Grass for Seed-Rusts

Brown Leaf Rust

Host Kentucky bluegrass.

Cause Puccinia brachypodii var. poae-nemoralis, a fungus that survives as mycelium from season to season in infected foliage. Primary inoculum is urediniospores produced in pustules on overwintering sources; secondary inoculum is produced in pustules from primary infections. Several urediniospore cycles can occur in a growing season. Teliospores are two-celled and develop with urediniospores in fall; they often are covered by epidermis.

Symptoms Pustules occur mainly on the lower surfaces of leaf blades but also develop on leaf sheaths. Urediniospores within the pustules are yellow-brown or reddish-yellow.

Crown Rust

Hosts Tall fescue, perennial ryegrass, bluegrass, and orchardgrass. The alternate host is buckthorn (Rhamnus spp.). Its importance varies considerably with its proximity to the grass host.

Cause Puccinia coronata, a fungus that overwinters on infected plants. Primary inoculum is urediniospores; secondary inoculum (urediniospores) is produced in initial pustules and disseminated by wind. Teliospores are two-celled and are produced in late summer. (The term "crown" is associated with the teliospore, not with a location on a plant.) The top of the spore is broad with a "crown" of finger-like projections.

Crown rust develops on leaf surfaces when free water is present and temperatures range from 65°F to 72°F. Epidemics are favored by urediniospore dispersal in warm temperatures (about 75°F to 80°F), in conditions that allow persistent dew formation. Survey seed production fields repeatedly to prevent a buildup of crown rust before applying fungicides to susceptible cultivars.

Symptoms Pustules occur as small, scattered blisters on upper and lower surfaces of leaf blades, but they also may appear on leaf sheaths. The epidermis along the margin of the pustule is slightly raised but not ragged like stem rust pustules. Urediniospores are bright orange-yellow. Urediniospore lesions (pustules) sometimes develop in stripes, which causes confusion with stripe rust in field diagnosis. Microscopic examination of urediniospores and teliospores is needed for proper diagnosis.

Fine Fescue Rust

Hosts Red, Chewings, and sheep fescue. The alternate host for fine fescue rust is snowberry (Symphoricarpos spp.), a common plant throughout the West.

Cause Puccinia crandallii, a fungus that survives from season to season on infected plants. Primary inoculum is urediniospores; secondary inoculum (urediniospores) is produced in initial pustules and disseminated by wind.

Symptoms Pustules are scattered on the leaf blade's upper surface. Urediniospores are cinnamon-brown. This rust species is confused easily with stem rust because the color of the urediniospores is similar. In the field, look for pustules on the upper leaf surface. Stem rust pustules are on the upper and lower leaf surface and on stems of seed heads. Identify species by microscopically examining urediniospores and teliospores. Urediniospores and teliospores of P. crandallii generally are similar in shape to those of P. graminis but larger. Pores in the urediniospores of P. crandallii are scattered rather than arranged at the equator as in P. graminis.

Stem Rust

Hosts Perennial ryegrass, tall fescue, Chewings fescue, orchardgrass, bluegrass. Principal alternate host is barberry (Berberis spp.).

Cause Puccinia graminis subsp. graminicola, a fungus that overwinters 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 50°F. At 50°F, time for a urediniospore-to-urediniospore cycle varies for cultivars but usually requires 13 to 17 days. At 65°F 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, bubble-like blisters form on the surface; they feel rough to the touch. After pustules break through the epidermis, surface tissues look ragged and torn.

Stripe Rust

Hosts In the Willamette Valley of Oregon, stripe rust is a serious disease in bluegrass. It also attacks orchardgrass. An alternate host for stripe rust is unknown. This population of stripe rust does not attack wheat, or vice versa.

Cause Puccinia striiformis, a fungus that overwinters on infected plants. In spring, primary infection is from windborne urediniospores produced on infected plants. Secondary spread continues from subsequent infections. As the season passes, urediniospore production drops or ceases; black teliospores are produced instead.

On bluegrass, the disease may develop rapidly when free moisture (rain or dew) occurs and temperatures range between 50°F and 55°F. Nearly every year it can be found as early as January or February.

On orchardgrass, the disease is most serious when free water is present and temperatures are 70°F to 75°F. In most years, stripe rust is not epidemic in orchardgrass because higher temperatures are required for growth and increase. However, in low spots in a field or during early warm weather, the disease can be serious.

Symptoms Pustules contain yellow to orange-yellow urediniospores that form in narrow, linear stripes on leaves' upper sides. Pustules also are on stems, the leaf sheath, and the outer and inner side of the glumes.

Cultural control

  • Many turf-type cultivars with crown rust resistance have been released.
  • Late planting in the fall or spring planting reduces stem rust in the first year of perennial ryegrass.

Chemical control Materials listed below may be applied for control of the rust diseases discussed above, see fungicide labels. The USDA-ARS has developed a stem rust model that predicts rust activity based on scouting findings and the model can be found on the Stem Rust Website at http://pnwpest.org/cgi-bin/stemrust1.pl . If the rust model is not used, begin applying fungicide when first rust pustules appear; repeat every 7 to 10 days for contact fungicides or every 14 to 21 days for systemic fungicides. Spray dates may vary due to yearly variations in rain and temperatures. Applications at flag leaf emergence, even if rusts are not visible, can help in a year when rust does not develop fully due to low temperatures.

