Growers are being asked to use the weeks prior to harvest as an opportune time to collect weed seeds for herbicide resistance testing.
Determining the status of herbicide resistance provides growers with 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.
GRDC crop protection officer – South Aaron Long said while weeds from any paddock where herbicide resistance was suspected could be tested, priority should be given to testing weeds in high risk paddocks where there is a lengthy history of herbicide use and herbicide survivors have been allowed to set seed.
“Results from testing will help inform growers’ integrated weed management strategies ahead of the 2019 cropping season and beyond,” Mr Long said.
Mr Long said while results from extensive herbicide resistance surveys conducted across the southern cropping region provided an indication of the resistance status of regional weed populations, it was important for growers to have a good grasp of the status of herbicide resistance within their own paddocks.
The University of Adelaide’s herbicide resistance researcher Peter Boutsalis said while pre-harvest was the perfect time to collect samples of weed seeds for testing levels of resistance, collection can also occur during harvest.
Dr Boutsalis said contaminated grain or header screenings could also be sent for testing as commercial testing services could separate weed seeds from other material.
The method of sampling employed 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 said.
“Alternatively, collect seeds from suspect areas,” he said.
“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 want 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 said.
“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,” he said.
Dr Boutsalis said it was important to provide sufficient seed to represent the area of interest.
“Sending more seed is better than not enough,” he said.
