Greenhouse IPM strategies applied in open field cultivation

In Wouwse Plantage, white buckets have been placed in recently planted onion and leek fields. These containers are still visible in mid-June but will become less noticeable once the crop canopy closes. Field signs will be added later in the season to indicate the presence of biological control in the crop management strategy.

Predatory beetle
VOF van Aert-Koolen is working with Handelsonderneming Klep for the third consecutive season to release the soil-dwelling predatory beetle Atheta coriaria. Before adopting this approach, Klep conducted multiple seasons of field trials with other beneficials. One previous candidate required more pollen than was typically available in these crops. This led to a shift toward Atheta, which functions independently of supplemental pollen or feed inputs.

To demonstrate the method, Johan Bogers and Steffie van Meer brought a bucket of beetles into the field on a Friday afternoon. The buckets have an opening on one side, allowing beetles to crawl out from the moist substrate once the bucket is placed in the soil.

Preventive strategy
Preventive application is recommended. "These beetles target thrips pupae," says Van Meer. "Early-season release is necessary to be effective."

Atheta coriaria is already used in greenhouse-grown crops such as strawberries. In open-field cultivation, its use is relatively recent. In contrast to protected cropping systems—where Klep is also active—biological control is not yet standard practice in arable vegetable production. "Working with beneficials is a learning curve," says Bogers.

Labor input and field management
The buckets at VOF van Aert-Koolen were placed at the start of the season. "By burying them, evaporation is reduced," Bogers explains. "Initial placement requires labor, but the reduced need for replenishing moisture and feed may lower total labor input over the season."

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To be clear, this sprayer in Johan's hand only serves to supply the buckets with nutrients and moisture.

Lifecycle and establishment in the field
The full lifecycle of Atheta, from egg to adult, occurs in the bucket. Adults exit and disperse into the field. "Unlike bees, which return to a hive, Atheta beetles leave and establish themselves in the soil to search for thrips pupae," says Bogers. Van Meer adds that Atheta is a native species in the Netherlands and can overwinter in humid microclimates, such as ditch margins.

Integration with crop protection strategy
The beetles are deployed at a broad scale and as a preventive measure. For compatibility, growers aligning with Atheta are advised to adjust the remainder of their crop protection plan. "Neudosan works well alongside this biological control agent," says Bogers. "But ideally, chemical inputs are avoided altogether."

Retail-driven demand also plays a role. The onions and leeks produced by VOF van Aert-Koolen are supplied via Bakker Barendrecht to Albert Heijn. These buyers encourage a reduction in chemical crop protection and support biological alternatives.

Concerns and additional research
Handelsonderneming Klep continues to run trials on expanded biological control strategies. Due to the withdrawal of active substances, Bogers expresses concern about crops such as lettuce. "For iceberg lettuce, the removal of Movento and Batavia limits options. We're seeing trial results indicating that Neudosan in combination with predatory mites could be effective."

Combination strategies under investigation
Klep is also researching combinations of biological agents. "Atheta can be deployed against various fly species such as fungus gnats (Bradysia spp.) and shore flies (Scatella spp.)," says Van Meer. In leek trials, Atheta is combined with three different soil-dwelling predatory mite species. One of these mites also targets root flies and onion flies.

Unlike Atheta, which can fly and is released from buckets, predatory mites must be distributed directly into the crop. The trade-off is that Atheta buckets require periodic maintenance with water and feed, while mites do not require such containers.

On this particular Friday in June, field maintenance is underway. "I can cover four hectares per hour," says the grower, walking the rows with a tank and sprayer supplying nutrient solution to the buckets. The wider adoption of biological agents is developing in coordination with growers and Klep's crop advisors.

For more information:
Johan Bogers
Trading company C.J. Klep B.V.
jbogers@klep-agro.nl
www.klep-agro.nl