How to prevent worms growing inside the cherries?
Adult cherry fruit fly maggots emerge from the ground in late spring to early summer, about 5 weeks prior to cherry harvest. The female can lay up to 200 eggs. These hatch into larvae that tunnel into the cherry and when mature in 15-21 days burrow back out and drop to the ground. There they burrow into the soil to pupate. The pupa overwinters and develops into the adult fly the next year.
The best defence is prevention. If you have a small tree it is relatively easy to cover it with a fine mesh netting that prevents the fly from reaching the developing cherries. It should be put in place after the flowers have been pollinated and the cherries are just starting to form but before the flies emerge. You can also hang traps consisting of a dark red ball coated with a sticky substance such as Tangle-trap. You will need 3 – 4 for a large tree and 1 for a dwarf. They need to be visible to the flies so hang at “eye level, 2 to 3 feet from branch tips.” Check them daily to clean and add more sticky solution.
Once the eggs have been laid, your next defence is to prevent them from reaching the ground to pupate. All infected cherries should be removed. For a large tree both of these solutions may be difficult. However infected cherries often drop early so should be promptly removed and destroyed. A thick layer of mulch or a permeable landscape fabric laid under the tree can help to prevent the larvae from burrowing into the soil.
For further information about fruit tree growing see Omafra’s on line Gardener’s Handbook at the link below.
https://omafra.gov.on.ca/english/crops/gardbk/gh-ch2-3pest.htm