with at least two light infections occurring every 

 week. 



Foliar apple scab infections were evaluated on 

 the basis of all leaves on 40 terminals per tree, 40 

 clusters per tree, 10 terminals per each row-border- 

 ing tree, and 10 clusters per each row-bordering 

 tree. Fruit apple scab infections were evaluated on 

 the basis 40 fruit per tree, and 10 fruit per each row- 

 bordering tree. Evaluations for fruit and foliar scab 

 were collected June 11 and September 18. Russet- 

 ting was evaluated September 13 on a 1 to 5 scale 

 related to coverage: l=no russetting, 2=1 to 25%, 3= 

 26 to 50%, 4= 51 to 75%, 5= 76 to 100%. In addition, 

 since one of the criticisms of heavy sulfur use has 

 been that it can acidify soil, we took soil samples in 

 each treatment. Four samples, 1 per quadrant, were 

 taken under the center tree in each replication and 

 pooled. Samples were also taken in the middle of the 

 drive alley adjacent to each sample tree. Acidity was 

 evaluated using a standard technique, i. e. measur- 

 ing soil/water solution with a pH meter. 



Lime sulfur and captan treatments showed simi- 

 lar scab control. However, significant damage was 

 associated with lime sulfur. This was apparent from 

 the third application. Leaves were visibly stunted 

 and had heavy residue deposits. In part, damage 

 and residues may be attributed to the relatively high 

 rates and frequent applications. Fruit damage due 

 to russeting was the most serious short-term prob- 

 lem caused by sulfur and copper. Our hypothesis is 



that the interactions of dormant oil applications and 

 lime sulfur, captan, and perhaps copper, contributed 

 to russeting damage. The lime sulfur plus copper 

 treatment and the captan treatment caused the most 

 russeting. The heavy russeting in the captan treat- 

 ment can be explained by the close application of 

 captan and oil on April 26 and 27, respectively. Lime 

 sulfur alone or sulfur plus copper resulted in signifi- 

 cantly less russeting than captan or lime sulfur plus 

 copper. These results suggest that the lime sulfur 

 plus copper, either alone or interacting with oil, can 

 cause more russeting than either material alone. We 

 cannot be sure how much oil contributed to the 

 russeting, since oil was applied to all treatments. 



Lime sulfur alone offers the most promise for 

 adequate scab control with the least russeting in a 

 low-input or 'organic' situation. However, the leaf 

 damage caused by lime sulfur may be significant. It 

 also is important to remember that the inoculum 

 levels in this test block were high, and that in a 

 commercial block, lower inoculum would allow for 

 less frequent applications of any fungicide. 



There has been some thought that the heavy use 

 of sulfur on apples could have an adverse effect on 

 soil. While soil acidity is not the only thing that 

 needs to be considered, it was interesting that there 

 were no significant differences in soil acidity among 

 treatements, or between soil under trees versus soil 

 in the drive alleys. 



Prom: Thotnai, J.J. 1906. The American Fruit 

 Cultural. Orange Judd Company, New York. 



Fruit Notes, Winter, 1991 



23 



