Take home messages
- Net form of net botch (NFNB) can be a damaging disease and requires proactive management in susceptible barley varieties, during favourable seasons.
- NFNB did not cause grain yield loss in RGT Planet at Birchip and Horsham during 2018, due to dry seasonal conditions.
- NFNB caused 13 per cent (0.5t/ha) grain yield loss in very susceptible rated barley breeding line, VB9613 at Horsham during 2018.
Background
Net form of net blotch (NFNB) can be a damaging stubble and seed-borne foliar disease of barley when conditions are conducive for infection and there is good yield potential. Experiments conducted near Horsham during 2017 showed that NFNB can cause up to 35% grain yield loss and affect grain quality by reducing grain plumpness and weight. Losses occur where susceptible varieties are grown using infected seed or sown into infected stubble and where seasonal conditions are favourable. This is typically where potential grain yields are more than 3t/ha and where growing season rainfall is average or better. The most important period for infection is during late winter and spring when NFNB can develop rapidly during wet and warm conditions. Net form of net blotch will be a common issue for growers where NFNB susceptible varieties such as RGT Planet are grown. Agriculture Victoria is conducting experiments to determine the potential losses for varieties with different resistance/susceptibility ratings in different environments and seasons.
Aim
To determine the grain yield and quality loss due to NFNB for barley varieties with different resistance/ susceptibility ratings, in the Wimmera and Mallee to inform disease management decisions.
Paddock details
| Locations: | Horsham and Birchip |
| Crop year rainfall (Nov-Oct): | Horsham – 300mm Birchip – 196mm |
| GSR (Apr-Oct): | Horsham – 197mm Birchip – 137mm |
| Soil type: | Horsham – Clay vertisol Birchip – Clay loam |
| Paddock history: | Horsham – Peas 2017 Birchip – Lentils 2017 |
Trial details
| Crop type: | Barley cultivar and NFNB reaction. Fathom – Moderately resistant to moderately susceptible (MRMS) Commander – Moderately susceptible (MS) RGT Planet – Susceptible to very susceptible (SVS) VB9613 – Very susceptible (VS) |
| Treatments: | 1. No disease, Systiva® @ 150mL/100kg seed, Prosaro® @ 300mL/ha @ GS31, GS39 and GS55. No infected stubble. 2. Disease, 1kg of NFNB infected stubble spread three weeks after sowing. No fungicide. |
| Target plant density: | 150 plants/m² |
| Seeding equipment: | Knife points, press wheels, 30cm row spacing |
| Sowing date: | Horsham – 8 May 2018 Birchip – 23 May 2018 |
| Replicates: | Six |
| Harvest date: | Horsham – 4 December 2018 Birchip – 13 November 2018 |
| Trial average yield: | Horsham – 4.5t/ha Birchip – 0.6t/ha |
Trial inputs
| Fertiliser: | Managed to maximise grain yield and quality according to soil test results. |
| Herbicide: | Weeds were controlled according to best management practice. |
| Insecticide: | Pests were controlled according to best management practice. |
| Fungicide: | All plots were sown with fertiliser treated with flutriafol @ 400mL/ha to control scald. At Horsham, foliar application of flutriafol @ 200mL/ha was also done 8 August and 23 September to suppress scald. |
Method
Two experiments were conducted during 2018, one near Horsham and another near Birchip. The trials consisted of three barley varieties with different resistance/susceptibility to NFNB and one very susceptible control as listed in the trial details. Six replicates of two treatments were applied as described in the trial details. Varieties and treatments were sown in a completely randomised block design. Wheat buffer plots were sown between each barley row to reduce disease influence from adjacent plots.
