The following is general information about aphid banker plants that are used to increase numbers of natural aphid enemies in the greenhouse as a biological control strategy.
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 both at the hanging basket and bench or floor level. The drip irrigation 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.
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.
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. Although some suppliers sell banker plants with A. ervi, these banker plants are not compatible with A. colemanii banker plants.
If this aphid is 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 pupates in the soil).
Reprinted from a January 29, 2009 posting on the New England Greenhouse Update website: http://www.negreenhouseupdate.info/greenhouse_update/?p=2548
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