

 June 10-11 



Fruit Bud Stage 



Del. Dorm, 



Pre-pre-pink 



Pink 



Mid-bloom 



Full bloom 



Calyx 



Before 1st Cover 



First Cover 



First Cover 



Second Cover 



Scab Spots Appeared 

 May 11-13 (Late pink) 

 May 16-17 (Early bloom) 

 May 2ii-26 (Calyx) 

 l'.a.y 31- June 2 

 June 3 (First Cover) 

 June 7-8 

 June 10-11 

 June 12-13 

 June Ii4-l5 

 June 20-21 



Most other sections in the vrestern half of the state, including the southern 

 half of V.'orcester County received the same infection periods. Upper ".Worcester 

 County and all the remaining eastern areas had fewer and shorter rainy periods and 

 consequently are experiencing less trouble vrLth Scab. 



Much of the difficulty vri.th Scab goes back to fruit spur leaf spots that 

 originated on April 20 and ii./30-5/l in the low elevation orchards, and on [i./30-^/l 

 and Hay 9-10 in the later or high elevation orchards. These spots were plentiful 

 in orchards that received no or inadequate fungicidal protection ahead of pre-pink 

 bud stage, and they were present and furnishing an abundance of summer spores for 

 secondary infections throughout the blossom period. Primary inoculum, as ascospores, 

 vras also available during bloom, although the supply diminished rapidly with each 

 wet period from pink bud onward. 



This was a season when at least two protective applications were needed during 

 bloom: ahead of the Vl7-l8 rain or the S/19-20 rain, depending vfhen the pink spray 

 was applied, and again ahead of or during the extended rain of IJay 2U-26. This 

 applies to loT/ elevation orchards. In fact, one dusting in some instances was not 

 sufficient for the Hay 2i;-26 rain, particularly when applied from one side only. 

 It seems, also, that very few groviers applied an eradicant fungicide follovdng that 

 protracted wet period even though it v;as tine for the regular petalfall spray. 



Infections that shovred up between June 1 and 10 originated during bloom in the 

 earlier sections, and they were definitely more pronounced vi-here early season 

 spur-leaf spots were present in the trees. In a few orchards observed, a moderately 

 heavy crop of Scab spots shoTred up on leaves around June 1^>, originating no doubt 

 in the rain of June 3j even though the calyx spray was applied about May 29. 

 Hovifever, the June 1-2 rain brought one inch of precipitation ahead of the infection 



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