An investigation into the increasing incidence of herbicide resistance in broadleaf weeds in the Victorian Wimmera-Mallee region has delivered fresh insights into the extent of resistance in wild radish and options for its management.
A Grains Research and Development Corporation (GRDC) “fast track” project, instigated by the GRDC’s southern Regional Cropping Solutions Networks (RCSNs) and conducted by BCG (formerly Birchip Cropping Group), has found that populations of wild radish are changing in their level of resistance.
This change is particularly evident with Group I and B herbicides which are now only effective in controlling 50 per cent of the targeted wild radish populations in the areas surveyed in Wimmera-Mallee.
BCG research agronomist Simon Craig says Group I and Group B herbicides failed to provide commercially acceptable control (70 pc reduction) of wild radish populations targeted in the survey.
“It will be inevitable that these populations will be completely resistant in the short-term future,” Mr Craig said.
The GRDC, through the RCSNs, last year commissioned BCG to conduct regional paddock surveys to highlight first hand to growers and advisers that resistance is developing.
“Lifting awareness of the increasing level of broadleaf weed resistance is needed in an attempt to delay or prevent its onset,” Mr Craig said.
As a result of the now-completed project, the following key messages are being presented to the region’s growers and advisers:
- Wild radish seeds have a long dormancy in the soil and can germinate four to five times a season with sufficient soil moisture
- Best chemical control is achieved if spraying early at the 1-2 leaf stage of the weed. Growers should not wait for five leaves or more before application
- Some radish plants can shield others from contact with spray so a high water rate is required for best plant coverage
- Research has shown a two-spray strategy is best for high-density radish plants or populations with multiple herbicide resistances
- Growers are urged to rotate herbicide groups applied to plants so the effectiveness of new Group H chemistry can be prolonged
- When collecting seeds for resistance testing, ensure samples are taken from a representative population or samples from suspected plants. Susceptible plants can still be present in the population and can give a false illusion of the resistant status.
During the course of the project, a range of herbicide options for controlling wild radish was applied to commercial paddocks (in strips) where wild radish is problematic.
BCG, in collaboration with agribusinesses AgriVision, AgriTech Rural, Tyler’s Rural Supplies, Landmark and Elders, identified 20 paddocks (10 in the Mallee and 10 in the Wimmera) with radish populations of suspected resistance.
These paddocks have acted as demonstration sites to provide a platform for engaging with growers, advisers and industry representatives to increase awareness of developing herbicide resistance in broadleaf weeds.
“The sites are being used for crop walks and information days for both growers and advisers, to assist in building awareness and understanding of the increasing threat of resistance,” Mr Craig said.
“This, in turn, will increase the likelihood of rotation of herbicide groups and better management of wild radish where resistance to at least one group is already present.”
Mr Craig said wild radish populations and their level of herbicide resistance was increasing across the Wimmera and Mallee cropping regions where growers have commonly selected herbicides according to their ability to control grasses such as ryegrass or brome grass.
“As a consequence, growers have placed less emphasis on rotating their broadleaf herbicide groups, thereby increasing the potential for resistance to develop in weeds such as wild radish, Indian hedge mustard and turnip.”
The project carried out by BCG and commissioned by the GRDC is one of several “fast track” projects – small scale, short time-frame and relatively small budget projects involving in-season responses – conducted across the southern cropping region in recent years as a result of localised issues being identified by the RCSNs, which support the GRDC Southern Regional Panel.
The four RCSNs networks cover the low rainfall, medium rainfall, high rainfall and irrigation zones and consist of growers, farming systems groups representatives, consultants and other grains industry stakeholders.
Members liaise with the wider grower community in their respective zone and by doing so identify and discuss local issues and then feed this information into the Panel which then assesses each issue and makes recommendations to the GRDC about potential activities to be addressed by investments.
Simon Craig, BCG
03 5492 2787
Sharon Watt, Porter Novelli
Caption: Herbicide-resistant wild radish is spreading in the Wimmera-Mallee. Photo Simon Craig, BCG.
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