I have been doing battle with fruit flies for years. There are many abandoned farmsteads around here. That is an ideal condition for fruit flies to multiply. Nature hates vacuum. As soon as fruits aren't harvested, there will be creatures to feast on the fruit. In this region, the Mediterranean fruit fly and the olive fruit fly are particularly bad.
You have to find a way of cutting the life-cycle: fruit fly > eggs > larvae > pupa > fruit fly.
Picking up fallen fruit under the trees usually isn't enough because the larvae often leave the fruits before they are ripe. Once they are in the ground they become pupas to turn into fruit flies the following year.
I have tried to pick the fruits before the larvae hedge, however, that's time consuming. It would be easier to destroy/pick all fruits before they are big enough for the flies to lay there eggs, but that means you won't have any fruit for 2 to 3 years because the pupas can hedge even after 2 or 3 years.
Hanging traps in the trees will catch some, but not all fruit flies. Usually, you use bottles with little holes painted yellow and filled with something to attract the flies. I dilute marmite, some use
urine, my neighbor uses the water in which he cooks his codfish.
In Japan, farmers use little paper bags to protect the fruits, but that's time consuming. You could also use a thin fabric or very fine netting to cover the whole tree. I have tried spaying the fruits with a solution of water and clay to cover the fruits with a clay layer before the fruit flies deposit their eggs. It seemed to help a little, but in the end, many fruits had larvae after all. It can also help to harvest the fruits before they are ripe and let them ripe in boxes. That too seems to help provided one can chose the right moment. Selecting fruit trees that bear fruit early in the year, before the fruit flies are active, can also help.
If you can't catch the flies or dispose of the fruits with larvae, you can try to do something about the pupas in the soil. It's recommended to till the soil so that the pupas are buried too deep to reach the surface. That's tricky because you risk damaging the
roots. I'm in the process of building a
chicken tractor low enough to fit under the fruit trees. Hopefully, the
chickens will find the larvae or pupas in the soil.
I haven't heard about burning. I would be worried about damaging the fruit trees. The fire would have to be strong enough for the heat to destroy the pupas or larvae in the soil, which you don't really know how deep they are.
Wonder if there are any other ideas.
Edit: covering the ground below the trees with plastic sheeting is another way of preventing the larvae from entering the soil. The plastic sheeting has to be big enough because the larvae can "jump" one to two feet. If the larvae can't enter the soil, they first bent and and then release their body so that the spring action makes them jump here and there.