The Science Behind Thermal Weed Control

Well actually “YES IT DOES”, but there is a little more to it than it sounds.

Universally weeds are a hassle for farmers, gardeners, property owners and landscape managers. Hand digging and mulching is the ‘go to’ method I use in my own garden but this can be problematic for commercial crops and public open space. With the wealth of information now in the public domain about the health and environmental issues related to chemical herbicides for killing weeds, there is a major shift to adopting non-toxic weed control methods.

Steam weed control falls under “Thermal Weed Control” category on non-toxic methods. These can be classified into the following Hot Dry and Hot Wet categories.Thermal Weed Control Methods

Hot Dry includes controlling weed with infrared radiation, flame and hot air. They all use propane/ LPG as their heating source.  There are a number of small flame units available which are comparatively portable and are used by home owners, land-care groups and some cities.  There are also larger ones such as HOAF and Sunburst with ride on or tractor versions.
There are some obvious limitations of using a blast of open flame to cook weeds.  Dry leaf litter and grass easily catches alight and the flame melts rubber soft fall in playgrounds and rubber paving, and irrigation lines melt on contact.

My observational experience of using flame is that it doesn’t really penetrate the crown of the plants. It cooks off the top pretty effectively but regrowth from the crown is observed within a few days after treatment.  This leads to having to treat frequently.

Hot Dry Weed Control

Let me explain why this is the case. I remember when I was in science lab at high school and we had Bunsen burners alight. My classmates and I would see how slowly we could pass our fingers through the flame. Despite feeling the heat, we didn’t end up with any blisters.

That is because as we passed our fingers through the flame we were exposed to dry heat and dry heat doesn’t linger. Whilst the temperature of the flame was in the vicinity of 1300° C / 2400° F the heat transfer of hot air and flame is quite slow and air cools as soon as the flame or other radiant heat source moves on, or in the case of our fingers, they moved to cool air.

When using a flame to cook weeds, in order to get better penetration and a consequently longer die back, the flame must be held in place for a period of time long enough for the soil around the root to heat up.  The problem with this is that it increases the chance of fire and damage to the assets you are trying to protect by weeding. I have observed better results in early morning when dew is present or after rain.  For a start its safer, but I also reckon the water boiling on the leaves is retaining the heat for longer and transferring the heat into the leaves more efficiently.

Hand held and push type flaming and radiant heat apparatus can be useful because of their portability but they come with high risk of off target damage.

Of the hot dry methods available flame and radiant heat from ceramics or metal plates heated by flame are the most effective.

Hot Wet methods of weed control include steam, hot water, hot water and insulating foam and saturated steam and boiling water.

Some hot wet methods are regarded as having superior control over weeds than hot dry method.  The reason for this is easily explained by comparing the Bunsen burner at 1300 °C/ 2400 °F to almost boiling water at 95 °C/ 203 °F.  The devastating burns that occur when a cup of freshly brewed tea is spilt onto skin is a perfect example showing how the water transfers heat so effectively and intensifies the damage as it stays on the skin.  Hot oil is even more effective as it doesn’t evaporate and heats to higher temperatures than water. People that work in kitchens learn soon enough that the worst burns are the hot wet oil and water scolds, rather than the more localised burns from touching a hot dry pan or oven rack.

Hot wet methods of weed control enable more rapid transfer of lethal heat into cell structure of weed. In hot wet methods, deeper penetration into the crown of the plants is achieved.  This is where the meristematic cells that are the central growing point of many weeds are.  Most common soft wooded, annual and perennial weeds by their nature are plants that have migrated or been introduced from environments such as grasslands, prairies and open forests.  In their natural environment they are grazed upon by ruminants and occasionally exposed to fire.  They are adapted to growing back from the meristematic cells, the crown of the plant that sits at about or just below soil surface.  They draw on the stored energy of their roots to regenerate new stems, often multiple stems, and a new flush of leaf growth to start the process of replenishing their root system and stored energy. Hot Wet Weed Control

What makes hot wet methods so effective is that they are unlike any process that the weeds are adapted to. The heated fluid penetrates and damages the growing tips, delaying the usual rapid regeneration that is experienced with dry thermal or mechanical cutting methods.

Have you ever hand weeded a garden bed, thinking that you have left the soil weed free, job done, only to have a veritable vegetative carpet of seedling weeds appear after the first moisture?

