Clean product is paramount at the propagation stage of woody ornamental production. Since pest problems in propagation can follow the plants through subsequent stages of production, propagators selling infested stock can easily lose customers who will look elsewhere for high quality material. Therefore, an opening exists to gain more widespread acceptance of biological control management techniques in the woody ornamental nursery industry by targeting propagators. We propose a series of experiments to evaluate the efficacy of Amblyseius swirskii Athias-Henriot for sustainable pest management in greenhouse and outdoor woody ornamental propagation. Amblyseius swirskii is a predatory mite that does well in hot, humid climates found in the southeast (Lee and Gillespie 2011, Hewitt et al. 2015). It is a generalist mite that can feed on thrips, whitefly, spider, eriophyid and broad mites (Calvo et al. 2015). In addition to its broad range of arthropod hosts, A. swirskii can survive and reproduce on pollen resources, which can aid in maintaining populations in plant stock when pest pressure is low (Goleva and Zebitz 2013). It can establish on mock orange, Murraya paniculata (L.) Jack (Juan-Blasco et al. 2012) and citrus (Palevsky et al. 2003), suggesting it may be an effective option in other woody ornamental trees and shrubs. These attributes make A. swirskii a promising biological control agent in woody ornamental nurseries, a production system which can be complicated to manage owing to its diversity of crops and grower resistance to non-traditional pest management approaches. We will compare a biological control program using A. swirskii to our conventional scouting/pesticide rotation. We will evaluate the effectiveness A. swirskii introduction/establishment methods as well as the cost involved for biological control and conventional methods in resources and time. This project will produce data on the efficacy of A. swirskii in woody ornamental propagation and inform future research studies and extension programs to optimize the integration of biological control into container and field nursery production in the southeast. In addition to directly serving the needs of woody ornamental producers the SSARE region, this research has a potential to impact woody ornamental production systems across the United States.
We will evaluate the following uses of A. swirskii in the summer of 2016 and 2017.
- Efficacy of A. swirskii on propagated cuttings of Hydrangea cultivars with different leaf trichome densities. The goal of this objective is to determine whether A. swirskii application in propagated cuttings performs equally well on plants with different leaf trichome densities.
- Comparison of banker plants, predator refuges and supplemental feeding in greenhouse propagation. The goal of this objective is to determine whether the use of banker plants, refuge plants and/or supplemental feeding improves the efficacy of A. swirskii in woody ornamental propagation.
- Optimal method for incorporating A. swirskii into outdoor woody propagation beds. This study will look at applications of swirskii directly to propagation beds post rooting.
- Pre-treatment of stock plants with A. swirskii. The results of this study will determine whether inoculating stock plants with predators will carry the population over into propagation and through the misting process. It will also determine whether such a method can provide pest control at a lower cost than broadcast applications directly onto the beds.
We will evaluate the following uses of A. swirskii in the summer of 2016 and 2017.
- Efficacy of A. swirskii on propagated cuttings of Hydrangea cultivars with different leaf trichome densities. The goal of this objective is to determine whether A. swirskii application in propagated cuttings performs equally well on plants with different leaf trichome densities. Hydrangea spp. cultivars with trichome densities ranging from none to > 100 per 0.5 in2 have been identified by the Alexander lab. This trial will work to aid in our prediction of which plants on which A. swirskii will perform best.
- Comparison of banker plants, predator refuges and supplemental feeding in greenhouse propagation. The goal of this objective is to determine whether the use of banker plants, refuge plants and/or supplemental feeding improves the efficacy of A. swirskii in woody ornamental propagation. Two methods of applying predatory mites include broadcast spreading across the crop or introduction of populations on banker plants, which allow the predators to naturally disperse across the crop. In the first treatment, A. swirskii will be applied across the flats at a rate of 5 mites/sq foot and a pest-free flowering ornamental pepper (Capsicum annuum ‘Explosive Ember’) will be placed in the center of the plot as an alternative pollen producing host (1 plot = 4 flats and one pepper). In a second treatment, a banker plant of flowering pepper will be placed in the center of the flats with 5 female A. swirskii applied to the plant 2 weeks in advance to initiate colony development. Two additional treatments will include: a plot with 5 mites/sq ft applied but no pepper plant to act as a refuge or banker and an equivalent plot with a pollen supplement (Nutrimite, BioBest USA Inc. or other suitable pollen alternative).
