Fungicides at seeding for management of cereal foliar diseases: Spot type net blotch (STNB) in barley

Key messages

• Registered systemic fungicides applied to seed, Systiva® (fluxapyroxad) or in-furrow on fertiliser Uniform® (azoxystrobin + metalaxyl-M), can provide significant reductions in development and severity of spot type net blotch (STNB) in barley.
• Yield response from single applications or combinations of at-seeding (Systiva, Uniform) or foliar (propiconazole, Prosaro®) fungicides ranged from 0-24% in six trials conducted in 2015 and 2016. Responses in the majority of trials were less than 10%. Greatest responses occurred when yields were more than 3t/ha.
• Yield response to Systiva seed treatment varied from 0-15% in five trials.
• Foliar fungicide applications before stem extension provide disease control but need additional follow up application for continued control and yield response.
• Systiva seed dressing can provide protection past head emergence from STNB and other necrotrophic diseases such as net type net blotch and scald.

Aims and background

Spot type net blotch (STNB) is a major disease of barley in Western Australia. This is primarily due to the predominance of susceptible varieties and increased exposure of crops to retained stubble, particularly with increasing area of continuous barley cropping. A range of foliar fungicide options are available for management of STNB and these are utilised widely in barley crops in WA. Recently both seed dressing (Systiva) and in-furrow (Uniform) fungicide options have also been registered for barley.

Foliar fungicides have been shown to provide significant reduction in severity of STNB infection and yield responses from reduced disease have also been demonstrated (Jayasena et al, 2002). However, yield impacts from STNB can be variable, dependent particularly on seasonal rainfall, and an economic response from fungicide management of STNB is not guaranteed (Hills et al, 2016).

During the 2015 and 2016 seasons a series of experimental field trials were carried out with foliar, seed dressing and in-furrow applied fungicides to determine the efficacy of these approaches in reducing STNB severity and providing a significant yield response in susceptible barley varieties sown onto barley stubble.

Method

Field trials established in 2015 and 2016 were designed to evaluate the efficacy of seed, in-furrow and foliar applied fungicide on the severity and yield impact of spot type net blotch (STNB) in barley. STNB susceptible varieties were sown with into STNB infected barley stubble at six locations: Coomalbidgup (Scope CL^A), Gibson (Hindmarsh , La Trobe^A), Arthur River (Hindmarsh^A, Bass^A) and Nukarni (Hindmarsh^A, Scope CL^A) in 2015 and Grass Patch (Rosalind^A, La Trobe^A) and Nukarni (Scope CL^A, Spartacus CL^A) in 2016. Seeding and foliar treatments were included at all sites except Coomalbidgup, where only foliar fungicides were used.

Fungicide products reported in this paper include: Systiva^® seed dressing (fluxapyroxad, 150mL/100kg seed); Uniform^® coated on granular fertiliser in-furrow (azoxystrobin+Metalaxyl-M, 400mL/ha) and foliar sprays Prosaro^® (prothioconazole+tebuconazole, 150mL/ha), propiconazole products (250g ai/L) (propiconazole, 250-500mL/ha), and Bayer product (prothioconazole+bixafen, 300mL/ha) applied at three timings (T1 = Z22-25, T2 = Z30-31, T3 = Z39-45) with appropriate water rates and adjuvants as per label recommendations. To avoid complications from smut diseases or rhizoctonia root rot, all untreated control seed was treated with Vibrance^® (180mL/100kg seed), this fungicide is not registered or recommended for STNB control.

Disease severity was assessed by estimating leaf area affected by STNB symptoms on the top three or four fully expanded leaves of at least ten randomly selected plants per plot regularly through the growing season. Yield was assessed by machine harvest and grain quality parameters including hectolitre weight, thousand grain weight and screenings (% <2.2mm screen). At Grass Patch in 2016, herbicide drift damaged several plots in Rep 1, affecting significance of yield responses.

Results

At all sites STNB was the dominant disease and was apparent from seedling–tillering stage. At sites where two varieties were tested there was negligible difference between variety responses and averaged results are presented.

