13- 



periods. Another severe infection period was recorded at petal 

 fall, when 38°6 of all potential scab spores were discharged dur- 

 ing a 34 hour wetting period, A moderate infection period on 

 June 20 and 21 ended the primary scab season. 



Table 1. Apple scab season at the Horticultural Research Center, 

 Belchertown, Massachusetts, 1981. 



Apple 



growth 



stage 



Date 



Wetting Mean Cumulative % potential 



period temp Rainfall scab spores scab infection 



(hrs) 



op 



(mm) 



discharged -*- severity^ 



Green 

 tip 



1/2" 

 green 



Tight 

 cluster 



Pink 



Bloom 



Petal 

 fall 



1/2" 

 fruit 



4/14 



4/17 



4/23-25 

 4/29-30 

 5/11-12 

 5/12-13 



11 



12 



50 

 27 

 16 



5/15-16 34 



5/29 9 



6/6 7 



1" fruit 6/9 11 



6/10-11 12 



6/12-13 12 



6/20-21 13 



45 



56 



50 

 59 

 62 

 55 



61 



70 

 66 

 69 

 57 

 59 

 67 



Trace 



0.3 



0.6 

 1.0 

 0.5 

 0.4 



36.8 



29.5 



8.9 

 20.3 



Trace 



Trace 



12 



END OF PRIMARY SEASON 



1 







60 



68 

 72 

 86 

 90 

 94 

 99 



No infection 



Light 



2 Severe 



8 Severe 



20 Moderate 



22 No infection 



Severe 



Light 



No infection 



Light 



Light 



Light 



Moderate 



Collected weekly. 



Infection severity was determined by the Mill's Table for primary 

 scab infection. 



