I have a problem with alot of my flowers dropping off the plant without setting tomatoes.I don't think it's weather related- we've had beautiful weather the past few weeks. Most of my plants are a variety of heirlooms. The cherokee purples seem to be OK and i have a bunch of tomatos on them. My brandywines, mr stripeys, caspian pinks, black tulas and box car willy's seem to be having a problem setting fruit. i have several plants with nothing on them , some with a few. I noticed some brown spots ( ? fungus) on the green part of some of the flowers that don't set but I don't seem to have a fungal problem on the leaves of any of the plants. my tomato patch is covered with netting to keep rodents and crows out, is the lack of fruit set related (maybe insects are discouraged by the netting) any help would be welcome.