Tips to manage net blotch in barley crops
Date: 24 Jul 2020
- Take a tactical approach to barley net blotch management in medium rainfall zones
- In dry seasons (lower disease pressure), returns can be marginal from fungicide use
- In areas with early wet conditions (high disease pressure), a double spray strategy can potentially lift grain quality, yield and returns
- For barley-on-barley crops, budget for a fungicide spray at Flag-1 stage every year.
Growers and agronomists are advised to monitor barley crops this winter for signs of spot and net form of net blotch (SFNB and NFNB).
Crops most at risk of production losses from these common diseases are:
- susceptible varieties (including Hindmarsh, LaTrobe and Scope CL)
- barley planted consecutively after barley
- those sown in paddocks with high stubble loads
- those paddocks/areas that experience regular rain events after plant emergence.
SFNB (caused by Pyrenophora teres f. maculata) and NFNB (caused by P. teres f. teres) are closely related fungal diseases and can occur alone or simultaneously in a crop. Severe levels of infection can reduce barley yields by 20-40 per cent and result in potential for high screenings at harvest.
SFNB and NFNB occur across Western Australia’s grainbelt. They are more likely to cause significant yield losses in high and medium rainfall zones, than the lower rainfall zones.
Incidence of these diseases appears to have been increasing in recent years as barley production has expanded and particularly where a higher frequency of continuous barley is used in rotations.
Fungicide resistance an emerging issue
Fungicide resistance is an emerging issue in these diseases and highlights the importance of implementing integrated control strategies. Options include variety choice, crop rotation, stubble management and use of at-seeding and foliar fungicides.
The GRDC and Curtin University-supported Centre for Crop and Disease Management (CCDM) discovered NFNB isolates with reduced sensitivity to Group 3 DeMethylation Inhibitors (DMI) fungicides in 2013 and mapped the occurrence between 2013 and 2016.
Importantly, a newly-discovered case in Scaddan, near Esperance - collected by Department of Primary Industries and Regional Development (DPIRD) plant pathologists - had a higher resistance to Group 3 DMI fungicides than the previously identified cases.
More research with GRDC investment is being carried out into fungicide resistance and CCDM researchers will use 2018 crop samples to assist with this effort.
If growers suspect that fungicides have reduced efficacy in their paddocks, they can contact the CCDM’s Fungicide Resistance Group at firstname.lastname@example.org.
To prevent further development of fungicide resistance in net blotches - and other crop pathogens - CCDM advises growers to:
- rotate fungicide modes of action between each use
- avoid using the same mode of action twice per season
- use fungicide mixtures with more than one mode of action
- use recommended label rates
- not use tebuconazole as a stand-alone product in barley for any disease as this could lead to problems of evolving resistance in the longer-term.
What to look for in the paddock
The two forms of net blotch have different symptoms and severity of impact. Appearance of symptoms can vary depending on barley variety, growth stage of the crop and stage of infection, according to DPIRD pathologist Geoff Thomas.
Barley crops infected with SFNB will appear spotty and blotched, yellowing and/or to be dying - right across the paddock.
At a plant level, affected leaves will have circular-to-oval shaped dark brown spots with yellow edges. As the leaf and spots age, they can grow bigger and join together to cause blotch symptoms.
If infection is severe, leaves turn yellow and die from the tips.
For more information about diagnosing stubble-borne fungal foliar disease, read the article 'Diagnosing spot type net blotch' on the DPIRD-GRDC MyCrop website.
Lesions of NFNB can start on leaves, appearing as pinpoint brown areas that elongate along leaf veins into thin brown streaks, or blotches. These can be up to several centimetres in length.
Dark brown longitudinal and horizontal lines sometimes develop in the lesions, creating a net like appearance, and a narrow zone of yellowing typically surrounds the lesion.
More information about diagnosis of this disease can be found on the DPIRD-GRDC MyCrop website here.
