Grass for Seed-Crown Rust

Cause Puccinia coronata, a fungus that overwinters on infected plants. Tall fescue, perennial ryegrass, bluegrass, and orchardgrass are all susceptible. The alternate host is buckthorn (Rhamnus spp.). Its importance varies considerably with its proximity to the grass host. 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 varieties.

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.

Cultural control

• Many turf-type varieties with crown rust resistance have been released.

Chemical control 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.

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.
  • Muscle 3.6 F at 4 to 8 fl oz/A on 14- to 16-day intervals. 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 only (SLN OR-090006). 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. 24-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 hr 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
• Regalia 12 (Group P5) at 13.33 to 53.33 fl oz/A on 7-day intervals. Does not benefit from the addition of an adjuvant. Preharvest interval is 0 days. 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. 12-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 hay to livestock within 27 days of last application. Preharvest interval is 14 days. 12-hr reentry.
• Premixes of fungicides are available for use.
  • Quilt (Group 3 + 11) at 14 to 27.5 fl oz/A (except bluegrass apply at 14 fl oz/A) or Quilt Xcel (Group 3 + 11) at 14 to 26 fl oz/A on 14-day intervals; not labeled for bermudagrass grown for seed. 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.
  • Trivapro (Group 3 + 7 + 11) at 16 to 27.4 fl oz/A on 14- to 28-day intervals. Do not make more than two (2) sequential applications of Trivapro or other Group 7 or Group 11 fungicides. Preharvest interval is 20 days. 12-hr reentry.