Management of beet rust in accordance with IPM principles

High disease pressure from beet rust (Uromyces beticola) has been registered in Denmark in recent years, increasing the need to manage this pathogen in accordance with principles of Integrated Pest Management (IPM). A revised disease cycle with all major steps has been proposed including spread of the disease by sea beets (Beta vulgaris subsp. maritima) acting as a green bridge. Locations with early onset of beet rust were investigated and indicated a connection between early rust occurrence and the presence of local wild sea beets. The impact of the disease was investigated through data from 15 years of testing. In field trials with significant infection, yield reductions up to 11% have been measured and two treatments with reduced doses of epoxiconazole + pyraclostrobin resulted in the highest economic returns on average. Fungicide efficacy and susceptibility of sugar beet cultivars were tested in greenhouse and under field conditions. Results indicated high sensitivity of the pathogen to major fungicides. In greenhouse trials high efficacy was obtained by all conventional fungicides (epoxiconazole, pyraclostrobin, epoxiconazole + pyraclostrobin, difenoconazole + propiconazole) both as preventive and curative treatments. Hydrogen peroxide was tested as control agent, but was not significantly different from the untreated control. The biological control agent Bacillus subtilis QST 713 provided 76% control of beet rust when used preventively (not significant). A ranking of relevant cultivars showed variation across years and differences in susceptibility where the least susceptible cultivar on average reduced disease severity to 66% of the most susceptible cultivar. Based on the relevant literature and the findings in this study an IPM management strategy for beet rust should include less susceptible cultivars, fungicides with different modes of action, appropriate doses and application should be carried out according to monitoring and predictions.