Cause The fungus, Erysiphe betae (= E. polygoni = Microsphaera betae). The disease has been widespread in several western states. Spores may be blown 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. Later, patches coalesce until white mycelium and spores cover the entire leaf. Leaves later become yellow, then purplish brown, and finally necrotic.
Cultural control
- The variety, Red Ace, has some tolerance.
Chemical control More than one application may be required.
- Bicarbonates are registered to control powdery mildew. Thorough coverage is essential.
- Bi-Carb Old Fashioned Fungicide at 4 teaspoons/2 gal water on 7- to 10-day intervals. May be applied up to the day before harvest. H O
- Kaligreen at 2.5 to 3 lb/A on 7- to 10-day intervals. May be applied up to the day before harvest. 4-hr reentry. O
- MilStop SP at 2 to 5 lb/A on 7- to 14-day intervals. Can be applied up to and including the day of harvest. 1-hr reentry. O
- Cevya (Group 3) at 3 to 5 fl oz/A on minimum interval of 7 days. Preharvest interval is 7 days. 12-hr reentry.
- Cueva (Group M1) at 0.5 to 2 gal/100 gal water on 10-day intervals. May be applied on the day of harvest. 4-hr reentry. O
- Fontelis (Group 7) at 16 to 30 fl oz/A on 7- to 14-day intervals. Do not make more than two (2) sequential applications before alternating to a labeled fungicide with a different mode of action (non-Group 7). Preharvest interval is 0 days. 12-hr reentry.
- JMS Stylet-Oil at 3 to 6 quarts/100 gal water. Do not spray if temperature is below 50°F or above 90°F or when plants are wet or under heat or moisture stress. 4-hr reentry. O
- Merivon Xemium (Group 7 + 11) at 4 to 5.5 fl oz/A on 7- to 14-day intervals. Do not make more than two (2) applications before alternating to a fungicide in different FRAC groups (non-Group 7 and non-Group 11). Preharvest interval is 7 days. 12-hr reentry.
- Miravis Prime (Group 7 + 12) at 6.8 fl oz/A on 7- to 10-day intervals. Do not make more than two (2) sequential applications before alternating to a labeled fungicide with a different mode of action. Preharvest interval is 7 days. 12-hr reentry.
- Regalia (Group P5) at 0.5 to 4 quarts/A plus another fungicide on 5- to 10-day intervals. Does not benefit from the addition of an adjuvant. Preharvest interval is 0 days. 4-hr reentry. O
- Strobilurin fungicides (Group 11) are labeled for use. Do not make more than one (1) application of a Group 11 fungicide be-fore alternating to a labeled fungicide with a different mode of action.
- Cabrio EG at 8 to 12 oz/A on 7- to 14-day intervals. Preharvest interval is 0 day. 12-hr reentry.
- Quadris Flowable at 9 to 15.5 fl oz/A on 5- to 7-day intervals. May be applied the day of harvest. 4-hr reentry.
- Sulfur formulations are available and can be very effective on powdery mildew. Sulfur is fungitoxic in its vapor phase and, therefore, is effective only when air temperatures promote volatilization. Sulfur volatilizes above 65°F but becomes phytotoxic above 95°F. Using it above 85°F is not recommended. Although sulfur reduces sporulation of established infections, it is primarily a protectant and must be applied before infection.
- Sulfur 6L (52% sulfur) at 0.66 gal/A at 18-day intervals. 24-hr reentry.
- Thiolux (80% sulfur) at 3 to 5 lb/A at 2- to 3-week intervals. 24-hr reentry.
- Switch 62.5WG (Group 12 + 9) at 11 to 14 oz/A on 7- to 10-day intervals. No more than two (2) sequential applications alternating with another fungicide with a different mode of action for two (2) applications. Do not allow cattle or other livestock to feed upon leaves of vegetables. Do not apply within 7 days of harvest. 12-hr reentry.
- Tilt (Group 3) at 3 to 4 fl oz/A on 14-day intervals. Preharvest interval is 14 days. 12-hr reentry.
- Topaz (Group 3) at 3 to 4 fl oz/A on 14-day intervals. Preharvest interval is 14 days. 12-hr reentry.
- Trilogy at 0.5% to 1%. Not labeled for use in Oregon. Do not use above 90°F or when plants are under heat or moisture stress. Do not use when foliage is wet as good coverage is essential. 4-hr reentry. O
Biological control Efficacy unknown in the Pacific Northwest.
- Actinovate AG at 3 to 12 oz/A as a foliar spray on 7- to 14-day intervals. 4-hr reentry. O
- Actinovate Lawn & Garden at 1/2 to 1 teaspoon/gal water. H O
- Double Nickel LC at 0.5 to 4.5 pints/A on 3- to 10-day intervals. Can be applied the day of harvest. 4-hr reentry. O
- Ecoswing at 1.5 to 2 pints/A. Preharvest interval is 0 days. 4-hr reentry. O
- Romeo at 0.45 to 0.68 lb/A on 7- to 10-day intervals starting prior to infection. Preharvest interval is 0 days. 4-hr reentry. O
- Sonata at 2 to 4 quarts/A on 7- to 14-day intervals. Can be applied up to and on the day of harvest. 4-hr reentry. O
Reference Harveson, R.M., Hanson, L.E., and Hein, G.L. 2009. Compendium of Beet Diseases and Pests, 2nd Ed. St. Paul, MN: APS Press.