Do seed treatments have a place with crown rot

Author: Steven Simpfendorfer, NSW DPI Tamworth | Date: 23 Feb 2016

Take home message

  • Treating EGA Gregory seed with Rancona® Dimension reduced establishment losses associated with the addition of crown rot inoculum to 6% compared to 23% when no seed treatment was used
  • In this instance Rancona Dimension did not provide a significant or consistent yield benefit in the presence of high levels of crown rot infection across the 12 trial sites in 2015
  • Growers should not expect Rancona Dimension to provide a significant and consistent reduction in yield loss from crown rot infection when used as a standalone management strategy
  • Growers considering the use of Rancona Dimension should follow the manufacturer’s advice and only consider it as part of an integrated management strategy against crown rot.

Background

Crown rot, caused predominantly by the fungus Fusarium pseudograminearum is a significant disease of winter cereal crops in the northern NSW and southern Qld.  Rancona® Dimension (ipconazole + metalaxyl) was recently registered in Australia as a fungicidal seed treatment with good activity against cereal bunts and smuts, pythium and suppression of rhizoctonia. Rancona Dimension is also the first seed treatment to be registered (at 320 mL/100 kg seed) for the suppression of crown rot. Suppression by definition indicates that the seed treatment reduces growth of the pathogen for a set period of time early in the season. This is distinct from the control which Rancona Dimension and other seed treatments provide against bunts and smuts of wheat and barley in that they prevent infection throughout the season. It is recommended by the manufacturer that Rancona Dimension is used as part of an integrated disease management strategy for crown rot and not as a standalone option. However, growers may still be tempted to try and use Rancona Dimension under medium to high crown rot risk situations where other management strategies have not sufficiently reduced inoculum levels. This is not uncommon following seasons with low in-crop rainfall, which limits the effectiveness of break crops such as chickpea, faba bean, canola and sorghum in decomposing cereal stubble which harbours the crown rot fungus. Under this scenario growers are often forced into sowing another winter cereal within the rotation sequence and may be tempted to resort to a seed treatment as their main option in trying to reduce yield loss associated with crown rot infection. Replicated research therefore appears warranted to determine the impact of Rancona Dimension on yield loss from crown rot infection across sites in the northern region. This will hopefully ensure that growers have a realistic expectation of what this seed treatment can achieve if used in isolation of other management strategies.

Research in 2015

Twelve replicated trials were conducted across northern NSW and southern Qld in 2015 with sites spread from Wongarbon in the south to Macalister in the north.  Background crown rot inoculum levels existed at half of the 12 sites, with medium background crown rot levels at Mullaley, Macalister and Merriwa while high background levels were measured at Coonamble, Wongarbon and Mungindi in PreDicta B soil cores collected across the sites at sowing. All trials were conducted in grower paddocks and generally co-located with GRDC funded National Variety Trials (NVT). One criterion for selecting sites is that they are generally paddocks with a good crop rotation, with all 12 sites having a non-winter cereal break (chickpea, canola or sorghum) as the previous crop within the rotation sequence. The medium to high background crown rot inoculum levels still evident at half of the sites highlights the continuing difficulty of managing stubble-borne inoculum levels of the crown rot fungus across the region. The trials used an inoculated versus uninoculated trial design to evaluate the relative impact of seed treatments on the yield impact associated with crown rot infection at each site. High levels of crown rot infection were induced in inoculated plots (added CR) by incorporating non-viable durum seed colonised by at least five different isolates of Fp into the seeding furrow (2.0 g/m of row) at sowing. The crown rot susceptible bread wheat variety EGA Gregory was used across all sites at a target plant population of 100 plants/m2 with seed treatments evaluated being:

  1. Nil seed treatment
  2. Rancona® Dimension (ipconazole 25 g/L + metalaxyl 20 g/L) at 320 mL/100 kg seed
  3. Dividend® M (difenoconazole 92 g/L + metalaxyl-M 23 g/L) at 260 mL/100 kg seed
  4. Jockey® Stayer® (fluquinconazole 167 g/L) at 450 mL/100 kg seed

Dividend M and Jockey Stayer are NOT registered for suppression of crown rot but were included to represent a commonly used wheat seed treatments for bunt and smut control or early control of the leaf disease stripe rust, respectively. Inclusion of four treatments across each site ensured statistical rigour of yield outcomes.

Impact on crop establishment

An across site analysis was conducted to assist in summarising the general trends in the performance of Rancona Dimension across the 12 sites in 2015. In the no added crown rot (CR) treatments, Rancona Dimension and Dividend M had no signficant impact on plant establishment compared to the nil fungicide treatment (Figure 1). However, establishment was slightly reduced with Jockey Stayer compared to the Rancona Dimension and nil treatments.

