Net form of net blotch is a damaging foliar disease of barley in susceptible varieties. Grain yield and quality losses occur where yield potential is greater than 3 t/ha. At least two, well timed fungicide applications are required to minimise losses.
Net form of net blotch (NFNB) is a major foliar disease of barley worldwide due to the cultivation of susceptible varieties (Fig. 1) and favourable climatic conditions.
It is becoming more common in Australia due to the cultivation of susceptible varieties and breakdown of resistance through the development of new virulences in the pathogen population.
If unmanaged, NFNB can defoliate crops (Fig. 2) and cause significant grain yield and quality losses. Previous research by Khan (1987) in Western Australia showed losses of up to 33% as well as losses to grain weight.
Agriculture Victoria conducted fungicide management field experiments (Fig. 3) during 2012-17 to determine the potential losses in new barley varieties and to identify the best fungicide strategies for its control.
Loss due to NFNB was dependant on grain yield potential and seasonal conditions. Grain yield potential needed to be greater than 3 t/ha and wet seasonal conditions present for losses to occur. Losses were greatest where potential grain yields were greater than 5 t/ha and where there were wet spring conditions. Similar to previous findings, up to 34% grain yield loss and significant reductions to grain plumpness were recorded in susceptible varieties. No losses were recorded in lower yielding environments.
Net form of net blotch progressed rapidly during the spring months, when climatic conditions were warm (20-25°C) and wet. The key growth stage for foliar fungicide application was flag leaf emergence (Z39), which provided the greatest suppression in most years. Another application of either seed-applied fungicide fluxapyroxad (Systiva®) or foliar fungicide at stem elongation (Z31) or ear emergence (Z55) was required to minimise loss. In some seasons, where yield potential was greater than 8 t/ha, three applications were necessary to minimise loss. In all seasons, a single fungicide application was generally ineffective.
These findings showed the importance of avoiding growing susceptible varieties where possible, avoiding sowing into infected barley stubble and having a proactive and effective fungicide strategy for susceptible varieties in high yielding environments.
McLean Mark S., Hollaway Grant J. (2019) Control of net form of net blotch in barley from seed- and foliar-applied fungicides. Crop and Pasture Science 70, 55-60. https://www.publish.csiro.au/CP/CP18142
Frank Henry, Agriculture Victoria
Hugh Wallwork, SARDI