I've been spraying mine Tim at fornightly intervals. Trouble is I've sprayed all of them so don't have any tomatoes, peppers, aubs or melon or sweet potatoes unsprayed for comparision. I just didn't want any of them to go down with anything nasty. I seem to be using about 1/2 gal. a go, just shelve the rest, give it a good shake two weeks later and use. My plants seem quite strong and healthy, but they might have been anyway.