The walnut fruit fly is one of the most important animal pathogens on nuts in general and walnuts in particular. Affected fruits turn black - and sometimes the nut core is also damaged. In fact, the walnut fly can also result in serious crop failure.

The larvae of the walnut fruit fly eat the pulp of the walnut

A brief introduction to the walnut fruit fly

The walnut fruit fly is a fruit fly (formerly Trypetidae, now Tephritidae) within the large group of flies. In terms of appearance and habits, it resembles the European cherry fruit fly (Rhagoletis cerasi), of which it is a relative.

Here is a brief optical portrait of the walnut fruit fly:

Colour: orange-brown
Size: 4 to 8mm
Special features: conspicuous wing markings (black bands), yellow dorsal label

The walnut fruit fly forms only one generation per year. The pupae overwinter in the ground. The adult flies hatch from the end of June. The main flight time of the insects is only July, but they are sometimes still on the move into September.

larvae as threats

The walnut fruit fly lays its eggs in the green shell of the walnut. The whitish-yellow larvae live there and feed on the pulp, which then becomes soft, black and slimy.

Note: There can be over 25 larvae in a single walnut shell!

After three to five weeks of feeding, the fly larvae drop out of the nut (or fall to the ground with it). They then bury themselves in the ground, where they pupate and form the next generation of flies the next year.

Symptoms of walnut fruit fly infestation

As already mentioned, the pulp is destroyed by the feeding activity of the larvae

  • soft,
  • black and
  • slimy.

When you open the fruit shell, you will find the light-colored larvae in the flesh.

Note: In the case of a very severe infestation, the nut kernel is often also affected, which makes the walnut in question inedible.

Caution: risk of confusion!

Fungal infections such as Marssonina disease and bacterial walnut smut also result in black fruit skins. This means that the discoloration alone does not mean that an infestation with the walnut fly must be the cause without a doubt.

Prevent and control walnut fruit flies

  • Destroy infested fruit immediately. But: Do not dispose of in the compost, but burn or dispose of as hazardous waste (otherwise risk of infection).
  • Cover the ground under your walnut tree before fruit drop and also in spring/summer (from the end of June). In this way you prevent pupation or overwintering) in the ground and also the hatching or fledging of the flies.
  • Set up yellow boards from July to catch some of the adult flies.

Category:

Vegetable garden