Radish control a mixed bag
Explosive populations of wild radish across the Central Wheatbelt could be better controlled by an integrated management plan, including herbicide and harvest weed seed control.
Wild radish is the second-most expensive weed to manage in Australia, after annual ryegrass, costing Australian growers about $54 million a year.
Its prominence in the Central Wheatbelt during the past two decades prompted its inclusion in a national 2014-17 Grains Research Development Corporation project.
In WA, the project was led WA by Department of Primary Industries and Regional Development research officer Abul Hashem.
Department of Primary Industries research officer Catherine Borger collaborated with Dr Hashem to run a long-term radish trial at Merredin.
She said the project finished this year, but has highlighted the value of an integrated weed management program.
“In an unpredictable season like 2017, wild radish emerges in multiple cohorts,” Dr Borger said.
“It cannot all be controlled by non-selective herbicides, but late in-crop control at stem elongation stage of wheat offers an excellent option to kill multiple cohorts of wild radish. As wild radish continues to emerge in this trial, it can’t all be controlled with in-crop selective herbicide.
“To prevent seed set at this site, it would be necessary to consider harvest weed seed control.”
The trial aimed to investigate the impact of single or double knockdown herbicides, low or high seeding rates, and early or late applications of in-crop selective herbicides.
This year, summer weed control was applied on January 18 and radish seed was spread at 200 pod segments a square metre on January 20.
Knockdown was applied on May 18 before Boxer Gold, as a split pre-seeding and post-plant pre-emergence application (for grass control), was applied on May 18 and May 23.
Mace wheat was sown at 50 or 100kg/ha at 22cm row spacing, with AgStar fertiliser at 100kg/ha on May 19.
In-crop grass herbicide was applied on June 23, and the first-in crop broad leaf herbicide on July 15, before the second in-crop broad leaf herbicide in July.
While initial wild radish density was low, 0.4-1.0 plants/sqm, a second wild radish cohort emerged before the in-crop herbicide application.
Plots with no in-crop herbicide averaged 4.6 plants/sqm, 1.7 plants/sqm in plots with Triathlon and 1.5 plants/sqm in the Velocity plots.
Most plants were affected by herbicide and died within weeks of the application.
However, a new cohort of wild radish plants emerged within every trial plot within three weeks.
Dr Borger said wheat crop density, across the 50kg/ha and 100kg/ha plots, was not affected by the knockdown treatment or in-crop herbicides.
While crop density did not have a consistent or significant impact on weed density, Dr Borger said high crop density would reduce weed biomass and seed set at the end of the season.
Populations of wild radish have developed resistance to a range of herbicides, including products in Group B (sulfonureas, sulfonamides, imidazolinones), Group C (triazines, triazinones), Group F (nicotinanalides) and Group I (phenoxies).
Dr Borger said because resistance was so widespread in WA, a long-term plan, incorporating effective knock-down herbicides, multiple in-crop herbicides and late season control was vital.
Wild radish can grow up to 1.5m high and produce dozens of seeds, competing with crops for moisture and nutrients.
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