- Fruits: berries (strawberries)
- Education and Training: decision support system, extension, on-farm/ranch research
- Pest Management: biological control, field monitoring/scouting, integrated pest management
Farmers are requesting in-depth knowledge about how to successfully integrate UAS (Unmanned Aerial Systems) into strawberry production to improve management practices. California produces 88% of US strawberries, with an annual value of approximately $2.6 billion, and the California Strawberry Commission identifies spider mite management a key research priority. Little is known about the spatio-temporal dynamics of spider mites in strawberry, and consequently, about the optimal timing to release predatory mites, their natural enemies. In this multi-disciplinary project, we will demonstrate that airborne remote sensing can be used to detect and diagnose spider mite hotspots and therefore pinpoint when and where predatory mite releases are needed. This three-year project will lead to the following outcomes: 1) demonstrate relationships between spider mite presence and unique changes in leaf reflectance features acquired from strawberry plants; 2) a spatially optimized, reliable and practically feasible sampling plan for spider mites in strawberry fields; 3) hyperspectral airborne remote sensing-based characterization of spider mite hotspots to spatially optimize releases of natural enemies. Deployment of novel, labor-extensive, and precise airborne remote sensing technologies to monitor crop health and mitigate pest risks, as well as aerial predator distribution techniques, are highly compatible with existing strawberry management practices. Educational outreach involves lectures on spider mite sampling at grower and ag professional meetings throughout the California strawberry growing region. Growers outside this area will be reached through publications in trade journals and other grower media. Both the educational outreach and research outcomes are easily transferable to strawberry growing regions elsewhere, and could be expanded to include monitoring for other pests and pathogens. This project will enhance efficacy of biocontrol agents and reduce dependence on miticides, enhancing sustainability of spider mite management practices in strawberry.
The research component of this project is based on two fundamental hypotheses (both supported by preliminary data):
1) Spider mite outbreaks are most likely in strawberry plants under abiotic stress (imbalances or deficiencies of nutrient fertilization or inadequate irrigation), and abiotic stress is closely linked to descriptive leaf traits (toughness and micro- and macro-element composition).
2) Airborne remote sensing data of strawberry canopy can be used to detect and map descriptive leaf traits (toughness and micro- and macro-element composition), which are important indicators of risk of spider mite outbreaks.
The educational outreach component of this project is based on the hypotheses that:
1) sampling of strawberry fields can be optimized through development of reliable and practically feasible sampling plans.
2) use of predatory mites for control of spider mite outbreaks in strawberry can be significantly improved through better detection (either through remote sensing or sampling) of spatio-temporal aggregations of emerging spider mite outbreaks.
As part of this 3-year project, we will address the following numbered objectives:
Objective 1: Experimental characterization of the relationship between: 1) leaf micro- and macro-element composition and leaf reflectance, and 2) spider mite-induced stress and leaf reflectance. This has been done in project years 1 (October – December 2017), 2 (January – March 2018), and 3 (February – April and September – November 2019). Quantifiable outcomes: 1) A research article describing a model of the factorial relationships between leaf micro- and macro-element composition, leaf reflectance, and spider mite-induced stress, while varying biotic stressors (i.e., spider mite, beet armyworm, whitefly, and non-infested plants). This because spider mites are rarely the only problematic arthropods in a strawberry field. 2) A research article describing a model of the aforementioned factorial relationships while varying plant fertilizer levels (i.e., 50%, 100%, and 200% fertilizer). This objective has started in October 2017 and has been completed in March 2020. Two replicates were performed for the first experimental study, in project year 1 and project year 2. Two replicates were performed for the second experimental study, both in project year 3. Preliminary results of both studies are described in the section “Results and discussion”.
Objective 2: Characterization of the spatio-temporal distribution of spider mites and their natural enemies in project year 2 (May – September 2018). Quantifiable outcomes: 1) Spatio-temporal data sets from 120 combinations of commercial strawberry field, sampling event, and growing season, 2) A research article describing a spatially optimized sampling plan for spider mites in strawberry fields. Moreover, sampling of spider mites in commercial strawberry fields will provide valuable insight into spatial trends in the distribution of emerging infestations and their spread. That is, we predict to document consistent “edge-effects” of spider mite infestations with highest spider mite densities near strawberry field edges, as edge-biased spatial distributions are commonly observed (Nguyen & Nansen, 2018). Quantitative information about prevailing spatial distribution patterns is critically important as part of optimizing both sampling/detection and releases of natural enemies. This objective has started in May 2018, and was completed in March 2020. We have collected over 1,500 strawberry samples on 4 commercial farms, both managed conventionally and organically. We are currently analyzing the data, and preliminary results are described in the section “Results and discussion”.
Objective 3: Hyperspectral airborne remote sensing-based characterization of hotspots with emerging spider mite outbreaks in project years 1 (May – July 2017) and 2 (May – July 2018). Quantifiable outcomes: 1) Hyperspectral airborne remote sensing data sets from 120 combinations of commercial strawberry field, sampling event, and growing season, 2) A research article describing the use of hyperspectral airborne remote sensing to spatially optimize releases of natural enemies to control spider mite outbreaks in strawberry fields, 3) A review article summarizing the available literature on use of drones in sustainable agriculture (published in December 2019). This objective has been completed in March 2020. Preliminary results are described in the section “Results and discussion”.
Objective 4: Educational outreach on how to improve spider mite sampling and on the potential of UAS in strawberry management and beyond. Quantifiable outcomes: 1) Dissemination of project results to a minimum of 300 growers and other stakeholders. 2) Publication of a review paper on use of UAS in sustainable agriculture; the paper will be distributed to the California Strawberry Commission and other stakeholder organizations. This objective has been completed in March 2020.