The BHU Future Farming Centre

Information - Weed Management

Disclaimer, copyright and licensing

Culinary oils as herbicides

The FFC has studied the effect of a range of culinary oils for their herbicidal effects on a range of weed and crop species.  It showed that some oils could kill some plants, and rapeseed oil was the best overall performer.  It is hoped that this preliminary look will be a springboard for future research.

Read the report as an FFC Bulletin article or download a PDF version of the report.

Non-chemical management of docks (Rumex)

This extension report, originally written by the FFC for Pesticide Action Network-Europe (PAN_EU), lays out all the key requirements and techniques for non-chemical management of docks.

Download report as a PDF

Download the PAN-EU report "Alternative methods in weed management to the use of glyphosate and other herbicides: Integrated weed management - many little hammers"

Mini-ridgers:  Lethal burial depths for controlling intrarow weeds

Updated research that supersedes the research previous report "The final frontier: Non-chemical, intrarow, weed control for annual crops with a focus on mini-ridgers" (see below) and is a stand alone mini-ridgers information source.

Download the report as a PDF file, or read the full report as an FFC Bulletin article.

Electrothermal weeder demonstration project

The BHU Future Farming Centre is launching a project to develop an electrothermal demonstration weeder for pasture and cropping weeds.  Electrothermal is both a ‘back to the future’ technology in that it has been extensively researched in the past, but lost out to herbicides, and a game changer as it is the only thermal and indeed non-chemical weeding technology that has a systemic effect, like glyphosate does, as it can kill the roots.  More info

False and Stale Seedbeds: The most effective non-chemical weed management tools for cropping and pasture establishment

Globally there is a growing need for non-chemical weed management tools due to multiple and increasing issues with herbicides.  Of the many non-chemical techniques ‘false seedbeds’ stands out due to its efficacy, ease of use, reliability and low cost plus it can be used for any kind of plant establishment from pasture through arable to vegetables.  Contrary to many peoples view of non-chemical weeding as being focused on killing weeds in the growing crop, this is a tillage / cultivation based technique, that can be used for any crop as it undertaken pre-planting. 

Download this report as a PDF file, or read the full report as an FFC Bulletin article.

The final frontier: Non-chemical, intrarow, weed control for annual crops with a focus on mini-ridgers

Addendum May 2018.  The FFC has undertaken further research on burial that supersedes the research in this report.  Please see the report “Mini-ridgers:  Lethal burial depths for controlling intrarow weeds” (see above) for information on burial depths.  This report still has a range of valuable information on intrarow weeding tools that the new report does not cover. 

Non-chemical weeding machinery has made huge advances over the last couple of decades and the combination of modular parallelogram hoes and computer guidance interrow hoeing is now a straightforward field operation.  The final frontier is now intrarow weeding between the plants, and this is being aggressively pushed back with a combination of both high and low tech approaches.  Download this report as a PDF file, or read the full report as an FFC Bulletin article.

Non-chemical weed management course handbook for sale

As part of the Sustainable Agriculture Series, the handbook from the 2014 non-chemical seminar workshop is available for purchase

Non-chemical management of Californian thistle: Subsoiling, and other less common techniques

Extension article on less common techniques for controlling and managing Californian thistle including subsoiling / deep ripping, that has the ability to immediately kill Californian thistle and therefore eliminate it from a field in one go.  Download report as a PDF file, or also view it as a FFC Bulletin article

Intrarow Soil Thermal Weeding 2013

Intrarow Soil Thermal Weeding (ISTW) is considered to be the only direct non-chemical substitute for herbicides, and that can outperform weed killers in a number of ways including: broad spectrum, i.e. kills all therophyte weeds; has a residual period as long as the crop’s production cycle; can be used in any row crop (economics notwithstanding); has a nil withholding period; has no risk of releasing chemicals into the environment; has exceptional reliability levels (i.e., always works); and has no risk of evolved resistance.  

FAR (Foundation for Arable Research) Non-chemical weed management articles

Non-chemical weed management: Stale and false seed beds (links to FAR website)

Non-chemical weed management - harvest and the weed seedbank (links to FAR website).

Non-chemical weed management - mechanical weeding (links to FAR website).

