Grower resistance on rise with IWM

FOR GROWERS who believe continuous cropping is the answer, WA trials are showing how disciplined IWM can beat the build-up of herbicide-resistant ryegrass.

The most successfullWM result from these trials has been seen at the 'Linden Hill' site at Dowerin.

In the five,year program since 1997, supported by growers and the Federal Government through the GRDC, IWM reduced in-crop ryegrass counts from 184 to 25-45 per square metre and, despite a firstyear loss, returned a gross margin of $1,278/ha ($257/ha per year), see Table 1.

Seed and on-site testing prior to the trials confirmed this to be one of the most resistant populations of annual ryegrass in WA. Ryegrass at the site showed considerable levels of resistance to all four major herbicide groups - A, B, C and D.

While chickpeas and the brown manure option at the start of the rotation was not economically attractive in the short term, it proved to be a winner in setting up the highly competitive dense wheat crops that followed.

Burning with a difference

The wheat crops also provided the fuel for prolific stubbles and for destroying seeds by burning within a stable soil environment. Chaff collection in the third year assisted the containment of ryegrass numbers in this program.

Hay-cut and pasture delivers

Much like the result at Dowerin, the trial at 'Northbourne' at York (see Table 2) showed that a disciplined IWM approach could turn an initial loss into positive gross margins averaging $254/ha per year ($1,269/ha over 5 years).

When researchers selected the York site in 1996, the estimated ryegrass population in the wheat crop was more than 850 per square metre and seed testing and on-site testing conlirmed high resistance to Group A (fops), B, C and D herbicides, Researchers then split the site into three areas:

  • cut early for silage and regrowth sprayed out with paraquat
  • cut for hay at normal hay time, and
  • harvested for grain.

Following the hay-cut operation in 1996, the program started with a two-year pasture phase during which no ryegrass was allowed to set seed, The combined effects of these two options all but eliminated a dense ryegrass population that has since been kept in check through three highly competitive and prolitable wheat crops.

Table 1: Summary of cropping program, aggregated ryegrass counts (ARC), in-crop ryegrass count (ICRC), crop yield and gross margin for most successful block at Linden Hill

*other than knockdown

SB = stubble burnt / SC = stimulation cultivation / BM = brown manured /CC = chaff carted

YearCropSignificant operationsHerbicide group*ARC m-2ICRC m-2Yield t/ha-1GM $/ha-1
1997ChickpeasSB/BMC184184--72
1998Brookton®SCD123283.99389
1999Brookton®SB/SC/CCD130253.58341
2000Westonia ®SB-95601.72152
2001Westonia ®SB-138452.94468
5 Yr total6701,278
Table 2: Summary of cropping program, aggregated ryegrass counts (ARC), in-crop ryegrass count (ICRC), crop yield and gross margin for program in section cut for hay at York (1996)

*other than knockdown+kg/ha-1 wool

SB = stubble burnt / SC = stimulation cultivation / BM = brown manured /CC = chaff carted

YearCropSignificant operationsHerbicide group*ARC m-2ICRC m-2Yield t/ha-1GM $/ha-1
1997Re-seed to cloverSTC860907.6+-79
1998PastureST-241239.764
1999Westonia ®SC/CC-834.68496
2000Westonia ®SB/SC-28282.47285
2001Arrino ®SB/SC-30202.79503
5 Yr total9501,269

Program 3

Contact : Mr Bill Roy 08 9641 1080