mines per 100 leaves in the second generation, 

 as we have no data to indicate the need to revise 

 these thresholds either upward or downward. 



In 1992, we hope to do more work on visual 

 trap captures as a predictor of leafminer prob- 

 lems. It should be possible again for second- level 



IPM growers who use Dimilin to withhold treat- 

 ment until flight of second-generation adults, 

 thus allowing first-generation mines to be ex- 

 pressed, so we can have another opportunity to 

 examine the trap-capture and mines per leaf 

 relationship. 



Predicting Infections of 

 Flyspeck on Apple 



Daniel R. Cooley and James W. Gamble 



Department of Plant Pathology, University of Massachusetts 



One of the problems with managing flyspeck 

 and sooty blotch on apple is that we understand 

 so little about the two diseases. The disease 

 cycles have been described, but they are based 

 on very little knowledge. For example, the 

 flyspeck disease cycle description indicates that 

 ascospores are released at pink (Figure 1). This 

 timing indicates that control measures should 

 begin at pink. Historically, most growers have 

 applied fungicide for scab at this time and know- 

 ingly or not may have controlled flyspeck. The 

 sterol-inhibiting fungicides, however, do not 

 control flyspeck or sooty blotch. A half rate of 

 captan at pink is probably effective for one to two 



Twig and fruit 



tissue infected 



Fruit Set to 



Mid- July 



Ascospores 

 are discharged 

 in rain 



late Pink 



Conidia produced in 

 lesions spread 

 during rain and 

 cause new infections 



Mid June to 

 Harvest 



Perithecia form 

 in orchard and 

 on wild hosts 



Dormant 

 to Pink 



Figure 1. The flyspeck life cycle. 



weeks, but the question is, how important is it to 

 put a fungicide on at pink to control flyspeck and 

 sooty blotch? It appears that the application of 

 fungicide through bloom, and perhaps until well 

 after petal fall, to control summer diseases is not 

 that important. 



In 1991, we studied flyspeck inoculum and 

 attempted to determine when it matured and 

 was able to infect apples. One major source of 

 inoculum is bramble canes, particularly black- 

 berry. We monitored the fungus on these canes 

 in the spring, in order to determine when sporu- 

 lation occurred. In 1991, ascospores were not 

 mature at pink. If fact, ascospores were not 

 mature until a week after petal- 

 fall. Unless there is another inocu- 

 lum source, no spores were avail- 

 able to cause flyspeck infections 

 before petal-fall. Rather than 

 spreading secondarily in min- 

 June, as indicated in Figure 1, 

 primary infections would have oc- 

 curred at this time. Therefore, 

 mid-June was the earliest time 

 that a fungicide should have been 

 directed at flyspeck. 



We also looked at the condi- 

 tions which drive flyspeck devel- 

 opment. Based on a model devel- 

 oped by Turner Sutton and Eliza- 



20 



Fruit Notes, Spring, 1992 



