Sustainable production of sweet cherry: maximising benefits from ecosystem services

To meet rising food demand, agricultural production has increased dramatically in the past 50 years. This has involved a greater proportion of land being converted to agriculture, combined with the use of inorganic fertilisers and extensive use of Plant Protection Products (PPPs). However, this has caused habitat and biodiversity loss, soil degradation, and land fragmentation and, as a result, pollinators and natural enemies of crop pests, on which many economically important crops depend, have also been negatively impacted. Sweet cherry is an economically important pollinator-dependent crop with a global annual production of around 2.56 million tonnes; an increasing demand has been met through new intensive production systems. If a greater reliance is to be placed on beneficial arthropods as part of more sustainable cherry intensification, their abundance and diversity must be supported by meeting their requirements such as alternative resources and shelter. Wildflower habitats are an approach that can enhance wild pollinators and natural enemies throughout the growing season supporting Conservation Biological Control as part of Integrated Pest Management programmes. In this PhD, to enhance the sustainability of sweet cherry production, native perennial wildflower strips (1 x 95 m) were established in alleyways in ten sweet cherry protected orchards in the West Midlands, UK. The effect of wildflower strips on natural enemies and pollinators and pest regulation and pollination services were investigated over a three-year period (2017 to 2019). The effects on abiotic factors, and fungal disease incidence were also considered. In each orchard, two different management treatments of sown wildflowers were compared; a Standard Wildflower Strip (SWS) managed with a single cut in September; and an Actively Managed Wildflower Strip (AMWS) managed with regular cutting to 20 cm height. These treatments were compared with unsown Control Strips (CS). Wildflower establishment and development over the three-year period was successful, with a cover of 75.7% (± 6.1) by year three. Both wildflower strip treatments increased the number of floral units by over 300% compared to CS, increasing the potential nectar and pollen resources for beneficial arthropods. Wildflower habitats were associated with an increased abundance of natural enemies in the alleyways (73.9% increase) and adjacent cherry trees (12.9% increase) compared to the CS. Resulting pest regulation services were also greater with 25.3% more aphids being depleted from baited cards in wildflower strips. Pollinating insects underpin cherry yields, with 30.2% fruit set in the presence of insects compared to only 1.4% when excluded. Pollinating insects also responded positively to wildflower strips with increased abundance. However, during the cherry blossom period only abundance was greater in AMWS with an associated 6.1% increase in fruit set. No differences between treatments were recorded with regards to humidity and temperature under protective covers, and the incidence of fungal disease was not increased. Supplementary pollination experiments indicated pollination deficits in the study orchards with the value of pollinating insects to sweet cherry in the UK estimated at £11.3 million (£14.7K ha-1). Although increases to £25.6K ha-1 could be achieved if pollination was optimised. In conclusion, this study has shown that wildflower strips can be effective in enhancing ecosystem services delivered by natural enemies and pollinators in intensive sweet cherry orchards under protective covers. The establishment of wildflower strips in alleyways between rows is therefore recommended for cherry growers, with greater benefits being delivered with regular cutting to a height of 20 cm (AMWS). The adoption of wildflower strips could allow growers to reduce PPP inputs and still increase cherry yields and profitability

Wildflower Strip Establishment for the Delivery of Ecosystem Services in Sweet Cherry Orchards

The practice of introducing wildflower habitats in cropped areas is an approach that can be used to enhance ecosystem services. The value of such an approach will be affected by the establishment success of the sown species. To investigate this, 12 strips of wildflower habitat were established in alleyways between rows of cherry trees at three sites in the West Midlands (UK). The establishment of plants in sown strips was compared to six untreated alleyways that received conventional management. Eight forb species and one grass species was sown in strips measuring 1 m × 95 m. The establishment success of the sown species and their contribution to the vegetation of the alleyway was determined using percentage cover assessments in replicate quadrats. Dactylis glomerata, Leucanthemum vulgare, Prunella vulgaris and Lotus corniculatus established most consistently and with greater cover values in the sown strips. However, the sown strips were also associated with a greater abundance of unsown species, some of which are classed as weeds

Wildflower strips in polytunnel cherry orchard alleyways support pest regulation services but do not counteract edge effects on pollination services

