Spore traps have detected the presence of airborne ergot ascospores around Kentucky bluegrass production areas in the Grande Ronde Valley.

*Figure updated on 5/21/20 to reflect the average number of cells per ascospore (Tiffany 1948).

Spore counts are relatively low and sporadic compared to other sites. However, a relatively few number of ascospores can begin an infection, and the honeydew (secondary) stage of the disease can amplify the disease in a field before harvest. Our research has shown that, at least in some cases, up to 30% of infections can be caused by honeydew.

It is also important to note that the spore traps currently being used at all sites sample a relatively small volume of air (about 3,800 gallons of air/day). Consequently, the ascospores that are detected and reported likely represent a small proportion of the total number in the area.

Spore trap results confirmed the presence of airborne ergot ascospores in the Lower Columbia Basin of Oregon (top) and Washington (bottom):

Spore counts in the Lower Columbia Basin of OR increased 6.8X during the week of May 4 – May 10 compared to April 27 – May 3.
*Figure updated on 5/21/20 to reflect the average number of cells per ascospore (Tiffany 1948).
A large spike of spores were observed on May 4 in the Lower Columbia Basin of WA.
*Figure updated on 5/21/20 to reflect the average number of cells per ascospore (Tiffany 1948).

The spore counts presented above are intended to show daily trends in spore production in their respective areas and do not necessarily indicate inoculum pressure in your field(s). Spore production can vary from field to field, and inoculum pressure tends to be higher in older fields with a history of ergot in the previous season, or in new fields planted next to established fields with a history of ergot.

A predictive model for ergot ascospores was developed for the Lower Columbia Basin of Oregon that uses accumulated degree-days (beginning January 1, with a base temperature of 50°F and upper threshold temperature of 77°F) to forecast when ascospores are likely to be present.

Accumulated degree-days as of May 10 were 435 in Hermiston, OR (orange line). According to the model, most ascospores are produced in the Lower Columbia Basin when accumulated degree-days are between 414 and 727.

At this time in 2019, accumulated degree-days were 365 (dotted line).

Spore trap results confirmed the presence of airborne ascospores in sentinal plots located at COAREC. A large number of spores were captured on the first day of trapping.

*Figure updated on 5/21/20 to reflect the average number of cells per ascospore (Tiffany 1948).

The cool, wet weather that is predicted for central Oregon over the next few days will likely be conducive to sclerotia germination and spore release. In general, ascospore production by the pathogen is favored by:

  • moderate temperatures (between 50°F and 80°F)
  • high soil moisture, rainfall, and/or irrigation.
  • conditions that delay or interfere with pollination, such as cool wet weather, can increase the period of susceptibility in grass seed crops.

It is recommended that growers scout fields as grass seed crops approach flowering (anthesis). Protective fungicides should be applied prior to the onset of anthesis to protect unfertilized flowers from infection, and cultivars with prolonged flowering periods may require multiple applications.

Please refer to the PNW Plant Disease Management Handbook for more information (https://pnwhandbooks.org/plantdisease/host-disease/grass-seed-ergot).

Germinating sclerotia were observed at several research sites in the Hermiston, OR area today. Grass seed growers and crop consultants can assume that ergot spores are currently present in the area.

Perennial ryegrass varieties are not yet flowering and susceptible to ergot, but earlier-flowering cultivars of Kentucky bluegrass may be ready for a fungicide application if ergot is a concern in your area.

Early-(left), middle-(center), and late-(right) maturing cultivars of Kentucky bluegrass at the OSU Hermiston Agricultural Research and Extension Center. Cultivars that are entering anthesis may be prone to ergot infection.

For maximum ergot control, fungicide applications should be timed to occur at the beginning of or immediately prior to flowering. Cultivars with long flowering periods may require (an) additional application(s).

More information on fungicide options for ergot in the Pacific Northwest can be found in the Pacific Northwest Disease Management Handbook: https://pnwhandbooks.org/plantdisease/host-disease/grass-seed-ergot .

Acknowledgement: This research is funded by the Eastern Oregon Kentucky Bluegrass Working Group, the Jefferson County Seed Growers Association, the Oregon Department of Agriculture Alternatives for Field Burning Research Financial Assistance Program, the Oregon Seed Council, the Union County Seed Growers Association, and the Washington Turfgrass Seed Commission.

Germinating sclerotia have been observed in artificially-infested sentinel plots at the Central Oregon Agricultural Research and Extension Center (COAREC). Grass seed growers and crop consultants can assume that ergot spores are currently present in the area. Spore trap updates from COAREC (and other locations in the Pacific Northwest) will be available soon.

Ergot sclerotia germinate to form stalked capitula, the small fruiting bodies that produce airborne ascospores. Our research has shown that ascospores contribute heavily to the spread of ergot both within and between fields.

Sources of sclerotia include established (2nd year or older) grass seed fields with a recent history of ergot. First-year fields are not likely to be sources of inoculum unless planted with seed infested with sclerotia. However, Kentucky bluegrass stands of all ages can potentially become infected with the disease.

Only unfertilized flowers are susceptible to infection, but the ergot pathogen has a wide host range among grasses. Other hosts include cereal rye, wheat, triticale, wheatgrass, and fescues. Cereal crops and grassy weeds can serve as alternative hosts and sources of inoculum in grass seed production systems.

Some Kentucky bluegrass varieties are in the early (~boot) stages of anthesis (flowering) and may be subject to exposure to ascospores. For maximum ergot control, fungicide applications should be timed to occur at the beginning of, or immediately prior to, anthesis. Since fungicides for ergot are protective and not curative, applying earlier is better than later. Cultivars with long anthesis periods may require (an) additional application(s).

More information on fungicide options for ergot in the Pacific Northwest can be found in the Pacific Northwest Disease Management Handbook: https://pnwhandbooks.org/plantdisease/host-disease/grass-seed-ergot .

Acknowledgement: This research is funded by the Eastern Oregon Kentucky Bluegrass Working Group, the Jefferson County Seed Growers Association, the Oregon Department of Agriculture Alternatives for Field Burning Research Financial Assistance Program, the Oregon Seed Council, the Union County Seed Growers Association, and the Washington Turfgrass Seed Commission.

Ergot spore production significantly decreased at all sites since our last update. Between June 4 and June 9 a total of 1,788 spores were captured at COAREC in Madras (compared to 24,763 spores captured between May 29 and June 3) and a total of  184 spores were detected at HAREC in Hermiston (compared to 2,440 spores detected between May 29 and June 3). Ergot spore production has also decreased at the La Grande site, with no spores detected between June 3 and June 6.

Ergot spores are being detected on a daily basis at most of the sites. An astounding 18,000 spores were captured at the HAREC site on May 28th. Spore production has increased at the artificially-infested site at COAREC in Madras, with thousands of spores being detected every day between May 29th and June 3rd.

Protective fungicides should be applied at the onset of anthesis to protect unfertilized flowers from infection, and cultivars with prolonged flowering periods may require more than one application. Based on field observations, many cultivars of Kentucky bluegrass and perennial ryegrass are flowering in central Oregon and Hermiston, respectively.