Green peach and foxglove aphids were observed on hanging baskets and other plants in greenhouses this week. 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, tap terminals over a white surface, look behind flowers and check stems. Yellow sticky cards can trap flying aphids, but they are not reliable for early detection.
There are many kinds of aphids but the most common aphids in greenhouses are green peach and melon aphids. Foxglove aphids are also very common, and they thrive especially in cool conditions (50-60° F). Aphids have a wide host range.
Biological controls, if used early in the crop cycle, can be very effective. Biological control agents are most effective if released preventively before aphids become a problem and should be matched to the kind of aphid and the environmental conditions, therefore correct identification is key. 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. Contact your supplier for more information on matching the aphids in your greenhouse to the appropriate biological controls.
Aphids can be difficult to control with insecticides, and insecticide resistance has been reported, especially with green peach aphids. With that said, there are several insecticides labeled for the control of aphids. Consult the latest edition of the New England Greenhouse Floriculture Guide (http://negfg.uconn.edu/). 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 development, and always read and follow the insecticide label.
For more information on aphids refer to the following link: http://e-gro.org/pdf/2021-10-05.pdf
- Geoffrey Njue, UMass Extension Greenhouse Crops and Floriculture Program