Cut flowers
In a cut-flower house the flower and the leaf are what you sell. UC IPM lists what goes wrong: western flower thrips cause blossom streaking and colour break and spread impatiens necrotic spot and tomato spotted wilt viruses; aphid honeydew, sooty mould and cast skins foul the plant; and leafminer mines make plants unmarketable when abundant, although they rarely kill them.
That changes how biological control is used. UC IPM says that, for aphids on the marketed parts of a plant, biological control alone generally does not give satisfactory control unless compatible methods are added. So releases here sit inside a program of screening, sticky cards and selective sprays. Gerbera, chrysanthemum, snapdragon, dahlia and zinnia are key plants on UConn's lists for thrips, aphids and mites.
Six pests that decide the crop
Greenhouse whitefly
Honeydew and sooty mould; gerbera and chrysanthemum are key hosts.
Broad mite
Hardens and twists gerbera tips; buds distort and flowers fail to develop fully.
Season calendar
NORTHERN HEMISPHERE · HEATED GLASS · QUALITATIVE| J | F | M | A | M | J | J | A | S | O | N | D | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Thrips | Jan: Quiet | Feb: Building | Mar: Building | Apr: Pest pressure high | May: Pest pressure high | Jun: Pest pressure high | Jul: Pest pressure high | Aug: Pest pressure high | Sep: Pest pressure high | Oct: Building | Nov: Quiet | Dec: Quiet |
| Aphids | Jan: Quiet | Feb: Building | Mar: Building | Apr: Pest pressure high | May: Pest pressure high | Jun: Pest pressure high | Jul: Building | Aug: Building | Sep: Building | Oct: Building | Nov: Quiet | Dec: Quiet |
| Leafminer | Jan: Quiet | Feb: Quiet | Mar: Quiet | Apr: Building | May: Building | Jun: Pest pressure high | Jul: Pest pressure high | Aug: Pest pressure high | Sep: Pest pressure high | Oct: Building | Nov: Quiet | Dec: Quiet |
| Whitefly | Jan: Quiet | Feb: Quiet | Mar: Building | Apr: Building | May: Pest pressure high | Jun: Pest pressure high | Jul: Pest pressure high | Aug: Pest pressure high | Sep: Pest pressure high | Oct: Building | Nov: Quiet | Dec: Quiet |
| Release window | Jan: Quiet | Feb: Release window | Mar: Release window | Apr: Release window | May: Release window | Jun: Release window | Jul: Release window | Aug: Release window | Sep: Release window | Oct: Release window | Nov: Release window | Dec: Quiet |
- Pest pressure high
- Building
- Release window
- Quiet
- Thrips · high pressure Apr–Sep
- Aphids · high pressure Apr–Jun
- Leafminer · high pressure Jun–Sep
- Whitefly · high pressure May–Sep
- Release window · release Feb–Nov
Starter program
A starting point for a heated cut-flower house with no residual insecticide in it. UC IPM suggests considering a treatment at an average of 5 to 10 thrips, or 5 to 10 aphids, per yellow card per week.
- FROM PLANTINGAmblyseius cucumeris10–50 mites per plant weekly (UC IPM), or slow-release sachets
- AT PLANTINGStratiolaelaps scimitusOnto the soil or media, where thrips pupate; 100–500 /m², once
- EARLY CROPOrius insidiosus2,000–4,000 per acre, several times during early crop growth (UC IPM)
- AT FIRST COLONIESAphidius colemani0.25–4 /m² per release, at least three releases; banker plants can sustain it
- AT FIRST MINESDiglyphus isaea0.25–3 /m² weekly, at least 3 releases; Dacnusa sibirica in cool houses
- ON FIRST WHITEFLYEncarsia formosa1–10 /m² per release, weekly
Setting the house up
In a crop sold on looks, the house has to be set up before the pests arrive.
Screen against thrips
UC IPM gives 145-micron (0.145 mm) screen for thrips. UMass warns that screen this fine makes ventilation a challenge.
Card the crop weekly
Yellow cards set vertically in the canopy. UC IPM found three cards per cultivar enough in greenhouse roses, and uses at least one leafminer trap per 10,000 sq ft.
Clear the algae
Purdue says shore flies breed in algae on growing media, benches and floors, and that removing the algae greatly reduces their numbers. UConn also advises managing the algae they feed on.
Check a spray before you use it
UC IPM rates floriculture insecticides and miticides by their toxicity to natural enemies and honey bees. Check a product there before spraying over releases.