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UC Pest Management Guidelines


Powdery mildew infecting Kentucky bluegrass leaves.

Turfgrass

Powdery Mildew

Pathogen: Erysiphe graminis

(Reviewed 9/09, updated 9/09)

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 (cleistotheicia) 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 Example trade names Ag Use
R.E.I.+
NonAg Use
R.E.I.+
(trade name)   (hours) (hours)

  Calculate impact of pesticide on air quality
When choosing a fungicide, consider general properties as well as information relating to environmental impact.
 
A. AZOXYSTROBIN Heritage  
  MODE OF ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11) 4 until dry
 
B FENARIMOL Rubigan  
  MODE OF ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3) 12 until dry
 
C. MYCLOBUTANIL Eagle  
  MODE OF ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3) 24 until dry
 
D. PROPICONAZOLE Banner Maxx  
  MODE OF ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3) 24 until dry
 
E. THIOPHANATE-METHYL Fungo 50, T-Methyl E-Pro  
  MODE OF ACTION GROUP NAME (NUMBER1): Methyl benzimidazole (1) 12 until dry
 
F. TRIADIMEFON Bayleton  
  MODE OF ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3) 12 until dry
 
G. TRIFLOXYSTROBIN Compass  
  MODE OF ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11) 12 until dry
 
1 Group numbers are assigned by the Fungicide Resistance Action Committee (FRAC) according to different modes of actions (for more information, see http://www.frac.info/). 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 (R.E.I.) 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
F. Wong, Plant Pathology, UC Riverside
M. A. Harivandi, UC Cooperative Extension, Alameda County
Acknowledgment for contributions to Diseases:
J. Hartin, UC Cooperative Extension, San Bernardino County
M. E. Grebus, Plant Pathology, UC Riverside

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