Progress report for FS24-371
Project Information
During the early 2023 growing season, we established a banker plant system in our greenhouses consisting of barley, bird cherry oat aphids, and Aphidius colemani wasps for the management of aphids on our cucumber crop. We considered this pilot experiment successful, which led us to believe banker plants may be an effective tool for aphid management on greenhouse crops in the Southeast. The goal of this proposal is to replicate our previous banker plant trials to generate data which can be shared with other growers in the Southeastern region to demonstrate the efficacy of banker plants for aphid management, expand our trials to include a second banker plant system consisting of fava beans, pea aphids, and Aphidius ervi wasps intended to control aphid pests of tomatoes, and provide data on the cost of implementing the banker plant method for these crops. We believe this will benefit growers by providing knowledge of a potentially cost-effective greenhouse aphid management technique that reduces the need for chemical pesticide inputs.
During the 2024 growing season, we were unsuccessful in establishing the fava bean / pea aphid / Aphidius ervi banker plant system. The exact cause for this is unknown, but we believe it may have been to unfavorable climate conditions in the Southeastern region. We were somewhat successful in establishing the barley / bird cherry oat aphid / Aphidius colemani system, and consistently saw at least some proof of parasitoid establishment on banker and crop plants as evidenced by the presence of aphid mummies on both, as well as various species of lady beetles and predatory midge larvae on the banker plants. However, banker plants rarely lasted for more than around 2-3 weeks, likely due to various factors including climate and feeding activity by aphids. We also were unable to gather sufficient data on the efficacy of banker plants at managing aphids on cucumbers, due to the failure of aphids to establish on the first crop during the spring, and the early loss of the second crop due to downy mildew in the fall. Additionally, we found certain elements of our experimental design to be incompatible with our production system. We intend to modify our methods for the 2025 season.
This project will utilize two banker plant systems. The first of these uses a barley banker plant infested with the bird cherry oat aphid (Rhopalosiphum padi), which is an alternative host for the wasp Aphidius colemani, a parasitoid of melon aphid (Aphis gossypii). The second uses a fava bean banker plant infested with pea aphids (Acyrthosiphon pisum) as a host for the wasp Aphidius ervi, which parasitizes larger aphids such as the potato aphid (Macrosiphum euphorbiae). We have previously identified melon and potato aphids as common aphid species on our greenhouse cucumbers and tomatoes, respectively.
Experiments will take place in a greenhouse divided into two 4000 square foot growing spaces. During the Spring growing season lasting between January and June, one of these spaces will be used to grow tomatoes, and the other will be used to grow cucumbers. During the Fall growing season, between August and December, one space is taken out of production to go into cover crops, so experiments will take place in a single growing space containing tomatoes and cucumbers.
Banker plant materials and beneficial insects will be purchased primarily from a commercial insectary (IPM Laboratories, Inc., Locke, NY). All practices for purchasing, planting, and maintaining banker plants follow manufacturer recommendations. Fava bean seed will be purchased 3 weeks prior to planting tomatoes, and pea aphids will be ordered as soon as fava bean plants have produced 5 pairs of leaflets. 250 A. ervi wasps will be released 1 week after introducing pea aphids to the banker plants to allow the aphids time to reproduce. Barley banker plant starter kits will be ordered 2 weeks prior to planting cucumbers. After 2 weeks, we will release 500 A. colemani wasps. For both fava bean and barley banker plants, we will place 2 of each banker plant adjacent to their respective crops (fava bean near tomatoes, barley near cucumbers). Banker plants will be maintained as instructed by the manufacturer, and new banker plants will be started every other week or as needed. Any additional purchases or parasitoids after the initial release will be noted.
To determine the efficacy of A. ervi and A. colemani banker plants for aphid management, we will select 12 tomato plants and 12 cucumber plants for observation. Because of the proximity of some plants to fans at the front of the greenhouse, which may interfere with aphid or parasitoid establishment, we will divide our plants into 2 blocks based on proximity to the fan, with 6 plants per block. These plants will be deliberately infested with aphids (M. euphorbiae for tomato, A. gossypii for cucumber), and half of them will have their leaves bagged with fine mesh garden netting to exclude parasitoid wasps or other natural enemies. The farm assistant will scout these plants once per week and count and average all aphids and aphid mummies on two leaves from each plant, as well as count all aphid mummies on the banker plants. Additionally, the farm manager and farm assistant will scout the entire crop area once per week to record a subjective measurement of the level of aphid infestation on both crops: 0 = no infestation, 1 = minor infestation, 2 = moderate infestation, 3 = severe infestation.
