Browsing by Person "Bischoff, Robert Thomas"

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Reducing pesticide use in apple orchards through biological control and mechanical barriers
(2025) Bischoff, Robert Thomas; Petschenka, Georg
With over 20 applications per year, apple is the most pesticide-intensive crop in Germany. Growers are under increasing pressure as the use of pesticides in agriculture comes under greater scrutiny, resulting in more restrictive legislation and a national action plan that calls for a significant reduction in overall pesticide use. Current reduction efforts are largely based on Integrated Pest Management (IPM), which essentially means that all non-chemical plant protection measures, including cultural practices, pest monitoring and biological control, should be used first, and only if pest problems persist is the use of chemical pesticides justified. While there are successful examples of IPM in fruit growing, such as the use of sexual pheromones and granuloviruses to control the codling moth, chemical control remains the dominant means of plant protection. Therefore, considering current political developments, there is a worrying lack of non-chemical control strategies for many important pathogens and pests in apple growing. In this doctoral thesis, we investigated non-chemical alternatives for pest and pathogen control in apple growing and their potential as IPM approaches. The aim was to identify new methods that would provide growers with a realistic alternative to chemical pesticides. We focused on conservation and augmentation biological control and physical methods to assess their potential for reducing pesticide use in apple production. Conservation biological control aims to enhance the biological control of pests by natural enemies and is influenced by a wide range of factors. We investigated the role of predator density, spatial complexity of apple branches and the provision of alternative food resources for predators for the effective control of apple pests. Predator density and the spatial environment of apple branches were crucial components influencing the efficacy of earwig predation on woolly apple aphids. On spatially complex branches, low and medium densities of earwigs failed to fully locate and consume woolly apple aphids, while high earwig densities were able to eradicate woolly apple aphids, including those hidden in spatially complex environments. Provisioning of additional food was investigated using predatory mites and their prey (such as apple rust mites) as a model system. Predatory mites are suspected to be prone to starvation, especially when prey is scarce. To avoid starvation and boost their populations, trees were sprayed with brine shrimp cysts, which are readily accepted as food by omnivorous predatory mites. Although no increase in predatory mites was observed, reduced populations of apple rust mites were found in plots sprayed with shrimp cysts. Other orchard predators, such as predatory flower bugs, may have been promoted and thus mediated the reduction in apple rust mites. In the same trial, the effect of an augmentative release of a predatory mite species naturally occurring in orchards was investigated. No clear effect of the predatory mite release on pest mite populations could be detected. Physical control measures are widely used in fruit growing to protect fruits from abiotic and biotic damage. While anti-hail nets are the dominant cover system used in apple orchards, plastic rain shields and exclusion nets have gained importance due to their ability to prevent scab infections and codling moth immigration, respectively. We compared chemical plant protection regimes under different cover systems, namely anti-hail nets, plastic rain shields, and plastic rain shields combined with exclusion nets, in an apple orchard. Fungicide and insecticide use could be drastically reduced under plastic rain shields and within the exclusion nets, respectively. However, due to microclimatic changes, powdery mildew and secondary pests increased in plots covered with plastic rain shields and plastic rain shields combined with exclusion nets. Despite these side effects, total pesticide use was substantially reduced in the new cover systems without incurring yield losses. These results show that a combination of conservation biological control focusing on predatory earwigs and physical control utilizing plastic rain shields and exclusion nets could be a promising approach to reduce pesticide use in apples. However, the increased costs of new plastic rain shields and exclusion nets compared to traditional anti-hail nets present a major obstacle to their large-scale adoption, and it remains unclear how apples could be produced economically using this approach.