What is herbicide resistance?

Herbicide resistance is an accelerated form of evolution in a weed species, or ‘survival of the fittest’.


When a weed species survives one or more applications of the same type of herbicide the species develops a tolerance to the herbicide site of action and continues to grow and produce seeds. These seeds typically survive for many years beyond when the herbicide was once effective.

Herbicide resistance is rapidly becoming a major issue in agriculture as costs to control resistant weeds increase. Cropping has become more intensive and so too has the reliance on chemical weed control. It’s important to rotate crops, rotate chemistry and incorporate mechanical weed control to help sustain cost effective chemical weed control options.

How has resistance come to be a problem in Australia?


The widespread adoption of post-emergent herbicides in the late 1970s heralded a new era for cost-effective weed control in Australian agriculture. Over time, and through incorrect usage of products - such as through the use of chemicals at lower than label rates, incorrect water rates or through simple over-usage - weed species have evolved at a rapid pace to combat the very products developed to eliminate them.

In Australia, the first instances of weeds showing signs of herbicide resistance were reported in 1982 in South Australia and Western Australia. Since the first signs of resistance were reported in annual ryegrass, to Group A ACCase inhibitors (Hoegrass®), Australia has recognised resistance to 69 unique weed bio-types, across a number of modes of action.

No matter where you are, it is likely that resistance is present on your property or in your area. Resistant weeds produce resistant weed seeds, which build up over time. Weed seed contamination cannot be contained to paddocks or kept inside fences and it’s just as important to manage weed seed levels, as it is to control resistant weeds.

What options do you have if resistance has become a problem on your property?

If you suspect resistance is becoming an issue on your property it is important to commence planning and implementing effective control strategies BEFORE cropping becomes too expensive, or worse still, no longer viable to you. To achieve the best weed control result and minimise the threat of resistance in your paddocks, ensure you always:

WeedLogic works by identifying the level of resistance within your paddock, to both single and multiple herbicide groups. This information is then used to develop a herbicide resistance management plan with recommendations for you to manage herbicide resistance.