Cause Puccinia graminis subsp. graminicola, a fungus that overwinters as slow-growing mycelium in overwintering plants. Susceptible hosts include perennial ryegrass, tall fescue, Chewing's fescue, orchardgrass, bluegrass. The principal alternate host is barberry (Berberis spp.). 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 varieties 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, varietal 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.
Cultural control
- Late planting in the fall or spring planting reduces stem rust in the first year of perennial ryegrass.
Chemical control 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://uspest.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.
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 varieties harvested in late June or early July. Fewer applications needed for early-blooming varieties.
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.
- Priaxor Xemium (Group 7 + 11) at 4 to 6.9 fl oz/A on 14- to 21-day intervals. Do not make more than two sequential applications of Priaxor before alternating to a labeled non-group 7 or 11 fungicide. Do not graze or feed forage or hay to livestock within 27 days of last application. Preharvest interval of 14 days. 12-hr reentry.
- 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 13.7 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.