A rare fungal disease is spreading through Willamette Valley wheat fields, in some cases infecting as much as 50 percent of individual fields.
The disease, sharp eyespot, has appeared sparingly in the valley over the years, and never at high levels, said Oregon State University field crops extension agent Nicole Anderson, who worked with OSU cereal pathologist Chris Mundt to identify the disease.
Anderson, who started receiving calls about the disease in early June, originally thought the problem was take-all root rot, a disease common in Willamette Valley wheat.
But Anderson noticed the disease was spreading more rapidly than take-all and was appearing in fields where wheat followed grass seed, unheard of for take-all. Anderson also did not see stunting in the plants, a symptom common in take-all.
The dissimilarities caused Anderson to check with Mundt, who took samples and on June 24 identified the disease as sharp eyespot. Mundt, who has been at OSU since 1985, told Anderson he had never seen such widespread infection.
Anderson, Mundt and Extension Cereals Specialist Mike Flowers issued an alert warning growers of the disease. The alert stated that the disease “does not result in the severe yield losses that occur from take-all root rot or strawbreaker foot rot.”
The notice also stated that many infected heads seemed to be well filled, but test weights could be lowered, and in cases where plants were infected early in the spring, yields could suffer.
The notice also stated that, similar to take-all, “chemical control options, including fungicides and seed treatments,” have not been effective at controlling the disease. The notice also stated that there are no known differences in varietal susceptibility. “We have confirmed sharp eyespot on Kaseberg, Goetze, Legion and SY Ovation,” the notice stated.
Caused by the fungus Rhizoctonia cerealis, sharp eyespot appears as oval-shaped lesions with dark outside margins near the base of stems. The R. cerealis pathogen typically produces no spores, but lives on crop residues in the soil. As plants mature, infected stems ripen prematurely, producing white heads and shriveled kernels.
To date, severe lodging caused by the disease has not been reported in the valley, Anderson said.
Anderson said researchers are speculating that abnormally dry conditions caused the pathogen to move into plants this spring.
The disease has appeared in the north and south valley, Anderson said, and in all commonly produced varieties.