Farm fences can’t keep resistance out. Wherever weed seeds can go (blown by the wind or carried by machinery, contaminated seed, hay or animals), so can the mutations that confer herbicide resistance.
Of course on-farm weed control strategies play a vital role in managing the level of resistance in weed populations, but no farm is immune to resistance and its presence isn’t a reflection of the quality of individual farm management.
As the world map shows, resistance is developing wherever broadacre crops are grown.
Half of the 60 wild radish samples received for annual herbicide resistance testing from growers across south-east Australia since 2009 have been verified as resistant to Group B and Group I herbicides. In Western Australia, 93% of wild radish populations are resistant to one or more modes of action.
Trace the development over the last 10 years and find out how badly your area is affected. The resistance maps have been developed using data obtained from the analysis of weed seed samples sent in from the field for testing. Where a coloured region appears within the map, this indicates the geographic equivalent of shires where at least one test result for herbicide resistance has been carried out for a grower, an agronomist or researcher. Susceptible implies no or a very low level of survival (< 20%) of the plants grown from the weed seed tested when sprayed at label rates of the test compound, whereas resistant means a high level (>20%) of the plants grown from the weed seed tested survived the label rate of the test compound.
The rate of discovery of herbicides with a new mode of action has slowed considerably in the past 20 years, driven in part by the increasing costs of discovery and development, the switch in some companies from a research focus on crop protection to developing seeds and traits, and the low profitability in farming.
So it’s important to get the best value out of each one.
Because newer products are usually more expensive, there is often a temptation to use them as a last resort and spray them as a follow-up when older products have failed. But you’ll get better value from them in every sense by incorporating them into your herbicide rotation now as the first and primary weed management tool.
By incorporating herbicides with new modes of action into your weed management program, you will be able to go on using the older chemistry for longer.