Collecting good and organically grown cherries can seem like a great challenge: the cherry tree is a rather delicate plant and often fungal diseases and harmful insects occur, compromising production.
Among the various adversities that can affect the cherry tree there is a kind of fly, the Rhagoletis cerasi, which has the bad habit of laying eggs in the pulp of fruits. The insect is commonly called "cherry fly", due to its specialization in attacking these fruits.
In reality, with due care, organic cherry cultivation is possible, promptness and consistency will be needed and we will be rewarded with healthy fruits, as well as the satisfaction of not polluting the environment. So let's find out how to monitor the presence of the cherry tree fly and how to defend the harvest with natural methods.
The biological defense of the cherry tree
The cherry tree is a plant that cannot be left to the mercy of events, it requires careful management, in the prevention and monitoring of parasites and adversities.
Growing organically does not mean letting nature take its course in a completely autonomous way, because plants in nature have the goal of perpetuating the species, while we are also interested in producing abundant quality fruit. Furthermore, agricultural ecosystems, even those richest in biodiversity, are rarely found in such a balance as to make any intervention against harmful insects superfluous, so it is right to think about intervening, but we can choose solutions with the lowest possible environmental impact.
Even if for some years the Drosophila suzukii, or the small fruit fly (which despite its name, in addition to attacking blackberries, raspberries and blueberries, does not disdain other fruit, including grapes and cherries ), the cherry fly remains one of the key insects for this plant, and therefore it is important to check its presence every year.
The insect Rhagoletis cerasi
The cherry fly belongs to the order of Diptera, is a close relative of the walnut fly (complete rhagoletis) and has a wide distribution range, since we can find it in all European countries and in every area of Italy. It is an oliphagous species, in the sense that it does not attack many plants, but is strongly specialized in eating the fruits of the sweet cherry.
The adult of Rhagoletis cerasi measures 3.5-4 mm, has a yellow head on the front and black on the back, with a brown triangle where the eyes are. The thorax is black with a thin yellow lateral line. The wings are blue black with bands.
The larva of cherry fly is whitish in color, without legs and a maximum length of 5 mm.
The insect overwinters at the pupal stage, the adults appear between the end of April and the beginning of May, after 10-15 days they mate and the females lay 50 to 80 eggs each inside a cherry. In fact, a single egg is laid in each cherry, because the female labels the fruit with a pheromone to prevent further oviposition of other females. After 10-12 days, a larva is born from each egg which then lives at the expense of the pulp. The larvae remain in the fruit for about 25 days, after which they come out, drop to the ground to pupate and return out of the ground as adults in the following spring. The cherry fly therefore makes one generation a year.
The damage to cherries
The biology of the insect is closely linked to the seasonal cycle of the cherry tree and the damage is determined by the trophic activity of the larva, which feeds on the pulp of the cherry down to the stone, bringing it to decay and compromising it completely. Affected fruits are also very easily exposed to attacks of monilia, a very common fungal disease on stone fruit.
Whereas each female lays 50-80 eggs, each in a cherry, we can imagine how much the uncontrolled presence of this fly can really undermine the harvest.
To limit the onset of the cherry fly we can meanwhile implement some preventive measures:
- Harrowing. Make a light harrowing of the soil in early spring, which exposes the pupae still overwintering to atmospheric agents. With a few plants it is possible to hoe all the space under the foliage.
- Early varieties. If we still have to plant the cherry trees, it is better to choose early ripening varieties such as Burlat, Precoce della Marca, or other new varieties that have recently come out of the various research centers, which at least partially escape the period of maximum presence. insect.
- Insect nets. Set up insect nets on the foliage, after fruit set, so as not to prevent the bees from entering when their pollination intervention is precious.
Food traps against the fly
The cherry fly is very attracted to yellow color, we can exploit this by creating food traps that in addition to the bait also have a chromatic appeal.
Tap Trap or Vaso Trap are very effective devices for capturing this insect, for both monitoring and mass capture purposes.
The bright yellow trap cap attaches to plastic bottles (tap traps) and glass jars such as honey in the 1 kg format (trap jar), both containers must be filled with attractive bait for the insect to be caught .
In the case of flies harmful to fruit trees, such as Rhagoletis cerasi, in each bottle you need to put half a liter of unscented ammonia (the one used for house cleaning) and some raw fish scraps such as sardines or anchovies, which acts as a protein bait.
The most effective method is to start with water and raw fish, catching some common flies and then add ammonia. We explained the procedure for the Mediterranean fruit fly, the same applies to the cherry tree fly and the walnut fly.
Placing traps on plants in a timely manner is essential, so they are present when the flickers begin. Periodically it is good to check the catch and replace the bait. The yellow traps can be reused every year safely, possibly changing the container of the bait which is specially designed as an external element.
Biological insecticide treatments
Against the cherry tree fly we can also intervene with insecticide treatments, obviously the advice is not to use synthetic pesticides, but only eco-compatible products.
If you have a professional organic cultivation of cherry trees, it is important to verify that the products allowed to carry out the treatments are also registered for that particular crop and for that specific insect to be combated. In addition, you must have a valid license and, as always, carefully read all the information on the label of the product purchased.
In any case, an eco-friendly and useful preventive treatment to combat the cherry tree fly is based on kaolin, a mineral powder that creates a thin veil on plants. The clear veil of kaolin protects plants from sunburn, but also forms a mechanical barrier against some harmful insects. The treatment should ideally be repeated every week, especially with an intense presence of the insect, and is distributed after dilution in water, in the indicative doses of 2.5-5 kg / 100 liters of water. The combination of this treatment with the presence of Tap Trap or Vaso Trap can be a good defensive strategy and avoids having to resort to insecticides.