Pacific Northwest 1998 An Online Guide to Plant Disease Control

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OSU Extension Office
 
Sunflower (Helianthus sp.) -- Powdery Mildew
 
Cause: The fungus, Golovinomyces cichoracearum (formerly Erysiphe cichoracearum), has been reported from Idaho and Washington. The disease has been found on a single plant sample sent to the OSU Plant Clinic. The fungus, reported to overwinter as chasmothecia on plant residue, is favored by conditions that produce high humidity but dry leaves. It is a highly specialized pathogen that forms a close association with the host. Conditions that favor the host also favor the pathogen. Much of the fungus remains outside the infected plant parts but sends in root-like structures, haustoria, to obtain nutrients. The white growth seen is composed of both mycelium and fungal spores.
Symptoms: White powdery areas appear on lower leaves first. All other aboveground plant parts may be affected. White areas turn gray, and small black fruiting bodies (chasmothecia) of the fungus appear in the gray areas. Severely infected leaves may turn yellow and dry up. Generally, lower leaves remain more heavily infected than upper leaves.
Cultural control:
  1. Space plants for good air circulation.
  2. Remove and destroy plant debris at the end of the season.
  3. Plant in an area that receives full sun most of the day.
Chemical control: Some labels may not allow seeds from treated plants to be used for food or feed. Fungicides will do best when used before symptoms develop. Few materials have good eradicant activity Use at 7- to 14-day intervals; using shorter intervals when environmental conditions favor disease development.
  1. Bayleton 50 T&O at 5.5 oz/275 to 550 gal water. Landscape only, not for use on plants for sale. 12-hr reentry.
  2. Eagle 20 EW at 6 to 12 fl oz/100 gal water. Seed from treated plants may not be used for feed or food. 24-hr reentry.
  3. Kumulus DF (80% sulfur) at 3 to 10 lb/A. 24-hr reentry.
  4. Safer Garden Fungicide (Ready To Use 0.4% sulfur) thoroughly sprayed over the entire plant. Do not use when the temperature is over 85°F or within 4 weeks of an oil spray.
  5. Spectracide Immunox at 1 fl oz/gal water. Not for food use.
  6. Strike 50 WDG at 1 to 2 oz/100 gal water for outdoor use only. 12-hr reentry.
  7. Thiolux Jet (80% sulfur) at 3 to 10 lb/A. For ornamental use only. 24-hr reentry.
References:
Saliman, M., Yang, S. M. and Wilson, L. 1982. Reaction of Helianthus species to Erysiphe cichoracearum. Plant Disease 66:572-573.
Content edited by: Jay W. Pscheidt on January 1, 2009
 
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