Jacqueline Rowarth: How should city councils control weeds?

The Californian ruling on glyphosate has raised cancer concerns yet again. Photo / Getty Images

COMMENT: The Californian ruling on glyphosate (commonly sold as Roundup) has raised concerns about possible links to cancer, yet again.

Monsanto, which manufactures Roundup, has been ordered to pay over $400 million to a groundsman suffering from Non-Hodgkin's Lymphoma.

The jury decided that glyphosate was a plausible contributing factor; the plaintiff did not have to prove that the chemical did cause the cancer.

Andrew Kniss, Professor of Weed Science at University of Wyoming, has calculated that 97 per cent of people with non-Hodgkin's lymphoma have had no exposure to glyphosate.

Nobody wants to be in the 3 per cent, however, just in case.

Alternatives to glyphosate, the most widely-used weed killer in the world, are being suggested.

Vinegar has been promoted in the press recently.

Vinegar is acetic acid. Just like citric acid (lemon juice), at sufficient concentration it burns leaf cells and destroys the tops of plants.

Boiling water, steam, or flames will do the same.

Unfortunately, the roots will often survive, and in some plants that means regeneration of leaves will occur.

Bristol City found this out to its cost.

In response to rate payer concerns about the use of glyphosate, the council spent a year comparing various ways of controlling weeds.

The council report states: "For acetic acid and hand weeding the weeds started re-emerging within a month. On comparison sites, treated with glyphosate, the weediness scores stayed low for five to six months."

Researchers calculated that it would cost at least three times as much to spray the city on a monthly basis with vinegar rather than glyphosate, and concluded that this cost would be financially 'prohibitive'.

Further concerns included corrosion in the equipment due to the acidic nature of vinegar and much greater requirement in terms of protective clothing for the operators than glyphosate.

In Massachusetts an investigation of pelargonic acid (a chemical found in several plants and therefore considered 'natural', like vinegar and lemon juice) gave immediate or short-term suppression of growth of vegetation, as did clove oil. The suppression lasted 'for three to six weeks after which growth was not distinguishable from untreated vegetation'. Again, a requirement for repeated applications was noted.

The research also reported that formulations of citric-acetic acid or a citrus-derived product (limonene) gave no control or only weak suppression of vegetative growth soon after application, and no suppression was evident after three to six weeks.

A similar suppression time was noted for steam, hot water and torching.

Mulching was the most successful alternative to glyphosate in the Massachusetts study, achieving weed suppression for up to two years.

The research concluded that 'because of the cost of materials and labour and need for repeated seasonal applications, all of the alternative practices will cost substantially more than the use of conventional herbicides.'

In a home garden, owners might choose to put in the dollars and time. The question remains 'do they need to'?

Environmental Protection Authorities and Agencies around the world have found no evidence of human health impacts when glyphosate is used as directed.

The EPAs value human health as well as safety, and it is clear that some of the products considered 'natural' must be handled carefully.

Vinegar at the concertation necessary to burn vegetation (which is greater than that required to enhance fish and chips) is corrosive and requires PPE – personal protective equipment. And it requires PPE every 3-6 weeks.

A report published in the Journal of the National Cancer Institute involving over 54000 agricultural workers and their families found that glyphosate was not statistically significantly associated with cancer at any site.

The authors noted an increased (but not statistically significant) risk of acute myeloid leukaemia (AML) in the highest exposure quartile compared with 'never users'.

AML can arise during non-Hodgkin's lymphoma treatment.

Nobody wants to be exposed to anything that might lead to health problems, and chemical companies such as Monsanto spend considerable amounts of money (the estimate is over $300 million per product) on research and development.

Human health is at the forefront of concerns, and the EPAs are focused on ensuring protective guidelines to reduce risk to operators.

All chemicals should be handled carefully.

All label recommendations should be followed.

Gardeners and councils have choices of products – knowing what the choices entail in terms of efficacy, health and cost will assist in making the best decisions for their circumstances.

- Jacqueline Rowarth has a PhD in Soil Science and has been analysing agri-environment interaction for several decades.