Orchard Site Factors Related to 

 Incidence of Flyspeck on Apples 



Daniel R. Cooley, Jennifer Mason, Starker Wright, and Arthur Tuttle 

 Departments of Plant Pathology and Entomology, 

 University of Massachusetts 



As part of our efforts to examine the effects of 

 the ehmination of summer fungicide appUcations 

 on apple diseases and arthropod pests, we focused 

 on the key summer disease, flyspeck (caused by 

 Zygophiala jamaicensis). During the summer of 

 1995, six growers were asked to refrain from spray- 

 ing fungicides on prescribed sections of their or- 

 chards from the end of the primary apple scab sea- 

 son through harvest. These 51 blocks were selected 

 to represent varying distances from sources of in- 

 oculum. In addition, each block was assessed for 

 other characteristics, such as elevation, slope, and 

 canopy density. Inoculum density parameters, in- 

 cluding the density of a major reservoir host {Ru- 

 bus spp.) and the amount of flyspeck on the host, 

 were measured also. A comparable check block was 

 chosen for each test block. Flyspeck incidence was 

 recorded weekly in each block over an eight-week 

 period from 24 July to 15 September by sampling 



200 fruit per block. 



Several factors had a significant effect on fly- 

 speck incidence. Not surprisingly, date, grower, and 

 treatment with fungicides all had significant effects 

 on flyspeck incidence (Tables 1 and 2). 

 Fungicide-treated blocks had much less disease than 

 the test blocks, and disease incidence increased rap- 

 idly during early August (weeks 3 and 4). Obvi- 

 ously, different growers have different fungicide 

 programs, and this can explain the variation be- 

 tween fungicide-sprayed trees in orchards. But 

 there is also variation between orchards for trees 

 which were not sprayed. Other factors must ac- 

 count for these differences. We looked at a number 

 of these in the test blocks. 



As in other experiments, foliage density in the 

 canopy had a significant effect on flyspeck incidence, 

 with more dense foliage leading to higher flyspeck 

 incidence. Yet several other factors also contrib- 



■ fng., low 

 fng., mid. 

 fng., high 



■ no fng., low 

 no fng., mid. 



• no fng., high 



1 2 3 4 5 6 7 8 



Week 



Figure 1. Flyspeck incidence in all grower blocks at different relative altitudes within the 

 orchard, for fungicide-treated and non-fungicide trees. 



Fruit Notes, Spring, 1996 



