Yield reduction in barley in relation to spot-type net blotch

To study the loss of grain yield associated with specific levels of spot-type net blotch of barley, experiments were conducted at three sites with between four and six different levels of application of the fungicide propiconazole or mixtures of propiconazole and iprodione applied to obtain a wide range of disease levels. Yield loss varied from 23 to 44%. There was a negative linear relationship between yield and the average disease severity on the top three leaves (flag, flag-1 and flag-2). The observed relationship was much stronger at the milk stage compared with early flag leaf emergence stage. On average, every 10% increase in disease severity on the top three leaves accounted for 0.4 t/ha yield loss. The yield response to disease was independent of locations and years. The disease affected grain quality, with grain protein and screenings consistently higher and grain size consistently lower than samples from undiseased barley.