Abstract
Oilseed rape (OSR; Brassica napus) is a globally important crop which is increasingly under pressure from pests, pathogens and weeds. We investigated the potential of achieving multifunctional crop protection benefits by intercropping oilseed rape with legumes. A field experiment was conducted in which winter oilseed rape was intercropped with the annual frost sensitive legumes berseem clover (Trifolium alexandrinum) or spring faba bean (Vicia faba), or with the winter grain legumes winter faba bean or winter peas (Pisum sativum). We tracked damage to winter oilseed rape by autumn and spring pests (slugs and insects), pathogens, weed biomass, as well as oilseed rape and intercrop yield in each treatment. Intercropping treatments resulted in pest damage that was equivalent or lower than in oilseed rape alone. Follow up field and lab assessments for the frost sensitive legume intercrops provided evidence for a reduction in autumn pest damage to OSR. Each legume intercrop had its own benefits and drawbacks in relation to pest, pathogen and weed suppression, suggesting that the plant species selected for intercropping with oilseed rape should be based on the pests, pathogens and weeds of greatest concern locally to achieve relevant multifunctional benefits. Our study provides a framework for further experiments in which the multifunctional effects of intercropping on pests, pathogens and weeds can be quantified.
Highlights
Oilseed rape (Brassica napus L., OSR) is a globally important crop, both for the production of high-value vegetable oil and protein-rich animal feed, and as a break crop in cereal-dominated cropping systems (Angus et al, 2015)
Slug damage in both September and November was low and similar in all treatments perhaps indicating the drawback of plot experiments in being able to evaluate the impacts of intercropping for mobile organisms
Larger field studies are an important step, but these findings indicate that intercropping does not increase slug damage to OSR plants and the cage study illustrates the potential for intercropping to reduce slug damage to OSR
Summary
Oilseed rape (Brassica napus L., OSR) is a globally important crop, both for the production of high-value vegetable oil and protein-rich animal feed (as exhausted rapeseed meal, a by-product from oil extraction), and as a break crop in cereal-dominated cropping systems (Angus et al, 2015). A range of pests, pathogens and weeds constrain OSR production, resulting in intensive pesticide use in conventional farming systems and yield instability in organic systems (ValantinMorison et al, 2007; Williams, 2010; Lutman, 2018; Zheng et al, 2020). New ways to reach profitable OSR yield levels by using more sustainable crop protection methods are urgently needed. Diversification of OSR production by increasing the crop and non-crop plant diversity on the local (field) and landscape scale holds promise for the development of more sustainable crop protection strategies (Isbell et al, 2017). Intercropping OSR with legumes is relatively understudied (but see Dowling et al, 2021), especially when it comes to the implications for crop protection. Intercropping studies rarely evaluate crop protection strategies against multiple crop antagonists simultaneously
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