beth Brown in North Carolina, we used wetness 

 and temperature to determine when the first 

 flyspeck symptoms would be visible. Beginning 

 ten days after petal fall, wetting periods and 

 heavy dews which exceeded three hours were 

 recorded. When the accumulated number of 

 hours of wetting reaches between 250 and 290, 

 the first symptoms should appear. Over four 

 years in North Carolina, this relationship 

 worked well (Table 1). It is hoped that this model 

 will have practical value in that an application 

 of Benlate™ or Topsin M™ just prior to symptom 

 expression should eradicate the symptoms. To 

 be conservative, such an application should be 

 made after about 230 hours of wetting. 



Massachusetts and North Carolina are very 

 different in terms of flyspeck and sooty blotch 



pressure. In general, the 

 season is two to four 

 weeks earlier in North 

 Carolina than in Massa- 

 chusetts, and pressure 

 from flyspeck and sooty 

 blotch is much greater. 

 It was not clear how well 

 the model would func- 

 tion in our climate. In 

 the Hudson Valley, in 

 the first year of running 

 the model, symptoms did 

 not appear until 370 hours of wetting. We were 

 pleasantly surprised in 1991. In our own obser- 

 vations at the University of Massachusetts Hor- 

 ticultural Research Center, we found symptoms 

 after 232 wetting hours, and within one day of 

 the predicted 250 hours (Figure 2 ). It is not clear 

 why there were major differences in the Hudson 

 Valley, or why we were slightly earlier than the 

 North Carolina observations. Possibilities in- 

 clude different criteria for deciding whether or 

 not a dew was a "heavy dew," placement of the 

 weather monitor relative to trees, and differ- 

 ences in the fungus. Weather monitor place- 

 ment could be critical to measuring wetness on 

 the fruit surface. 



In 1992, we will continue this study and will 

 expand the monitoring and model work. 



300 x 



to 



3 

 O 



0> 



250 



.C 200 -■ 

 CO 



~ 150 H 

 to 



100 -■ 

 50 -■ 



o c 



Predicted 1" flyspeck, July 13, 250 hrs. 



■ Accumulated Wetting 

 □ Daily Wetting 



First flyspeck observed 

 July 12, 232 hrs. 



J.l.l.1 .l.i.i.i.i,t. 



6 12 18 24 30 5 11 17 23 29 5 11 



May May May May May June June June June June July July 



Figure 2. Accumulated hours of wetting and the timing of the first 

 observations of flyspeck symptoms in Massachusetts in 1991. 



Fruit Notes, Spring, 1992 



21 



