Conventional herbicides – public perceptions take a dive. Despite the community benefits that herbicides have provided with improved weed control, the perception of conventional herbicides, in the eyes of the public, has taken a few hits.
They have heard via all forms of media that compounds like glyphosate may pose a greater threat to health. There have been many cases being won in favour of various plain-tiffs for large sums of money, suspecting potential links of glyphosate with cancer.
Herbicide resistant weeds are also reducing the value of some products due to poor control. Herbicide resistance, originally found in cropping paddocks with selective herbicides, is now widespread, affecting many situations (road sides, vineyards, non-crop areas etc). Glyphosate resistance in plants is becoming more common, due to its increased use. There has also been steady increases on resistance to other mode-of-action herbicides over the past 20 years. To rub salt into the wounds, reliance on limited herbicide rotations could also result in species shift and/or selection of tolerant species. For example, there have been steady increases in glyphosate toler-ant plants such a Coolatai grass along roadsides, as glyphosate was never 100% effective on this species.

Worldwide trend for herbicide resistance has affected many situations Image: Weedscience.org

Adding to these issues is the general trend in the community for organic, ‘purer’ and safer produce. As such, there is likely to be a greater interest in alternative chemical weed control.

Conventional herbicides – other issues

Off-target damage, such as desirable plant injury or death is a concern. A common example is the physical drift or movement of herbicides; this can then be deposited onto sensitive crops, animals or environments. Classic examples of this are 2,4-D drift onto cotton crops and the movement via water of diuron into the Great Barrier Reef.


Spray drift onto cotton: left untreated and right 2,4-D at 0.1% of standard dose rate Image: Tony Cook
Some of the older herbicides of the 1960’s to 70’s have left a lingering stigma with the public due to serious health effects. Despite the better regulation and testing standards of our federal regulator, the Australian Pesticides and Veterinary Medicines Authority (APVMA), people often remember Agent Orange and other less user-friendly herbicides like arsenic pentoxide. Modern standards have reduced the toxicity of herbicides but really haven’t translated into better perception of modern synthetic herbicides. To make the situation more precarious, a re-cent World Health Organisation review on glyphosate has not improved the profile of conventional herbicides.
The review of many compounds by our regulators could place more restrictions on their use or could result in loss from the market.
About half the synthetic herbicides have some residual activity. Although this can extend weed control, it could be restrictive to planting other crops and infers environmental persistence.

Critique of non-conventional herbicides
A move to alternative herbicides does not necessarily mean a complete step away from all these is-sues. Their introduction as herbicides could have their own list of pros and cons.
But firstly, before we investigate this alternative group of herbicides, let’s get our definitions set. What constitutes the definition of non-conventional herbicides (chemicals)?
Plant based organic herbicides or non-synthetic products.
Chemical exudates from plants or other natural organisms that control weed growth eg. allelopathic crop residues or oils.
The defini