With the winter cropping season now upon us, the major issue facing grain growers around Australia is herbicide resistant weeds. This has come about largely by the reliance on a few chemical groups used each year.
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Leading researchers from around Australia are convinced that the problem is getting worse each year and we need to fund research programs to find alternate methods. A recent survey of farmers showed that 25% used chemicals as their only weed control method, 60% had herbicide resistance confirmed and another 25% weren’t sure.
Many of the techniques we are doing at present such as rotating chemical groups are only buying us time. When resistance to one chemical is apparent in weed species there is a much greater chance that these species will quickly develop resistance to other groups. Studies have shown the combination of herbicide options (rotation, mixtures or combinations) can provide acceptable control of low level resistant weeds but it is only part of the integrated weed management tactics.
Even when we have crop rotations with long pasture phases resistant weed species such as annual ryegrass will maintain that resistance even if it is not exposed to chemicals during that time. If we let the seed bank build up during the pasture phase then the problem only gets worse when we come back into crop. For ryegrass we need at least two seasons of control in the pasture phase (usually by pasture topping techniques) to run the seed numbers down before we come back into crop.
Using alternate control techniques such as windrow burning and chaff carts to collect seeds at harvest as used successfully in Western Australia may need to be adopted more widely here. Research into other methods such as use of microwave or laser technology is being done but is not practical on a farm scale yet.
Testing for herbicide resistance should be done regularly, targeting weeds in paddocks where suspect plants have survived. A weed spray can cost thousands of dollars but this will all be wasted if resistant weeds are present. Testing will identify which herbicides will work on your weeds. Charles Sturt University offer a testing service and information about this can be found with this link. (http://www.csu.edu.au/research/grahamcentre/people/wwg/strategies/herbicide-resistance.htm)