Steam and fish fertilisers: A potential organic systemic herbicide?  2006

The full colour booklet (hard copy) from the Non-Chemical Weed Management Workshop held on the 19 June 2012 is available for purchase at a cost of NZ$30.00 + GST inc. P&P.The booklet includes all the slides from the presentations in PowerPoint 'handout' format of six slides per page.  The booklet is 48 pages long and contains 248 slides of information, including references.To purchase a copy please email This email address is being protected from spambots. You need JavaScript enabled to view it.

The BHU Future Farming Centre

Information - Weed Management

Intrarow Soil Thermal Weeding (ISTW)

Disclaimer, copyright and licensing

The FFC's work on thermal weeding including intrarow soil thermal weeding has been featured on TV1's Rural Delivery program.

This research was funded by the Sustainable Farming Fund, project number L12-104. 

1. Expanding the Potential of Intrarow Soil Thermal Weeding. May 2013. Report number 4-2013 Version 2. Jump to Executive Summary

2. Intrarow Soil Thermal Weeding Supplemental Report:An Analysis of the Potential for Ex-field Heat Treatment. July 2013. Report number 6-2013

3. Intrarow Soil Thermal Weeding Supplemental: Final In-Field Design for Low Energy Consumption and High work rates - version 2. August 2016. Report number 2-2016

Expanding the Potential of Intrarow Soil Thermal Weeding - Executive Sumary

  • Globally, herbicide based weed management is facing the triple threats of herbicide resistance, dwindling discovery and legislative prohibition, to the point that leading weed scientists are proposing a post-herbicide era.
  • It is therefore vital that non-chemical (non-herbicide) weed management techniques are rapidly expanded.
  • Intrarow soil thermal weeding (ISTW) is potentially unique among non-chemical weeding tools, in that it is a direct replacement for herbicides and it can outperform herbicides efficacy.
  • ISTW works by killing the emergable weed seedbank in the intrarow, thereby completely eliminating therophyte weeds from the crop row, for the entire length of the crop production cycle. As it is applied prior to crop establishment, it works with any (row)crop.
  • However, current ISTW machine designs use steam as the heat transfer media, which considerably increases the mechanical complexity, size, cost, etc., of the technology, and they use large quantities of fossil fuels.
  • This report analyses the current ISTW technologies, and proposes using hot air as the transfer medium to address the mechanical complexity issue, and more critically, to allow recycling of the heat in the treated soil so potentially significantly reducing energy / fuel use.
  • It also analyses the potential to use renewable fuels to replace fossil fuels, showing that vegetable oil and biogas (methane) are mechanically simple to substitute for diesel and natural gas (respectively) and as these are also among the most common farm produced biofuels their uptake is not inhibited by supply issues, although cost is still a factor.
  • The synthetic literature review section identifies a number of key parameters / variables affecting the efficacy of ISTW, which are:
  • Soil and seed moisture;
  • Soil aggregate size;
  • Temperature.
  • Experiments were therefore undertaken to further study these effects. These found that:
  • Moisture has multiple interactions including higher moisture increasing seed death, increasing the energy required to heat soil and, for silt and clay soils, facilitating a loss of soil structure, potentially leading to severe compaction.
  • Increasing soil aggregate size resulted in decreased weed seed kill;
  • Temperature alone is not a good predictor of seed death and that thermal time (treatment temperature × heating duration) is likely to be a better predictor.
  • The research also found that hot air was an effective medium to heat soil, however, weed seed mortality was lower than for steam, possibly due to the lower moisture levels of hot air, but also possibly due to other unknown factors.
  • The outcome of this report is to provide a theoretical underpinning for the construction of prototype hot air recycling ISTW machinery with the ultimate aim of agricultural machinery manufactures producing farm-ready machines for farmers and growers to use.

The BHU Future Farming Centre

Information - Weeds

Steam and fish fertilisers: A potential organic systemic herbicide?

Disclaimer, copyright and licensing

This was a Sustainable Farming Fund, funded project.  (The report on the SFF site is the same as the one below).

