Amalgamated Sugar Co. crop consultants have found powdery mildew in beet fields near Adrian, Ore., and in nearby southwestern Idaho.
Growers should apply fungicides every two to three weeks, depending on the disease pressure experienced as well as the fungicide type and chemistry used, the Pacific Northwest Pest Alert Network reported June 27.
Proactive field tests in early June by the University of Idaho found spores but no symptoms. Amalgamated consultants found symptoms June 27, prompting the company to recommend growers begin spraying by the July 4 weekend — or earlier in fields that have powdery mildew already, or are in or near the primary area where it was found, said Oliver Neher, plant health manager for Amalgamated.
Fungal spores can blow in from overwintering sources, a network handbook said. Overwintered seed beets, if infected, can be sources of infections. The fungus tolerates a wide range of environmental conditions.
Symptoms include small white patches on leaf surfaces followed by the leaves turning yellow, then purplish brown. The disease has been present in several Western states since 1974.