At all sites, Systiva seed dressing provided significant reduction of STNB severity up to flowering-grainfill growth stages. Combinations of Systiva seed dressing or Uniform in-furrow with foliar application at flag leaf–booting growth stage (T3 timing) provided similar protection (Table 1).

All double spray foliar fungicide treatments provided significant disease reduction up to grain fill. Single applications at stem extension ~Z30-31 (T2) provided lasting protection but were significantly less effective than double spray treatments that included that timing (Table 1). A single foliar application at early tillering ~Z22 (T1) at Coomalbidgup (Table 3) did not provide long term protection but inclusion of the tillering timing (T1) in two spray programs was effective (Table1, 3).

Yield responses to fungicide treatment varied between sites. At Gibson in 2015, with an untreated yield of 4.3t/ha, responses of >0.6t/ha (15-24%) occurred in all treatments including 15% response to Systiva as a stand-alone treatment (Table 2). At Coomalbidgup with untreated yield of 4.0t/ha, multiple spray treatments resulted in significant yield responses (9-11%) but the single early tillering (Z22, T1) foliar fungicide application did not (Table 3), reflecting poor long term disease control.

Despite significant reduction in STNB, treatment yield responses did not necessarily follow suit at other sites when spring rainfall was low. Responses ranged from 0-400kg/ha, with the majority being between 50-200kg/ha (2-6%). At both Grasspatch in 2015 (11%) and Nukarni in 2016 (6%), Systiva seed treatment plus foliar fungicide at Z39-45 (T3) resulted in greatest yield response (Table 2).

Grain quality differences were evident where yield responses were significant and even in some cases where they were not. At Nukarni (2015), screenings were reduced (from >33% to 18-25%) in Scope CL^A by all multiple fungicide application treatments despite the lack of yield impact (data not presented).

Inclusion of Systiva treated Litmus^A barley in inoculated small plot disease nurseries at South Perth and Medina indicates that fluxapyroxad has long term impact on a range of diseases, as indicated on the product label. Severity of the necrotrophic diseases, spot and net type net blotch and scald were significantly lower in treated plots compared to untreated controls when assessed at flowering (data not presented).

Table 1. Effect of seed, in-furrow and foliar applied fungicides on severity of spot type net blotch (average % leaf area diseased of Flag-1 to Flag-3) in barley at five field sites (average response across varieties at each site) in 2015 and 2016. Coomalbidgup data presented in Table 3.

* SD = Systiva seed dressing (150mL/100kg), IF = Uniform in-furrow (400mL/ha)         

^# Fungicide timing all sites:       T1 = ~Z25, T2 = Z30-31, T3 = Z39-45

^# Fungicide treatments at each site:

Gibson & Arthur River 2015     T2 & T3 = a: propiconazole (250mL/ha), b: Prosaro (150mL/ha), c: Bayer product (300mL/ha)

Nukarni, 2015                            T1 & T3 = Prosaro (150mL/ha), T2 = propiconazole (250mL/ha)

Grass Patch, 2016                    T1 & T2 = propiconazole (250mL/ha), T3= Prosaro (150mL/ha)                             

Nukarni, 2016                            T1, T2, T3 = propiconazole (500mL/ha)                                                  

Table 2. Effect of seed, in-furrow and foliar applied fungicides on grain yield (t/ha) of spot type net blotch infected barley at five field sites (average response across varieties at each site) in 2015 and 2016. Coomalbidgup data presented in Table 3.

* SD = Systiva seed dressing (150mL/100kg), IF = Uniform in-furrow (400mL/ha)         

^# Fungicide treatments and timings as per footnote in Table 1

Table 3. Effect of timing of foliar applied fungicide (Prosaro 420 SC) on spot type net blotch severity (average % leaf area diseased of Flag-1 to Flag-3) and grain yield (t/ha) of Hindmarsh barley at Coomalbidgup in 2015.

