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Ramularia leaf spot of barley in New Zealand

Ian Harvey: PLANTwise Services Limited

<div>Ramularia leaf spot of barley caused by the fungus <em>Ramularia collo-cygni</em> (Rcc) was first identified in New Zealand in the early 1980’s. Until the last few years, occurrence and damage from Rcc has been sporadic, but the disease has recently become more widespread and an important constraint to barley production. Four aspects of the disease are being actively studied: epidemiology; control with fungicides; development of fungicide resistance in Rcc; and the role and importance of seed-borne inoculum. Appearance of the disease in the field can vary between seasons and fields. Leaf wetness in host growth stages 28-32 relates to disease severity later in affected crops. During the wet 2017 spring, early infections of lower leaves were observed in crops. These may or may not have arisen from seed-borne inoculum, but can lead to rapid disease development resulting in significant losses of green leaf tissue and grain yield reductions. Rcc has been detected in most seed lines tested in Canterbury, and these infections often translated into seedling infections. Isolates of Rcc exhibiting reduced control by SDHI fungicides have been detected in fields, but combinations of some triazoles and protectant fungicides such as chlorothalonil and folpet are still giving effective control. Resistance to strobilurin fungicides has been present in the field for several seasons. Management options using fungicide mixtures and alternations integrated with other management practices can minimise losses from this disease</div>