Download paper given to the 7th workshop of the European Weed Research Society working group: Physical and Cultural Weed Control, 11-14 March 2007 Salem, Mecklenburg-Western Pomerania, Germany

A range of people including growers, a steam weeder manufacture and some researchers believed that the use of a foliar fish fertiliser in conjunction with steam produces a systemic weed kill.  A systemic herbicide is one that is translocated throughout a plant such that it kills both roots and aerial parts ensuring complete plant death; glyphosate being the most (in)famous of these.  In comparison, thermal weeders’ mode of action is contact only, i.e., they can only kill the parts of the plant structure that the heat can reach, which in practice means only the aerial parts.  If a plant has sufficient underground reserves and is able to re-grow from underground growing points then they will be immune to thermal weeding.  This type of weed includes all the monocotyledons, e.g., grass, wheat, maize and onions, and rosette and tap rooted weeds such as shepards purse and doc.  If a combination of fish fertiliser and steam had a systemic weed killing effect this would be a truly enormous step forward for organics.  It would allow the introduction of no-till/zero till and solve a considerable number of other weed management issues.  That this could be done with relatively benign technologies such as steam weeding and a fish processing by-product would be even more amazing.  However, despite considerable enthusiasm and anecdotal evidence no rigorous null control trials had been completed.  Considering the enormous potential for this technique it was essential that these claims were properly tested.  Therefore, the Biological Husbandry Unit (BHU) at Lincoln University successfully applied for a Sustainable Farming Fund grant from the Ministry of Agriculture to research this technology. 

Advocates for the approach believed that the steam was opening up the plant tissues, thus allowing the fish fertiliser to get into the vascular system, translocating to the roots and thereby killing the whole plant.  While this is not impossible, it seemed rather unlikely as the principle action of thermal weeders, both flame and steam, is to coagulate proteins and burst cell walls though water expansion.  These processes would more likely inhibit material from entering the plant’s vascular system not enhance it.  The mode of action was therefore unclear.  However, the fish fertiliser contains around 15% fish oil which is very rich in the health giving omega-6 essential fatty acids.  These compounds are known to be chemically very reactive, and are also found in vegetable oils such as flax.  For example, David Musgrave of Functional Wholefoods says that after only half an hour, raw flax oil starts to corrode stainless steel and take on its taste!  It may be possible that the highly reactive fish oil was responsible for the systemic effect.  It was therefore decided to test two fish fertiliser products, ‘BioSea Omega +’ from Sealord Group and ‘Simply Organic’ from Fluid Fertilisers NZ Ltd. along with raw linseed oil from Functional Wholefoods which has high levels of essential fatty acids and a refined, bleached and deodorized (RBD) canola cooking oil which has very low reactivity. 

It was also unclear where the products should be applied to the vegetation in relation to the steam.  Therefore, three approaches were tested, applying the products onto the vegetation immediately before the steamer, applied at the same time as the steam, or applied just after the steamer has passed.  A randomized complete block (four blocks) split-plot design was used with product and application position as the two factors, application position as the sub-plot, with a steam only and null controls with analysis by ANOVA.  Three trials were conducted, two on mixed pasture swards containing grasses, clover and chicory, the other was a predominantly red clover stand with some grass.  For one of the mixed pasture and the red clover trails herbage samples were taken six weeks after treatment and dry weights recorded, unfortunately stock were mistakenly introduced to the other trial before samples were taken, but visual records were obtained.  There was no statistical difference (p>0.1) between the dry herbage weights for all treatments and controls.  Visual assessment on all three trials found no evidence at all of any systemic kill, with all steamed plots showing sustained plant regrowth.  Considering the number of products trailed and different application positions it is clear that when used with steam none of the products had any systemic weed killing effect. 

Advocates of the steam and fish fertiliser approach also believed that using steam with the organic certified contact herbicide ‘Interceptor’ from Certified Organics Ltd produced a systemic weed kill effect.  With the failure of the fish fertiliser and oils to kill plants it was decided to test Interceptor with steam.  A complete randomised block design was used, with the treatments being the three application positions, a steam only and null controls with analysis by ANOVA.  The trial was on a mixed pasture, predominately grass and red clover with some chicory.  Interceptor works by causing plants to desiccate by disrupting cell membranes, as such it is unusual as most herbicides interfere with plants’ biochemistry.  Interceptors’ physical mode of action means that it works best in hot conditions, and when used in conjunction with the steam it was very effective indeed, with the plant foliage dying off extremely quickly.  However, it only took a few days for the plants to start regrowing with visual inspection revealing no difference between steam treated plots.  Foliage samples taken five weeks after treatment found no difference (p>0.4) between any of the treatments.  While the steam helped Interceptor kill the foliage it clearly did not result in a systemic killing of the pasture. 

