Treating wild radish (Raphanus raphanistrum L.) early in the growing season in the northern wheatbelt as part of a two-spray strategy - using robust herbicide rates and excellent application - can boost wheat yields by 0.5-1 tonne/hectare.
Northern wheatbelt agronomist Grant Thompson, of Crop Circle Consulting, has found two spray strategies are most effective in controlling multiple herbicide resistant wild radish.
That is a key finding from large-scale 2013 trials initiated by the GRDC’s Geraldton port zone Regional Cropping Solutions Network (RCSN) and run by Grant Thompson, of Crop Circle Consulting.
The research was carried out at sites in Northampton, Casuarinas and Chapman Valley and aimed to:
- Develop herbicide solutions and sequences that avoid using the same product twice in a single growing season
- Get herbicide timing and application rates right
- Delay the onset of wild radish resistance to - and prolong the efficacy of – new actives pyrasulfotole (Group H - eg. Velocity® and Precept®) and pyraflufen-ethyl (Group G - eg. Ecopar®)
- Develop a best practice management guide for control of wild radish with multiple herbicide group resistance.
Herbicide resistance in wild radish
There is an increasing threat of multiple herbicide group resistant wild radish and ‘stacked’ resistance in the northern wheatbelt.
In this region, there is already widespread wild radish resistance to herbicides such as SU’s, diflufenican, MCPA and 2,4-D amine.
Newer registered chemicals, such as pyrasulfotole and pyraflufen-ethyl are highly effective at controlling radish.
But there is industry concern about repetitive use of these products and a need to prolong their effectiveness.
The value of older herbicides
In the first year of GRDC’s RCSN-funded wild radish control trials in the northern wheatbelt in 2012, Peter Newman - then with the Department of Agriculture and Food WA (DAFWA) and now a consultant with the Australian Herbicide Resistance Initiative (AHRI) and Planfarm - demonstrated older herbicide groups could still be effective against wild radish.
The keys to success were:
- Targeting weeds when small – about the size of the top of a beer can
- Using a timely two-spray strategy with a quick and timely second spray
- Ensuring herbicide rates are robust
- Using correct water volumes, nozzles and speed.
2013 trial results and observations
Some wild radish populations at Grant’s 2013 sites were resistant to up to four herbicide modes of action, including SUs, IMI’s, diflufenican, MCPA and 2,4-D amine.
His results backed-up the 2012 RCSN project findings that - for such resistant populations - the best practice management was early spraying, followed by a quick and timely second spray using robust herbicide rates.
Using two sprays
When a two spray strategy was implemented, wheat yields ranged from 3.1t/ha to 3.64t/ha across the trial sites.This was about 0.5t/ha higher than wheat yields of 2.63t/ha to 3.06t/ha across trial plots where a single late spray was used - and wheat yields were up to 1t/ha higher in some plots.
At Northampton and Casuarinas, the efficacy of 56 two-spray herbicide combinations (not including IMIs) was tested. Almost all achieved 100 per cent weed control when the first spray occurred at 1.5-2 leaf stage of the wheat crop (or as early as the label allowed) and was followed four weeks later (at five leaf stage) with a second spray to control subsequent germinations and ‘mop up’ any survivors.
Early applications of Jaguar® (Group C and F) at a rate of 1 litre/hectare and Velocity® (Group C and H) at 670 ml/ha were the most effective - regardless of the chemistry of the second spray (which included 12 combinations).
Bromicide 200® (Group C) used as the first spray at a rate of 1.5 l/ha also achieved good wild radish control.But it was marginally less effective than Jaguar® or Velocity®, regardless of the herbicide applied four weeks later.
Grant found there was a consistent wheat yield advantage of 0.4-0.5t/ha if an early two leaf spray of Bromicide 200®, Jaguar® or Velocity® was used and followed up with any number of the five leaf spray options.
Including application, early two leaf spray treatments in the trials cost about $19-$29/ha.
Given consistent wheat yield improvements of 0.4-0.5t/ha, this led to a net profit increase of about $90-$130/ha (based on a wheat price of $290/t) compared to a single spray.
Grant’s trials showed there were many alternatives for a second spray to 2,4-D amine, which is now ineffective in many areas of the northern wheatbelt.
Using a single early spray
When no late spray was used, Velocity® was the most reliable early option.
Using a single late spray
As mentioned, results across all trial sites showed using one late spray reduced wheat yields by about 0.5t/ha - and in some cases up to 1t/ha - compared to using two sprays.
Five leaf stage herbicide applications were put under a lot of pressure, with wild radish populations often reaching 200 plants/m2.
One late spray achieved unacceptable results in many cases, with control ranging from 0-90 per cent.
The average effectiveness in one-spray plots using Jaguar®, LVE MCPA and an experimental herbicide from FMC ranged from 43-67 per cent weed control when applied on July 4.
Velocity® was the exception at one trial site, achieving 100 per cent control when applied late as a single spray.
But at another site, one late spray of Velocity® at five leaf stage achieved 93 per cent control, compared to an early spray of this herbicide at two leaf stage that achieved 100 per cent control.
At the Chapman Valley site, holding off for a single late herbicide application produced the worst wild radish control results across all of the trial sites.
On farm implications
The 2013 RCSN trials demonstrated significant improvements in weed control efficacy and grain yields – of up to 1t/ha at some sites - by implementing a two spray strategy rather than using one late application when radish density is high.
Grant’s data also clearly shows there are effective alternatives to use in a two spray strategy than two consecutive doses of pyrasulfotole.But he found herbicide mixes containing pyrasulfotole were highly effective and reliable in many conditions.
Grant warns that many effective alternatives to pyrasulfotole used in the trials contained Bromoxynil and it was vital not to over-use either of these herbicide groups.
NOTE: Grant will be presenting this trial data and discussing management of stacked resistant wild radish at the 2014 Agribusiness Crop Updates in Perth on February 24. For registrations go to: www.giwa.org.au/2014-crop-updates
Grant Thompson, Crop Circle Consulting, 0427 652 521, firstname.lastname@example.org
Cameron Weeks, RCSN Geraldton port zone, 0427 006 944, Cameron@planfarm.com.au
Contact Grant Thompson for a full copy of the final report ‘Controlling Herbicide Resistant Radish with Herbicides in the Northern Agricultural Region of WA’ and a Best Management Practice Guide.
WeedSmart information hub: www.weedsmart.org.au
Australian Herbicide Resistance Initiative (AHRI): www.ahri.uwa.edu.au
RCSN groups: www.grdc.com.au/rcsn
GRDC Project Code
West, North, South