Establishing biofumigation as a sustainable replacement for pesticides

A number of key findings will either direct future research or influence biofumigation best practice:

• Seedling density has little effect on isothiocyanate-release potential (in terms of biomass and glucosinolate concentration) of biofumigant crops at incorporation
• Optimum incorporation time for a biofumigant crop is when plants are flowering
• The major biofumigant compound (allyl ITC) is lost rapidly from soil after brown mustard incorporation, but other, less well-studied chemicals (dimethyl sulphide and dimethyl disulphide) increase in soil over time and may contribute to pest/pathogen toxic effects.
• Volatile halide compounds are produced by root of growing brassicas and are lethal to potato cyst nematode juveniles at very low doses.
• Standard glucosinolate extraction techniques were improved to provide a new method that give cheaper, quicker and more accurate results.
• An imaging and detection system has been developed to monitor behaviour of nematodes in transparent microcosms. This can be used to assess effects of biofumigation chemicals.
• Two soil-borne fungal pathogens; Rhizoctonia solani and Verticillium dahlia are differentially sensitive to a range of isothiocyanates, but symptoms of R. solani on potato were not reduced by biofumigation with brown mustard in a glasshouse trial.
• In raised bed trials, there was a significant decline in viability of potato cyst nematodes both during growth of a brown mustard crop and after its incorporation. This outcome differed with soil type.
• In polytunnel trials, boxes filled with soil known to contain high levels of FLN, biofumigation with either brown mustard or radish Bento had no significant effect on any of the growth parameters of subsequently cultivated raspberry plants, on the total number of nematodes in the soil, or on the number of Pratylenchus and Longidorus nematodes in the soil.
• Two trials investigated biofumigation with either a brown mustard or radish (Bento) prior to drilling a carrot crop. In one trial, there was no significant effect on subsequent yield of carrots or the proportion of FLN-damaged carrots.  In the second trial, biofumigation with brown mustard, but not radish, increased the proportion of pre-pack class carrots, but not the total yield.  The percentage of carrots displaying FLN damage was significantly reduced in the plots treated with brown mustard compared to fallow plots.

Soil-borne pests and pathogens, including many nematode and fungal species, are major constraints to profitable crop production in the UK. The problem will be exacerbated in the immediate future by removal of approved chemical control strategies. New approaches are required that have broad efficacy and are suitable for use on a wide range of crops. Biofumigation involves the incorporation into soil of brassicaceous plants, which produce a range of secondary metabolites including glucosinolates, able to control pests and pathogens. However, inconsistencies in efficacy and a lack of detailed data on deployment under a range of agronomic situations threaten the widespread uptake of this technique for sustainable pest control.

Aim:

To provide a fundamental understanding of the biochemistry of metabolic processes of brassica accessions underpinning effective biofumigation strategies.

Objectives:

1. Measure the glucosinolate profiles of selected biofumigant plants and determine how they alter over the course of plant development and in response to environmental factors.
2. Characterise novel compounds, other than glucosinolates, in plant accessions shown to be effective against pests and pathogens.
3. Establish optimal agronomic practices for the management of G. pallida using biofumigation.
4. Determine the effectiveness of biofumigation against trichodorids and longidorids on potato, carrot and soft fruit.
5. Establish the potential of biofumigation to control the fungal pathogen Rhizoctonia solani.
6. Analyse the impact of biofumigant crops on biotic aspects of the below ground food web.