- Optimal method for incorporating A. swirskii into outdoor woody propagation beds. This experiment will be performed in outdoor propagation beds at Herd Farms Nursery, Belvidere, TN. Propagation beds will be divided into treatment units: (1) conventional production (2+ miticide treatments per season) (2) beds with 5 predatory mites/sq ft applied directly to cuttings and (3) beds with 5 predatory mites/sq ft applied directly to cuttings with supplemental pollen feeding to aid in population establishment.
- Pre-treatment of stock plants with A. swirskii. Predatory mites will be applied to red maple stock plants at Herd Nursery Farms at a rate of 5 mites/square foot of canopy two weeks prior to propagation. Prior to sticking, 10 cuttings from each predator inoculated and control stock plants will be evaluated for the presence of predatory mites and pests. Plant material will be propagated using standard methods. The results of this study will determine whether inoculating stock plants with predators will carry the population over into propagation and through the misting process. It will also determine whether such a method can provide pest control at a lower cost than broadcast applications directly onto the beds.
Evaluations. Predator and pest insect counts (broad mite, thrips, spider mite, whitefly) will be made at 2 week intervals in all trials. At the end of the evaluations, new growth of plants will be measured on 50 randomly selected rooted cuttings in all experimental beds. Growth measurements will be analyzed by analysis of variance. Count data for predators and prey will be analyzed with a generalized linear model with a log link and negative binomial distribution.
- Efficacy of A. swirskii on propagated cuttings of Hydrangea cultivars with different leaf trichome densities. More swirskii were recovered from ‘Ruby’ oak leaf hydrangea than cultivars with lower trichome density (‘Decatur Blue’ and the crosses 1100 and 1200). This lower recovery of predators was despite the presence of prey items on the other cultivars.
- Comparison of banker plants, predator refuges and supplemental feeding in greenhouse propagation. Based on the first trial of this test, it appears the banker plants have the most variability in this system where plant canopies are not touching. The limitation of this method being dispersal ability of the mites from the banker to the crop plants. Mites applied directly to the crop in the presence of pollen – either cattail pollen applied directly with the mites at 500g/ha (0.0046 g/sq ft) or in the form of a refuge crop (‘Explosive Embers’ pepper) were most consistent in suppressing greenhouse pests.
- Optimal method for incorporating A. swirskii into outdoor woody propagation beds. Predators were applied to propagation beds using a makita blower. Mites were applied with or without a pollen supplement. Stock treated liners and untreated liners were also evaluated. Predatory mite recovery was low in all treatments. Predators were recovered from untreated controls as well as treated plants. During peak broad mite activity, the number of broad mites was significantly lower in the stock treated plants than in the untreated and swirskii bed treated plants. The results of the 2017 data should be interpreted cautiously, since lower maple liner establishment in the stock plant beds may have impacted results. Despite lower establishment in the stock beds, the new growth for the tree liners over the 2017 season was not significantly different between the treatments.
- Pre-treatment of stock plants with A. swirskii. Stock plants were treated in May, 1 month prior to propagation at a rate of 0.5 mites per cubic foot. Stock plants were re-sampled in August and September. More predators were recovered on treated stock plant samples compared to untreated controls. However, predatory mites were recovered from control plants as well. Predatory mites were recovered in propagation beds following the mist cycle, suggesting that stock plant applications can survive the misting process during propagation. Due to the difficulty of identifying Phytoseiid mites to species, samples in 2018 will be analyzed using DNA barcoding to determine what % of mites recovered are swirskii.
