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.