Net form of net blotch severity was assessed by visually estimating percentage leaf area affected on four occasions: 2 August, 13 September, 27 September and 18 October 2018 at Horsham and on one occasion: 2 August 2018 at Birchip. The first three assessments at Horsham and assessment at Birchip were whole plot estimates of NFNB severity. The last assessment at Horsham was of leaf area affected on the top three leaves of ten individual tillers from each plot. Scald severity was estimated for each variety and treatment on 18 October at Horsham. Grain yield was determined by measuring grain weight from each plot at harvest. Grain quality assessments of protein, retention, screenings and test weight were measured post-harvest.
Results and interpretation
The Birchip site had well below average rainfall during the growing season. Less than 5% of leaf area was affected by NFNB during the winter period (data not shown) and grain yield was less than 0.7t/ha in all varieties and treatments (data not shown), indicating that soil moisture was the main limiting factor and NFNB did not affect grain yield due to the dry conditions.
The Horsham site was sown into a paddock with good sub-soil moisture, providing grain yields of approximately 4.5t/ha, despite growing season rainfall being well below average. Up to 24% of leaf area was affected by NFNB infection in the very susceptible control line VB9613 during the growing season. This resulted in a 12% reduction in grain yield (Figure 1) and losses to grain plumpness and weight (Figure 2). This demonstrated the importance of avoiding growing barley varieties that are rated as very susceptible (VS) to NFNB as they can have significant losses during any season with good yield potential. Net form of net botch developed late in the season in the susceptible to very susceptible (SVS) rated RGT Planet but was not sufficient to cause grain yield loss and only caused minor grain quality loss. This contrasted with the Horsham site during 2017, where RGT Planet had 22% grain yield loss and significant losses to grain quality. This demonstrated that seasonal conditions are an important factor for risk of loss due to NFNB and that NFNB is unlikely to be a limiting factor during dry seasons. Especially where there is an extended dry period during the spring months, such as during 2018. Fathom (MRMS) and Commander (MS) had little or no NFNB infection and no losses to grain yield or quality, showing that moderately susceptible (MS) or better rated varieties can be sufficient to avoid loss due to NFNB in some seasons. Scald infection was present in Fathom, Commander and RGT Planet, which may have affected grain yield slightly.
Figure 1. Net form of net blotch and scald severity and grain yield loss of three barley varieties and one very susceptible control at Horsham during 2018. (* = statistically significant at 0.05).
Figure 2. Grain quality loss of three barley varieties and one very susceptible control in response to net form of net blotch and scald infection at Horsham during 2018. (* = statistically significant at 0.05).
Commercial practice
Risk of production loss in barley due to NFNB is high in susceptible varieties. Varieties rated SVS, such as RGT Planet, can have grain yield losses of up to 25% as well as grain quality losses during seasons favourable for the disease. NFNB resistant varieties (those rated MR and better) have no risk of loss, especially in a Mallee environment.
Seasonal conditions influence NFNB infection and subsequent loss in susceptible barley varieties. Monitoring susceptible crops for early infection, seasonal climate outlooks and estimated grain yield potential can be used to provide an indication of crops at risk. In general, susceptible crops with yield potential of 3t/ha or greater should be managed, especially where barley stubble is present.
Net form of net blotch is seed and stubble-borne, so avoid sowing barley into barley stubble from the previous two seasons and monitor crops for early infection. This will help to identify crops that need to be managed using fungicides.
Fungicides can be used to minimise losses due to NFNB infection. Timely fungicide applications are important, with at least two applications required during favourable seasons in susceptible varieties. Our research has shown that seed applied Systiva® in combination with foliar fungicides or multiple foliar fungicide application can be effective. In the Wimmera, foliar fungicide application at flag leaf emergence (GS39) was the most beneficial and should be included in all fungicide strategies. While application at stem elongation (GS31) at ear emergence (GS55) also provided benefit. In the shorter season Mallee environment, foliar fungicide application at stem elongation (GS30-33) along with another at flag leaf emergence (GS39) would likely provide the greatest benefits.
Acknowledgements
The authors would like to thank the Grains Research and Development Corporation and Agriculture Victoria for investment (DAV00129).
