Stubble-borne diseases such as yellow leaf spot (YLS) of wheat and spot form of net blotch (SFNB) of barley will need to be monitored during 2016 and foliar fungicides applied where necessary. These diseases will be common and most severe in early sown crops with wet seasonal conditions across the south eastern and western grain growing areas, where susceptible varieties are grown and stubble retention practices are undertaken.
Growers should start to look for symptoms during the tillering stages to determine risk and need to apply registered foliar fungicides throughout the season. It is important to apply foliar fungicides during stem elongation and/or flag emergence stages to maximise disease suppression in high risk situations. Applications of foliar fungicide during tillering or ear emergence are unlikely to provide economic return.
In the Southern Region, Agriculture Victoria research has shown that YLS causes 10-15% grain yield loss in susceptible varieties, while SFNB causes 5-25% yield loss, depending on the season. SFNB can also cause significant reductions in grain quality, including grain plumpness and weight. Research in WA has shown grain yield gains from SFNB control of 5 – 59% with a reduction in screenings and improved grain weight, hectolitre, brightness and protein levels.
Yellow leaf spot
The first symptoms appear on leaves as small tan oval spots or lesions surrounded by a yellow halo (Figure 1). Individual lesions may vary in shape and size, often expanding and joining together with other lesions. The tips of severely affected leaves soon yellow and die. Accurate disease identification is important as symptoms of yellow leaf spot can be confused with other disorders like aluminium toxicity, physiological leaf spotting or herbicide damage.
Where YLS is present with infection moving up the canopy, a foliar fungicide should be applied prior to or just after rain, between flag leaf emergence and late booting. This will prevent the disease from moving up onto the flag leaf. Fungicides are most likely to give an economic return when:
- disease conducive weather is likely in the weeks following application;
- yield potential is above 3.0 t/ha;
- a susceptible variety is being grown; and
- 5 per cent of the Flag (-2) leaf and Flag (-3) leaf are affected.
Further information on yellow leaf spot can be found here:
- Yellow leaf spot Agnote – Agriculture Victoria
- Managing yellow spot and septoria nodorum blotch in wheat – DAFWA
Spot form of net blotch
Symptoms are most commonly found on leaves and develop as circular dark brown spots 3-6 mm in diameter, surrounded by a yellow chlorosis (Figure 2).
Foliar fungicides are most effective when applied during stem elongation (Z31-4) and flag leaf emergence stages (Z37-9). A single application of foliar fungicide during early to mid tillering (Z21-5) is generally ineffective in suppressing SFNB and may be insufficient to eliminate grain yield and quality loss. Where seasonal conditions favour disease development, a second application may be needed.
The new seed treatment Systiva® (fluxapyroxad), is very effective at suppressing SFNB during the emergence and tillering stages. If disease pressure is sustained during wet seasonal conditions, then an additional application of foliar fungicide with a different mode of action should be applied during flag-ear emergence.
Further information on sport form of net blotch can be found here:
- Managing net-type net blotch and spot-type net blotch in Western Australia – DAFWA
- Spot form of net blotch yield loss and management – GRDC Update Paper 2016
- Yield response to fungicide control of barley spot type net blotch in Western Australia – GRDC Update Paper 2016 and Presentation
Mark McLean, Agriculture Victoria
Hugh Wallwork, SARDI
Geoff Thomas, DAFWA
Ciara Beard, DAFWA