Heterorhabditis-System is able to exert such rapid and effective control of vine weevil because of the way in which it works. When applied to the compost, the nematodes seek out larvae already present in the root zone. They enter the larvae through natural body openings or by penetrating the cuticle directly.

Once inside, they release symbiotic bacteria. A larva which is attacked will colour yellow to reddish brown and will die after about two days. The nematodes reproduce inside the insect and as it decomposes, a new generation moves off in search of further prey.

Heterorhabditis-System contributes to a rapid and effective control of vine weevil provided that:

• It is used curatively, i.e. the larvae must be present at the time of treatment.
• The humidity of the compost is high and the compost temperature does not fall below 12°C for 2 weeks following treatment.

In practice, for most crops this means that there are two periods in which Heterorhabditis-System is used:

• Treatment between August and late September will be effective against larvae which have developed from eggs laid earlier in the year, and before significant damage is done.
• Treatment in April-May will be effective against larvae which have escaped an autumn treatment. The nematodes will penetrate the body of the larvae of the beetles before they pupate.

Late spring applications will greatly reduce the numbers pupating and emerging as well as the number of adult weevils. It should be noted that Heterorhabditis-System remains effective for about four weeks after application. Larvae which result from eggs laid after this time will be inadequately controlled. As in heated glasshouses all stages of the vine weevil may occur at any time, it is possible to control the whole year round.

Heterorhabditis-System is delivered as a clay formulation. By mixing with water, the nematodes form a suspension, which can be applied easily to the compost surface.

For individual treatments (e.g. through drip irrigation) 10.000 nematodes are used per liter potting compost. One pack of Heterorhabditis-System 50 million nematodes will treat 50 m² open ground or 100 m² containerized crops. A package of 5 million nematodes is also available for a treatment of 5 m².

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