Simpfendorfer Steve seed 1

Figure 1. Impact of fungicide seed treatments on establishment of EGA Gregory in the absence and presence of added crown rot inoculum – average 12 sites in 2015

The addition of CR inoculum at sowing significantly reduced the establishment of EGA Gregory by 23% averaged across sites when no seed treatment was applied (Nil; Figure 1). Rancona Dimension and Dividend M significantly improved establishment in the presence of added CR with losses reduced to only 6% and 8% respectively compared to the Nil – No added CR treatment. Jockey Stayer did not significantly improve establishment in the presence of added CR. Severe early infection from crown rot - as can occur with the addition of CR inoculum in the furrow at sowing - may result in seedling blight which reduces crop establishment. Rancona Dimension may provide a useful level of protection against seedling blight associated with severe early Fusarium infections but further research is required to prove this.  

What does it mean in terms of yield?

An across site analysis of the 12 trials conducted in 2015 found that Dividend M had a minor yield reduction (0.07 t/ha) compared to using no seed treatment (Nil) in the no added CR treatment (Figure 2). Rancona Dimension did not have a significant impact on yield in the absence of added CR over the Nil treatment but was only slightly (0.09 t/ha) higher yielding than Dividend M.  Across sites, yield loss in the added CR treatment was 28% with Dividend M, 31% with Rancona Dimension and 32% with Jockey Stayer. The extent of yield loss was unaffected by the seed treatments with none significantly different from what was measured in the Nil treatment (31%; Figure 2). Rancona Dimension® unfortunately did not provide a consistent yield benefit in the presence of high levels of crown rot infection across the 12 trial sites in 2015.

Simpfendorfer Steve seed 2 v2

Figure 2. Impact of fungicide seed treatments on the yield of EGA Gregory in the absence and presence of added crown rot inoculum – average 12 sites in 2015

Implications

Rancona Dimension is registered in Australia for the suppression of crown rot infection. Rancona Dimension reduced establishment losses associated with severe early infection - created by the addition of crown rot inoculum to the seed furrow at sowing - to 6% compared to 23% in the absence of a seed treatment. Further research is required to determine if this improvement in establishment is associated with reduced Fusarium seedling blight. It should also be established whether such severe establishment losses are an artefact of the inoculation process used in the trials or whether they occur naturally in paddocks with high stubble-borne inoculum loads. In a separate larger trial conducted at Tamworth in 2015 in which infected stubble at the surface was the inoculum source Rancona Dimension did not have a significant impact on the establishment of EGA Gregory compared to the Nil seed treatment (data not presented). Establishment benefits apparent in the 12 trials unfortunately did not translate into any improvement in grain yield. Rancona Dimension did not provide a significant yield benefit over the use of no seed treatment or the two other commonly used seed treatments examined in this study under high crown rot pressure across 12 sites in 2015.

Although Rancona Dimension is registered for the suppression of crown rot, with activity against early infection and potential establishment losses evident in this study, growers should not expect this to translate into a significant and consistent reduction in yield loss from crown rot infection when the product is used as a standalone management strategy. Integrated management remains the best strategy to reduce losses to crown rot. Growers may like to consider including Rancona Dimension (320 mL/100 kg seed) as one additional component in their integrated management of crown rot.

Acknowledgments

The research undertaken as part of project DAN00175 is made possible by the significant contributions of growers through both trial cooperation and the support of the GRDC, the author would like to thank them for their continued support. The project is co-funded by the NSW state government through the NSW DPI who are also thanked for their support in fully funding my position and laboratory and other infrastructure costs.  Technical assistance provided by Robyn Shapland, Tim O’Brien, Finn Fensbo, Patrick Mortell, Carla Lombardo, Chrystal Fensbo, Kay Warren, Karen Cassin and Rachael Bannister is gratefully acknowledged.  Soil-borne pathogen levels were determined using the DNA based soil test service PreDicta B provided by the South Australian Research and Development Institute. We are also extremely thankful to NVT operators Peter Matthews (NSW DPI), Douglas Lush (QDAF) and Research Agronomist Rick Graham (NSW DPI) and their staff for sowing, managing and harvesting the trials and co-operating growers for use of their paddocks.

Contact details

Dr Steven Simpfendorfer
NSW DPI
Mb: 0439 581 672
Email: steven.simpfendorfer@dpi.nsw.gov.au

Varieties displaying this symbol beside them are protected under the Plant Breeders Rights Act 1994


Reviewed by: Dr Guy McMullen, NSW DPI

GRDC Project code: DAN00175