Does anyone have any suggestions as to what I should use to kill fruit flies that lay eggs on my cherries? I understand they are in the ground under the tree and hatch out when the cherries are starting to turn color.
If you want to eat your cherries (we have several magnificence trees) then do not use commercial sprays once the fruit is forming. The non-toxic solution is to get a bag of lemons, pulp them then boil them to make a kind of citric acid dilute (it is called something like lemonic acid, although it is alkaline...). Mix it with some bio washing or washing up liquid (the former is cheapest) they spray it on the fruiting areas. The washing liquid makes the lemon base stick that is all. If you are having the rain we have at present both that and the commercial, toxic sprays will be washed off and then it will have to be repeated, which in the former case is expensive and builds up toxins that penetrate. Neither eradicates anyway, but reduces and lets you get more than enough cherries to satisfy.
They breed and their eggs are laid on the ground, where the worms remain until the next spring. Treat the base of the trees up to the first fruit bearing branches in the autumn and again in the spring then the flies will not hatch and climb the trees because they are repelled before flying up to the flowering parts.
I am not a raving green who only uses bio alternatives. It is just that this problem, like peach leaf curl that has killed some of our fruit trees, were demanding the trees be sprayed so often that my OH took a peach to the local laboratory to be tested and came back angry and forbade me to use the commercial ones for the sakes of our daughters. I have tried various natural remedies from umpteen web searches and this one works best, but none of them is perfect.