Sweet cherry (Prunus avium) production relies on modern growing practices like polytunnel coverings to improve yields but this may interrupt arthropod-mediated ecosystem services. The distribution of beneficial arthropods (natural enemies and flower visitors) and the ecosystem services they provide may be affected under polytunnel systems, especially at orchard edges. Across 10 commercial cherry orchards grown in polytunnels, we explored how wildflower strips mitigated edge effects on beneficial arthropods and pest regulation and pollination services. In each orchard, we established a standard wildflower strip (SWS; single cut at the end of the season) and an actively managed wildflower strip (AMWS; regularly cut at 20 cm height) between tree rows and compared this to a conventional control strip (CS). We recorded natural enemies in alleyways and cherry trees post-cherry anthesis (flowering) and flower visitors during and post-cherry anthesis at different distances from the orchard edge (2017–2019). In 2019, we deployed insect prey bait cards in trees to measure pest regulation services and recorded fruit quality (2017–2019) and fruit set (2018–2019) to measure pollination services. Distance from the orchard edge did not affect natural enemy density or diversity in any year or under any alleyway treatment, but pest regulation services decreased towards orchard centres with CS (by 33.0% reduction). Flower visitor density (−34% individuals) and diversity declined with distance from the edge during cherry anthesis. For post-cherry anthesis, marginal negative edge effects were observed for flower visitor density and diversity and behaviour. Overall, fruit set decreased towards the orchard centre while fruit quality increased. Our results suggest that wildflower strips are an effective tool to mitigate edge effects on pest regulation services but have limited effects on flower visitors and pollination

The potential of wildflower strips to enhance pollination services in sweet cherry orchards grown under polytunnels

Sweet cherry production benefits from insect pollination, but the extent to which wildflower strips can boost pollinator visitation under polytunnels is unknown. Wildflowers were established in alleyways between tree rows under polytunnels in 10 commercial cherry orchards. Their management involved either a single cut in September (Standard Wildflower Strips (SWS)) or being actively maintained to 20 cm with regular cutting (Actively Managed Wildflower Strips (AMWS)), compared with unsown Control Strips (CS). Flower visitors of cherry and wildflowers were recorded by visual observations for 3 years (2017–2019), while cherry production (quantity and quality) was assessed in 2019. In total, 67 visitor species were identified; managed commercial species (Apis mellifera and Bombus terrestris) made up ~74% of all records. During the cherry blossom period (anthesis), AMWS had the highest visitor density to cherry blossoms compared with CS and SWS but no significant difference in harvestable fruit was recorded. After anthesis, greater visitor density, diversity and richness were observed in both wildflower treatments compared with CS, being greatest in SWS, which was consistent with differences in floral communities between treatments. Although visitor density was not correlated with fruit set, pollinating insects were key for fruit yields and quality. Fruit set was ~17% from blossoms exposed to visitors compared with <1% when excluded. Furthermore, hand pollination resulted in ~32% fruit set, indicating greatest pollination deficits in CS (~50%) compared with AMWS (~28%) and SWS (~35%). Synthesis and applications. Sweet cherry is highly dependent on pollinators to underpin commercial yields, and pollination deficits exist under polytunnels. Growers should, therefore, reconsider their pollination strategies and look to combine effective pollinator management with polytunnel use to mitigate deficits; establishing and actively managing wildflowers in alleyways could enhance wild visitors and pollination

Wildflower strips in polytunnel cherry orchard alleyways support pest regulation services but do not counteract edge effects on pollination services

Sweet cherry (Prunus avium) production relies on modern growing practices like polytunnel coverings to improve yields but this may interrupt arthropod-mediated ecosystem services. The distribution of beneficial arthropods (natural enemies and flower visitors) and the ecosystem services they provide may be affected under polytunnel systems, especially at orchard edges. Across 10 commercial cherry orchards grown in polytunnels, we explored how wildflower strips mitigated edge effects on beneficial arthropods and pest regulation and pollination services. In each orchard, we established a standard wildflower strip (SWS; single cut at the end of the season) and an actively managed wildflower strip (AMWS; regularly cut at 20 cm height) between tree rows and compared this to a conventional control strip (CS). We recorded natural enemies in alleyways and cherry trees post-cherry anthesis (flowering) and flower visitors during and post-cherry anthesis at different distances from the orchard edge (2017-2019). In 2019, we deployed insect prey bait cards in trees to measure pest regulation services and recorded fruit quality (2017-2019) and fruit set (2018-2019) to measure pollination services. Distance from the orchard edge did not affect natural enemy density or diversity in any year or under any alleyway treatment, but pest regulation services decreased towards orchard centres with CS (by 33.0% reduction). Flower visitor density (-34% individuals) and diversity declined with distance from the edge during cherry anthesis. For post-cherry anthesis, marginal negative edge effects were observed for flower visitor density and diversity and behaviour. Overall, fruit set decreased towards the orchard centre while fruit quality increased. Our results suggest that wildflower strips are an effective tool to mitigate edge effects on pest regulation services but have limited effects on flower visitors and pollination