For the duration of the experiment, we will keep detailed notes on banker plant growth and maintenance, as well as of all costs associated with the project. Estimated costs for any materials purchased prior to the start of the experiment, as well as the number of hours spent on banker plant maintenance and scouting, will also be recorded. This will allow us to estimate the overall costs associated with establishing and maintaining banker plants for this period of the growing season.
-Updates for 2024-
The following changes were made early into our experiment during the 2024 growing season:
- Initial parasitoid releases were made directly onto banker plants in cages and allowed 1 week to reproduce before deployment into the greenhouse. Approximately half of the total number of wasps (250 A. colemani, 125 A. ervi) were released per cage. This was done to assist in the initial establishment of wasps on banker plants, and to ensure that parasitoid activity on crop plants was the result of colonization from banker plants.
- Rather than bagging leaves on 6 plants per crop, we opted to surround the entire plants with caged made of PVC pipe and garden netting, and count aphids from 3 leaves from low, middle, and high regions of the plant. This was because the bags were causing the leaves to become stunted in their growth, and the growth of the plants made it impractical to repeatedly sample the same leaves over time.
- Because it was impractical to attempt to count all aphid mummies on the barley plants, we instead took 3 samples of 5 blades of grass from each plant on each sampling date and counted the number of aphids on those.
-Updates for 2025-
Due to our lack of success with various aspects of our project during the 2024 season, we propose the following changes:
- Because we could not establish the fava bean / pea aphid / Aphidius ervi banker plant system, we will be discontinuing this portion of the project.
- Because keeping control crop plants caged led to stunted growth and economic damage, we will instead be growing seperate cucumber plants in pots adjacent to our main cucumber crop to use specifically for our experiment. We will grow 8 plants in total, 4 of which will be covered by cages prior to the introduction of banker plants. We will take counts of aphids and mummies on 3 leaves as before, but from a 2.25 square inch area using a hand lens as in Eid et al. 2018.
- We will continue scouting our main crop of cucumber plants and assign a rating to aphid and parasitoid populations, but we will use a new rating system adapted from NC State University Extension recommendations for scouting aphids on cotton (Cotton Aphid _ NC State Extension). The new rating system for aphids is: 0 = no aphids, 1 = occasional low numbers of aphids, 2 = low numbers of aphids common, 3 = most plants with some aphids, few plants heavily infested; 4 = heavily infested plants common, 5 = many heavily infested plants. The rating system for parasitoids is: 0 = no aphid mummies, 1 = a few aphid mummies present within isolated groups of aphids, 2 = most aphid colonies with a few mummies present, 3 = estimated 10% of aphids are mummies, 4 = estimated 20% of aphids are mummies, 5 = estimated 50% of aphids are mummies.
Additionally, to confirm that the aphid mummies we see on the banker plants belong to Aphidius colemani, we will collect 5 mummies each from the banker plants and cucumber plants once per month after parasitoids become established, and send the wasps that emerge to Dr. Abigail Martens, an expert in Braconid wasps at South Dakota State University, for identification at the end of the summer and fall growing seasons.
Cooperators
- (Researcher)
- (Researcher)
Research
During the 2024 growing season we assessed two well known banker plant systems to see if they were viable for the management of aphids on greenhouse cucumbers and tomatoes in the Southeast. Banker plant systems are a form of biological pest management that provides a beneficial insect predator or parasitoid with a continuous supply of alternative hosts so they can maintain a small population that can react to invasion by pests.
We used two banker plant systems. The first used barley infested with bird cherry oat aphids (Rhopalosiphum padi), which are a non-pest alternative host for the parasitoid wasp Aphidius colemani, which also parasitizes the cotton aphid Aphis gossypii, a common pest of greenhouse cucumbers. The second used fava bean plants infested with pea aphids (Acyrthosiphon pisum), which are an alternative host for Aphidius ervi, a parasitoid wasp that also attacks the potato aphid Macrosiphum euphorbiae, which commonly infests greenhouse tomatoes.
