Aphid banker plants are used to manage green peach and melon aphids. Banker plants are used to rear, release and sustain aphid parasites before aphids appear in the crop. Barley plants or wheat plants are ordered from suppliers with bird cherry oat aphids on the plants. Cherry bird oat aphids attack only monocotyledons and should not be used in greenhouses with crops such as Easter lilies, Alstroemeria, ornamental grasses, orchids, day lilies, irises, spring bulbs (tulips, daffodils), palms, onions and garlic. Once the bird cherry oat aphids are established on the plants, Aphidius colemani (parasite wasp) are sprinkled on the bird cherry oat aphids. A. colemani parasitizes and emerges from the bird cherry oat aphids. Once parasitized mummies are observed, the banker plants are then placed throughout the greenhouse where emerging A. colemani will parasitize green peach and melon aphids on the crop.
Here is the procedure used by some New England growers for using aphid banker plants.
- Place orders for banker plants up to 6 weeks before aphids are expected in your greenhouse.
- Upon arrival, transplant the banker plant plugs into larger sized pots (10 inch) so that the barley or wheat plants have plenty of room to grow. Some growers divide plants in half so one plant can be split into two hangers. They plant in the middle of the pot and sow barley seed around outside edge of the banker plant. Wheat and barley are best, (oat can also be used) the cultivar does not seem to matter, so use whatever cultivar is commercially available. This provides a continuous supply of new plants for the aphids. Your goal is to raise a good population of bird cherry oat aphids to eventually support a large population of parasites. If grown in the greenhouse, the plants need to be grown in a “starter cage” to protect the bird cherry oat aphids from being parasitized by existing Aphidius in your greenhouse. Some growers grow banker plants under lights in a separate building or basement, away from the greenhouse.
- Wait one or two weeks for cereal feeding aphid populations to reproduce on the plants.
- Next, move the banker plants (except for one), into the greenhouse, group them together and sprinkle the Aphidius on top of the banker plants. It takes about two weeks for the Aphidius to reproduce and parasitize the bird cherry oat aphids. Use the saved plant to start new banker plants.
- Check banker plants weekly and look for newly parasitized aphids ("light brown aphid mummies"), which indicate that the parasitoids are establishing on the banker plants.
- Once parasitized aphids (mummies) are observed on the banker plants, hang the bankers to the existing drip irrigation lines, where they will remain for the spring season.
Maintenance: If any part of the original banker plant dies, remove only the dead part of the plant and reseed with barley again. The Aphidius will continue to reproduce.
From these original banker plants, continue to make your own banker plants. Sow barley or wheat seeds in the middle of hanging baskets. Place the old banker plants close to the newly seeded pots. Cut foliage (grass) off of the “saved” banker plant containing the bird cherry oat aphids and place the infested grass over the top of growing media in new pots. When the barley comes up, the bird cherry oat aphids will move onto the new sprouts and continue to reproduce. This takes about two weeks to make a new batch of banker plants. More barley or wheat seed is added around the outside of each hanger before moving the banker plant out into greenhouse. The second batch of plants is moved into the greenhouse near a banker plant that has aphid mummies on it so the cereal aphids will be parasitized, or more Aphidius colemani will need to be ordered. The process is continued for the spring season.
It is important to evenly distribute them throughout a greenhouse. General recommendations suggest that banker plants should be placed approximately 130 feet apart, using 4-5 banker plants per 10,000 ft2, in order to increase parasitization. Many growers distribute banker plants, among the main crop at a rate of one banker plant per 1,000 ft2 before aphids are detected. Recommended rates may vary; start with these rates and adjust 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.
Watch the crop closely for aphid mummies. If you find aphid colonies in the crop that do not have any mummies, check the aphid species. Aphidius colemani is not used to parasitize larger aphids such as the foxglove aphid and potato aphid. If foxglove or potato aphids are your predominant species, another 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). These plants will need to be irrigated separately.
Tina Smith, UMass Extension and Leanne Pundt, UConn Extension
Resources
Aphid Banker Plant System for Greenhouse IPM , Step by Step. 2015. University of Vermont Entomology Research Laboratory
Boosting Bankers, Greenhouse Canada
Biological Control of Aphids, UConn Extension
Managing Aphids in Greenhouses (photos of species), UConn Extension
Tips on Scouting Spring Ornamental Crops, UConn Extension
