Are you sure they're being biten off? Could be, due to environmental reasons, that they're merely aborting. Happens a lot with tomatoes.
Are you seeing other signs of insect infestation?
As to the rest, I can't offer advice because I never use synthetic chemicals in my garden, so have no idea how they do or don't work. Besides which, "that bug spray" is kind of a nebulous term, as there are probably a dozen or more brands and chemicals sold for that purpose. |