Aphid Banker Plants
Thursday, 29 January 2009 16:49
Aphid banker plants are containers with winter barley or common rye or oats on which colonies of grass-feeding aphid species such as the corn-leaf aphid (Rhopalosiphum maidis), greenbug (Schizaphis graminum), and/or bird-cherry aphid (Rhopalosiphum padi) are established. Banker plants are primarily used to rear prey or hosts, in order to attempt to have a sufficient population of continually reproducing natural enemies.
Banker plants need to be placed along walkways and at the end of benches. It is essential to evenly distribute them throughout a greenhouse. General recommendations suggest that banker plants should be placed approximately 131 feet apart, using 4-5 banker plants per 10,000 ft2, in order to increase parasitization. Some growers will place the banker plants at the hanging basket levels with drip irrigation that also insures that the banker plants will remain irrigated without inadvertently washing the aphid natural enemies off of the plant.
It has also been recommended to distribute containers of rye or barley, with the grass-feeding aphid, among the main crop at a rate of one banker plant per 1,000 ft2 even before aphids are detected. It should be noted that existing recommended rates may vary since limited research has been conducted; start with these rates and adjust in succeeding years based on your experience. In research with aphid banker plants in greenhouse pepper production in the Netherlands, 4 banker plants per acre were introduced every two weeks and were able to keep the aphids below threshold. With this rate and frequency of introduction of banker plants, the average number of Aphidius caught per sticky card (3.9" by 9.75") per week was 10 per card per week.
Banker plants may have to be placed closer together or placed in greater frequency within a given area in order to allow parasitoids such as Aphidius colemani to find prey on plants, since research has found that this parasitoid migrates just 3.2 - 6.5 feet from the point of release.
Starter aphid banker plants are available from several biological control suppliers.
- Place orders for banker plants up to 6 weeks before aphids are expected in your greenhouse.
- Transplant the plugs into larger sized pots (10 inch) so that the grass plants have plenty of room to grow.
- Wait one or two weeks for grass feeding aphid populations to grow.
- Lightly release the "aphid mummies" or Aphidius colemani adults onto the starter banker plants. For example, 100 hundred Aphidius per banker plant before it is divided and repotted. Aphidius colemani attacks the grass-feeding aphid, which is not an aphid pest of most greenhouse-grown crops except monocots such as ornamental grasses.
- Check banker plants weekly and look for newly parasitized aphids ("aphid mummies"), which indicate that the parasitoids are establishing on the banker plants.
- Start new banker plants on a regular basis because they will decline and die within a few weeks.
- Inoculate new banker plants by physically transferring aphids from old banker plants onto new ones every 2 weeks.
- It may be necessary to "protect" or isolate your replacement banker plants from natural enemies (either established in your greenhouse or naturally occurring natural enemies that may enter the greenhouse from outdoors during warmer weather). If so, place banker plants in "starter cages" so you can build up your population of grass feeding aphids before releasing A. colemanii. (see photo).
Keep in mind that the bird-cherry aphid is too small for the parasitoid, A. ervi, to develop. A. ervi parasitizes larger aphids such as the foxglove or potato aphid. If foxglove or potato aphids are your predominant species, one option is to use the predatory midge, Aphidoletes aphidimyza for release onto your banker plants. If using predatory midges, placing the pots in trays with moist sand will help provide pupation sites for the predatory midges. (The predatory midges pupate in the soil).
Adapted from: Cloyd, R. Pest Management in Greenhouses. Biological control. From 2009-2010 New England Greenhouse Floriculture Guide.
Thanks to Carol Glenister, IPM Laboratories and Ron Valentin, BioBest for there suggestions.
Photos: Banker Plants, Banker Plants with aphids, Starter Cage
Leanne Pundt, University of Connecticut
Updated 7/09
