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ARS Home » Pacific West Area » Corvallis, Oregon » Forage Seed and Cereal Research Unit » Research » Publications at this Location » Publication #175666
Title: YIELD LOSS ESTIMATES ASSOCIATED WITH PANICLE DISEASES OF ORCHARDGRASS

Author
item Alderman, Stephen
item OCAMB, CYNTHIA - OREGON STATE UNIVERSITY

Submitted to: Seed Production Research at Oregon State University
Publication Type: Experiment Station
Publication Acceptance Date: 2/28/2005
Publication Date: 4/30/2005
Citation: Alderman, S.C., Ocamb, C. 2005. Yield loss estimates associated with panicle diseases of orchardgrass. Seed Production Research at Oregon State University. p. 123.

Interpretive Summary: In 2003, a survey of orchardgrass fields was initiated to determine the significance of seed head diseases on orchardgrass seed production. Four hundred seed heads from each of 10 orchardgrass fields were examined for choke (Epichloe typhina), Rathay's disease (Rathayibacter rathayi), or stem rot (unknown cause). Choke, Rathay's and stem rot were found in 9, 6, and 7 of the 10 fields, respectively. Collectively the diseases reduced seed yields 5 to 14% in 8 of the 10 fields.

Technical Abstract: In 2002, a decay of immature panicles (stem rot) was observed in several orchardgrass fields. Freezing injury of the immature panicle while still in the stem, and subsequent colonization by one or more bacteria, is believed to be the principal cause of the problem. However, research is under way to establish whether or not freezing temperatures contribute to the stem rot and the role that bacteria recovered from symptomatic stems may have in the development of stem rot. During 2003, a survey was conducted in 10 orchardgrass fields, four of which exhibited stem rot in 2002. Fields surveyed were located in Benton or Linn County. One hundred panicles were collected along each of four transects across each field in a W-shaped pattern. In addition to stem rot, presence of choke and Rathay's were also recorded. Rathay's disease is a bacterial disease of the grass flower, characterized by a sticky, yellow exudate that covers a part or all of the seed head. The nematode Anguina is believed to vector the bacterium. Choke is a common and serious fungal disease of orchardgrass. It is characterized by a proliferation of fungal growth in the upper half of the reproductive tiller, which prevents emergence of the panicle. The white, felt-like growth turns orange and resembles a small orange cattail. Stem rot was observed in 8 of the 10 fields, affecting 0.5 to 1.9% of the panicles (Table 1). Rathay's disease was detected in 7 of the 10 fields, with incidence as high as 5.3%. Choke occurred in 9 of the 10 fields sampled, with incidence as high as 8.6%. Since there is little to no seed produced on panicles infected with these diseases, percentage of panicles infected roughly equates to an equivalent percentage of seed loss. Collectively, the panicle diseases reduced seed yield as much as 14%, and choke was responsible for the greatest portion of the loss. The level of choke is consistent with previously published choke surveys. Rathay's disease has occurred in Willamette Valley orchardgrass fields for decades and there is no indication that this disease has increased in recent years. However, the potential increase of stem rot in orchardgrass is not known. Annual surveys for orchardgrass panicle diseases are planned for the next few years.