Most sprays are just preventative. After infection, as per the first link I provided, only oil is an effective eradicate. And you can not use oil for two weeks after applying sulfur based dusting or sprays.Will spraying for it now eradicate the problem?
Canopy management is indeed important in disease control. A link to Wilcox's study (it is worth reading for anyone with a vineyard):Wayne Wilcox at Cornell has done studies showing how sunlight is effective at killing PM.