Banker plants are plants that are different from the primary crop being grown. They assist in establishing, supporting and maintaining a population of one or more biological control agents that are released on the banker plants. Banker plants support the biological control agents with pollen or other plant material, or a host pest that doesn’t affect the primary crop grown. In the last few years, two banker plant techniques related to aphids and thrips have received increased interest from ornamental plant growers.
The aphid banker plant system is based on introducing cereal aphids into a greenhouse on cereal plants (i.e., rye, barley, wheat). Cereal aphids serve as food source for the parasitic wasp Aphidius colemani. Photos courtesty of Biobest, CanadaAphid banker plants
The aphid banker plant system is an open rearing system. For it to be most effective, the banker plants need to be introduced as early in the crop as possible before aphids appear.
Producing banker plants Banker plants can be purchased or growers can produce their own. Producing your own allows growers to increase the number of plants that can be put into the greenhouses and keeps the banker plants system affordable. Production of banker plants needs to be done in A. colemani exclusion cages. Otherwise it is impossible to produce sufficient amounts of cereal aphids on the banker plants that are grown in-house.
Banker plant considerations
When using banker plants, it is important to identify the aphid pests to ensure good control is achieved. A. colemani is an excellent parasite for green peach aphid (Myzus persicae) and black melon aphid (Aphis gossypii). However, A. colemani does a poor job of controlling foxglove aphid (Aulacorthum solani) and potato aphid (Macrosyphum euphorbiae). For these two aphid species, use aphid parasite Aphidius ervi.
Some growers who produce their own banker plants use A. colemani excluusion cages to raise cereal aphids on cereal plants. Another benefit of the aphid banker plant system is the plants attract outside naturally occurring aphid predators such as lady bugs, lace wings, syrphid flies and gall midges — especially during the spring. These predators are attracted by the aphids on the banker plants, even if there are no aphid pests present on the greenhouse crops. In traditional pest management programs, these naturally occurring predators would not survive pesticide applications.
Pepper banker plants
Orius has five nymph stages and completes its life cycle from egg to adult in 30–35 days. Use in greenhouse pepper production has shown it takes two generations to get Orius established in a crop. After its release, it takes eight to 10 weeks before the Orius population is high enough to have an impact on a thrips population. Once Orius is established, the thrips numbers drop very quickly.
Orius usually lays its eggs in growing tips and buds, which can be a problem in ornamental plant production when finished ready-for-sale flowers and plants are being shipped to retailers. Under short-day conditions, Orius diapauses and becomes inactive.
Greenhouse pepper crops usually stay in production for nearly a year. Orius is introduced early in the crop, and once established, it usually remains active for the better part of the crop. Even though Orius is effective once it’s established, pepper growers still use other biological control agents (Amblyseius cu-
The compact ‘Black Pearl’ ornamental pepper has become the Orius banker plant of choice. Since pepper plants germinate and grow slowly, plants need to be started well in advance to be used as banker plants. When sown in October, pepper plants flower in late January. Its many flowers provide pollen for Orius to feed on in the absence of thrips. Orius can be introduced as early as late February under natural day length conditions. Extension of the day length with supplemental lighting allows Orius to be released earlier.
After Orius is released on pepper plants, nymphs can usually be found three to four weeks later. Once established in the greenhouse, it is not unusual to count dozens of Orius on yellow sticky cards each week and virtually no thrips.
The system has been used with a variety of crops including cyclamen, African violets, both cut and potted mums and gerbera, alstroemeria, snapdragon and a variety of spring crops.