Intercropping Winter Oilseed Rape (Brassica napus L.) Has the Potential to Lessen the Impact of the Insect Pest Complex

Abstract

Winter oilseed rape (Brassica napus) is a global major crop used for the production of vegetable oil. Typically sown in late summer and grown throughout winter and spring, it allows for interesting cultural practices, such as frost-sensitive intercropping with companion plants. This practice not only provides nitrogen resources much needed by the crop in the spring, but companion plants can also prevent weed growth in autumn, thereby reducing common herbicide use. Additionally, intercropping has the potential to protect the crop from insect pests. During winter 2019–2020, B. napus was grown alone (i.e., as a control) or intercropped with a mixture of faba bean (Vicia faba) and grass pea (Lathyrus sativus); because of the unusually clement weather conditions, the faba bean did not freeze, which allowed for the evaluation of the impact of these companion plants on the insect pest complex in spring. Insect damage by the beetles Psylliodes chrysocephala, Ceutorhynchus napi, and Brassicogethes aeneus was assessed in both treatments. The larval density of P. chrysocephala was significantly lower in the crop grown with service plants. Egg laying and damage by C. napi were significantly reduced when B. napus was intercropped, and the number of B. aeneus captured was significantly lower in the presence of service plants than in the control. Moreover, the yield from oilseed rape was significantly higher in the part of the field with service plants than in the pure crop control. The underlying mechanisms are only partially understood, but intercropping winter oilseed rape with frost-resistant service plants seems to be an ecologically sound practice with a very high level of potential to reduce insect pest pressure and increase crop yield. This may eventually reduce our reliance on chemical inputs in one of the most treated crops.

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

“…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.…”

“…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.…”

“…Observations conducted by Breitenmoser et al found a protective effect of a legume (Vicia faba) on OSR against CSFB larval infestation with an increase in plant biomass. 24 The mismatch between the effect of companion plants on adult CSFB attack and larval infestation could be explained by the different ways in which the companion plants affect host plant location and acceptance for feeding and oviposition. Companion plants could mask the cues, both visual and olfactory, used at distance by the insects during the crop colonization phase, 48 and could explain the difference in feeding damage observed.…”

“…The addition of companion plants can deliver additional ecosystem services such as a reduction in infestation by other insect pests (e.g. aphids, cabbage root fly, stem mining weevils and pollen beetles), 24,[51][52][53] increased biological control services from natural enemies, 54,55 or improved weed management. 56 By providing a more functionally complex habitat in the crop, companion planting systems by their nature of increased plant diversity can also promote an increased diversity of insects within the field 4 and can help farmers to farm more sustainably and mitigate the negative effects of food production on the environment.…”

“…These plants can provide nutrients to the crop and improve its growth (particularly N from nitrogen-fixing bacteria that colonize the rhizosphere of leguminous plants) 19,20 and have also been reported to influence CSFB attack. [21][22][23][24] (ii) The addition of other Brassicaceae species. Some plant species such as turnip rape (Brassica rapa oleifera) are known to be preferred by CSFB over OSR and can be used in trap cropping systems.…”