Pacific Northwest 1998 An Online Guide to Plant Disease Control
 
Grass for Seed -- Stem Rust
Hosts: Perennial ryegrass, tall fescue, Chewings fescue, , orchardgrass, bluegrass. Principal alternate host is barberry (Berberis sp.).
Cause: Puccinia graminis subsp. graminicola, a fungus that over-winters as slow-growing mycelium in overwintering plants. In spring, the fungus resumes more vigorous growth and produces primary inoculum (urediniospores) that are windborne. Initial pustules often are few and scattered and may be difficult to see because new plant growth obscures those formed within the plant canopy. Urediniospores from these sources produce secondary inoculum which infects the same or other plants, and the disease spreads. Epidemics result from repeated sporulation cycles (production and spread of urediniospores). After seed harvest and as plants continue to grow, black teliospores are produced within the pustules formerly occupied by reddish brown urediniospores.

This disease develops when free water (rain or dew) is present on plant foliage and temperatures are above 50oF. At 50oF, time for a urediniospore-to-urediniospore cycle varies for cultivars but usually requires 13 to 17 days. At 65oF and above, the disease develops rapidly, and cycles of urediniospores can be produced in 8 to 9 days. Once the pustule ruptures, urediniospores are disseminated and infect other plants or newly exposed plant surfaces. At higher temperatures, cultivar differences in the rate of disease development are less apparent. Because urediniospores are produced and disseminated rapidly, disease cycles often overlap on the same plant or within the same field.

Symptoms: Pustules hold masses of dark reddish brown urediniospores that form on both sides of the leaves, on leaf sheaths, and on spikes or panicles. In early-season or light infections, pustules often are scattered and separate. In late-season or heavy infections, pustules often coalesce. As pustules develop, bubblelike blisters form on the surface; they feel rough to the touch. After pustules break through the epidermis, surface tissues look ragged and torn.
 
This shows the telial stage on the lower set of tall fescue plants. Notice the pustules containing urediniospores on perennial ryegrass leaves.
This shows the telial stage on the lower set of tall fescue plants. Notice the pustules containing urediniospores on perennial ryegrass leaves.

 
Cultural control: Late planting in the fall or spring planting reduces stem rust in the first year of perennial ryegrass.
Chemical control: Begin applying fungicide when first rust pustules appear; repeat every 7 to 10 days for contact fungicides or every 14 to 21 days for systemics. Spray dates may vary due to yearly variations in rain and temperatures.

Application at flag leaf emergence, even if rust is not visible, can help in a year when rust does not develop fully due to low temperatures.

Perennial ryegrass—one (1) to three (3) applications for stem rust control beginning about May 20 to 25.

Tall fescue—one (1) to three (3) applications for stem rust control in late-blooming cultivars harvested in late June or early July. Fewer applications needed for early-blooming cultivars.

Although there are no documented fungicide-resistant rusts in grass seed fields, rotating fungicides with different modes of action may reduce the potential for resistance to develop. There are now fungicides labeled that provide an effective rotation program.

