Grains Research and Development

Date: 26.06.2015

Local research targets septoria in Bannister* oats

Author: Melissa Williams

*Bannister oats are subject to Plant Breeders Rights

Caption: GRDC’s Kwinana West Port Zone Regional Cropping Solutions Network (RCSN) group funded trials into fungicide management of septoria leaf blotch on Bannister oats last year, carried out by ConsultAg’s Ashton Gray and Garren Knell. Photo: ConsultAg.

Caption: Septoria leaf blotch on Bannister oats. Photo: ConsultAg.

Using fungicides to control septoria leaf blotch in Bannister oats may improve crop yields when good spring rain is received, but can’t be relied on to reduce grain staining at the end of the season.

That has been the major finding of a GRDC Regional Cropping Solutions Network (RCSN) Kwinana West Port Zone group project carried out in 2014.

In a high rainfall environment, yield responses of up to 0.6 tonnes per hectare were achieved in Bannister oats after tactical fungicide use.

But the research found in-crop leaf staining from septoria blotch, which is caused by the fungus Phaeosphaeria avenaria, was not strongly linked to end-of-season grain staining.

Currently it is thought that groat staining is associated with weather staining and saprophytic fungi - and not necessarily related to the level of septoria in the canopy.

Project background

Bannister was bred for improved disease resistance, specifically for WA conditions, through the National Oat Breeding Program. This is a partnership between the GRDC, Department of Agriculture and Food (DAFWA), South Australian Research and Development Corporation (SARDI) and Rural Industries Research and Development Corporation (RIRDC).

It has better stem rust and leaf rust resistance compared to many other main oat varieties used in this State, but is still rated susceptible (S) to septoria.

In its first commercial growing season in 2013, some WA growers who produced Bannister oats for grain had deliveries rejected due to severe discolouration caused by fungal staining on the seed.

The Great Southern region, in particular, experienced a very wet spring that year and local growers and agronomists noted high levels of septoria on leaves and fungal staining of grain in the wake of these disease-conducive conditions.

To assess whether septoria would impact on the yield and grain quality of Bannister every year, or just in years with a wet finish, the RCSN Kwinana West Port Zone group funded trials in 2014 in commercial crops at west Highbury (high rainfall) and Wagin (medium rainfall).

These were carried out by Ashton Gray and Garren Knell, of ConsultAg, with DAFWA providing plant pathology support last year and undertaking further analysis of grain staining in glasshouse trials in 2015.

Optimising fungicide timing and tactics

The RCSN trials were set up in Bannister crops, sown on oat stubbles to increase disease pressure, and they assessed single and double applications of propiconazole fungicide at a range of timings.

Ashton says fungicide timing had a significant impact on the severity of leaf blotching caused by septoria at both sites.

The most effective strategy to protect the flag and flag-1 leaves against disease was a double fungicide application at stem elongation and again at either flag leaf or head emergence.

There was a significant yield response of up to 0.6t/ha to fungicide timing at the Highbury site, which received good spring rainfall, and all treatments out-yielded the untreated control plot (except a single late spray application at head emergence).

At this site, fungicide timing also impacted on grain staining levels – which reached 3.3 per cent in the untreated lines.

A single fungicide application at flag leaf, or a double application at stem extension and again at either flag leaf or head emergence, were the most effective strategies for significantly increasing yield and reducing grain staining to meet Oat 1 receival classification.

At the lower-yielding Wagin site, which received less overall growing season rainfall than at Highbury, there was no significant yield response or grain staining reduction with any fungicide treatments.

Staining incidence at Wagin was five-ten times higher than at Highbury - at 15-25 per cent - and grain from all fungicide treatments and timings at this site was downgraded to Oat 2 classification.

Ashton says it appears rainfall from crop senescence to harvest has a big impact on grain staining, particularly with early sowing.

Economic analysis points to fungicide benefits

ConsultAg’s economic analysis indicated that either a one or two-spray approach - at stem elongation and again at flag leaf emergence – in Bannister crops could provide an economic return on investment when disease was evident from stem extension.

At Highbury, higher yields and better quality grain that made the Oat 1 classification increased returns by $148-$216/ha, with the greatest response observed when two sprays were used (see Table 1 below).

Treatment

Wagin

Highbury

Grade

Yield

Net $/ha

Gain $/ha

Grade

Yield

Net $/ha

Gain $/ha

Untreated Control

Oat 2

3.7

814.2

0

Oat 2

4.1

902.5

0

Propiconazole  400mL/ha Z32

Oat 2

3.7*

813.8

-0.4

Oat 1

4.2*

1050.7

148.2

Propiconazole 400mL/ha Z43

Oat 2

3.7*

806.9

-7.4

Oat 1

4.4*

1094.1

191.6

Propiconazole 400mL/ha Z32 & Z43

Oat 2

3.8*

825.7

11.5

Oat 1

4.5*

1115.9

213.4

Propiconazole 400mL/ha Z57

Oat 2

3.4*

736.4

-77.8

Oat 2

4.1*

894

-8.5

Propiconazole 400mL/ha Z32 & Z57

Oat 2

3.6*

773.9

-40.3

Oat 1

4.5*

1118.7

216.2

Table 1. Economic analysis of fungicides for septoria control at Wagin & Highbury site. Table: ConsultAg.

Ashton says, given the trials were deliberately carried out where disease pressure was high, it appears that using a double-spray can be economic in high yield-potential crops in a year with a wet finish and when infection occurs at/after stem extension.

When to use a single spray

In lower disease situations, such as crops not sown onto oat stubble or in seasons with a drier start - and where infection hits the canopy later in the season - a single application at/around flag leaf is likely to be able to protect crop leaves, help prevent infection developing in the mid and upper canopy and provide a yield benefit.

Single sprays applied after head emergence limited disease build-up on the flag leaf in the 2014 RCSN trials at Highbury and Wagin, but this was not reflected in the yield response or in grain quality.

Grain staining analysis

Ashton says oat crop senescence occurred earlier at the Wagin site (which had soils with poor water holding capacity and inadequate crop nutrition) last year than at Highbury, exposing the maturing grain to late spring rainfall.

He says this probably meant high staining levels occurred because of secondary weather damage, as well as fungal staining.

Regardless of this, it appears difficult to prevent fungal staining of grain or to increase yields by using foliar fungicides after head emergence and/or in seasons where there is significant rainfall between grain fill and crop senescence.

This year, DAFWA plant pathologist Geoff Thomas is analysing grain from the Wagin site in glasshouse experiments to further determine fungal pathogens present and conditions that favour grain staining.

What to look out for this year

Septoria blotch is the most common oat disease in WA, affecting all production areas and being most severe in high rainfall zones.

It is a stubble-borne disease and, therefore, continuous oat crops are at greatest risk of infection.

Sowing oat crops in rotation with other non-host crops will help to limit disease development, especially in early growth stages.

The fungus infects leaves, sheaths, stems and – in some cases – also the oat heads and grain.

Symptoms can begin as small, dark brown-to-purple spots, which develop to tan-to-dark brown blotches with dark brown centres. These are restricted and distinct at first, but may enlarge and coalesce to cover most of the leaf.

Several fungicide active ingredients and products are registered for suppression of septoria leaf blotch in oats. Many of these contain propiconazole, which was the fungicide used in the RCSN/ConsultAg trials.

ENDS

Contact Details

Contact

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

Contact

Melissa Williams, Cox Inall Communications
042 888 4414
melissaw@coxinall.com.au

Useful resources

GRDC Project Code TAR0003

Region West