Now's the time to harvest weed seeds for resistance testing
Harvest is an opportune time for grain growers to collect weed seeds for testing the herbicide resistance status of weeds growing on their properties.
Seed samples collected at this time of the year can be tested for resistance, with the results made available to growers to help inform their weed management strategies ahead of next year’s sowing programs.
Herbicide resistance researcher Dr Peter Boutsalis, from the University of Adelaide and Plant Science Consulting, says determining the status of weed resistance provides valuable information on the effectiveness of herbicides on target weeds, potentially preventing the wasteful use of ineffective herbicides and reducing the spread of herbicide resistance.
“And now is the perfect time to be collecting samples of weed seeds for testing levels of resistance, especially before harvest,” Dr Boutsalis says.
“Alternatively, during harvest the header cabin provides the perfect vantage point for spotting weeds that have survived over the crop growing season.
“Seed samples can also be collected after harvest, as seed heads can often be found between the crop rows, but the most convenient time for farmers is usually before harvest when inspecting paddocks.
“For weeds that shed readily, such as wild oats, brome and barley grass, seeds are usually found on the soil surface.”
Dr Boutsalis says contaminated grain or header screenings can also be sent for testing as commercial testing services can separate weed seeds from other material.
Sampling will depend on the resistance situation of each paddock.
“If resistance is widespread, seeds should be collected following a ‘W’ shaped area every 10-20 metres across the suspected paddock or problem area,” Dr Boutsalis says. “Alternatively, collect seeds from suspect areas.
“It is important that growers and advisers do not bias the samples by collecting seeds from a small number of plants – they should instead aim to collect a similar number of seeds from each plant.”
If the seeds are not completely dry, they should be sent in paper envelopes to avoid rotting in plastic packaging.
If growers wish to have ryegrass seed tested, about one cup equivalent of clean ryegrass (about 50 seed heads) is required.
“Where there are lots of ryegrass individuals in the paddock don’t collect from only a few, but try to collect one seed head per plant,” Dr Boutsalis advises.
“For species with larger seeds such as wild oats, brome, barley grass and wild radish, an ice-cream container full is sufficient – this is equivalent to an A4 sized envelope full of seeds.”
Dr Boutsalis says it is important to provide sufficient seed to represent the area of interest: “Sending more seed is better than not enough.”
Any paddock where herbicide resistance is suspected as the cause of a spray failure can be tested.
Priority should be given to testing weeds in high risk paddocks where there is a long history of herbicide use and herbicide survivors have been allowed to set seed.
Weed seed resistance testing services are available via:
- Peter Boutsalis, Plant Science Consulting, Adelaide (SA). Phone 0400 664460, email firstname.lastname@example.org, web http://www.plantscienceconsulting.com.au
- John Broster, Charles Sturt University, Wagga Wagga (NSW). Phone (02) 6933 4001, email email@example.com, web https://www.csu.edu.au/weedresearchgroup/herbicide-resistance.
More information on herbicide resistance and weed management is available via the GRDC’s Integrated Weed Management hub at http://ww.grdc.com.au/IWMhub and the GRDC-supported WeedSmart resource centre at http://www.weedsmart.org.au.
Peter Boutsalis, University of Adelaide
Sharon Watt, Porter Novelli