Wildflower strips in polytunnel cherry orchard alleyways support pest regulation services but do not counteract edge effects on pollination services

Sweet cherry (Prunus avium) production relies on modern growing practices like polytunnel coverings to improve yields but this may interrupt arthropod-mediated ecosystem services. The distribution of beneficial arthropods (natural enemies and flower visitors) and the ecosystem services they provide may be affected under polytunnel systems, especially at orchard edges. Across 10 commercial cherry orchards grown in polytunnels, we explored how wildflower strips mitigated edge effects on beneficial arthropods and pest regulation and pollination services. In each orchard, we established a standard wildflower strip (SWS; single cut at the end of the season) and an actively managed wildflower strip (AMWS; regularly cut at 20 cm height) between tree rows and compared this to a conventional control strip (CS). We recorded natural enemies in alleyways and cherry trees post-cherry anthesis (flowering) and flower visitors during and post-cherry anthesis at different distances from the orchard edge (2017–2019). In 2019, we deployed insect prey bait cards in trees to measure pest regulation services and recorded fruit quality (2017–2019) and fruit set (2018–2019) to measure pollination services. Distance from the orchard edge did not affect natural enemy density or diversity in any year or under any alleyway treatment, but pest regulation services decreased towards orchard centres with CS (by 33.0% reduction). Flower visitor density (−34% individuals) and diversity declined with distance from the edge during cherry anthesis. For post-cherry anthesis, marginal negative edge effects were observed for flower visitor density and diversity and behaviour. Overall, fruit set decreased towards the orchard centre while fruit quality increased. Our results suggest that wildflower strips are an effective tool to mitigate edge effects on pest regulation services but have limited effects on flower visitors and pollination

Wildflower strip establishment for the delivery of ecosystem services in sweet cherry orchards

The practice of introducing wildflower habitats in cropped areas is an approach that can be used to enhance ecosystem services. The value of such an approach will be affected by the establishment success of the sown species. To investigate this, 12 strips of wildflower habitat were established in alleyways between rows of cherry trees at three sites in the West Midlands (UK). The establishment of plants in sown strips was compared to six untreated alleyways that received conventional management. Eight forb species and one grass species was sown in strips measuring 1 m × 95 m. The establishment success of the sown species and their contribution to the vegetation of the alleyway was determined using percentage cover assessments in replicate quadrats. Dactylis glomerata, Leucanthemum vulgare, Prunella vulgaris and Lotus corniculatus established most consistently and with greater cover values in the sown strips. However, the sown strips were also associated with a greater abundance of unsown species, some of which are classed as weeds

Active management of wildflower strips in commercial sweet cherry orchards enhances natural enemies and pest regulation services

