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ARS Home » Pacific West Area » Corvallis, Oregon » Forage Seed and Cereal Research Unit » Research » Publications at this Location » Publication #175516
Title: REGIONAL DEVELOPMENT OF ORCHARDGRASS CHOKE DISEASE AND ESTIMATION OF SEED YIELD LOSS

Author
item Pfender, William
item Alderman, Stephen

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/6/2005
Publication Date: 2/28/2006
Citation: Pfender, W.F., Alderman, S.C. 2006. Regional development of orchardgrass choke disease and estimation of seed yield loss. Plant Disease.90:240-244.

Interpretive Summary: Choke is a disease that interferes with production of seed by grasses, including orchardgrass, that was recently introduced into the Pacific Northwest grass-seed production region. The rate of spread of the disease, and its economic impact, has not previously been reported for US orchardgrass seed production. We conducted a survey for choke disease in orchardgrass seed-production fields in the Willamette Valley, OR, from 1998 to 2003. In 40% of the 99 fields surveyed, there was a significant increase in disease severity, and in 3% there was a significant decrease in choke disease. Yearly disease severity increase was as high as 29%, and the average yearly increase was 5-8%. In 1998, 60% of all surveyed fields were infested with choke disease, and by 2003, 90% of all surveyed fields were infested. Seed yield loss was found to be directly equivalent to disease severity. If the disease severity is 10%, the grower can expect a 10% seed yield loss. We found that disease severity can be efficiently estimated by simply counting the number of samples positive for choke disease in a field, instead of exhaustive counting of infected tillers. We estimate regional loss to the 2004 orchardgrass seed crop due to choke disease to be approximately $0.8 million.

Technical Abstract: An annual survey for choke disease in orchardgrass seed-production fields in the Willamette Valley, OR, was conducted from 1998 to 2003. Ninety-nine fields were visited, some in more than one year, to produce a set of 217 observations. Of the 99 fields included in the survey, 57 fields were visited in more than one year. In 40% of the revisit observations there was a significant increase in disease severity, and in 3% there was a significant reduction. Yearly disease severity increment was as high as 29%, but the average yearly increase during the period 1999 to 2003 was 5-8%. In 1998, 60% of all surveyed fields were infested with choke disease, and by 2003, 90% of all surveyed fields were infested. Average disease severity in fields in their first year of production was < 2%, and the average of disease severities in all older fields was approximately 10% in 2003. Seed yield loss was directly equivalent to disease severity (percentage of tillers diseased). We found no significant yield compensation in diseased stands. An observed correlation of disease severity with disease prevalence (proportion of sampled sites infested within a field) may permit simple estimation of within-field severity, and thus of potential economic loss. We estimate regional loss to the 2004 orchardgrass seed crop due to choke disease to be approximately $0.8 million.