Spot form of net blotch (SFNB) is a common foliar disease of barley in south-eastern Australia. It is favoured by the intensive cultivation of susceptible varieties in close rotation and the use of stubble retention practices.
Spot form of net blotch has been shown to cause grain yield and quality loss where climatic conditions are favourable and yield potential is greater than 2.5t/ha. Experiments conducted in the Wimmera region of Victoria during 2005-11 demonstrated yield losses were typically about six per cent, while grain quality losses included up to a five per cent increase in screenings, 13 per cent reduction in retention and six per cent reduction in grain weight (McLean and McColl, 2015).
The Department of Economic Development Jobs Transport and Resources (DEDJTR) and BCG are in the second season of collaborative experiments investigating the grain yield and quality loss associated with SFNB in the Mallee region of Victoria in the GRDC funded project DAV00129.
During 2015, experiments were conducted to investigate the effect of growing varieties with different susceptibility ratings and the efficacy of the new seed treatment fungicide, Systiva® and foliar fungicide Prosaro® applied at different timings with the aim of suppressing SFNB and improving grain yield and quality. The treatments selected were based on the most effective identified in previous research conducted in the Wimmera during 2005-11 (McLean et al. 2015).
TAKE HOME MESSAGES
- Spot form of net blotch (SFNB) was at low levels during 2015 due to dry seasonal conditions
and was unlikely to have caused grain yield or quality loss in the Mallee.
- SFNB severity peaked at 9% leaf area affected at flag leaf emergence in very susceptible
rated varieties at the Quambatook site.
- Cultivation of moderately susceptible or better rated varieties or the application of fungicide
significantly reduced SFNB severity, but did not improve economics because of low yield
To compare SFNB severity, grain yield and quality of barley varieties with different susceptibility ratings and to identify effective fungicide strategies for managing SFNB.
Soil type: Sandy clay loam
Annual rainfall: 225mm
GSR (Apr-Oct): 165mm
Crop type: Barley (see Table 1)
Sowing date: 6 May
Seeding equipment: Knife points, press wheels, 30cm row spacing
Target plant density: 150 plants/m²
Harvest date: 1 December
Trial average yield: 1t/ha
Fertiliser: Granulock Supreme Z @ 50kg/ha at sowing and 90kg/ha of urea applied @ GS22
Fungicides: Refer to Table 2.
Weeds and pests were controlled as per best management practice.
Two replicated experiments were conducted at Quambatook. The site had residual barley stubble infected with SFNB which provided a source of inoculum. The first experiment included eight barley varieties with different resistance/susceptibility ratings (Table 1). Two treatments were tested for each variety.
Treatment 1: Fungicide Systiva® @ 150ml/100kg seed applied to seed and Prosaro®
@ 150ml/ha as foliar application at GS32 and GS45 to minimise disease.
Treatment 2: Disease. No fungicide applied.
The second experiment consisted of the very susceptible variety, SY Rattler treated with six different fungicide treatments (listed in Table 2.) Wheat buffer rows were sown between each barley row in both experiments.
Spot form of net blotch severity was determined by visually estimating percentage leaf area effected on three occasions: 7 August (GS32), 31 August (GS37) and 30 September (GS89). Grain yield was determined by measuring grain weight from each plot at harvest. Grain quality measurements of protein, retention, screenings and test weight were measured post-harvest.
RESULTS AND INTERPRETATION
Spot form of net blotch severity was low for most of the 2015 growing season due to dry seasonal conditions. SFNB severity peaked at nine per cent leaf area infection in VS rated varieties at flag leaf emergence (GS37), then reduced to about one per cent at ripening (Table 3). SFNB severity varied between the varieties tested and increased according to higher susceptibility rating.
Spot form of net blotch did not cause significant grain yield or quality loss at the Quambatook site during 2015. This was expected, given that SFNB severity was less than 10 per cent throughout the growing season and that yield potential was low. Grain protein and screenings were high and retention low due to a lack of rainfall during the spring months.
All six fungicide treatments tested were effective in suppressing SFNB, but there was no significant difference between treatments due to low disease pressure and no significant effect on grain yield or quality, indicating that fungicides were of no economic benefit.
Spot form of net blotch is a common foliar disease of barley in the Mallee region of Victoria. However, its severity and impact on grain yield and quality vary depending on climatic conditions and yield potential. SFNB is unlikely to cause loss when yield potential is less than 2.5t/ha or when growing season rainfall is below average, as was observed during 2015. This was in contrast to 2014 when grain yield loss of very susceptible rated varieties was 6-11 per cent.
Spot form of net blotch will need to be managed during 2016 in ‘susceptible’ and ‘very susceptible’ rated varieties in which inoculum from the 2014 and 2015 growing seasons is present and favourable climatic conditions occur during winter and spring. An application of foliar fungicide at GS31-39 is the most effective method for suppressing SFNB but two applications may be necessary if frequent rainfall occurs during the spring months. The new seed treatment, Systiva, is also very effective during the early stages of crop development.
The best way to minimise loss due to SFNB is by avoiding growing very susceptible and susceptible rated barley varieties. In susceptible varieties, application of seed (Systiva) or foliar fungicides can provide effective suppression of SFNB and reduce the risk of loss. However, application of fungicide may not provide economic benefit during below average rainfall seasons such as 2015. Monitor crops during winter and apply fungicide when yield potential is above 2.5t/ha and SFNB infection is high (eg. greater than 10 per cent leaf area infected).
McLean M., McColl S., 2014, 2014 BCG Season Research Results, ‘Spot form of net blotch yield loss and management in the Mallee’, pp. 109-112.
McLean M.S., Weppler R., Howlett B.J., Hollaway G.J., 2015, Australasian Plant Pathology (online), ‘Spot form of net blotch suppression and yield of barley in response to fungicide application in the Wimmera region of Victoria, Australia’.
The authors thank Grains Research and Development Corporation (DAV00129) and Department of Economic Development Jobs Transport and Resources for funding and support.
For further information pertaining to the 2015 season, please use the links below.
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