Stubbles set scene for disease tactics

Image of blotch disease on barley

Spot type net blotch in barley.

PHOTO: Mike Ford

How stubbles are treated at the end of this year could play a big part in management strategies for barley spot type net blotch (STNB) in 2017 in susceptible areas.

Incidence of barley STNB in Western Australia’s medium-rainfall zone (MRZ) has been increasing in recent years, as growers plant more barley – including consecutive barley crops – on the back of high profits.

New research has shown there is a potential 10 per cent yield gain from using fungicides when disease pressure is high from retained stubbles in low-rainfall years in WA’s MRZ.

But when there is a dry finish to the season and where stubbles are burnt before sowing and disease pressure is low, there may be no yield or economic advantage from using fungicides to control STNB in barley crops.

These are the findings of trials set up near Corrigin in 2014 and 2015 to investigate best-practice foliar fungicide management for this stubble-borne disease in barley-on-barley sequences.

The trials were carried out by ConsultAg agronomists Ashton Gray and Garren Knell and supported by the GRDC’s Kwinana West Regional Cropping Solutions Network (RCSN) group.

But many varieties grown in this system are either susceptible or moderately susceptible to this disease and management can be difficult, Mr Gray says.

He says there is a need to better understand the interactions of STNB, stubble management and fungicides on the impact of disease, yield and profitability in barley-on-barley rotations. Researchers also want to see if higher disease levels are associated with head loss pre-harvest.

The Corrigin trial site was planted to Scope barley in 2014 and 2015 on burnt and retained stubble areas and 14 different fungicide treatments were assessed. This included single application at growth stage GS31 (first node formed) and multiple applications at GS31 and GS37 (flag leaf visible).

The site received 190 millimetres of growing-season rainfall in 2015, which was 90mm below the long-term average, and a dry spring limited late-season disease development.

Retained stubble

Key 2015 findings where stubble was retained and disease pressure was high included the following:

  • all fungicide treatments significantly reduced STNB severity compared with the untreated control;
  • multiple fungicide applications were most effective at reducing leaf disease severity;
  • all fungicide treatments led to increased yields of about 10 per cent – an average of about 0.2 tonnes per hectare – compared with the untreated control;
  • screenings were reduced by up to 20 per cent in some fungicide treatments;
  • there was little difference between fungicide treatments for grain weight and head loss; and
  • there was a marginal economic benefit of $20 to $40/ha from using fungicides (at a 0.2t/ha yield response) in a low-rainfall year.

Burnt stubble

Key findings in 2015 where stubble had been burnt before the second barley crop was sown – and disease pressure was low – included the following:

  • all fungicide treatments reduced STNB severity compared with the untreated control;
  • multiple fungicide applications were more effective than a single treatment to control disease, but did not result in higher yields;
  • there was no significant yield response to any fungicide treatment or timing;
  • this means there was a $10 to $30/ha loss associated with fungicide use and application;
  • some fungicide treatments resulted in less screenings; and
  • later timing of fungicides led to less head loss.

Burnt versus not burnt

Mr Gray says that overall the trial found crop yields were consistently about 0.4t/ha higher where stubbles were burnt and disease pressure was lower, compared to retained stubble areas.

He says disease severity was also much less where stubbles had been burnt, especially at the early stages of plant growth, and screenings were lower compared to retained stubble areas.

Mr Gray says the trial highlighted that fungicide use for barley STNB control contributes significantly to improving both grain yield and quality (less screenings). “In the retained stubble trials, some fungicide treatments kept screenings at the same level as the burnt stubble trial,” he says.

“In a wetter year, yield responses are likely to be much higher and a two-spray fungicide strategy might be needed where stubbles are retained – although there is no point applying the first fungicide before the five-leaf stage.”

ConsultAg is repeating the trial work to better understand the responses to fungicides and disease pressure in different seasons in the MRZ.

More information:

Ashton Gray, ConsultAg,
08 9881 5551,
ashton@consultag.com.au

RCSN

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GRDC Project Code TAR00006

Region West