Cause A fungus, Blumeria graminis (syn. = Erysiphe graminis; anamorph Monilia hyalina), that overwinters on infected plants or as chasmothecia associated with debris and is most commonly observed on tall fescue, fine fescue, and Kentucky bluegrass but all cool season grasses are susceptible, including native perennial grasses. Spores can be dislodged easily and spread by wind. Cool, humid, cloudy conditions favor spore development and infection. Powdery mildew develops over a wide temperature range but is most rapid between 59°F and 70°F. The disease generally is most severe in spring and autumn.
Symptoms Isolated colonies of fine, whitish mycelia on leaves and leaf sheaths. It spreads rapidly under favorable conditions to form a dense white to light gray mass of spores on upper and lower leaf surfaces. Older leaves tend to be more heavily infected than young ones. Eventually, heavily infected leaves turn yellow or light brown as they die.
Chemical control Powdery mildew usually does not cause enough damage to justify chemical control.
- 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.
- 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.
- 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.
- 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 or Quilt Xcel (Group 3 + 11) (except bluegrass apply at 14 fl oz/A) 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.