University of Idaho and Amalgamated Sugar Company personnel have identified cercospora leaf spot in fields near Parma, Wilder and Glenns Ferry, Idaho. Incidence is still low; however, most fields have closed rows. Cercospora spores have been detected in spore traps deployed in the Treasure Valley, and environmental conditions have been conducive for infection for a couple of weeks now.

In case fungicide applications have not yet occurred, we are strongly encouraging everyone to start spraying against cercospora leaf spot. There are several fungicides available, but be aware of multiple fungicide-resistant strains of cercospora. Depending on the disease pressure and chemistry used, applications with different chemistries should be repeated every 14 days. The use of a protectant such as copper products, ethylene bisdithiocarbamates (EBDCs) or hydrogen peroxide with every spray is strongly recommended.

Contact your crop consultant from the Amalgamated Sugar Company to discuss suitable fungicides for your area, to report a loss of fungicide efficacy or if you have any questions.

For a resource, review the cercospora leaf spot pages in the PNW Plant Disease Management Handbooks.

—From Pacific Northwest Pest Alert Network, July 6, 2024