What Part do Flyspeck Ascospores 

 Play in Disease Deveiopment? 



S. Lemer, T. Kliorina, and D. R. Cooley 



Department of Microbiology, University of Massachusetts 



Flyspeck is one of the major summer- 

 disease concerns of apple growers in the 

 Northeast. Yet for most of the season, there is 

 little evidence of the fungus within the orchard. 

 In a dry year, signs of infection may not appear 

 until as late as August. 



For several years we have been conducting 

 investigations aimed at gaining a better 

 understanding of the natural biology of this 

 fungus. We know that it survives the winter on 

 a number of wild hosts that are common to most 

 orchard borders such as blackberry, maple, 

 grape, Virginia creeper, and red oak. We also 

 know that, like the apple scab fungus, it 

 produces two types of spores: ascospores in the 

 late spring and repeating cycles of conidia or 

 asexual spores later in the season. 



However, unlike apple scab, which pro- 

 duces its first cycle of spores within the orchard 

 where well-timed sprays can control the 

 disease, flyspeck ascospores are produced 

 primarily in the orchard borders on alternate 

 hosts. We wanted to know what part these 

 early spores play in disease development later 

 in the season. 



The flyspeck spots that form on apples, 

 blackberries, and other hosts in late summer 

 are pseudothecia, the overwintering structure 

 of the organism. By late winter these 

 structures have matured and are ready to 

 produce spores. In the laboratory, we have seen 

 that spore development is driven by both 

 temperature and humidity. Humidity must be 

 quite high - mature spores are produced at 99% 

 humidity but not at 96%. Average tempera- 

 tures above 50°F are also necessary for spores 

 to develop and mature. In New England, these 

 conditions can be met for significant portions of 

 the day in the field by late May. 



In the spring of 1997, blackberry canes with 

 pseudothecia were gathered weekly from three 

 sites in Western Massachusetts from late May 

 into July. Fifty pseudothecia from each cane 

 were examined microscopically and the 

 presence of mature spores was recorded. Table 

 1 shows the results of this study. 



The 1997 information conforms with data 

 gathered in Amherst during 1996 that showed 

 that there is a single period of ascospore release 

 that occurs in late spring to early summer. An 

 unusually warm, wet spring in 1996 com- 

 pressed the period of ascospore maturity to a 

 shorter period of time, earlier in the season. 

 Apple-tree phenology can be used as an aid to 

 predict when this period will occur in a given 

 year. 



The ascospores produced on the host plants 

 in the orchard borders are released into the air 

 but we do not know if they are transported as 

 far as the orchard block. 



Even if these initial spores are carried to 

 apple trees however, it is likely that the spray 

 program aimed at controlling apple scab 

 ascospores will also control early-season 

 infections of flyspeck. 



Information from Dr. David Rosenberger 

 indicates that the broad-spectrum protectant 

 fungicides commonly used for scab, Mancozeb 

 and Captan, will protect against flyspeck for a 

 significant period. Mancozeb used at 1 lb/100 

 gal. or Captan SOW at 2 lb/100 gal. will protect 

 fruit for at least 21 days or 2.5 inches of rain, 

 whichever comes first. Captan SOW at lb/100 

 gal. protects for 14 days or 2 inches of rain. If 

 the last scab spray of the season contains one of 

 these fungicides, and is made in early to mid- 

 June, fruit will be protected to late June or 

 early July. 



Fruit Notes, Volume 62 (Number .3), Summer, 1997 



