Using risk models for control of leaf blotch diseases in barley minimises fungicide use - experiences from the Nordic and Baltic countries

The disease pressure from Pyrenophora teres, Rhynchosporium graminicola, and Ramularia collo-cygni varies widely between years and locations, which highlights the need for using risk models to avoid unnecessary use of fungicides. Three disease risk models were tested in thirty-three ?eld trials during two seasons in ?ve countries in order to validate and identify situations favourable for barley leaf blotch diseases in the Nordic-Baltic region. The tested models were: The Crop Protection Online (CPO), which uses number of days with precipitation (>1 mm), cultivar resistance and disease data as basis for risk assessments; the humidity model (HM) which signals a risk warning after 20 continuous hours with high humidity, and the Finnish net blotch model (WisuEnnuste), which calculates a risk based on previous crop, tillage method, cultivar resistance and weather parameters. The risk models mostly gave acceptable control of diseases and yield responses compared with untreated and reference treatments. In the dry season of 2018, the models recommended 88-96% fewer applications than the reference treatments, while in 2019, the number of applications was reduced by 0-76% compared to reference treatments. Based on yield increases, the recommendations were correct in 50-69% of the trials compared to one-treatment references and 69-80% of the trials when references used mainly two treatments.