Spot form of net blotch (SFNB) has been shown to reduce grain yield (0-25%), increase screenings (5%), reduce retention (13%) and grain weight (6%) in the Wimmera region of Victoria (DED Vic unpublished data). During six years of study, losses have varied in response to seasonal conditions, with greater losses experienced during seasons with average or above average rainfall during the winter and spring months.
Losses were uncommon during seasons with dry August and spring months. Information about grain yield and quality losses due to SFNB is required for the Mallee region of Victoria to help growers prioritise management strategies and make informed decisions about when to apply fungicides.
DED and BCG conducted a trial at Quambatook during 2014 as part of the GRDC funded project DAV00129. The experiment compared grain yield and quality loss in eight barley varieties with different susceptibility ratings to SFNB. It is part of an ongoing five year project which will see similar experiments conducted during the 2015 and 2016 growing seasons.
TAKE HOME MESSAGES
- SFNB caused yield losses of 0.2-0.3t/ha in a very susceptible barley varieties at Quambatook during 2014.
- SFNB increased screenings by up to seven per cent in very susceptible varieties.
- Avoid growing very susceptible and susceptible rated barley varieties to reduce the risk of grain yield and quality loss due to SFNB.
AIM
To compare grain yield and quality of barley varieties with different susceptibility ratings to SFNB and develop management strategies for the Victorian Mallee.
TRIAL DETAILS
Location: Quambatook
Soil type: Clay loam without sub-soil constraints
GSR (Apr-Oct): 168mm
Crop type: Barley (Refer to Table 1)
Sowing date: 7 May
Seeding equipment: Knife points, press wheels, 30cm row spacing
Target plant density: 150 plants/m²
Harvest date: 12 November
Trial average yield: 3.2t/ha
TRIAL INPUTS
Fertiliser: Granulock Supreme Z + Intake Hi-load Gold @ 50kg/ha at sowing plus 90kg urea (top-dressed) applied on June 19 and again on July 18.
Herbicides:
Pre-sowing Trifluralin @ 2L/ha + Avadex® Xtra @ 2L/ha, IBS
In-crop Velocity® @ 670ml/ha + Hasten @ 1% v/v Fungicides:
Treatment 1 Prosaro® @ 150ml/ha + Hasten @ 1% v/v on 26 June (GS21-25) Prosaro® @ 300ml/ha on 20 July (GS31) Prosaro® @ 300ml/ha on 18 September (GS39)
Treatment 2 No foliar fungicide
METHOD
A replicated field trial containing eight barley varieties with varying susceptibility ratings for SFNB was established on a pea stubble at Quambatook (Table 1). The trial site had residual 2012 Hindmarsh barley stubble, which acted as a source of SFNB inoculum. Wheat buffer rows were sown between each barley row.
SFNB severity was determined by visually assessing barley plots to determine the percentage of leaf area affected by foliar disease. These assessments were carried out on three occasions: 7 August (GS33), 27 August (GS39) and 3 October (GS89). Grain yield was determined by measuring grain weight at harvest. Grain quality measurements of protein, screenings, retention and test weight were recorded post-harvest.
RESULTS AND INTERPRETATION
SFNB severity varied between the eight barley varieties, increasing according to higher susceptibility ratings (Figure 1). Infection levels fluctuated throughout the season, being more severe earlier (GS33) in response to wet conditions. Most of the infection was present on the lower leaves, as there were few rainfall events after flag emergence. The exception was SY Rattler which had 20-26% leaf area affected, evenly distributed on the upper and lower leaves. Disease levels in the fungicide treated plots were typically less than 2 per cent (data not shown) indicating that the three applications were effective in suppressing SFNB.
SFNB reduced grain yield by 0.2-0.3t/ha in Hindmarsh (VS) (P<0.1) and SY Rattler (VS) (P<0.05), while screenings were increased by 4-7% and retention reduced by 3-13% in two of the susceptible and two very susceptible varieties (P<0.1). These results demonstrate that SFNB management using fungicides is warranted in the Mallee environment where very susceptible varieties are grown and reasonable yields expected.
The moderately resistant and susceptible varieties had negligible yield losses (0-0.1t/ha; NS), increased screenings of 0-3% and reduced retention of 3-10% indicating that they were less affected by SFNB and that fungicide management would be less beneficial. Grain protein and weight were unaffected by SFNB (data not shown). These results emphasise that the best option for SFNB management is to avoid growing very susceptible rated barley varieties.
COMMERCIAL PRACTICE
SFNB inoculum is common in all barley growing regions of Victoria and will result in losses to very susceptible varieties under favourable climatic conditions. To reduce the risk of loss in grain yield and quality, avoid growing barley varieties rated as very susceptible into paddocks with SFNB infected barley stubble. During favourable seasons, an application of foliar fungicide (such as Prosaro or propiconazole) at stem elongation (GS31) and/or flag emergence (GS39) provides good suppression of SFNB. However, the benefits are seasonally dependent and will not necessarily eliminate loss. A new seed treatment called Systiva is expected to be available during 2016; it will be a good option for managing SFNB and other foliar diseases such as scald and net form of net blotch during the early crop growth stages.
ON-FARM PROFITABILITY
This trial demonstrated a potential loss of profits of $47-70/ha (based on $233 per tonne, feed barley price at Quambatook on 25 November 2014) from reduced grain yield in very susceptible rated varieties. There were also potential loss in profits of $50-76 from downgrading from Malt quality grain to Feed. Fungicide application at $5-20/ha per application would have reduced some losses if applied at GS31-39. It is important to choose an effective product that will suit the budget.
The economic benefits of SFNB management depend on the seasonal conditions and the yield potential of the crop. Susceptible crops grown during seasons of average or above annual rainfall and yield are likely to benefit from foliar fungicide application. Seasons of below average rainfall and yield are unlikely to see benefits from fungicide application when managing SFNB.
ACKNOWLEDGEMENTS
This trial was funded by GRDC through the ‘Improving grower surveillance, management, epidemiology knowledge and tools to manage crop disease in Victoria’ project (DAV00129) and the Victorian Government. Thanks to the Horsham cereal pathology team (DED) for scientific input and technical assistance, and BCG technical staff for assistance.
