Project Overview
Commodities
Practices
Proposal abstract:
One way to enhance the capabilities of biological control agents such as N. californicus is to provide additional resources to improve their survival within the field. Neoseiulus californicus preferentially feeds on spider mites, but they will also feed on other arthropods or even pollen when the spider mite population is too low for survival (McMurtry et al. 2013). Releases of N. californicus could be done early in the season as a preventative treatment, and companion plants could be used to provide resources such as food and shelter for the predatory mites when spider mite populations are low. This could, in turn, prevent the need for multiple releases of predatory mites. The companion plants could also provide resources for other native predators and, thus, increase their numbers in the strawberry planting too.
Sweet alyssum, Lobularia maritima (L.), is a common companion plant in greenhouses and agricultural fields in areas with warmer climates. Sweet alyssum is inexpensive and easy to grow, making it an economical option for small organic growers. It flowers continuously and the pollen and nectar provide food for various beneficial insects (Amorós-Jiménez et al. 2014, Pumariño and Alomar 2004), including N. californicus (Ragusa et al. 2009). Ragusa et al. (2009) found that N. californicus survived on sweet alyssum pollen for 10 days but could not reproduce on it.
A previous study by Hyte et al. (2023) found that the addition of sweet alyssum did not improve the efficacy of N. californicus released against spider mites in strawberries. However, sweet alyssum was planted only at the ends and in the middle of each treatment plot with 12 feet between each clump of sweet alyssum. Only predatory mites on the strawberry plants closest to the sweet alyssum clumps were able to utilize the resources provided by the sweet alyssum. Also, Neoseiulus californicus was only released in the strawberries and not on sweet alyssum. In addition, samples were not collected from the sweet alyssum flowers to determine if N. californicus mites were present. Lastly, the experiment was conducted on a research farm where numbers of other native predators were too low to collect data on the effect sweet alyssum has on their populations.
When plants are damaged by the feeding activities of herbivores, they may release volatiles in response to attract beneficial arthropods. Strawberry plants infested with spider mites are more attractive to N. californicus than those without spider mties (Rezaie et al. 2018). Other factors can also impact volatile release rates in plants, such as interactions with soil microbes. Soil inoculations using beneficial bacteria has been shown to increase the attractiveness of certain plant species to parasitoid (beneficial) wasps (Pangesti et al. 2015). In strawberries, inoculation of the soil with bacteria Bacillus subtilis may increase the attractiveness of the plants to predators such as N. californicus. Our preliminary work has found that soil inoculations using B. subtilis led to significantly reduced mite populations. It was also found that the addition of B. subtilis led to the attraction of the predatory mite, N. californicus, while none were found in untreated control plots. These findings indicate that soil bioinoculants may be used to increase the recruitment of beneficial arthropods in the field.
Our initial objective is to investigate different tactics of deploying sweet alyssum in the strawberry production system to determine the best method of enhancing biological control services. This is based on the hypothesis that the establishment of sweet alyssum will improve biological control services of N. californicus and other endemic predators in the system. Two layouts for interplanting sweet alyssum with strawberries will be compared to the layout from Hyte et al. (2023) and a control treatment where N. californicus mites are released but no sweet alyssum is planted. The first layout involves planting sweet alyssum along one side of each strawberry bed. This should avoid competition between the sweet alyssum and the strawberry plants while providing a continuous stand of sweet alyssum for predators to utilize. Potential drawbacks to this arrangement are that the sweet alyssum could be too far away from the strawberry plants, or it could slow harvest since only one side of each bed will be accessible to pickers. The second layout involves planting the sweet alyssum on the beds in between the two rows of a typical strawberry bed. This keeps the sweet alyssum out of the harvesters’ way and places it close to the strawberry plants.
A secondary objective is to investigate the use of soil bioinoculants for enhancing the biological control of N. californicus. The hypothesis is that the inoculation of the soil with the bacteria, Bacillus subtilis may increase the attractiveness of the strawberry plants to predators such as N. californicus and effectively reduce the population of twospotted spider mites. We will first investigate how inoculation of the soil with B. subtilis may impact spider mite populations alone. Soil inoculation may recruit natural enemies (beneficial arthropods) to provide control of spider mites, as indicated by our preliminary study. Soil inoculants are also known to provide additional benefits to plants such as improved yield and resistance to pests (Esitken et al. 2010, Pappas et al. 2021). However, it is possible that inundative releases of N. californicus are needed to maximize the benefits of soil inoculation. Therefore, we will also investigate the combination of B. subtilis soil inoculation and N. californicus releases. Pairing B. subtilis and N. californicus should enhance biological control of spider mites and lead to a greater reduction in spider mites than either B. subtilis or N. californicus individually. The additional benefits of soil inoculation, improved yield, and resistance to pests should also be seen in this system. While this system has the potential to reduce the grower’s costs by reducing the number of predatory mite releases needed in a season, it is also possible that B. subtilis is effective enough on its own.
