The Potential of Intercropping for Multifunctional Crop Protection in Oilseed Rape (Brassica napus L.)

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.

Companion plants and straw mulch reduce cabbage stem flea beetle (Psylliodes chrysocephala) damage on oilseed rape

“…This is likely to be because of reduced establishment of the Berseem clover in experiment 1 compared with experiment 3. The effect of clover, and especially Berseem clover, on reducing CSFB adult feeding damage has been observed previously 23,39 and is confirmed by our results. Clover has the benefit of not competing with the OSR (pers.…”

“…The effect of companion plants on CSFB larval infestation has already been reported for legumes. 23,24,39 Differences between larval infestation in OSR plants in control plots and plots with companions were found in this study, but they are not consistent from one trial to the other. The fact that we found a strong positive relationship between OSR plant biomass and larval infestation suggests that under conditions of high insect pressure, plant biomass can be a limiting factor for the larvae and that larval infestation is more dependent on host plant biomass than the presence or absence of companion plants.…”

“…The effect of companion plants on CSFB larval infestation has already been reported for legumes 23,24,39 . Differences between larval infestation in OSR plants in control plots and plots with companions were found in this study, but they are not consistent from one trial to the other.…”

“…18 Combining OSR with companion crops, leaving volunteers or stubble trash in the field (here simulated by the sown cereal treatments and the addition of a straw mulch, respectively) have been proposed as potential ways to reduce CSFB infestation. 21,23,24,29,30,39 Many farmers are taking up this practice, 40,41 but there is little evidence to support efficacy. In the current study, four field experiments were conducted to test the effect of different companion plants and other management measures on CSFB attack by both adult and larval stages.…”

“…CSFB is a major pest of OSR in Europe and farmers currently lack reliable options to manage this insect 18 . Combining OSR with companion crops, leaving volunteers or stubble trash in the field (here simulated by the sown cereal treatments and the addition of a straw mulch, respectively) have been proposed as potential ways to reduce CSFB infestation 21,23,24,29,30,39 . Many farmers are taking up this practice, 40,41 but there is little evidence to support efficacy.…”