If you’ve been growing vegetables in the same beds for a few years, you may have noticed plants wilting, stunting, or dying for no obvious reason. The culprit is often invisible - soil-borne pathogens like Verticillium, Fusarium, Pythium, or root-knot nematodes that build up over time. Chemical fumigants exist, but they’re expensive, toxic, and kill beneficial soil life along with the bad.
There’s a plant-based alternative that’s been studied by Australian and international researchers for over 30 years: brassica biofumigation.
What Is Biofumigation?
Every plant in the brassica family - mustard, broccoli, radish - produces sulphur-containing compounds called glucosinolates. These are stored inside the plant’s cells, kept separate from an enzyme called myrosinase.
When you chop the plant and turn it into moist soil, the cells break open. Glucosinolates and myrosinase mix together, and in the presence of water, a chemical reaction produces volatile compounds called isothiocyanates (ITCs). These are the same class of compound that the synthetic fumigant metham sodium breaks down into, but are produced naturally by the plant itself.
These ITCs are toxic to many soil-borne fungi, bacteria, nematodes, and even some weed seeds. CSIRO researchers Kirkegaard and Angus first described this process in 1993 and coined the term “biofumigation.” It has since been confirmed in hundreds of peer-reviewed studies worldwide.
Not All Brassicas Are Equal
Different brassica species produce different types and amounts of glucosinolates, which matters because different pathogens are more susceptible to different ITCs. Research by Sarwar and Kirkegaard (1998) at CSIRO tested multiple ITC types against soil pathogens and found that toxicity varied significantly depending on the compound.
Indian mustard (Brassica juncea) is the most widely studied biofumigant. It produces high concentrations of sinigrin, which converts to allyl isothiocyanate - a highly volatile compound that spreads well through soil air spaces. CSIRO screened over 85 Brassica varieties and consistently found Indian mustard among the highest glucosinolate producers.
Broccoli (Brassica oleracea var. italica) produces a different glucosinolate profile, including glucoraphanin and glucoiberin. It’s a moderate-glucosinolate species - not the highest producer - but it has the strongest published field evidence for Verticillium wilt suppression, based on trials by Subbarao et al. at UC Davis (1999, 2007). Research also shows that incorporated broccoli residues shift soil microbial communities toward beneficial organisms that help fight pathogens.
Daikon radish (Raphanus sativus) contributes its own glucosinolate types (glucoraphasatin, glucoraphenin), but its real strength is physical. Under good conditions, its taproot can extend beyond a metre into the soil, reaching nematode populations and pathogen pockets that surface-only incorporation misses. The root channels left behind also improve water infiltration and aeration for your next crop.
Using a blend of species gives you multiple glucosinolate types attacking pathogens through different chemical pathways - the same principle as a broad-spectrum approach in medicine.
What Does the Research Actually Show?
In the lab, ITCs consistently kill pathogens. In the field, results depend heavily on how well you execute the process. Here’s what the evidence supports:
Strongest evidence: Verticillium wilt suppression (especially with broccoli residues) and root-knot nematode reduction (especially with mustard and radish). Australian field trials by Duff and Firrell (2021) at the Queensland Department of Agriculture confirmed that brassica biofumigants can suppress Sclerotinia, Sclerotium, and Macrophomina across multiple growing seasons.
Promising but variable: Fusarium, Pythium, and Rhizoctonia show suppression in some studies but not others. Gimsing and Kirkegaard (2006) found that even under ideal lab conditions, only about 30% of available ITCs end up active in the soil. Field efficiency is typically lower. This doesn’t mean biofumigation fails - it means technique matters enormously.
One important warning: do not use brassica biofumigation in soil with known clubroot infection. Brassica cover crops can harbour clubroot and worsen the problem. If clubroot is present, avoid planting brassicas for at least 5 years.
The 7-Step Technique That Makes or Breaks It
Research consistently shows that most biofumigation failures are failures of technique. Follow every step:
1. Sow at 8–15g per square metre when soil temperature is above 12°C. Best windows in Australia: Sep–Nov or Feb–Mar.
2. Grow for 8–12 weeks to early flowering - this is when glucosinolate levels peak.
3. Chop finely - the more you break open plant cells, the more glucosinolates meet myrosinase. A mower or line trimmer works for small beds; a flail-mower works for larger areas.
4. Turn into soil within 30 minutes. ITCs are volatile gases. Leave chopped material sitting on the surface, and they evaporate into the air instead of entering the soil.
5. Water heavily immediately after - apply 10–15 mm. Water is chemically necessary for the reaction and helps carry ITCs into the soil.
6. Cover with plastic or tarp for 7–14 days. This traps the volatile ITCs in the soil and extends their contact time with pathogens. Some studies show improved outcomes; at minimum, firm the surface with a roller.