That’s the seed bank being triggered to life by the warming of the soil, previously shaded from the sun by the weeds you removed, perhaps some exposure to light and certainly some available moisture. So, what I have seen time and time again in weeding with boiling water is that the combination of adding heat and water to the soil surface germinates some species in seed bank. Some species of seeds can’t tolerate the heat and are de-natured, they die and decay in the soil, whilst others love it, as it splits the hard seed coat and allows their first embryonic roots and shoots to emerge. Either way it’s a bonus.  It’s a bonus because we can now deplete the seed bank which means that we can control next year’s weeds this year.

Seed Bank Diagram

I won’t go into the environmental contamination and potential health effects caused by chemical methods of pre-emergent seed bank control, because seriously we can manage the seed bank with just water.  Really, really hot water!

 – Excerpt of an article written by Jeremy Winer

If you still have an itch to learn more, feel free to read Jeremy’s Holistic Vegetation Management Report.  This paper further explores methods of thermal weed control and cites scientific research into weed management practices from around the globe.

Holistic Vegetation Management Report

Does glyphosate increase production in farming systems?

I often hear that we won’t be able to feed the world without herbicide use and GM crops. On the other side of the equation, I hear that productivity of GM crops is no better now than before their introduction.  These charts may give some understanding to a complex set of factors.

This is a specific study of US agriculture. I stand to be corrected, here’s my interpretation.

Chart a. In 1992 8% of soybean was ‘Round up ready’ and treated with glyphosate to control weeds. By 2014, 95% was glyphosate treated.  In terms of acres, glyphosate coverage has increased from less than 5 million acres in 1992 to over 80 million in 2014.

Chart b. Soybean production can be affected by a range of climatic factors, pests and disease and as well as cultivar developments.  Chart b shows variability and I really can’t determine if the glyphosate had any effect.  What is does show is that the exponential increase in the use of glyphosate has not resulted in any proportionate increase in yield.

Chart c is interesting as it shows that the rate of application of glyphosate since 1992 has more than doubled, the number applications have increased from 1 to 1.6 and for a few years glyphosate was practically the only herbicide used.  Since 2008, as a percentage of herbicides used it has decreased, but this doesn’t mean less usage.

Chart d reinforces Chart c. Herbicide use since 1992 per acre has doubled and the number of herbicides being used in 2014 is within cooee of 1992, glyphosate is having less effect and herbicide resistant weeds are requiring additional types of chemical treatment to manage.

In summary for the Soybean records in US agriculture demonstrated in these graphs, GM round-up Ready Soybean has resulted in no fewer number of herbicides being used, a doubling the quantity per acre on 75 million more acres with perhaps a 20% increase in average yield.

In 1992 my eldest daughter was 2, in 2014 my youngest daughter was 16.  They do not know life without GM crops and glyphosate exposure in industrial food.  It remains to be seen the consequences of this exponential increase in glyphosate load has on my unborn grandchildren.  Personally, I can’t see the benefits in yield and necessity that the chemical and GM seed manufacturers would have us believe.

Thanks for reading,
Jeremy Winer.

AusEcoSolutions Toxicology Risks in Wetlands

Thermal Weed Control to Remove Toxicology Risks in Wetland Environments.

“With hydrothermal technology added to our kit bag for weed management we need to move away from the low cost “it’s cheap and quick poison” approach. Thermal technology has numerous potential as well as demonstrated economic benefits and removes toxicology risks associated with Roundup and glyphosate products for people (particularly horticultural and conservation workers), flora and fauna.

Adopting fresh no chemical approaches such as hydrothermal weed management serve to support stressed ecosystems to regenerate themselves without residual off target toxicological effects.”

Click here or on the image to download the report.

Is glyphosate carcinogenic to humans? The WHO says it probably is.

The International Agency for Research on Cancer (IARC), the specialised cancer agency of the World Health Organisation

It’s in our food, it’s in our water and it’s even been found in mother’s milk – the world’s most widely-used chemical herbicide, glyphosate, has permeated our everyday lives.

That’s why it’s especially troubling that The International Agency for Research on Cancer (IARC), the specialised cancer agency of the World Health Organisation, came to the conclusion that glyphosate should now be classified as a carcinogenic substance in Group 2A (probably carcinogenic to humans), based on “limited evidence” in human experiments and “sufficient evidence” in animal experiments.

Should I really be worrying about ‘probably’?

