In 3 to 4 weeks, from mid-May to early June depending on the weather, cherry fruit flies (Rhagoletis cerasi) will begin to emerge from the ground to initiate their breeding cycle. Their offspring is the cherry worm. If there were worms in your cherries last year, there will be again this year, you can unfortunately be sure.
But nothing is lost, end of April is the right time to get ready to eliminate them. It is quite possible without insecticide. We explain our method.

The cherry fly

The cherry fruit fly is a specialized insect, its entire life cycle is based on cherry trees, whether cultivated or wild. Once fertilized, the female pricks the still green or semi-ripe fruits, before the complete veraison, and inserts a single egg. The larva, at first tiny, will settle near the stone, then consume the pulp and spoil the fruit. Towards the end of the harvest, the worm (which can reach 5 millimeters) will dig a hole and drop to the ground. There it will bury itself of a few centimeters then form a pupa and let pass the seasons. In May and June of the following year the pupae will hatch and emerge from the ground as flies, both male and female. And the cycle begins again.
Note that if you find several worms, much smaller, it is another parasite: the drosophila suzuki (drosophila suzukii), a midge also very prolific.

Early May: blocking the flight

The pupae that will soon release the flies are all in the ground, under the cherry tree. We will try to block them as soon as they emerge. To do this we will put a veil or a net on the ground, all around the trunk.

You need a very thin veil or net, the fly measures only 3 to 5 millimeters. We used non-woven fabric and covered an area of about 50 square meters all around the tree.

To hold it down, use boards or rocks, but it does not have to be placed on the ground. The important thing is that it doesn’t have too many holes. If you are using multiple sails, as in our case, make sure to put boards at the joints.

Since there is a lot to do in the garden in May, you can set the sails in advance. we did it as soon as the flowering started in April. If the cover is well sealed, the vast majority of flies will stay under the veil and die of hunger (or perhaps boredom).

Mid-May: set a trap

No matter how effective the veil is, there are bound to be survivors. To capture them while respecting other insects, the specific pheromone trap is the most suitable. Today, they are easily available in stores or on the Internet. It consists of two parts: the trap itself and the bait (pheromones).

The trap is generic: a small roof to protect a sheet of glue on which the flies will stick.

They are easy to set up, follow the manufacturer’s instructions provided with the generic trap. The only tricky part is the glue plate, to be put into the trap once the protective film is removed. Try not to stick your fingers too much on it so that it keeps its effectiveness.

The pheromone capsules are specific. They reproduce the odor of the female of the targeted species and will only attract the males of that species. By eliminating the males, we prevent the females from fertilizing, so they won’t go and sting the fruits. The pheromone capsules are contained in hermetically sealed bags, to be opened cleanly with scissors. Avoid touching them with your fingers to avoid compromising their effectiveness. To be poured directly from the bag into the small container that comes with the generic trap.

When the pheromone capsule (red) is in its box (green), hang it in the trap above the glue. Only one capsule, never mix two different pheromones.

When the trap is ready and loaded, hang it from a branch of the tree, towards the middle. Rather on the north side, or the most shaded.

One capsule is effective for 4 to 6 weeks. To be on the safe side, you can change it after one month. The capsule has a strong and, strangely, very pleasant and floral smell. It is understandable that males are irresistibly attracted.

In addition, yellow chromatic traps can be hung, usually several for each tree. They are simple colored glue plates. But they will also attract other insects and can load up quite quickly.

After doing all this, you can expect your cherries to grow without getting stung.
We will see in early June if they are crisp and worm-free!