blotch symptoms occurred after an average of 

 270 hours of accumulated leaf wetting. They 

 believe this that information is useful for 

 timing eradicant (benzimidazole) fungicide 

 spraying. An admitted limitation of this model 

 is the questionable relevance it has for regions 

 outside the southeastern United States. Sooty 

 blotch and flyspeck disease pressure are 

 extremely high in the Southeast. Weather 

 there is particularly favorable for these 

 diseases. Therefore, the model might fail to 

 predict accurately the onset of sooty blotch and 

 flyspeck symptoms for several reasons: 1) 

 summer temperatures and relative humidities 

 in New England are usually lower than in 

 North Carolina; 2) the precision and accuracy 

 of different leaf wetness sensors can vary 

 considerably; and 3) infection of apple trees 

 with the fungi causing flyspeck occurs about 

 one month later in New England than in North 

 Carolina. However, the existance of an 

 empirical model predicting flyspeck and sooty 

 blotch diseases anywhere raises the possibility 

 of constructing such a model in New England. 

 While noting the limitations and possible 

 sources of error, Brown and Sutton's model is 

 still a good starting place. Additionally, one 

 only needs hourly leaf wetness data available 



over the course of at least one year in order to 

 use their model. These leaf wetness data are 

 readily available from records taken from 

 hygrothermographs or Campbell computerized 

 weather stations located in several Massachu- 

 setts orchards. Thus, beginning with leaf 

 wetness data collected from nine different 

 orchards in 1995 and 1996, we tested Brown 

 and Sutton's model for the prediction of 

 flyspeck and sooty blotch. 



Table 1 from Brown and Sutton's article 

 shows wetness data collected from 1987 

 through 1994. Symptom occurrence ranged 

 from late June through early July, with a mean 

 wetness duration of 270 hours between the 

 beginning date and symptom occurrence. Note 

 that Brown and Sutton began counting wetness 

 hours starting from the first significant 

 wetness period at least 10 days after petal fall. 

 Thus, their starting date ranged from early to 

 mid May. 



In contrast, Table 2 shows data collected 

 from Massachusetts orchards during 1995 and 

 1996. Using Brown and Sutton's criteria, the 

 mean leaf wetness accumulation of four hours 

 or greater from 10 days after petal fall to 

 symptom occurrence was 366 hours (standard 

 deviation = 120 hours; the larger the standard 



22 



Fruit Notes, Volume 62 (Number 4). Fall, 1997 