7. Wait 2–3 weeks before planting your next crop. This allows remaining ITCs to dissipate so they don’t affect your seedlings.
The Honest Bottom Line
Brassica biofumigation is real science, backed by three decades of peer-reviewed research. It is not a silver bullet. It will not sterilise your soil the way chemical fumigants do. But when executed correctly with the right species blend, it offers genuine suppressive activity against some of the most damaging soil-borne diseases home gardeners face - while adding organic matter, improving soil structure, and supporting beneficial microbial communities.
What's the difference between biofumigation that works and biofumigation that doesn’t? Technique. Every time.
Shop now: BioFume Intensive - Maximum Strength Biofumigation Seeds
Key Research References
The following peer-reviewed studies and extension publications underpin the claims made in this product description. We encourage growers and advisors to consult these sources directly.
Foundational Biofumigation Research
Angus, J.F., Gardner, P.A., Kirkegaard, J.A. & Desmarchelier, J.M. (1994). “Biofumigation: Isothiocyanates released from Brassica roots inhibit growth of the take-all fungus.” Plant and Soil, 162, 107–112. CSIRO Plant Industry, Canberra.
https://link.springer.com/article/10.1007/BF01416095
Kirkegaard, J.A. & Sarwar, M. (1998). “Biofumigation potential of brassicas. I. Variation in glucosinolate profiles of diverse field-grown brassicas.” Plant and Soil, 201, 71–89.
https://link.springer.com/article/10.1023/A:1004364713152
Matthiessen, J.N. & Kirkegaard, J.A. (2006). “Biofumigation and enhanced biodegradation: Opportunity and challenge in soilborne pest and disease management.” Critical Reviews in Plant Sciences, 25, 235–265.
https://www.researchgate.net/publication/248936768
Glucosinolate Concentrations and ITC Release
Gimsing, A.L. & Kirkegaard, J.A. (2006). “Glucosinolate and isothiocyanate concentration in soil following incorporation of Brassica biofumigants.” Soil Biology and Biochemistry, 38, 2255–2264.
https://www.sciencedirect.com/science/article/abs/pii/S0038071706001246
Sarwar, M., Kirkegaard, J.A., Wong, P.T.W. & Desmarchelier, J.M. (1998). “Biofumigation potential of brassicas. III. In-vitro toxicity of isothiocyanates to soil-borne fungal pathogens.” Plant and Soil, 201, 103–112.
https://link.springer.com/article/10.1023/A:1004381129991
Field Trials and Comparative Studies
Kirkegaard, J.A. et al. (2000). “Field studies on the biofumigation of take-all by Brassica break crops.” Australian Journal of Agricultural Research, 51, 445–456. CSIRO/GRDC.
https://www.publish.csiro.au/cp/AR99106
Duff, J.D. & Firrell, M.C. (2021). “Biofumigation: A cover crop option 12 months of the year to manage three soilborne pathogens ailing the Australian vegetable industry.” Global Journal of Agricultural Innovation, Research & Development, 8, 87–99. Department of Agriculture and Fisheries, Queensland.
https://www.researchgate.net/publication/356581143
Walters, T.W. et al. (2015). “Biofumigation performance of four Brassica crops in a green chile pepper rotation system in southern New Mexico.” HortScience, 50(2), 247–253.
https://journals.ashs.org/hortsci/view/journals/hortsci/50/2/article-p247.xml
Extension Guides and Practical Resources
Oregon State University Extension (2025). “Biofumigation cover crops: Enhancing soil health and combating pests.” EM 9530.
https://extension.oregonstate.edu/catalog/em-9530-biofumigation-cover-crops-enhancing-soil-health-combating-pests
SARE (Sustainable Agriculture Research & Education). “Brassicas and mustards.” Managing Cover Crops Profitably, 3rd Edition.
https://www.sare.org/publications/managing-cover-crops-profitably/nonlegume-cover-crops/brassicas-and-mustards/
Best4Soil (EU). “Biofumigation: Practical information.” Factsheet No. 11.
https://www.best4soil.eu/assets/factsheets/11.pdf
GRDC (Grains Research and Development Corporation). “CSP274 – Exploiting the biofumigation potential of brassicas in farming systems.” CSIRO/GRDC project report.
https://grdc.com.au/research/reports/report?id=6599
Disclaimer: Biofumigation results are influenced by soil type, climate, pathogen species, biomass production, and incorporation technique. The information in this document is based on published research and is provided for educational purposes. It does not constitute a guarantee of specific disease control outcomes. Individual results will vary. Growers are advised to consult local agronomic advice and conduct small-scale trials before committing to large-scale biofumigation programs. Happy Valley Seeds is not responsible for crop outcomes resulting from the use of this product.