FROM POTTING
Western flower thrips
Scars flowers and leaves, spreads impatiens necrotic spot virus, and pupates in the media.
Crop hub · Under glass · Commercial
Bedding plants
Bedding plants are grown as many short crops in one house, and much of the stock arrives as cuttings or plugs. UConn's key-plant lists show the pattern: thrips, aphids and two-spotted spider mite turn up across most of the range, broad mite on New Guinea impatiens, begonia, verbena and gerbera, and greenhouse whitefly on fuchsia, lantana and salvia.
Biological control works here, but it has to start clean. UConn warns that some insecticide residues can harm natural enemies for up to three to four months, and a New Hampshire grower that roots over 10 million cuttings a year says sprays used on imported cuttings can affect its program. In a UMass thrips trial with three growers (bedding plants at two Massachusetts sites, potted dahlias in New York), all three were satisfied with plant quality using Amblyseius cucumeris alone.
crop context · spring bedding house, mixed annuals
Seven pests to plan for
FROM STICKING
Fungus gnat
Larvae feed on young roots, worst in propagation; succulent-stemmed begonia, geranium and coleus are especially susceptible.
WITH THE PLUGS
Shore flies
Breed in algae on wet benches and trays; UConn calls the adults a nuisance pest.
LATE WINTER ON
Green peach aphid
Aphids colonise new growth of calibrachoa, fuchsia, pansy, verbena and more; honeydew and white cast skins spoil sale plants.
SPRING
Two-spotted spider mite
Builds in hot, dry spots and in hanging baskets that miss overhead watering.
ON KEY PLANTS
Broad mite
Toxic saliva twists and hardens tip growth; New Guinea impatiens, begonia and verbena are key hosts. Needs a microscope to see.
ReleaseNeoseiulus californicusNo broad-mite rate published; 100–200 /m² is Biobest's spider-mite hot-spot rate
ON FUCHSIA, SALVIA
Greenhouse whitefly
Worst where stock or "pet plants" are kept over winter (UConn).
ReleaseEretmocerus eremicus1–10 /m² per release, weekly; UMass gives 1–2 /ft² weekly for bedding plants
Season calendar
NORTHERN HEMISPHERE · HEATED SPRING HOUSE · QUALITATIVE| J | F | M | A | M | J | J | A | S | O | N | D | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Fungus gnats | Jan: Pest pressure high | Feb: Pest pressure high | Mar: Pest pressure high | Apr: Building | May: Building | Jun: Quiet | Jul: Quiet | Aug: Quiet | Sep: Quiet | Oct: Quiet | Nov: Quiet | Dec: Building |
| Thrips | Jan: Quiet | Feb: Building | Mar: Building | Apr: Pest pressure high | May: Pest pressure high | Jun: Building | Jul: Quiet | Aug: Quiet | Sep: Quiet | Oct: Quiet | Nov: Quiet | Dec: Quiet |
| Aphids | Jan: Building | Feb: Building | Mar: Pest pressure high | Apr: Pest pressure high | May: Pest pressure high | Jun: Building | Jul: Quiet | Aug: Quiet | Sep: Quiet | Oct: Quiet | Nov: Quiet | Dec: Quiet |
| Spider mite | Jan: Quiet | Feb: Quiet | Mar: Quiet | Apr: Building | May: Pest pressure high | Jun: Pest pressure high | Jul: Building | Aug: Quiet | Sep: Quiet | Oct: Quiet | Nov: Quiet | Dec: Quiet |
| Release window | Jan: Release window | Feb: Release window | Mar: Release window | Apr: Release window | May: Release window | Jun: Release window | Jul: Quiet | Aug: Quiet | Sep: Quiet | Oct: Quiet | Nov: Quiet | Dec: Release window |
- Pest pressure high
- Building
- Release window
- Quiet
- Fungus gnats · high pressure Jan–Mar
- Thrips · high pressure Apr–May
- Aphids · high pressure Mar–May
- Spider mite · high pressure May–Jun
- Release window · release Jan–Jun, Dec
Starter program
A starting point for a spring bedding house with no residual insecticide on the stock, drawn from a UMass thrips trial and the UMass and UConn fact sheets. Adjust it from your own card and plant counts.
- AT STICKINGSteinernema feltiaeDrench the trays 2–3 days after sticking; repeat weekly to every 10 days while larvae are found
- WEEK 1Amblyseius cucumeris10,000 per 1,000 sq ft in weeks 1, 2, 3, 5 and 7 (UMass trial), or sachets at 1 per 2.5 m², with a fresh set in week 6
- WEEK 1Aphidius colemani0.25–4 /m² per release, at least three releases; barley banker plants can keep it going
- ON FIRST WHITEFLYEretmocerus eremicus1–2 per sq ft per week (UMass rate for bedding plants)
- ON FIRST MITESPhytoseiulus persimilis2–50 /m² per release; repeat weekly, at least twice where mites are established
- KEY PLANTSNeoseiulus californicusEarly in the crop and at high rates on New Guinea impatiens, begonia and other broad-mite hosts (OMAFRA); no broad-mite rate is published, and 100–200 /m² is Biobest's spider-mite hot-spot rate
Setting the house up
Most bedding-plant programs that fail do so before the first release.
Ask what was sprayed on the cuttings
UConn advises asking every plant supplier for a list of the pesticides applied. Many residues, especially pyrethrins and organophosphates, can harm natural enemies for up to three to four months.
Keep a weed-free strip
UMass recommends a 15 ft weed-free barrier around the greenhouse to cut thrips entry. Inside, UConn notes that weeds under benches shelter pests, and that many thrips weed hosts have yellow flowers.
Card and check weekly
At least one yellow sticky card per 1,000 sq ft, with extras near doors and vents, changed weekly (UConn). Potato slices checked after 48 hours show fungus gnat larvae (UMass).
Go easy on nitrogen
UConn notes that over-fertilising, especially with nitrogen, encourages aphids, whiteflies, mealybugs and two-spotted spider mites.