Kentucky bluegrass-one (1) to three (3) applications for stripe rust control beginning about April 15 to 20.

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.

  • Chlorothalonil products (Group M5) such as:
    • 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.
    • Echo 720 at 1 to 1.5 pints/A or Echo 90DF at 0.875 to 1.25 lb/A at 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 before harvest. 12-hr reentry.
  • Demethylation-inhibiting (DMI) fungicides (Group 3) are labeled for use.
    • 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. 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. 12-hr reentry.
    • Folicur 3.6F at 4 to 8 fl oz/A on 14- to 16-day intervals. Do not apply within 14 days of 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.
    • Laredo EC at 8 to 12 fl oz/A on 14- to 21-day intervals is labeled for use on Kentucky bluegrass in Oregon, Washington, and Idaho only (SLN OR-000002, SLN WA-020026, SLN ID-020021). Do not graze treated fields for one year after applying. 24-hr reentry.
    • Muscle 3.6 F at 4 to 8 fl oz/A on 14- to 16-day intervals. 12-hr reentry.
    • Orius 3.6 F at 4 to 8 oz/A on 14- to 16-day intervals. Chaff, screenings and straw from treated areas may be used for feed purposes; however, do not feed forage, cut green crop, or use seed for feed purposes. Regrowth may be grazed 17 days after last application. 12-hr reentry.
    • PropiMax EC at 4 to 8 fl oz/A (except bluegrass apply 4 fl oz/A) on 14- to 21-day intervals. Make the last application at least 20 days before seed matures. Do not feed hay cut within 20 days of the last application. Do not graze treated areas within 140 days of the last application. 12-hr reentry.
    • Rally 40WSP at 5 to 7 oz/A in a minimum of 10 gal of water on 14- to 21-day intervals. Oregon and Washington only (SLN OR-090006; SLN WA-090007). Do not use within one year of harvesting grass hay, grazing of the field. No portion of the treated field, including seed, seed screenings, hay forage or stubble may be used for human or animal feed. 12-hr reentry.
    • Tebusha 3.6FL at 4 to 8 fl oz/A on 14- to 16-day intervals. Do not forage or cut green crop for feed purposes. Chaff, screenings, and straw from treated areas may be used for feed purposes. Regrowth may be grazed starting 17 days after the last application. Preharvest interval is 4 days. 12-hr reentry.
    • Tebustar 3.6L at 4 to 8 fl oz/A on 14- to 16-day intervals. Preharvest interval is 4 days. Chaff, screenings, and straw from treated areas may be used for feed purposes. Regrowth may be grazed 17 days after last application. 12-hr reentry.
    • Tilt at 4 to 8 oz/A (maximum 4 oz on bluegrass) when infection is noticeable and increasing in number, in late spring or early summer. Repeat on 14- to 21-day intervals. Last application at least 20 days before seed matures. Preharvest for hay is 20 days; do not graze within 140 days after last application.12-hr reentry.
    • Toledo at 4 to 8 fl oz/A on 14- to 16-day intervals. Do not apply within 4 days of harvest. Do not forage or cut green crop for feed purposes. Chaff, screenings, and straw from treated areas may be used for feed purposes. Regrowth may be grazed starting 17 days after the last application. 12-hr reentry.
  • JMS Stylet Oil at 1 to 2 gal/A. Slightly effective when used alone but most effective when 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, when temperature is above 90°F, or when plants are wet or under heat or moisture stress. Spray with at least 20 gal/A water. 4-hr reentry. O
  • Strobilurin fungicides (Group 11) are labeled for use. Do not make more than two (2) applications of any Group 11 fungicide before alternating to a labeled fungicide with a different mode of action.
    • Abound at 6 to 15.5 fl oz/A on 10- to 14-day intervals. May be applied up to 8 days before swathing. 4-hr reentry.
    • Absolute 500 SC at 5 to 7.7 fl oz/A on 21-day intervals. Do not apply within 4 days of harvest. Do not forage or cut green crop for feed purposes. Chaff, screenings, and straw from treated areas may be used for feed purposes. Regrowth may be grazed starting 17 days after the last application. 24-hr reentry.
    • Headline at 6 to 12 fl oz/A. First application should be at the flag leaf stage or at the early onset of disease. Make a second application 14 to 21 days later. Do not graze or feed forage or hat to livestock within 27 days of last application. Preharvest interval is 14 days. 12-hr reentry.
  • Premixes of Group 3 + 11 fungicides are available for use. Do not make more than two (2) applications of any Group 11 fungicide before alternating to a labeled fungicide with a different mode of action.
    • Quilt at 14 to 27.5 fl oz/A (except bluegrass apply at 14 fl oz/A) or Quilt Xcel at 14 to 26 fl oz/A on 14-day intervals. Make the last application at least 20 days before seed matures. Do not feed hay cut within 20 days of the last application. Do not graze treated areas within 140 days of the last application. For use in Oregon, Washington, Idaho, Minnesota, and Nebraska only. 12-hr reentry.

Biological control Efficacy in the Pacific Northwest is unknown.

  • Regalia (Group P5) at 1 to 4 quarts/A plus another fungicide on 7- to 10-day intervals. Preharvest interval is 0 days. 4-hr reentry. O
  • Serenade MAX at 1 to 3 lb/A on 7- to 10-day intervals. Applications can be made up to and the day of harvest. 4-hr reentry. H O