To establish banker plants, we followed standard procedures recommended by our supplier, IPM Labs, who sold us starter kits for our banker plants. Plants were grown in cloth screen cages and were watered from below using plastic trays. When alternate host aphids were well established, we released parasitoid wasps into the cages to parasitize the aphids. After allowing the wasps a week to reproduce, we deployed the banker plants into the greenhouse with our tomato and cucumber crops. In each crop, two banker plants were deployed (two fava beans in tomatoes, two barley in cucumbers). We continued to grow additional banker plants after this point so that old banker plants could be replaced if they died. We did not release wasps onto these additional plants because we expected the wasps from the old banker plants to colonize the new ones.
To assess the viability and efficacy of our banker plants, we collected 3 kinds of data:
- We took weekly counts of aphid mummies (aphids which have been parasitized by wasps) on our banker plants. We did this to see if the wasps were successfully reproducing on the aphids, which would be indicated by an increase in the number of aphid mummies on the plants over time. For barley, we counted aphid mummies on 3 samples of 5 leaves per plant, and for fava beans we counted every aphid mummy on both plants.
- We flagged 12 random plants each from throughout our tomato and cucumber crop to count for aphids and aphid mummies. If the plants we selected didn't have pest aphids on them, we deliberately introduced aphids found on other plants in the greenhouse. Half of these were kept in cages to exclude parasitoid wasps, which was our control group. We counted aphids and mummies from a low, middle, and high leaf on each plant every week. We did this to see if parasitoids were colonizing the crop plants from the banker plants, and to see if they were reducing the aphid population, with our expectation being that caged control plants would have more aphids and fewer aphid mummies than non-caged plants.
- In case we couldn't get aphids to establish on our experimental crop plants, we also scouted the entire tomato and cucumber crop once per week and estimated the severity of aphid infestation using a scale of 0 to 3, which 0 indicating no aphids and 3 indicating a severe infestation. Presence of aphid mummies was also noted. Although this would not result in scientifically useful data due to the lack of a control group, we believed that it may provide useful anecdotal information if we noticed a decline in the severity of aphid infestations over time.
These procedures were repeated for each of our two main greenhouse plantings: Spring, which lasted between March and May; and Fall, which lasted between August and November.
Finally, we kept track of all expenditures on materials or labor involved in maintaining banker plants. Labor costs were calculated at a rate of $20 per hour, and only included time spent maintaining banker plants, not on data collection. This was to allow growers to estimate if the cost of using banker plants is practical for their system.
We had some success establishing the barley banker plants in our greenhouse. During the Spring season, we saw a general increase in the number of aphid mummies recorded on the banker plants. However, plants would often die after only 2-3 weeks, possibly due to high temperatures and damage from the aphids. During the Fall season, we saw very little parasitoid activity on the barley plants. This may have been due to high temperatures in August when we began collecting data, the presence of ants which had infested the banker plants and may have been protecting the aphids; or due the establishment of cotton aphids on our cucumber plants later in the season, which may have been a more appealing host to the wasps and reduced the need for the banker plant.
Another notable discovery was the presence of multiple species of lady beetles and predatory midges that had colonized the barley plants during both seasons. This appears to indicate that this banker plant system can support other beneficial insects in addition to parasitoid wasps.
We could not establish the fava bean banker plant system in the Spring or the Fall. Although we do not know for sure what caused this failure, we believe high temperatures in the greenhouse may have been unfavorable to the establishment of the pea aphids or Aphidius ervi wasps. Regardless, we believe that this banker plant system is not viable for use in the Southeast.
Educational & Outreach Activities
Participation Summary:
Should our project be successful, we intend to use the results to create an informational brochure to inform other growers in the Southeastern region on how to use banker plants for greenhouse pest management, including aspects of aphid identification, choosing the right banker plant system, how to maintain banker plants, and the cost of implementation. This will include an itemized list of costs associated with using banker plants, which will be broken down further into one-time versus repeated costs and will include the estimated number of hours of labor which will be required.
Additionally, we intend to give a presentation on banker plants, including the results of our project, at the 2026 Georgia Organics conference.