Each program is based around the following rules. 



•k Orchards with economic scab levels (1% or 

 higher) in the previous season should not 

 delay, or should be treated with a fall benzimi- 

 dazole spray. 



*At about 5% ascospore maturity, or tight clus- 

 ter to pink, whichever comes first, start the SI 

 program. Use 2 oz/100 gal Nova or 4 oz/100 gal 

 Rubigan plus 1/2 rate of dodine or captan (de- 

 pending on oil use) in the first application. 



* Repeat applications, using 1.5 oz/100 gal Nova 

 or 3 oz/100 gal Rubigan plus 1/2 rates of protec- 

 tants, at as close to 8- to 10-day intervals as is 

 practical, and apply a minimum of 3 treat- 

 ments. 



*If the 10-day interval is exceeded, particularly 

 when scab pressure is high and occurs when 

 protective/post-infection activity is minimal, 

 then two consecutive applications should be 

 made 7 days apart. 



■frAfter 95% of the ascospores have been dis- 

 charged, at about 1/4-inch fruit, the SI pro- 

 gram should stop. However, if there is a heavy 

 infection period between the last SI applica- 

 tion and 95% discharge, an additional SI 

 application should be made. 



How did the loss of the EBDCs 

 affect what was done in the delayed 

 10-day program? 



When the EBDC fungicides became unavailable 

 in 1990, options for early-season disease control 

 became extremely limited. As a result, growers 



looked to the Sis even more than they had previ- 

 ously. 



On the surface, it might seem possible to have 

 replaced the EBDCs with captan; however, the in- 

 compatibility of captan with oil is a critical impedi- 

 ment to making the substitution. Oil applied as late 

 as pink is essential to IPM mite management, savi ng 

 multiple miticide applications in the summer. Since 

 it is necessary that between 2 and 3 weeks elapse 

 between an oil application and a captan application 

 to avoid phytotoxicity, captan is of little use in 

 primary season scab management. Cyprex is an- 

 other option against apple scab, though fungal resis- 

 tance is known to be present in numerous sites 

 throughout New England. As a result, growers in 

 1990 were faced with using an inferior protectant, 

 either with or without the Sis, or using the Sis alone. 

 Generally, growers chose to use an SI, but whether 

 or not they used a protectant, and what type of 

 protectant they used, varied. 



Given all the changes, how did the 

 program work last year? 



Several thousand acres of apples were grown 

 under a 10-day, delay-SI program in 1990. Scab 

 pressure generally was heavy, with at least 2 Mills' 

 infection periods occurring each week from April 15 

 through the end of primary season. According to 

 squash-mount evaluations, ascospores were mature 

 in all areas by the last week in April. By the time of 

 the first fungicide applications, spore discharge in 

 all areas ranged between 8% and 20%, as estimated 

 from samples at 4 sites throughout the state. Fun- 

 gicide applications were difficult to make, because 



Fruit Notes, Spring, 1991 



21 



