Description of the Disease
Powdery mildew causes grayish white, powdery growth to develop on the leaf surfaces. It begins in isolated patches before spreading over larger areas. In advanced stages of the disease, the leaf blades may turn pale yellow. The fungus survives as small, hardened fruiting bodies (cleistothecia) and may be spread into turfgrass plantings by airborne asexual spores (conidia) from other grasses and hosts.
Susceptible Turfgrasses
All turfgrasses are susceptible to powdery mildew, but it is most severe on Kentucky bluegrass and fescues.
Conditions Favoring Disease
Powdery mildew is most injurious in shady areas with high humidity and poor air circulation with temperatures at about 65°F.
Management
In areas that are prone to powdery mildew, plant less susceptible species. The incidence of powdery mildew can be reduced by improving air circulation and reducing shade. Be sure that moisture and fertility are adequate, and raise the mowing height where feasible. Fungicides are generally required only in severe cases.
| Common name | Amount to use | Ag Use REI‡ |
NonAg Use REI‡ |
|
|---|---|---|---|---|
| (Example trade name) | (hours) | (hours) | ||
| Not all registered pesticides are listed. The following are ranked with the pesticides having the greatest IPM value listed first—the most effective and least likely to cause resistance are at the top of the table. When choosing a pesticide, consider information relating to the pesticide's properties and application timing, honey bees, and environmental impact. Always read the label of the product being used. | ||||
| A. | AZOXYSTROBIN | |||
| (Heritage) | 0.2–0.4 oz/1000 sq ft | 4 | Until dry | |
| MODE-OF-ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11) | ||||
| B. | MYCLOBUTANIL | |||
| (Eagle 20EW) | 1.2 fl oz/1000 sq ft | 24 | Until dry | |
| MODE-OF-ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3) | ||||
| C. | PROPICONAZOLE | |||
| (Banner Maxx) | 1–2 fl oz/1000 sq ft | 12 | Until dry | |
| MODE-OF-ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3) | ||||
| D. | THIOPHANATE-METHYL | |||
| (Fungo Flo) | Label rates | 12 | Until dry | |
| MODE-OF-ACTION GROUP NAME (NUMBER1): Methyl benzimidazole (1) | ||||
| E. | TRIADIMEFON | |||
| (Bayleton 50 Turf and Ornamental) | Label rates | 12 | Until dry | |
| MODE-OF-ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3) | ||||
| F. | TRIFLOXYSTROBIN | |||
| (Compass) | Label rates | 12 | Until dry | |
| MODE-OF-ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11) | ||||
| 1 | Group numbers are assigned by the Fungicide Resistance Action Committee (FRAC) according to different modes of action. Fungicides with a different group number are suitable to alternate in a resistance management program. In California, make no more than one application of fungicides with mode-of-action group numbers 1, 4, 9, 11, or 17 before rotating to a fungicide with a different mode-of-action group number; for fungicides with other group numbers, make no more than two consecutive applications before rotating to a fungicide with a different mode-of-action group number. |
| ‡ | Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Agricultural use applies to sod farms and commercial seed production. |