Beat down annual ryegrass – not your profit

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Photo of wheat being managed witih a low-cost strategy showing more annual ryegrass

Wheat in the fourth season of a long-term management strategy contains more annual ryegrass in the low-cost management strategy (MS1, pictured) than in the high-cost strategy (MS3, below) at Lake Bolac, 2015.

When choosing the best integrated weed management (IWM) strategy for your situation, it is important to understand your yield potential. Choosing the most expensive options in areas where wheat yields less than two tonnes per hectare can put your profit at risk.

Photo of wheat being managed with a high-cost strategy showing less annual ryegrass

Wheat in the fourth season of a high-cost management strategy (MS3).

To reduce annual ryegrass numbers in problem paddocks, choose rotations that allow ryegrass seed-set to be controlled two years in a row, such as hay followed by a pulse crop. Take every opportunity to employ annual ryegrass seed management tactics.

Cutting hay, if a nearby market is available, is the best option to reduce annual ryegrass seedbanks in the low and medium-rainfall areas. This practice, followed by controlling regrowth, can reduce annual ryegrass seedbanks by 85 per cent.

Resistant weeds

In wheat, where no post-emergent herbicides are available due to resistance, choose a more effective pre-emergent herbicide package. For example, in the higher-rainfall zones, choose Sakura® plus Avadex® Xtra, instead of Boxer Gold®.

Where clethodim resistance is a problem, consider a pulse crop instead of canola. In pulses, the higher rates of Factor® that can be used than in canola and crop topping is likely to be more effective.

In high-rainfall zones, pre-sowing cultural controls such as inversion ploughing and autumn tickle have limited long-term efficacy because annual ryegrass will emerge late in the crop. Late-season control such as crop-topping in canola and pulses is more effective.

With so many options, choosing the correct integrated weed management strategy for your farming system can be complex and time-consuming.

Long-term trials

Graphic showing crop yield and estimated returns from three weed management strategies

Figure 1 Crop yield and estimated economic returns for the three different weed management strategies at Roseworthy, 2010 to 2012.

Graphic showing annual ryegrass seedbanks measured prior to sowing at Lake Bolac with three management strategies

Figure 2 Annual ryegrass seedbanks measured prior to sowing at Lake Bolac from 2012 to 2016 with three management strategies (MS).

SOURCE: Chris Preston

At Adelaide University we conducted a series of long-term weed-management trials in the medium to high-rainfall zones at Roseworthy and Hart in South Australia and near Frances and Lake Bolac in Victoria to identify the most effective and profitable rotations and practices for integrated management of annual ryegrass.

In each of the trials we chose three management strategies (MS) that ranged from low to high cost. MS1 was typically a single post-emergent or pre-emergent herbicide application. MS2 was typically a combined pre-emergent and post-emergent herbicide strategy with seed-set control in some crops. MS3 used a more expensive pre-emergent herbicide mix, included post-emergent herbicides where available and employed ryegrass seed management tactics in every year.

The trials have run for between three and six years and we measured the gross margins and the annual ryegrass seedbank before sowing each year.

At Roseworthy, MS1 failed to effectively reduce the annual ryegrass population because we failed to crop top in the pea phase. MS2 generated an extra $207 per hectare over the three cropping years, whereas MS3 generated an extra $578/ha (see Figure 1).

In this environment, reducing ryegrass populations to a very low number allowed wheat to yield very well in the favourable 2011 season.

At Lake Bolac, annual ryegrass populations have increased in all MS due to the inability to control late-germinating weeds and the lack of practical weed seed management options in some crops. However, MS3 has been able to limit the increase in population size more than the other two MS (see Figure 2).

By maintaining a lower annual ryegrass population in MS3 at Lake Bolac, crop yields have been 1.8t/ha higher than yields in MS1 over the five years of the trial.

More information:

Dr Chris Preston,
08 8313 7237,
christopher.preston@adelaide.edu.au

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Tackling the brome grass seedbank

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Finding genetic traits behind weed-competitive crops

GRDC Project Code UA00113, UA00134 and UCS00020

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