You cannot use pesticides (fungicides, insecticides, etc.) that must be sprayed onto foliage in a way that distributes the chemical into the soil system. Not only will it not work, but it's not environmentally sound.

If the garden work is cumbersome, you may want to consider cutting back a little next year. Or, evaluate the kind of sprayer that you are using. Be sure that you are following smart gardening practices that help prevent certain plant problems, too. Good horticultural practices (fostering the soil, housekeeping, proper watering, etc.) go a long way in making our outdoor tasks easier.