Cause The fungus, Erysiphe betae (= E. polygoni = Microsphaera betae). 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 leaf surfaces that can be very diffuse and difficult to see. Later, patches coalesce until white mycelium and spores cover the entire leaf.
Cultural control
- Provide good plant spacing to ensure adequate air movement.
- Avoid over-application of nitrogen fertilizers; use an optimum, balance fertility regime.
- Avoid continuous cropping of susceptible beets and chard.
- Practice a 3-year rotation with nonsusceptible crops and manage volunteer beets and chard.
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. HO
- 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 0 days. 12-hr reentry.
- Cueva (Group M1) at 0.5 to 2 gal/100 gal water on 7-day intervals. May be applied on the day of harvest. 4-hr reentry. O
- Fontelis (Group 7) at 14 to 24 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 3 days. 12-hr reentry.
- Merivon Xemium (Group 7 + 11) at 4 to 11 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 1 day. 12-hr reentry.
- Miravis Prime (Group 7 + 12) at 9.2 to 13.4 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 0 days. 12-hr reentry.
- Regalia (Group P5) at 0.5 to 1.5 quarts/A 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 12 to 16 oz/A on 7- to 14-day intervals. Preharvest interval is 0 day. 12-hr reentry.
- Quadris Flowable at 6 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 Trilogy• Actinovate 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.
- Thiolux (80% sulfur) at 4 to 6 lb/A at 10- to 14-day intervals. 24-hr reentry.
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