Effects of Sulfur and Copper Fungicid 

 on Fruit Finish, Scab, and Soil Acidity 



Daniel R. Cooley, James W. Gamble, and Mark Mazzola 

 Department of Plant Pathology, University of Massachusetts 



Sulfur and copper have been used for over 100 

 years in commercial apple orchards as broad spec- 

 trum fungicides. More recently, these chemicals 

 have been used by growers seeking an 'organic' or 

 low-input approach to disease management. To de- 

 termine how effective sulfur or lime sulfur and early- 

 season copper applications are in controlling apple 

 scab, 12-year-old scab-susceptible apple trees on M.7 

 rootstock were treated with different combinations 

 of sulfur and copper fungicides starting at half-inch 

 green. 



The experimental block had unusually high scab 

 inoculum. Treatments were applied to 5 cultivars, 

 'Mcintosh,' 'Empire,' 'Golden Delicious,' 'Delicious,' 

 and 'Cortland.' Primary scab treatments were ap- 

 plied on the following dates: April 20, 26, May 3, 11, 

 18, 25, and June 1. The first application was made 

 at the half-inch green growth stage, and according to 

 ascospore maturity evaluations, a significant 

 amount of inoculum had been released in an infec- 

 tion period the previous week. Summer cover treat- 

 ments were applied on June 15, 29, and July 13. 



Treatments were the following: 



1. lime sulfur @ 2 gal/lOOgal; 



2. lime sulfur @ 2 gal/100gal+ copper (Kocide 101™) 



@ 41bs/100gal; 



3. sulfur (95WP) @ 5 lbs/lOOgal + copper @ 41bs/ 



lOOgal; 



4. captan (50WP) @ 21bs/100gal.; 



5. an untreated control 



Treatments which included copper were applied 

 as copper only on the first spray date (April 20; trees 

 in half-inch green), and as sulfur or lime sulfur alone 

 thereafter. A dormant oil application (2 gal/100) was 

 made on April 27 to all trees. 



All treatments were sprayed to runoff using a 

 handgun at approximately 200 psi with a base rate 

 of 300 gal/acre, and approximately 2 gal/tree. For 

 the 3 secondary scab applications, all sulfur and lime 

 sulfur treatments were sprayed with sulfur 95WP at 

 5 lb/100 gal , while the captan treatment was contin- 

 ued at 2 lbs/100 gal. Mill's infection periods occurred 

 consistently through primary apple scab season, 



22 



Fruit Notes, Winter, 1991 



