How to Manage Pests

UC Pest Management Guidelines

Turfgrass

Powdery Mildew

Pathogen: Erysiphe graminis

(Reviewed 9/09, updated 9/09, pesticides updated 12/16)

In this Guideline:


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
PHI‡
(Example trade name)   (hours) (days)

UPDATED: 12/16
Calculate impact of pesticide on air quality
Bee precaution pesticide ratings
When choosing a pesticide, consider its usefulness in an IPM program by reviewing the pesticide's properties, efficacy, application timing, and information relating to resistance management, honey bees (PDF), and environmental impact. Not all registered pesticides are listed. 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 actions. 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 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.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Turfgrass
UC ANR Publication 3365-T

Diseases

A. Downer, UC Cooperative Extension, Ventura County
M. A. Harivandi, UC Cooperative Extension, Alameda County

Acknowledgment for contributions to Diseases:
F. Wong, Plant Pathology, UC Riverside
J. Hartin, UC Cooperative Extension, San Bernardino County
M. E. Grebus, Plant Pathology, UC Riverside

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