Tips and tools to manage SFNB in the growing season
It is important to correctly identify SFNB to rule out other abiotic factors, such as nutrient or seasonally-induced deficiencies or toxicities, affecting the crop.
Disease testing is available through DPIRD’s Plant Pathology services (part of the DPIRD Diagnostic Laboratory Services, DDLS). More information can be found here.
There are a range of registered fungicides for the barley net blotches.
Applying fluxapyroxad-based seed dressing, or the azoxystrobin product Uniform®, in-furrow has been shown to provide protection from early season SFNB infection.
Foliar fungicides are also registered for SFNB and results from trials conducted in WA in 2015, 2016 and 2017 by ConsultAg and DPIRD highlight the value of using these tactically - depending on seasonal conditions.
ConsultAg adviser Trent Butcher says the trials found that in high rainfall zones in years when SFNB pressure was high, a double fungicide spray strategy typically improved grain quality, yields and returns.
He says a fungicide application at Zadoks Growth Scale Z31-Z32 reduced disease pressure and protected the canopy until a second application at Flag-1 stage.
In low rainfall areas, the trials indicated growers could typically get away with one spray application around the Flag-1 stage for barley-on-barley crops.
But Trent says decision-making is more difficult in medium rainfall zones, where fungicide use is best determined according to unfolding seasonal conditions and disease load.
At the medium rainfall zone trial sites, all fungicide products that were trialled significantly reduced SFNB disease severity, compared to the untreated control, and boosted yields by about 10 per cent (175 kilograms/ha) when a double spray strategy was used at Z31 and Z37.
This led to a marginal economic response of about $20-40/ha under high disease pressure (retained stubble) in a low rainfall year.
The second-best treatment to lower disease levels was a single late application at Z37.
A single early application at Z31 reduced leaf infection, by about half compared to the untreated control, but disease was able to re-enter the canopy later in the season.
Full results from the ConsultAg-DPIRD project ‘Best practice management of SFNB in barley and interaction with stubble management and head loss’ can be found on the GRDC’s Online Farm Trials website here.
Previous DPIRD-led research, with GRDC investment, has shown registered foliar fungicides suppress SFNB disease development but seldom provide complete crop protection.
Researchers have found that propiconazole, prothioconazole, pyraclostrobin, azoxystrobin and epoxiconazole-based fungicides are more effective than tebuconazole-based fungicides. But effectiveness depends on the product, rate used, timing of application and disease pressure.
More information about timing and use of registered foliar fungicide active ingredients can be found here.
Tips and tools to manage NFNB in the growing season
Applying a registered foliar fungicide - following label recommendations - is key to controlling NFNB in medium and high rainfall regions when disease threatens high-yield potential crops.
DPIRD advises that the choice of a single or double-spray strategy depends on the environment in which the crop is growing, the time of onset of disease and use of seed dressing or in-furrow fungicides.
Researchers say in high rainfall environments, two sprays may be needed at early stem elongation and three to four weeks later.
In medium rainfall regions, it is recommended to consider one well-timed spray between late stem elongation and early flag leaf emergence (Z33 - 39) to protect leaf two (Flag-1).
Resistance R&D continues with GRDC investment
GRDC is continuing to invest in research at the CCDM that aims to increase understanding of the mechanisms for SFNB and NFNB fungicide resistance - and emerging issues of cross resistance to a broad range of fungicides.
This underpins the successful long-term use and sustainability of fungicides and helps to advance genetic improvement of crops.
Both approaches need to occur simultaneously and the recent Group 3 DMI resistance findings in WA highlight the need to keep pace with rapid changes occurring in the landscape.
Trent Butcher, ConsultAg, 08 6253 2000, email@example.com
Geoff Thomas, DPIRD, 08 9368 3262, firstname.lastname@example.org
Dr Fran Lopez-Ruiz, CCDM, email@example.com
GRDC Project Code: TAR00007-A; TAR00006; CUR00023Back to Paddock Practices
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