Western flower thrips and aphids were observed this week. Thrips were observed on Dracaena and vinca vine, and aphids were observed on Fuchsia.
Western flower thrips is one of the most common and notorious pests of bedding plants in the greenhouse. Thrips damage looks like silvery streaks or spots on leaves and flower petals. This feeding damage reduces the aesthetic quality and marketability of ornamental plants. Western flower thrips is also an important vector of virus diseases including impatiens necrotic spot virus (INSV) and tomato spotted wilt virus (TSWV).
Removing weeds, old plants and plant material debris from the greenhouse is the first line of defense in minimizing problems with Western flower thrips. Weeds must be removed from both inside and around the outside perimeter of the greenhouse. Use yellow sticky cards to monitor for thrips and routinely inspect sticky cards, plants, and flowers for the presence of thrips.
Biological control of thrips should be started early before populations increase. The S. scimitus mite is a predatory soil dwelling mite and feeds on thrips in the pupal stage. The S. feltiae entomopathogenic nematode targets first and second instar nymphs. Predatory mites include Neoseiulus cucumeris and Amblyseius swirskii; N. cucumeris works best at lower temperatures of 50-77 °F and targets first instar nymphs, and A. swirskii works better in higher temperatures above 77°F and also targets first instar nymphs. Predatory bug Orius insidiosus feeds on all plant dwelling stages of thrips (nymphs and adults). Consult your biocontrol agent supplier for more information.
Some of the chemical insecticides available for control of thrips include Aria, BotaniGard ES, Pylon, Mainspring, Overture, Mesurol, and Pedestal. Insecticides with contact or translaminar activity are more effective. Make sure to rotate between different classes to prevent resistance development. For more on insecticides available to control thrips please consult the New England Greenhouse Floriculture Guide (http://negfg.uconn.edu/ ). Make sure to always read and follow the insecticide label
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 on a white surface, look behind flowers and check the 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 especially thrive in cool conditions (50-60 °F). Aphids have a wide host range.
Biological control 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. It is important to correctly identify the aphids before releasing biological control agents. 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 control.
Aphids can be difficult to control with chemical 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. Some labeled materials include Altus, Aria, azadarachtin + M-Pede, BotaniGard, Distance, Endeavor, Enstar II, and Mainspring. 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 build up. Always read and follow the insecticide label.
- Geoffrey Njue, UMass Extension Greenhouse Crops and Floriculture Program with Jim Mussoni, Private IPM Scout.