largely driven by 

 temperature. To evaluate 

 this possibility, we 

 calculated degree-days 

 from green tip using 

 various base temperatures 

 from 32° to 60°. We found 

 that 90% of the maturation 

 could be explained by 

 degree-days calculated 

 from a 32° base (Figure 2). 

 We developed a model that 

 predicts that 5% of the 

 thyriothecia will mature at 

 540 degree days, and 95% 

 will mature by 1630 degree 

 days. The first mature 

 spores were actually 

 observed at 550 degree 

 days, and no spores were 

 observed beyond 2100 

 degree days. 



We needed to compare 

 this to the degree days in 

 the laboratory experiments. 

 Obviously, it was taking 

 only 2 to 9 days to go from 

 no spores to mature spores 

 in the lab, while it was 

 taking weeks to see similar 

 development in natural 

 setting. In terms of degree 

 days, the laboratory 

 thyriothecia matured after 

 a mean of 125 degree days 

 (Table 1). The average 

 degree days from green tip 

 to the first mature 

 thyriothecia in the field was 

 763, over six times greater 

 than m the laboratory 

 experiments (Table 2). 



It is possible that the 

 results differed because the 

 thyriothecia in the 

 laboratory were always 



exposed to high relative humidity, while those in nature 

 have only short periods where relative humidity meets 

 or exceeds 95%). We calculated degree-day values at 



o 



o 

 >^ 



t- 

 



TO 

 O 



o 



c 

 o 



00 

 CD 

 O) 

 CO 



0) 



o 



Q) 

 Q. 



26-Apr 



10-May 



24-May 

 Date 



7-Jun 



21-Jun 



Figure 1 . Percent thyriothecia on blackberry canes that matured during each year, 

 1997, 1998, and 1999, in five Massachusetts orchards: Aslifield (B), Belchertowii 

 (J), Briinfield (H), Shelbume (F), and Sterling (E). Times of bloom (B) and petal 

 fall (PF) of Mcintosh m 1998 and 1999 are shown, ±3 days depending on the 

 orchard, while in 1997 the phenological stages are indicated for each site. 



the orchard sites for those periods when relative 

 humidity was 95% or greater. Five of the nine data 

 sets had hourly humidity data sufficient to calculate 



Fruit Notes, Volume 69, Summer, 2004 



