Abstract
The use of trap crops to manage pest insects offers an attractive alternative to synthetic pesticides. Trap crops may work particularly well at smaller production scales, being highly amenable where crop diversification and reduction of synthetic inputs are prioritised over yield alone. This paper describes a series of experiments. The first was to demonstrate the potential of turnip rape (Brassica rapa L., var. Pasja) as a trap crop to arrest flea beetles (Phyllotreta spp.) to protect a main crop of cauliflower (Brassica oleracea L., var. Lateman). The subsequent experiments explored two possible approaches to improve the function of the trap crop—either by separating trap and main crop plants spatially, or by introducing companion plants of tomato (Lycopersicon esculentum Mill., cv Amateur) into the main crop. In caged field experiments, feeding damage by flea beetles to crop border plantings of turnip rape far exceeded damage to cauliflower plants placed in the same position, indicating a “trap crop effect”. Neither turnip rape plants nor cauliflower as a border significantly reduced flea beetle damage to main crop cauliflower plants, although the numbers of feeding holes in these plants were lowest where a turnip rape border was used. In similar cages, leaving gaps of 3–6 m of bare soil between turnip rape and cauliflower plants significantly reduced feeding damage to the latter, as compared to when plants were adjacent. The results of a small-scale open field trial showed that a turnip rape trap crop alone reduced flea beetle damage to cauliflower, significantly so later in the season at higher pest pressures, but that addition of tomato companion plants did not improve pest control potential.
Highlights
Farm businesses and subsistence producers at all scales are under increasing pressure to decouple crop production from inputs of synthetic pesticides [1]
The aim of the current study was to demonstrate this by: (1) confirming that a trap crop could attract flea beetle feeding damage and protect a main crop, and (2) exploring the potential of spatially separating trap and main crop plants, or introducing companion plants of tomato within the crop, to ascertain if either approach could improve the effectiveness of the trap crop for pest control
There was no statistically significant difference between treatments in the number of feeding holes made by flea beetles in the leaves of the ‘inner’ main crop cauliflower plants, a p-value approaching significance was obtained (F(2,24) = 2.581, p = 0.097, cage aspect and interaction with treatment not significant) (Figure 4)
Summary
Farm businesses and subsistence producers at all scales are under increasing pressure to decouple crop production from inputs of synthetic pesticides [1]. Approaches to pest management that pose reduced risks to non-target organisms in the environment, avoid issues of pest resistance, promote biodiversity and mitigate consumer exposure to pesticide residues in produce are of particular interest to all stakeholders involved in the food supply chain. Whilst development of a new generation of (bio)pesticides offers one approach to reducing the use of ‘traditional synthetic pesticides’ [2], inclusion and management of additional flora in the farmed environment could provide a solution. By substituting external inputs of any kind with additional plant diversity, promotion of “associational resistance” can be achieved [3], either by manipulation of resource concentration effects, or by the promotion of biological control [4].
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