Yes. ‘Probably’ means it has caused cancer in laboratory animals and that there is enough evidence to surmise that it will probably – not maybe or could, but probably – cause non-Hodgkin’s lymphoma in humans. The most vulnerable are children, developing babies in uterus, pets and people who use glyphosate products.

So what does this mean for councils, farmers and land care practitioners who continue to use glyphosate for weeding?

This announcement will have an impact on how glyphosate is perceived and dramatically alter the tolerance for its continued use.

While some parties may argue against the validity of the WHO’s re-evaluation of glyphosate, the reality is that either way, it will have an impact on how glyphosate is perceived by Australians and dramatically alter their tolerance for its continued use in their environment.

In fact, we have recently heard from a few councils who have already been contacted by concerned residents, asking the councils to justify their continued use of glyphosate in the face of the WHO’s findings and the availability of so many compelling non-chemical alternatives. Unfortunately, these councils were caught off-guard with no plan in place to move away from the use of chemical herbicides and are scrambling to put together responses to their communities.

The WHO’s announcement will also have a deep impact on the operators tasked with spraying the glyphosate. Until now, they have been repeatedly assured that glyphosate is safe and therefore, many operators do not wear sufficient protective gear when conducting applications. In addition to the health concerns of operators who have been exposed to repeated applications of glyphosate in the past, there will also undoubtedly be a strong call-to-action to enhance the OH&S requirements to protect these workers into the future.

Adding to this increased complexity, the costs associated with administering ‘No Spray’ zones may also increase, with glyphosate likely to be deemed as unsuitable for use in more locations than ever before.

How can councils, farmers and land care practitioners get on the front foot with this issue?

Get educated on the alternatives

Glyphosate (and other chemicals) are not the only answer. There are numerous non-chemical weeding alternatives that you can leverage. Last year, I dedicated time to review large amounts of scientific research on each of these various methods and compiled an Urban Weed Control Methodologies Matrix which weighs the costs and benefits of leveraging these weeding methodologies. Click here to download the outcome of this review and to evaluate your options for yourself.

Develop a strategy

Going chemical-free is hard to do overnight. This is especially so in the municipal situation, with numerous stakeholders, large areas and chemically subsidised budgets. But rather than being discouraged by this, there are a number of steps you can take right now to develop a strategy and move away from chemical weeding:

  1. Determine tolerance levels for weed presence. Called ‘presentation standards’, they define the tolerable level of weed growth in a specific location. The higher the presentation standard, the more inputs will be required to control the weeds.
  2. Identify ‘no toxin’ zones. These are areas that are environmentally or socially sensitive, where the hazards of toxins represent higher risks to the environment, community and decision makers.
  3. Design to reduce weeds. Hard surface finishes, soil and mulch types, watering regimes, fertilisers, plant species selection and planting densities can all be optimised to reduce the level of weed proliferation.
  4. Adopt a variety of weed control methods. There’s no silver bullet to weed control. Having knowledge, skill and a range of methods at your disposal will allow for long-term cost efficiency in weed management.
  5. Record, analyse and review the methods employed and their efficacy in managing weed species over time. Nature will always fill a void. With local knowledge, we will be able to manage more effectively what appears in the void.

 Highlight your savings

Despite the common perception that chemical weed control is cheaper than most non-chemical weed control methods, there are actually a number of significant costs associated with chemical weed control – but unless you look at chemical weeding from a whole-of-life point of view, these costs may be hidden.

So, when developing your non-chemical weed management budget, don’t only consider the upfront costs of capital purchases and higher labour inputs. Instead also take into account the benefits of long-term weed abatement and the indirect cost savings achieved by mitigating the risks associated with chemical application – especially following the WHO’s findings.

A final thought

Reducing public and operator exposure to probable carcinogens is an imperative, while also creating a catalyst for green employment opportunities. At a time when the government are actively promoting green initiatives and job creation, it would seem that the problem has become a solution.

If you are concerned about any of the issues discussed please contact us.

Jeremy Winer has 30 years of practical experience in assisting councils, farmers and businesses implement an integrated, holistic approach to weed management across urban landscapes, recreational parklands and wetlands. He is principal at Weedtechnics, Australia’s only specialist network of companies providing chemical reduction and non-toxic weed control programs to municipalities across Australia. He has developed, patented, manufactured and commercialised the Steamwand method of creating saturated steam for vegetation control, which is one of a variety of recommended modes of weed control in the non-chemical weed control toolbox.