FROM STICKING
Fungus gnat
Larvae feed on developing roots, causing poor rooting and wilting of cuttings (Clemson).
Crop hub · Under glass · Commercial
Propagation house
UConn puts it plainly: many insects and diseases can enter a greenhouse on infested cuttings, plugs or plants. Moist, peat-based rooting media suit fungus gnats, whose larvae cause poor rooting and wilting of cuttings (Clemson), and shore flies feed and breed on algae where water stands on benches and floors (UConn, UMass).
D.S. Cole Growers in New Hampshire, which roots more than 10 million cuttings a year, shows what a working program looks like. Over 85% of its unrooted cuttings come from offshore, and it warns that products used on the stock may affect its biocontrol. It sprays Steinernema feltiae onto most liner trays in propagation every week, releases Amblyseius cucumeris weekly and Neoseiulus californicus every two weeks, and says fungus gnat and thrips problems seem greatly reduced.
crop context · mist bench, rooting cuttings
Six pests that start in propagation
UNDER MIST
Shore flies
Feed and breed on algae mats on wet benches, floors and standing water (UMass).
ON ARRIVAL
Western flower thrips
Comes in on cuttings; shipping infected or thrips-infested plants spreads INSV and TSWV between growers (UMass).
ReleaseAmblyseius cucumeris50–100 /m² per release (Koppert), or 10–50 per plant weekly (UC IPM), or sachets
ON STOCK PLANTS
Two-spotted spider mite
Builds up on tropical foliage crops; D.S. Cole refreshes stock plants often to avoid pest issues.
POINSETTIA CUTTINGS
Silverleaf whitefly
Sweetpotato (silverleaf) whitefly is a key pest of poinsettia (UConn).
ON KEY PLANTS
Broad mite
Distorts the tips of New Guinea impatiens, begonia and verbena.
ReleaseNeoseiulus californicusNo broad-mite rate published; 100–200 /m² is Biobest's spider-mite hot-spot rate
Season calendar
NORTHERN HEMISPHERE · YEAR-ROUND PROPAGATION · QUALITATIVE| J | F | M | A | M | J | J | A | S | O | N | D | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Fungus gnats, shore flies | Jan: Pest pressure high | Feb: Pest pressure high | Mar: Pest pressure high | Apr: Building | May: Building | Jun: Building | Jul: Pest pressure high | Aug: Pest pressure high | Sep: Pest pressure high | Oct: Building | Nov: Building | Dec: Building |
| Thrips | Jan: Building | Feb: Building | Mar: Building | Apr: Pest pressure high | May: Pest pressure high | Jun: Pest pressure high | Jul: Building | Aug: Building | Sep: Building | Oct: Quiet | Nov: Quiet | Dec: Quiet |
| Whitefly (poinsettia) | Jan: Quiet | Feb: Quiet | Mar: Quiet | Apr: Quiet | May: Quiet | Jun: Quiet | Jul: Building | Aug: Pest pressure high | Sep: Pest pressure high | Oct: Pest pressure high | Nov: Building | Dec: Quiet |
| Release window | Jan: Release window | 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: Release window |
- Pest pressure high
- Building
- Release window
- Quiet
- Fungus gnats, shore flies · high pressure Jan–Mar, Jul–Sep
- Thrips · high pressure Apr–Jun
- Whitefly (poinsettia) · high pressure Aug–Oct
- Release window · release Jan–Dec
Starter program
What one New Hampshire young-plant grower released in 2019 (D.S. Cole Growers, reported by UConn). The numbers are whole-site totals for about 5 acres of glass, not per-area rates, so scale them to your own houses.
- WEEKLYSteinernema feltiaeOne 250-million tray over the propagation area each week, and a second when volume is high; low-pressure sprayer, filter removed
- WEEKLYAmblyseius cucumeris250,000 a week across liners and finished crops
- EVERY 2 WEEKSNeoseiulus californicus25,000 every two weeks, diluted in vermiculite, for spider mites
- WEEKLYStratiolaelaps scimitus62,500 a week; on seed-sown herbs, mixed into the covering media at about 62,500 per 5.6 ft³
- POINSETTIAEretmocerus eremicus5,000 a week early in the crop, rising to 10,000 as it is spaced
- CUTTING DIPBeauveria bassianaPoinsettia cuttings dipped in BotaniGard at 1.25 g/L plus M-Pede at 0.5%
Setting the house up
In propagation, the defences go up before the cuttings arrive.
Ask for the spray record
UConn advises asking every plant supplier for a list of the pesticides applied. Many insecticide residues can harm natural enemies for up to three to four months.
Empty the house between runs
A fallow of at least four weeks, with the house completely empty, may reduce pest pressure (UConn).
Control algae and weeds
Algae feeds shore flies. UMass recommends a 15 ft weed-free barrier around the house to cut thrips entry.
Monitor gnats two ways
Yellow cards at one per 1,000 sq ft, checked weekly, for adults; raw potato slices pushed into the media for larvae (Clemson), checked after 48 hours (UMass).
Apply nematodes gently
Keep spray pressure under 300 psi (Clemson). D.S. Cole sprays at low pressure with the filter removed and checks viability at the nozzle.