FROM TRANSPLANT
Green peach aphid
UC IPM rates it the more important of the two common lettuce aphids; it contaminates heads and carries viruses.
Crop hub · Under glass · Commercial
Leafy greens
On lettuce the harm is contamination more than feeding. UC IPM says large numbers of aphids stunt seedlings and contaminate heads bound for market, and that leafminer larvae contaminate heads even after mined leaves are removed. UConn's scouting guide for vegetable transplants flags aphids on leafy vegetables, whiteflies on leafy greens, and leafminers on spinach, beet and chard.
The aphid species matters more here than in most crops. UC IPM rates green peach aphid the more important of the two it finds commonly on lettuce, alongside potato aphid, while lettuce aphid feeds deep in the heart. In a Danish laboratory test, Aphidius colemani parasitised 60% of green peach aphids and none of the lettuce aphids, while Aphelinus abdominalis parasitised 39% of them.
crop context · greenhouse lettuce, gutter system
Six pests to plan for
SPRING, AUTUMN
Potato aphid
The other common lettuce aphid in UC IPM's guidelines; A. colemani is the wrong parasitoid for it.
SPRING–AUTUMN
Lettuce aphid
Hides in the heart on the youngest leaves; A. colemani does not parasitise it.
Season calendar
NORTHERN HEMISPHERE · YEAR-ROUND GLASS · QUALITATIVE| J | F | M | A | M | J | J | A | S | O | N | D | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Aphids | Jan: Quiet | Feb: Building | Mar: Pest pressure high | Apr: Pest pressure high | May: Pest pressure high | Jun: Building | Jul: Building | Aug: Building | Sep: Pest pressure high | Oct: Pest pressure high | Nov: Building | 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 |
| 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
- Aphids · high pressure Mar–May, Sep–Oct
- Leafminer · high pressure Jun–Sep
- Release window · release Feb–Nov
Starter program
A starting point for a greenhouse lettuce or leafy-greens house. UC IPM's field guidelines hold aphid sprays until there are more than 20 aphids per plant before heading, and treat leafminer at more than one mine per leaf; both are field numbers, not greenhouse ones.
- AT TRANSPLANTSteinernema feltiaeDrench the media or blocks; repeat weekly to every 10 days while larvae are found
- AT TRANSPLANTAphidius colemani0.25–4 /m² per release, at least three releases, against green peach aphid
- IF POTATO APHIDAphidius ervi0.25–2 /m² weekly
- IF LETTUCE APHIDAphelinus abdominalisGeneral rate 0.25–4 /m² per release; its use on lettuce aphid rests on laboratory work (Shrestha 2014, 2017)
- AT FIRST MINESDiglyphus isaea0.25–3 /m² weekly, at least 3 releases
- SMALL LARVAEBt kurstakiLabel rate, on young loopers; repeat as the label directs
Setting the house up
In a crop sold as leaf, prevention carries most of the program.
Check the transplants
Inspect seedlings before they go in. UC IPM finds most leafminer mines on the cotyledons and first true leaves.
Name the aphid
Green peach, potato and lettuce aphids each suit a different parasitoid. UConn notes that host-specific parasitoids need the aphid identified to species.
Card over the crop
Yellow cards at one per 1,000 sq ft or more catch winged aphids, leafminer adults and fungus gnats. Change them weekly and record the counts (UConn).
Keep the house weed-free
UConn advises keeping the inside and outside of greenhouses weed-free, and clearing weeds and debris from walkways and under benches to head off pest outbreaks.