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The Trials & Tribulations of Banker Plant Production
| Roger McGaughey
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>> Published Date: 6/25/2012
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 For those who don’t know what a banker plant is: it’s a single plant or a collection of plants that act as a host or home for an insect predator that preys on unwelcome pests of the specific crop being grown. The basic banker plant is barley acting as a host to a cereal aphid, which, when parasitized by an Aphidius species, produces more parasitic wasps that attack unwanted aphids in the surrounding crop.
In-house production of banker plants on a large scale is not without challenges and I’ve learned a lot of lessons again this year. Initially, it’s imperative to secure a good, regular source of cereal aphids and this has proved to be very difficult. Both my BCA suppliers have had issues this season, which means that any population you can obtain has to be treasured and carefully protected.
Aphids like to live on young tissue, so if the plant grows too fast the hardened tissue becomes less inviting. One way of combating this is to consecutively sow more seed around the pot on a regular basis and hope that the host aphid population moves onto the new, young, germinating seedlings. Contamination by natural predators is a real threat (that is what happened to both suppliers), so the in-house bankers need to be protected from unwanted visitors.
This year we used a large domed hair net—which initially worked well, but when the plant got too tall and the temperature increased, some rot set in. The plant looked like a mini hay field and certainly was not very conducive to a healthy aphid population. I drenched some pots with Bonzi, which helped until a period of rainy weather arrived bringing with it a mildew infection of the cereal plants. An application of Cease protected the new young seedling growth, but did nothing to make the infected foliage green again. Some plants were badly infected and had to be thrown away. Treatment with Cease will be incorporated into the program at an earlier stage.
In spite of this, we managed to rear a reasonably good crop of parasitized cereal aphids, having bought in supplies of Aphidius colemani and A. ervi. At one stage, we thought we didn’t have any aphids on our bankers, but it coincided with a hot spell and the aphid population had retreated to the lower parts of the plant. Amazingly, once the weather cooled down the aphids moved back up to the softer tissue at the top of the plant. This hot spell resulted in another twist—an influx of Hover flies at our second location, which was quite a surprise. The long plastic houses have roll-up sides that are used as ventilation aids—but they offer an inviting destination for natural insects. This was good and bad, since they started feeding on both the pest and banker aphid populations. Some parasitic wasps also appeared and aphid mummies resulted a few weeks later. On reflection, this invasion really shouldn’t have surprised us. Our weekly nematode spray program continues to be very successful and not spraying nasty chemicals has the distinct benefit of providing a clean environment conducive to natural predators. The downside of this process showed up when we moved bankers to our main location. Hover fly larvae came with them, resulting in a crop of adults a week later, which helped to diminish our home cereal aphid supply.
I’m currently making a batch of multi-purpose banker plants that contain pollen-bearing species and are habitats for Orius incidius, the thrips predator. These pots are going outside on drip irrigation around our perennial and mum fields like last year and will aid in keeping the thrips population to an acceptable level. One of our customers recently purchased a quantity of these, but I had to give him a rain check on the aphid banker portion. Thankfully, our BCA companies’ delivery of these is finally back on track so we can keep a regular supply of aphids available for our resident Aphidius population.
Keeping the balance tipping in the right direction is vitally important in any biological program. Within a few weeks, we’ll be able to provide a small pot full of aphid mummies so the Aphidius portion of the homeowner’s natural habitat will be complete. GT
Roger McGaughey, head grower at Michael’s Greenhouses in Cheshire, Connecticut, was educated in Northern Ireland and England and has 40 years experience as a grower.
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