Cause:
The fungus Erysiphe polygoni (E. betae) affects plants in the Polygonaceae. The disease has been widespread in several western states since 1974. Fungal spores may blow in from overwintering sources. Overwintered infected seed beets may also be sources of infections. The fungus tolerates a wide range of environmental conditions.
Symptoms:
Small, discrete, white patches on both leaf surfaces. Patches coalesce until white mycelium and spores cover the entire leaf. Leaves later become yellow, then purplish brown, and finally necrotic.
Chemical
control: Begin applying when mildew is first observed. If necessary, repeat application to maintain 10% or lower leaf area diseased through the growing season. Sulfur dust provides superior control to liquid applications and is the preferred treatment. Research in south-central Idaho indicates it is economically feasible to apply sulfur to fields developing initial powdery mildew infections up to 5 weeks before harvest (or about September 1 in that area).
Eminent 125 SL at 13 fl oz/A. Do not make more than one (1) application of Eminent (triazole fungicide) or other Group 3 fungicide before alternating to a labeled fungicide with a different mode of action. Do not apply within 14 days of harvest.
12-hr reentry.
Gem at 6 to 7 oz/A on 10- to 14-day intervals. Do not make more than one (1) application of Gem or other Group 11 fungicide before alternating to a labeled fungicide with a different mode of action. Do not apply within 21 days of harvest. 12-hr reentry.
Headline at 9 to 12 fl oz/A. Do not make more than one (1) application of Headline or other Group 11 fungicide before alternating to a labeled fungicide with a different mode of action. For resistance management, it is recommended to tank-mix with sulfur. Do not use silicone-base adjuvants. Preharvest interval is 7 days. 12-hr reentry.
Inspire SB at 7 fl oz/A on 10- to 21-day intervals alternating with a non-group 3 fungicide. Preharvest in-terval is 7 days. 12-hr reentry.
Kaligreen at 2.5 to 3 lb/A at 7- to 10-day intervals. Might supplement a normal program when powdery mildew is first observed. May be applied up to the day before harvest.
4-hr reentry.
MilStop (85% potassium bicarbonate) at 2 to 5 lb/A. 1-hr reentry.
Proline 480 SC at 4.3 to 5.7 fl oz/A on 14- to 21-day intervals. Alternate every application with a non-group 3 fungicide. Preharvest interval is 7 days. 48-hr reentry.
Quadris at 9 to 15.5 fl oz/A on 5- to 7-day intervals. Do not apply more than one (1) foliar application of Quadris or other Group 11 fungicide before alternating to a labeled fungicide with a different mode of action. May be applied the day of harvest. 4-hr re-entry.
Sulfur dusts give better coverage than liquid formulations. Sulfur is manufactured under many trade names, and a few are listed here.
Kumulus DF at 10 to 20 lb/A. 24-hr reentry.
Sulfur 6L (52% sulfur) at 0.66 gal/A at 18-day intervals. 24-hr reentry.
Dusting Sulfur (98% sulfur) at 35 to 50 lb/A each
application.
Thiolux Jet (80% sulfur) at 10 to 20 lb/A on 10- to 30-day intervals. 24-hr reentry.
Tilt at 4 fl oz/A on a 10- to 14-day interval. Preharvest interval is 21 days. 12-hr reentry.
Topsin M WSB at 0.5 to 1 lb/A. Do not use alone; use another non-benzimidazole fungicide with Topsin M WSB for disease resistance management. Resistant strains can persist for many years. It is preferable to not apply more than once during the season. Make alternating applications with a non-benzimidazole fungicide. Do not apply within 21 days of harvest. 12-hr reentry.
References: Braun, U. 1995. The Powdery Mildews (Erysiphales) of Europe. Gustav Fischer, New York, 377 pp.
Whitney, E.D., and J.E. Duffus. 1986. Compendium of Beet Diseases and Insects. St. Paul, MN: APS Press.
Content edited by:
John Gallian and Cynthia M. Ocamb on
January 1, 2009