  1. Abound at 6.2 to 15.4 fl oz/A on a 10- to 14-day schedule following the resistance management guidelines. Do not apply more than two (2) sequential foliar applications of Abound or other Group 11 fungicides before alternating with a fungicide that has a different mode of action. Do not make more than two (2) applications of Abound or other Group 11 fungicides per acre per year. Do not apply more than 1.44 qt (0.75 lb a.i.) per season. May be applied up to 8 days before swathing. 4-hr reentry.
  2. Bumper 41.8 EC at 4 to 8 fl oz/A (maximum 4 fl oz on bluegrass) in a minimum of 20 gal water/A for ground application or 10 gal water/A for air application on 14- to 21-day intervals. Do not apply more than 32 fl oz/A/year. Make last application 20 days before seed matures. Do not feed cut hay within 20 days of last application nor graze treated areas within 140 days of the last application. 24-hr reentry.
  3. Chlorothalonil products such as:
    1. Bravo Ultrex at 0.9 to 1.4 lb/A on 14 day intervals. Do not apply within 14 days of harvest. Do not allow livestock to graze in treated areas or feed treated plant parts to livestock. 12-hr reentry.
    2. Echo 720 at 1 to 1.5 pt/A beginning during stem elongation when conditions favor disease in Oregon only (SLN OR-980010). Re-apply at flag leaf emergence and repeat on 14-day intervals. Do not apply within 14 days of harvest. Do not apply more than 6 pt/A/season. Do not allow livestock to graze in treated areas or feed treated plant parts to livestock before harvest. Feeding of treated plant parts to livestock after harvest of seed is allowed. 12-hr reentry.
    3. Echo 90DF at 0.875 to 1.25 lb/A at 14-day intervals in Oregon only (SLN OR-980011). Do not apply within 14 days of harvest. Do not apply more than 5 lb/A/season. Do not allow livestock to graze in treated areas or feed treated plant parts to livestock before harvest. Feeding of treated plant parts to livestock after harvest of seed is allowed. 12-hr reentry.
  4. Folicur 3.6 F at 4 to 8 fl oz/A in a minimum of 20 gal/A water (ground). A maximum of 16 fl oz /A per season may be applied. May be applied up to 4 days before harvest. Chaff, screenings, and straw may be used for feed, but do not forage, cut green crop, or use seed for feed. Regrowth may be grazed starting 17 days after harvest. 12-hr reentry.
  5. Headline at 6 to 12 fl oz/A. Begin applications at the flag leaf stage or at the early onset of disease. Make a second application 14 to 21 days later. Do not apply more than twice per season. Apply with adjuvant to enhance performance. Do not graze or feed forage or hat to livestock within 27 days of last application. Preharvest interval is 14 days. 12-hr reentry.
  6. JMS Stylet-Oil at 1 to 2 gal/A. Slightly effective when used alone but most effective when is tank mixed with Tilt at 4 to 6 oz/A. Do not spray when freezing temperatures are anticipated within 48 hours of an oil application, above 90° F or when plants are under heat or moisture stress. Spray with a minimum of 20 gal of water per acre. Do not spray when foliage is wet. Good coverage is essential. 4-hr reentry.
  7. Laredo EC at 8 to 12 fl oz/A oat 14- to 21-day intervals (SLN OR-000002, SLN WA-000011, SLN ID-000020). Do not apply more that 48 fl oz/A/season. Do not graze treated fields for one year following application. 24-hr reentry.
  8. Quilt at 14 to 27.5 fl oz/A (except bluegrass apply 14 fl oz/A) on a 14-day interval. Make the last application at least 20 days before seed matures. Do not make more than two (2) sequential applications of a Group 11 fungicide before alternating to another product with a different mode of action than Group 11 fungicides. Do not apply more than 110 fl oz/A/season of Quilt. Do not feed hay cut within 20 days of the last application. Do not graze treated areas within 140 days of the last application. Do not apply more than 0.90 lb a.i. Propiconazole-containing products /A/year. Do not apply more than 0.75 lb a.i. azoxystrobin-containing products/A/year. 24-hr reentry.
  9. Tilt at 4 fl oz/A. Do not apply more than 32 fl oz/A per season. Using grass seed crop waste, hay, and seed screenings is now permitted provided the final treatment was at least 20 days before harvest. Regrowth may be grazed 140 days after the last treatment. Has systemic activity. 24-hr reentry.
Content edited by: Cynthia M. Ocamb on January 1, 2009
 
Edited by Cynthia M. Ocamb, Extension Plant Pathology Specialist, Oregon State University, Corvallis, OR 97331-2903 World Wide Web site and scripting by Eric T. Peterson and Bryan Capitano at Capitano NetSolutions, Inc., HTTP://www.capitanonetsolutions.com. Access the Plant Disease Control Guide on-line at HTTP://plant-disease.ippc.orst.edu/

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