Educational & Outreach Activities
Led a workshop session and predatory mite training in coordination with Xerces Society and NRCS at the Nursery Research Center in McMinnville, TN. Discussed ongoing research on the topic of biological control in woody ornamental production and landscapes.
Participated in the IPPS Southeastern Nursery Tour and provided growers and other stakeholders with information regarding the use of predatory mites in nursery production. Herd Farm Nursery, Belvediere, TN. October 23rd, 2018.
Karla M. Addesso, Paul A. O’Neal and Lisa Alexander. 2019. Amblyseius swirskii as a tool for pest management in nursery production. 2019 Proceedings of the Southern Nursery Association Research Conference. Vol 63.
Karla Addesso, Paul O’Neal and Anthony Witcher. Amblyseius swirskii as a tool for pest management in nursery production. Pos Entomological Society of America Annual Meeting, Vancouver, BC, Nov 2018.
Karla M. Addesso, Anthony Witcher, Donna Fare and Paul A. O’Neal. 2018. Swirski Mite Controlled-release Sachets as a Pest Management Tool in Container Tree Production. Hort Technology. 28:391-398
Learned about the existence of biological control agents for use in woody ornamental propagation and what pests can be managed with them.
How and when to apply predatory mites to propagation beds.
The importance of keeping stock plants clean to prevent pest entry into propagation beds.
This project demonstrated the opportunities and challenges of using predatory mites under the unique conditions of woody ornamental propagation beds. There were four important outcomes of this study. First, we were able to establish A. swirskii on stock plant rows prior to propagation in June. Second, A. swirskii was able to survive under misting while cuttings were being rooted. Third, we observed that A. swirski establishment differed on different species/cultivars of the same plant genus (‘Ruby Slippers’ Hydrangea was preferred over other hybrids). This result was consistent with previous reports of the mite preferring plants with more trichomes on which to deposit their eggs. Additionally, establishment trials in the greenhouse demonstrated that the mites were able to establish with or without supplemental feeding when prey was abundant, but populations lasted longer when banker plants were present.
Several challenges to predatory mite efficacy in field propagation were identified and will be pursued in future avenues of research. The first challenge was that establishment and spread of mites in propagation beds was hindered by uneven establishment of crops and resulting discontinuous canopies. Predatory mites do best when they are able to disperse freely across a crop in search of food. This is a challenge in propagation beds where the leaves of cuttings do not always touch and ‘dead zones’ can result in predatory mites being unable to disperse unless they move across the ground.
The second challenge was application of predators directly to the beds. When mites were applied directly to the propagation beds, it was observed that the carrier material (and presumably the mites) landed both on the cuttings and on the ground beneath them. The survival of these predators that landed on the soil substrate was not evaluated and it is unknown whether allowing the mites to land on the soil decreased their effectiveness. The third challenge of working in propagation beds was the ability of predators to disperse to adjacent, untreated blocks.
In addition to these challenges, variability in pest populations made evaluating the effectiveness of the predators more difficult. Based on our greenhouse studies, we hypothesize that the presence of flowering plants producing edible pollen or supplemental pollen application might be necessary to improve predatory survival in beds. A final challenge observed in field trials, was the difficulty in recovering and identifying A. swirskii in field collections due to the diversity of native mites present in the system. In the future, we will use PCR methods to confirm identity of predators following morphological identification.
As of the conclusion of this study, we do not feel comfortable recommending the use of A. swirskii in field propagation. Greenhouse use is recommended, provided the mites have sufficient pollen as a backup feed, and growers are aware that plant canopies should be contiguous and that the mites might not reproduce equally well on all plant cultivars, particularly those with more glabrous leaves.
We plan to continue with this work in the future. We are developing a PCR protocol to quickly confirm A. swirskii identity in field collections. We will continue work on bed management and will also look at other species of predatory mites that might be able to establish on stock plants and remain present in the field year after year.