Banker plants provide an alternative food source, habitat and often a reproduction site for natural pest enemies. Banker plants can be particularly useful during periods of high nitrogen boosted growth i.e. when the apices are actively growing like the tomatoes above.
Even though we operate in controlled environments, working with the natural ecosystem in a greenhouse could help to cheaply and efficiently control pests alongside trap tapes and other biocontrols.
Tansy is just one example of a useful banker crop in controlled hydroponic greenhouses.
Tansy flower or ‘Yellow Buttons’ as it’s more commonly known could be a great banker crop to protect more valuable plants from pests.
Tansy (Tanacetum Vulgare), is of the genus Tanacetum in the Aster family. The leaves and flowers are irresistible to ladybirds who lay their eggs on it. They will hatch and enjoy an aphid banquet.
Tansy will host beneficials such as braconid parasitoid wasps and minute pirate bugs. These predators will gobble up aphids, mites and thrips in the greenhouse.
Tansy can be easily grown in hydroponics, and is cold hardy under natural light and can grow 2-3 ft in summer. Growing Tansy in hydroponics is easy with low EC.
Tansy also grows well in full sun, here seen in full bloom on a rooftop terrace in Edinburgh.
If banker plants are grown in soil, they can provide a safe haven for parasitic wasps to emerge from chrysalis in a natural order to keep aphids and thrips in check. Parasitoids lay their eggs in or on a target insect. The eggs hatch into larvae and devour the host.
Before (left) and after (right) effects of parasitic wasp (Aphidius colemani) mummification of the green peach aphid (myzus persicae). The wasp’s life cycle requires soil for hatching and the tansy provides its first food source so wasps multiply to hunt down every single aphid they detect. Hint: identifying your specific pest is important in biocontrol.
Other production horticulture banker crops
Aside from our suggestion of Tansy, there are many more common banker plants which include:-
- winter wheat
- barley
- millet
- castor bean
- corn
- ornamental pepper
The variety chosen is important in terms of supporting a specific host which effectively controls an identified pest in the greenhouse. We don’t advise Tansy if you are on a grazing site with farm animals as over ingestion is known to have noxious effects. Check local state legislation on the use of Tansy.
The proof is in the pudding – an interesting side note – you could eat the banker too.
Tansy cake has a long tradition as an English pudding. Although a few sprigs appear safe, it should be noted Tansy contains high levels of the alkaloid, pyrrolizidine and advice should be sought prior to eating. It may also cause a contact dermatitis for some so be cautious prior to use. There are alternatives listed above. Aside from the dubiety, (generally from long term excessive ingestion), Tansy has other benefits in its curative effects, particularly for roundworm and threadworm infections and as an insect repellent. We have used Tansy as our example as we found it grows well in hydroponics but you can use an of the alternative banker crops.
If you want support in understanding natural biocontrols in CEA, get in touch with Hort Americas technical service.