To protect sweet cherry (Prunus avium L.) against pests in commercial orchards, pesticides are frequently used, but some have adverse environmental impacts. Natural enemies can deliver protection against pests but compared to the surrounding non-crop habitat their abundance is usually low in intensively managed agricultural systems. Wildflower interventions established for Conservation Biological Control as part of Integrated Pest Management (IPM) can reinstate habitat for natural enemies within cropped areas and enhance natural pest control. Over a three-year period, this more sustainable approach to crop protection was investigated in eight sweet cherry orchards protected under polytunnels in the West Midlands (UK). Wildflower strips were established in alleyways between rows of cherry trees and managed under two cutting regimes, Standard Wildflower Strips (SWS) (a single cut in late September) and Actively Managed Wildflower Strips (AMWS) (regularly cut to a height of 20 cm throughout the growing season). These were compared to unsown Control Strips (CS) (original vegetation dominated by grass species). To investigate natural enemy populations and pest regulation services, direct search, Vortis suction sampling, beat sampling, and aphid bait cards were used. Araneae (40.0% of records) and parasitoid wasps (22.7%) were the most frequent natural enemies recorded in alleyways, whilst Anystidae (51.8%) and Araneae (20.8%) were most abundant on cherry trees. Wildflower treatments almost doubled the abundance of natural enemies in alleyways, and increased abundance in cherry trees by ~15% compared to the CS. Wildflower strips increased predation of aphids (bait cards) in cherry trees by 25%. No difference in natural enemy abundance, richness or pest control was recorded between the two wildflower management regimes. Differences in natural enemy abundance and predation rates were detected despite the continued use of pesticides by growers (an average of 5.4 (± 0.4) applications per orchard per year). This study demonstrates that creating wildflower habitat in commercial sweet cherry orchards under polytunnels can boost natural enemies and the associated pest regulation services. Relative to CS, the novel grower-friendly approach of maintaining wildflower strips at a height of 20 cm with regular cutting increased flower resource availability and pest regulation services, demonstrating the potential for growers to adopt this approach as part of a robust IPM strategy

Field Suppression of Spotted Wing Drosophila (SWD) (Drosophila suzukii Matsumura) Using the Sterile Insect Technique (SIT)

Drosophila suzukii (spotted wing drosophila—SWD) is an economically important pest of soft and stone fruit worldwide. Control relies on broad-spectrum insecticides, which are neither fully effective nor environmentally sustainable. The sterile insect technique (SIT) is a proven, effective and environmentally friendly pest-management tool. Here, we investigated, for the first time, the potential of using SIT to control D. suzukii in field conditions without physical barriers that limit insect invasion. A proprietary method of rearing and irradiation with X-rays was used to obtain males that were &gt; 99% sterile. Sterile males were released twice per week from April to October 2021 on a site in Kent, UK, where everbearing strawberries were grown in open polytunnels. The infestation of wild female D. suzukii was monitored weekly using red sticky traps with dry lure at the treated site and at two similar control sites that did not receive sterile male releases. Releases of sterile males suppressed the wild female D. suzukii population by up to 91% in comparison with the control sites. We thus demonstrated the feasibility of SIT to achieve season-long control of D. suzukii using early, sustained and dynamically targeted releases of sterile males. This provides a promising environmentally friendly method to control this important pest

Wild bees are less abundant but show better pollination behaviour for sweet cherry than managed pollinators

Pollinating insects provide pollination services to many crop species, including sweet cherry (Prunus avium L.), and this can be delivered by both managed and wild pollinators. Managed pollinators are often used to pollinate a range of fruit crops, but increasingly the role of wild insects is being studied. However, the importance of pollinator species depends on their relative abundance and pollination effectiveness, which depends on their foraging activity and their variability throughout the day. In this study, insect visitors of blossoms were observed in commercial sweet cherry orchards to explore abundance, diversity and pollination foraging behaviour of different insect pollinator groups throughout the day. A total of 1,174 pollinators from 31 different species were recorded visiting cherry blossoms over 2 years, of which 71.0% of total visits were by managed pollinators (western honeybee, Apis mellifera L. and buff-tailed bumblebee, Bombus terrestris L.) compared to 29.0% by wild pollinators. On average, solitary bees visited a sweet cherry blossom for the longest duration (20.7 (±2.0 SE) seconds), whereas wild queen bumblebees visited the greatest number of flowers per minute (mean of 19.0 (±1.3 SE)). As both these pollinator groups contacted cherry stigmas more often and moved more frequently between tree rows than managed bees and hoverflies, they are more likely to facilitate cross-pollination. The different pollinator groups also showed variation in behavioural parameters throughout the day, but less variation was recorded when all pollinator groups were considered altogether. This suggests diverse pollinator communities might be expected to provide a more stable pollination service to sweet cherry. This study demonstrates that whilst cherry blossoms were more frequently visited by managed pollinators, wild solitary bee and bumblebee behaviours are likely to be more effective at enhancing pollination in sweet cherry orchards, which, in turn, might lead to increased yields