Project objectives from proposal:
Both field studies will be conducted at Frog Song Organics (John Bitter) farm in Hawthorne, FL, during the Florida strawberry growing season, which is from mid-October to mid-March. Each study will be replicated twice, once in the 2024/2025 growing season and again in the 2025/2026 growing season. Strawberry plants will be transplanted into the field as plugs at the start of the season. The strawberry variety used will be selected by the grower. All plants will be grown on double-row, raised beds covered in black plastic mulch and be irrigated using a drip irrigation system. Strawberry plants will be allowed to grow for approximately four weeks following transplanting before treatments and sampling begins.
For objective 1 to investigate different tactics of deploying sweet alyssum in the strawberry production system to determine the best method of enhancing biological control services. The sweet alyssum/strawberry plots will be 7.6 m x 2.1 m, consisting of two double-row beds with plants spaced 30 cm. apart (100 plants per plot). The sweet alyssum study will have five total treatments, 1) an untreated control (without predatory mites and sweet alyssum), 2) predatory mite N. californicus, 3) sweet alyssum grown in the beginning, middle, and ends of each plot, 4) sweet alyssum grown continuously along the sides of each bed, and 5) sweet alyssum grown continuously along the center of each bed. Neoseiulus californicus will be released once against twospotted spider mites in the field. The predatory mites will be released at the preventative rate of 25 per m2 after arrival to the laboratory. A small sample of N. californicus, ~ 5 mL of bran, will be examined under a dissecting microscope after arrival and before release to ensure that the mite predators are in good condition. Sweet alyssum will be planted in a greenhouse at the University of Florida in Gainesville, FL. The sweet alyssum will be allowed to grow three weeks before being transplanted into the field at the same time the strawberry plants are transplanted.
For objective 2 to investigate the use of soil bioinoculants for enhancing the biological control of N. californicus. The study plots will be 73.2 x 73.2 cm., consisting of three double-row beds with plants spaced 30 cm apart (32 plants per plot). For both studies, plots will be spaced 7.6 m apart to provide a buffer zone between individual plots. Treatments in both studies will be arranged in a randomized complete block design for each study, with four replicates per treatment. The bioinoculant study will have a total of four treatments, 1) an untreated control (without soil inoculant and predatory mites), 2) predatory mite N. californicus, 3) the soil bioinoculant, and 4) predatory mites and soil bioinoculant combined. The same protocol for N. californicus used in the sweet alyssum study will be used for the treatments containing N. californicus in the bioinoculant study. For the treatments with the soil bioinoculant, Fulzyme™ SP (Bacillus subtilis) will be applied to the soil around every strawberry plant at the recommended rate (2.24 kg/ha) in 20 mL of water. The soil bioinoculant will be applied once every two weeks.
In both experiments, leaf samples will be collected every week from both plots to monitor populations of twospotted spidermite, N. californicus, and other relevant arthropods. Six trifoliates will be randomly collected from each plot and stored in a press-and-seal bag. Leaves will be brought back to the Small Fruit and Vegetable IPM laboratory in Gainesville, Florida, for observation under a dissecting microscope with at least 10x magnification. The number of twospotted spidermite and N. californicus motiles (all non-egg stages) and eggs will be counted and recorded. Other relevant arthropods will also be recorded. While not being observed, leaves will be kept refrigerated (<4.4 °C). All leaf samples will be processed within one week to minimize the effects of leaf decay and mite reproduction on sample quality.
In the sweet alyssum study (objective 1), flower samples from sweet alyssum and strawberry plants will be collected to determine if predators are using the pollen as a food resource. Twenty-five sweet alyssum flowers will be randomly sampled from each plot by placing them in 50 ml centrifuge tubes containing 10 ml of 70% ethanol. Once strawberry flowers begin to appear in November, 5 strawberry flowers per plot will be collected using the same method as for sweet alyssum flowers. Samples will be processed using the shake-and-rinse method developed by Arévalo and Liburd (2007). Briefly, the tubes will be shaken for 1 min and then the contents dumped onto a mesh screen placed over a white 300 ml polyethylene container. The flowers will then be rinsed with DI water and then discarded. The rinsate will then be poured into a 9-cm petri dish and examined under a dissecting microscope. Numbers of predatory mites, other predators, and any pests, such as flower thrips, will be counted and recorded.
Fruits will be harvested from every plot and weighed for both experiments. Harvesting will occur as necessary, up to three times per week, starting from when the first ripe fruit is detected in the field. Collected fruits will be rated as either fresh marketable, processing marketable, or unmarketable. Unmarketable fruits include those that have been severely damaged by pests or fungal pathogens. Processing marketable fruits are those that are not suitable for fresh market sales due to aesthetic injuries, but still useable for processed products such as jam. The remaining healthy fruits are categorized as fresh marketable.