^# T1 = Z22, T2 = Z31, T3 = Z42

Conclusion

The recent registration of seed dressing and in-furrow products for STNB control has provided new management options for this disease in barley crops, particularly those sown on barley stubble. Both Systiva (fluxapyroxad) as a seed dressing and Uniform (azoxystrobin + metalaxyl) as an in-furrow treatment significantly reduce progress of STNB in susceptible varieties sown into infested stubble. In the trials reported here, the period of protection they provided was evident until at least flag leaf-booting stage (Z39-45) and for Systiva until flowering-grain fill (Z65-75).

Systiva seed treatment gave longer period of disease control than foliar sprays applied prior to stem extension. At Coomalbidgup, application during early tillering (Z22) gave short term reduction of disease severity but this was not enough protection to contribute to yield responses without follow up foliar fungicide application. Where early, sustained disease control is required, seeding fungicides are likely to be more effective.

Yield responses to fungicide application are not guaranteed despite significant reductions in STNB severity (Hills et al 2016). Under high disease pressure and with good spring rainfall supporting yield potential, responses of greater than 0.6t/ha (>15%) were measured, including from Systiva seed dressing without foliar fungicide support. However, in other trials yield responses were typically <10% (<250kg/ha) with associated grain quality improvements (screenings) in Scope CL^A at Nukarni and Comalbidgup. Economic benefits are more likely where disease pressure is high and seasonal conditions, particularly spring rainfall, favour higher yield potential.

Use of either Systiva seed dressing or Uniform in-furrow can significantly reduce STNB severity in barley crops. Disease protection from Systiva alone resulted in significant yield response in one trial and when supported by foliar application at flag leaf-booting growth stage (Z33-45) significant yield response to seeding treatment was as likely as from a multiple spray approach.

Some care should be employed in utilisation of these products, both in regularity of use of individual products between seasons and with choice of foliar fungicide groups to follow within season. Despite being applied prior to crop growth, they are the first application in a fungicide program and, as such, subsequent foliar fungicide choice and fungicide group rotation needs to account for the ingredient used (eg. DMI – triadimenol, fluquinconazole, SDHI – fluxapyroxad, QoI – azoxystrobin). Utilisation of the same product in repeated years without the use of an alternative foliar fungicide group for support constitutes a risk for resistance developing. Rotation of at-seeding product groups and foliar fungicide groups, and including other integrated management options (especially avoiding barley on barley rotations), should reduce risks associated with fungicide resistance.

Inclusion of Systiva seed dressing (fluxapyroxad) or Uniform in-furrow (azoxystrobin + metalaxyl) can be an effective approach for management of barley diseases, particularly stubble borne diseases like STNB. Utilisation in the second year of a continuous barley rotation could provide a significant benefit. They are an effective addition to an integrated approach including variety choice, crop rotation, stubble management and foliar fungicide application.

References

Hills AL , G Thomas , A Grey , M Field , R Horbury , K Jayasena , C Beard and B Paynter (2016) Yield response to fungicide control of barley spot type net blotch in Western Australia. 2016 GRDC Grains Research Update, Perth GIWA website

Jayasena KW, Loughman R and Majewski J (2002) Evaluation of fungicides in control of spot-type net blotch on barley. Crop Protection 21: 63-69

Acknowledgments

DAFWA research support units at Esperance (Chris Matthews, Jolie Delroy), Merredin (Vince Lambert, Adrian Cox, Dave Allen) and Katanning (Daniel Cox, Russell Quartermaine) for trial management.

DAFWA, N. Smith, T. Scott, P&T Piggott for hosting trials.

GRDC and DAFWA for funding.

GRDC Project Number: DAW00229 Improving grower’s surveillance, management, epidemiology knowledge and tools to manage crop disease

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^A Varieties displaying this symbol are protected under the Plant Breeders Rights Act 1994

Disclaimer: Mention of trade names does not imply endorsement or preference of any company’s product by Department of Agriculture and Food, Western Australia. Only registered fungicide products are recommended. When choosing fungicides, consider the range of diseases that threaten your crop. Consult product labels for registrations. Read and follow directions on fungicide labels carefully.