This lead to the conclusion that if steam was not making any of the products work as systemic herbicides then the nail in the coffin of this technique would be if steam stopped a known systemic herbicide from working.  A randomised complete block trial (four blocks) was completed with four treatments of a null control, steam, glyphosate and steam + glyphosate, with the glyphosate being applied at the rear of the steam weeder.  Three weeks after treatment visual inspection of the plots found that the vegetation in the steam treatment was regrowing but with the glyphosate and steam + glyphosate treatments both dead.  Clearly the initial plant damaged caused by the steam was insufficient to stop the glyphosate working, contrary to expectations.  That the plants were able to translocate material applied immediately after steaming is interesting and means that it is not possible to rule out using steam with other products to alter or enhance their mode of action. 

In conclusion, the use of steam in conjunction with foliar fish fertilisers, plant seed oils, and Interceptor clearly do not result in systemic plant death, contrary to previous claims by Welte (2005) and others. 

There have also been claims by farmers that spraying neat foliar fish fertiliser onto weeds and pastures kill them.  A trial on a well watered vigorous grass and red clover sward with undiluted FluidFert and BioSea and BioSea diluted 1:4 with water applied to run off showed that the products had the ability to desiccate and destroy foliage they touched but the pasture has continued to grow for two months post application so there is clearly no systemic kill. 

There are occasional but regular anecdotal reports of fertilisers, both organic and synthetic, killing plants when “applied” at high doses, i.e., typically when accidentally spilt on the ground.  This is to be expected, fertilisers by their nature contain concentrated plant nutrients which if applied to the soil in sufficient quantities will kill any plants growing there.  This does not make them suitable for use as herbicides.  The rapid and severe imbalances to soil nutrient levels caused by applying concentrated fertilisers will have serious negative impacts on most soil properties such as microbial life, soil structure, pH etc.  This is totally contrary to organic principles, good soil management and quite possibly certification rules. 

These results are a good demonstration of why we need objectively measured scientific experiments.  Anecdotal observations may be correct, but unless they are tested in a properly replicated and statistically analysed trial there is no way to know.  Without experiments, anecdotal observations that are wrong or even damaging can propagate far and wide potentially causing financial and environmental damage.  Unless you are sufficiently qualified or experienced please get specialist advice before using products for anything apart from their designed use. 

Charles “Merf” Merfield is an organic vegetable production system consultant specialising in weed management at the BHU and Lincoln University. 


Welte, A. (2005). Organic weed control using Biosea product and Vaporjet steam system. Shaping Sustainable Systems: Proceedings of the 15th IFOAM Organic World Congress: , Adelaide, Australia, The International Federation of Organic Agricultural Movements.


The BHU Future Farming Centre

Information - Weed Management

Resource files for the seminar-workshop on non-chemical weed management 2014

Handbook 27 MB
Presentation 1: The Big Picture: A Little Context (as PDF) 4 MB
Presentation 2: Think like a weed: key biological and ecological knowledge (as PDF) 4 MB
Presentation 3: Doing it in the field - the weed management hierarchy (as PDF) 2 MB
Presentation 4: Doing it in the field - Pre-emergence weeding (as PDF) 7 MB
Presentation 5: Doing it in the field: Post-emergence weeding (as PDF) 12 MB

  Part 1: The Big Picture: A Little Context
  • Context - the changing face of weed management: resistance and customer / societal attitudes;
  • Integrated weed management (IWM), how herbicide and non-chem weed management relate;
  • The different components of non-chem weed management
  Part 2: Think like a weed:  key biological and ecological knowledge
  • Lifecycles and morphology
  • The ‘bud perspective’
  • The weed seed bank - the ‘root’ of the problem
  Part 3: Doing it in the field - the weed management hierarchy
  • Weed seed rain
  • Rotations what they can and can’t do for weed management
  • The relevance, and lack of relevance, of soil conditions inc nutrient status for weed management
  • The role of crop and pasture choice and grazing management
  Part 4: Doing it in the field - Pre-emergence weeding
  • Tillage
  • False and stale seedbeds
  • Sowing, planting & related techniques
  Part 5: Doing it in the field: Post-emergence weeding
  • Broadacre weeding
  • Interrow weeding - perennials and annuals
  • Intrarow weeding
  • Hand weeding