Cucumber is one of the crops where predatory mites work best under glass. In greenhouse trials on cucumber, the Swirski mite controlled western flower thrips significantly better than Amblyseius cucumeris (Messelink and others, 2006). It also eats the eggs and young nymphs of silverleaf whitefly, and it breeds on pollen, so it can go in before either pest arrives. UMass Extension names cucumber, with tomato, as a long crop where Encarsia formosa controls greenhouse whitefly well.
The losses to plan for are leaves and virus. UC IPM notes that heavy spider mite infestations lower cucurbit yield and fruit quality. Melon aphid carries cucumber mosaic virus, and UC IPM warns that biological control does not reduce virus spread. Start the aphid parasitoid soon after planting, and keep aphids out with vent screens.
Stipples and scars leaves and other plant parts. On cucumber the Swirski mite out-performed A. cucumeris in trials, and it takes whitefly in the same release.
Heavy infestations lower yield. The predator spreads where leaves touch, and above 86 °F (29 °C) with humidity under 40 % it retreats down the plant (K-State).
Colonies sit on leaf undersides and it carries cucumber mosaic virus. The first mummies appear 10–14 days after the first release.
Honeydew and sooty mould on leaves and fruit. Cucumber is a long crop, which is where Encarsia works best.
The Swirski mite eats its eggs and first two nymphal stages. Older scales are left for a parasitoid such as Eretmocerus.
Pale winding mines in the leaves. Broad-spectrum sprays for other pests kill its parasites and set off outbreaks.
| J | F | M | A | M | J | J | A | S | O | N | D | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Western flower thrips | Jan: Quiet | Feb: Quiet | Mar: Quiet | Apr: Building | May: Pest pressure high | Jun: Pest pressure high | Jul: Pest pressure high | Aug: Pest pressure high | Sep: Building | Oct: Building | Nov: Quiet | Dec: Quiet |
| Spider mite | Jan: Quiet | Feb: Quiet | Mar: Quiet | Apr: Quiet | May: Building | Jun: Pest pressure high | Jul: Pest pressure high | Aug: Pest pressure high | Sep: Pest pressure high | Oct: Quiet | Nov: Quiet | Dec: Quiet |
| Melon aphid | Jan: Quiet | Feb: Quiet | Mar: Quiet | Apr: Quiet | May: Building | Jun: Building | Jul: Pest pressure high | Aug: Pest pressure high | Sep: Pest pressure high | Oct: Pest pressure high | Nov: Building | Dec: Quiet |
| Whitefly | Jan: Building | Feb: Building | Mar: Building | Apr: Building | May: Building | Jun: Pest pressure high | Jul: Pest pressure high | Aug: Pest pressure high | Sep: Pest pressure high | Oct: Pest pressure high | Nov: Building | Dec: Building |
A starting point for a first season, assuming the house has no residual insecticide and no resident pest populations. Adjust the rates to your own scouting counts and your supplier's advice.
Most of what decides a release program is the house itself: what was sprayed, the climate, and what gets in through the vents.
Koppert says it is not effective below 64 °F (18 °C), and it is sensitive to humidity below 60 %. UConn, citing trials on chrysanthemum, says both mites controlled thrips under short winter days, and A. cucumeris is the cheaper choice then.
Cornell reports that the Swirski mite and A. cucumeris eat each other when they are released together.
UC IPM gives 0.355 mm (355 microns) or finer to keep out winged aphids, and 0.145 mm or finer for western flower thrips. Fine screen restricts airflow, so add screen area or adjust the ventilation.
UConn advises removing yellow sticky cards before and after each Encarsia release, and continuing releases until 80–90 % of the whitefly are parasitised.