The unseasonably warm and sunny weather that we experienced last week increased aphid populations in greenhouses, and especially large populations were observed on pansies.
Aphids are common pests of spring greenhouse crops, but they can easily escape detection early in the season when numbers are low. Scout for aphids by checking new growth for shiny honeydew, white cast skins, and/or the aphids themselves. Look under the leaves, growing terminals, behind flowers and check the stems. Yellow sticky cards can trap flying aphids, but they are not reliable for early detection. A regular monitoring and scouting program is needed to detect aphids early before populations explode. This is particularly important for hanging baskets.
There are many species of aphids but the most common in greenhouses are green peach and melon aphids. Foxglove aphids also frequently show up, and they most often thrive in cool conditions (50-60 °F). Aphids have a wide host range and therefore can occur on a wide variety of crops.
Correct identification of aphid species is important, especially when biological controls are being used. Biological control agents don’t control different species equally well. For example, Aphidius colemani is best used to control small aphids such as green peach and melon aphids. For larger aphids such as foxglove and potato aphids, Aphidius ervi is the most effective. Some growers when uncertain about the aphid species use a mixture of wasps, either preventatively, or when numbers are low - Aphidius colemani (for green peach and cotton aphid) and Aphidius ervi (for the larger potato and foxglove aphids). The predatory midge, Aphidoletes aphidimyza, and lacewings, Chrysopa spp, can be used to clean up aphids in hot spots. Biological controls can be very effective, as long as they are deployed early in the crop cycle.
Some of the insecticides available for control of aphids include:
- Altus (flupyradifurone - Group 4D): Contact, systemic and translaminar insecticide labeled as a drench or spray.
- Endeavor (pymetrozine – Group 9B): Systemic, ingestion and translaminar activity and selective feeding blocker. Aphids stop feeding within hours after treatment and eventually starve to death.
- Mainspring (cyantranilprole - Group 28): Translaminar and systemic activity. Apply as a preventativedrench on aphid prone ornamentals. Aphids stop feeding and become paralyzed after ingestion.
- Pradia (flonicamid & cyclaniliprole - Group 28 & 29): Contact, ingestion and translaminar activity. Excellent plant safety except for pansy and viola.
- Rycar (pyrifluquinazon – Group 9B): Contact and translaminar activity. Aphids quickly stop feeding.
- Tristar (acetamiprid- Group 4A): Contact insecticide with high absorption and upward systemic mobility.
Systemic insecticides are more effective because aphids ingest large amounts of sap. For contact insecticides, thorough coverage of the underside of leaves is needed to achieve good control. Be sure to rotate between different insecticide classes (modes-of-action) to prevent resistance build up. Always read and follow the insecticide label.
For more information, consult the latest edition of the New England Greenhouse Floriculture Guide (https://greenhouseguide.cahnr.uconn.edu/sectionB.php#B6)
- Geoffrey Njue, Extension Specialist, UMass Extension Greenhouse Crops and Floriculture Program