Cause The fungus, Leveillula taurica (syns. Oidiopsis taurica, Oidiopsis sicula), is in only scattered sites in the Pacific Northwest.This disease is restricted to warm, semiarid regions. The fungus has a wide crop and weed host range on which it can overwinter. Temperatures below 86°F favor infection; higher temperatures accelerate symptoms once infection is established. Cool nights permit infection in areas with high daytime temperatures.
Symptoms Light-green to bright-yellow, irregularly-shaped blotches develop on upper leaf surfaces of older leaves; the lesion centers later turn necrotic. Younger leaves remain unaffected until they mature. Drooping of infected leaves and upwards curling of leaf edges may be observed, and such leaves often die and fall off the plant. Fruit may exhibit sunburn if the plant is defoliated. The fungus usually is on the leaf's lower side, and can sporulate profusely.
Cultural control Usually the disease does not require control measures.
Chemical control
- Chlorothalonil (Group M5) formulations are labeled.
- Bravo Ultrex at 1.4 lb/A on 7- to 10-day intervals. Preharvest interval is 3 days. 12-hr reentry.
- Echo 720 at 1.5 pints/A on 7- to 10-day intervals. Preharvest interval is 3 days. 12-hr reentry.
- Demethylation-inhibiting (DMI) fungicides (Group 3) are registered for use. Alternate or tank-mix with a non-Group 3 fungicide for resistance management.
- Mettle 125 ME at 6 to 8 fl oz/A on 7- to 14-day intervals. Application can be made the day of harvest. 12-hr reentry.
- Rally 40 WSP at 2.5 to 5 oz/A on 10- to 14-day intervals. Can be applied on day of harvest. 24-hr reentry.
- Rhyme at 7 fl oz/A on 7- to 14-day intervals. Preharvest interval is 0 days. 12-hr reentry.
- Topguard at 14 fl oz/A on 7-day intervals. Preharvest interval is 0 days. 12-hr reentry.
- Fontelis (Group 7) at 10 to 24 fl oz/A on 7- to 14-day intervals. 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, above 90°F or when plants are wet or under heat or moisture stress. 4-hr reentry. O
- Mettle 125 ME (Group 3) at 6 to 8 fl oz/A on 7- to 14-day intervals. Application can be made the day of harvest. 12-hr reentry.
- Potassium bicarbonate formulations are registered.
- Bi-Carb at 4 teaspoons/2 gal water on 7- to 10-day intervals. Thorough coverage is critical. May be applied up to the day before harvest. H O
- Carb-O-Nator at 2.5 to 5 lb/100 gal of water on 5- to 14-day intervals, depending on disease pressure. Preharvest interval is zero (0) days for all listed crops. 4-hr reentry. 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 at 2 to 3 lb/A on 7- to 14-day intervals. May be applied on the day of harvest. 1-hr reentry. H O
- Quintec (Group 13) at 4 to 6 fl oz/A on 10- to 14-day intervals. Do not make more than two (2) consecutive applications without alternating to a fungicide with a different mode of action. Do not apply within 3 days of harvest. 12-hr reentry.
- Regalia (Group P5) at 1 to 4 quarts/A plus another fungicide on 7- to 10-day intervals. Does not benefit from the addition of an adjuvant. Preharvest interval is 0 days. 4-hr reentry. O
- Strobilurin-type fungicides (Group 11) have efficacy on powdery mildew. Do not apply more than one (1) foliar application any Group 11 fungicide before alternating to a labeled fungicide with a different mode of action.
- Cabrio EG at 8 to 16 oz/A on 7- to 14-day intervals. Preharvest interval is 0 days. 12-hr reentry.
- Quadris Flowable at 6 to 15.5 fl oz/A on 7- to 14-day intervals. Do not apply with an adjuvant. May be applied the day of harvest. 4-hr reentry.
- Sulfur formulations can be very effective for 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.
- Microthiol Disperss at 3 to 10 lb/A on 10- to 14-day intervals. Do not apply if temperature will exceed 90°F
- Torino (Group U6) at 3.4 fl oz/A on no shorter than 14-day intervals. Preharvest interval is 0 days; can be applied the day of harvest. 4-hr reentry.
- Premixes of fungicides are available and offer ease for fungicide resistance management. Do not make more than one (1) application of a Group 11 fungicide before alternating to a labeled fungicide with a different mode of action; for other fungicide groups apply no more than two (2) sequential applications alternating with another fungicide with a different mode of action.
- Aprovia Top (Group 7 + 3) at 10.5 to 13.5 fl oz/A on 7- to 10-day intervals. Preharvest interval is 0 days. 12-hr reentry.
- Dexter Xcel (Group M3 + 11 +3) at 48 fl oz/A on 7- to 10-day intervals. Preharvest interval is 7 days. 24-hr reentry.
- Inspire Super (Group 3 + 9) at 16 to 20 fl oz/A on 7- to 10-day intervals. Preharvest interval is 0 days. 12-hr reentry.
- Miravis Prime (Group 7 + 12) at 9.2 to 11.4 fl oz/A on 7- to 21-day intervals. Can be applied day of harvest. 12-hr reentry.
- Orondis Opti (Group M5 + 49) at 1.75 to 2.5 pints/A on 7- to 10-day intervals. Preharvest interval is 3 days. 12-hr reentry.
- Priaxor Xemium Brand (Group 7 + 11) at 6 to 8 fl oz/A on 7- to 14-day intervals. Preharvest interval is 0 day. 12-hr reentry.
- Quadris Top (Group 11 + 3) at 8 to 14 fl oz/A on 7- to 10-day intervals. Can be applied the day of harvest. 12-hr reentry.
- Switch 62.5WG (Group 9 + 12) at 11 to 14 oz./A on 7- to 10-day intervals. May be applied the day of harvest. 12-hr reentry.
Biological control Efficacy in the Pacific Northwest is unknown.
- 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 0.5 to 1 teaspoon/gal water. H O
- Ecoswing at 1.5 to 2 pints/A. Preharvest interval is 0 days. 4-hr reentry. O
- Sonata at 2 to 4 quarts/A on 7- to 14-day intervals can suppress powdery mildew. Can be applied up to and on the day of harvest. 4-hr reentry. O
Reference Glawe, D.A., Barlow, T., Eggers, J.E., and Hamm, P.B. 2010. First report of powdery mildew caused by Leveillula taurica of field-grown sweet pepper (Capsicum annuum) in the Pacific Northwest. Online. Plant Health Progress doi:10.1094/PHP-2007-0708-01-BR.