Weeds seem to grow anywhere and everywhere. When they turn up in our gardens, competing for nutrients in soil and filling all available gaps, it is tempting to seek an easy way of getting rid of them. But currently, only 2 products that might do that are listed in our Garden Product Guide – Safe for You ‘n’ Nature as being low impact. This may come as a bit of a surprise when there are so many weed killers on the market.

IMG_0070When trying to live sustainably, we want to reduce the incidence of harm caused by the products we use. And how difficult is this getting!!!

According to the Environmental Protection Agency in the USA, there are over 84,000 chemicals in overall commercial use with between 500 and 1000 added each year1. Many of these have some degree of toxicity for humans or the environment. We don’t have statistics on chemicals specifically for garden use.

At SGA, we want to minimise harmful effects. So, together with the Burnley College of Melbourne University, we developed a rating system for commercially available garden products so that we could differentiate between those which had low, medium or high undesirable impacts. This system is based on a number of criteria relating to the product’s effects on aquatic life, insects and other invertebrates, birds, pets and humans. Scores for each criterion are weighted and the combined results lead to an overall rating. There are a few differences in criteria used for products for control of weeds and pests or for fertilisers.

For each product, we consult the Material Data Safety Sheet, which the manufacturer is required to publish, the information on the packaging and other published data. Here we find information about the contents, government regulated levels of safety and effects on various aspects of the environment.

An important observation is that products containing glyphosate, are rated as medium impact. This is particularly so because the glyphosate-containing Roundup is widely used in agricultural contexts. Canola, which is the source of cooking oil and is used in much processed food, has been released in NSW in the genetically engineered Roundup-Ready form. This means that the crop still grows after being sprayed with glyphosate to kill weeds. Many different weed killers for domestic use also contain glyphosate.

So, let’s look at each of the rating criteria and at some of the chemicals that earn medium or high impact scores.

Is the product made from “natural” non-synthesised ingredients?

Chemicals that have been synthesized have generally caused the consumption of more energy during their manufacture than natural materials such as vinegar and salt. For most weedicides, the answer to that question is “no”.

What is the Schedule heading?


By law, chemical products must be labeled according to the Poisons Schedule which is primarily directed to protect human safety2. Products have a “schedule heading” (a number preceded by “S”) and a “signal heading”. Products with no schedule heading i.e. below S5, are deemed safe to use. But they may have a signal heading such as “keep out of reach of children” or “read safety directions”.



Products labelled S5 have a signal heading of “Caution” and may also have statements about keeping out of children’s reach and safety directions.

Those labelled S6 have a heading of “poison” and those classified as S7 have a heading of “Dangerous Poison”. S7 chemicals are not permitted to be sold, stored or used in domestic situations. Clearly products with schedule headings of S5 or higher have higher potential impacts than those that are unscheduled.

Products containing glyphosate are classified as S5 and carry a signal heading of “Caution” and usually with advice to keep out of reach of children and to read safety directions. This is because if it is mishandled it can cause irritation of the skin, respiratory and gastrointestinal tracts and eyes, Some other chemicals in weed killers scheduled S5 on the basis of animal testing are propyzamide (carcinogen), MCPA (2-methyl-4-chlorophenoxyacetic acid) (affects liver and kidneys) although their concentrations and other chemicals in products can increase their schedule heading to S6 Poison. Weedicides that kill broadleaf weeds, paspalum, nutgrass, bindii and clover generally are generally S6 poisons.

Is it hazardous to bees, amphibians, pets or fish?

Who sprays weedicides on pets, frogs or fish? Most of us draw the line at that, but need to remember that we are effectively doing that if the chemical finds its way into streams or ponds or if pets are around when the product is being used. For example, some glyphosate products are harmful to aquatic organisms and dicamba and MCPA have slight toxicity to fish. * See comment below

Is it pre-mixed and ready to apply?

We all know how easy it is to spill stuff when you have to pour it into a container. So products which are pre-mixed and ready for use are less hazardous than those that require dilution and mixing since they are less likely to spill on either people, soil or non-target organisms.

Is it an aerosol and Schedule 5 or more?

Why fuss about aerosols? Substances sprayed from cans or bottles can easily be inadvertently inhaled from the aerosols, so S5 products which have a caution warning, and, of course, S6 products can cause problems. Trigger sprays produce larger droplets than pressurized cans, and these droplets are less likely to travel far enough to be inhaled or reach non-target plants or animals.

Is the packaging well-designed and robust in relation to the schedule heading?

Robust plastic bottles with safety screw tops are difficult to be accessed by children, while trigger spray bottles are more prone to accidents. The higher the schedule heading the more important is the form of the packaging in safety assessments.

If you read the labels on weed killers taking this information into account, it is easy to see why so few earn a low impact rating and what care needs to be taken in using any product if you don’t want to go the really low impact route – hand pulling!

1. United States Environment Protection Agency. www.epa.gov/oppt/existingchemicals/pubs/tscainventory/basic.html

2. Australian Government Pesticides and Medicines Authority.