Cause Golovinomyces cucurbitacearum (formerly G. cichoracearum and Erysiphe cichoracearum) and Podosphaera xanthii (formerly P. fuliginea and Sphaerotheca fuliginea) are fungi that can have several strains and/or races. They overwinter on dead melon vines or weeds. They also attack cucumber, squash, and pumpkin. The chief damage, reduced fruit quality and reduced yield, is proportionate to the time the plants have been diseased.
Symptoms Powdery white spots appear first on leaves, ultimately covering the entire leaf surface. Black, pinpoint-size, fruiting bodies (chasmothecia) of the fungus occur occasionally. Premature defoliation may follow infection.
Cultural control
- Resistant varieties offer the most practical control measures. For example, varieties resistant to strain 1 include Durango, Top Mark, Hy-Mark, Larado, Magnum-45, Sierra Gold, Top Score, Tasty Sweet, All Star, Market Star, Road Runner, Saticoy Hybrid, and Super Market. Varieties resistant to strains 1 and 2 include Edisto and Edisto 47.
- Practice good weed control.
Chemical control The following chemical treatments have been useful in other states but have not been tested in Oregon. Resistant fungi may develop rapidly, so alternate or tank-mix fungicides with different modes of activity or in different chemical families.
- Actigard 50WG at 0.5 to 1 oz/A on 7-day intervals. May be applied the day of harvest. 12-hr reentry.
- 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
- 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 5 lb/A on 7- to 10-day intervals. Might be used to supplement a normal program when powdery mildew is first observed. 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. May be applied on the day of harvest. 1-hr reentry. O
- Chlorothalonil (Group M5) formulations are labeled.
- Bravo WeatherStik (Group M5) at 2 to 3 pints/A on 7-day intervals. Preharvest interval is 0 days. 12-hr reentry.
- Echo 720 (Group M5) at 2 to 3 pints/A on 7-day intervals. Preharvest interval is 0 days. 12-hr reentry.
- Copper formulations (Group M1) offer limited control and are not good as stand-alone products.
- Cueva at 0.5 to 2 gal/100 gal water on 7- to 10-day intervals. May be applied on the day of harvest. 4-hr reentry. O
- Cuprofix Ultra 40 Disperss at 1.25 to 2 lb/A on 5- to 7-day intervals. 48-hr reentry.
- Kocide 2000 at 1 to 2.25 lb/A or Kocide 3000 at 0.5 to 1.25 lb/A on 5- to 7-day intervals. 48-hr reentry. O
- Liqui-Cop at 2 to 3 teaspoons/gal water. H
- Previsto at 0.75 to 2 quarts/A on 5- to 7-day intervals. 48-hr reentry. O
- Demethylation-inhibiting (DMI) Fungicides (Group 3) are labeled for use. Alternate or tank-mix with a non-Group 3 fungicide for resistance management.
- Mettle 125 ME at 8 fl oz/A on 7- to 10-day intervals. Application can be made the day of harvest. 12-hr reentry.
- Procure 480SC at 4 to 8 fl oz/A on 7- to 14-day intervals. Can be applied up to the day of harvest. 12-hr reentry.
- Rally 40WSP at 2.5 to 5 oz/A on 7- to 10-day intervals. Application can be made on day of harvest. 24-hr reentry.
- Rhyme at 5 to 7 fl oz/A. Preharvest interval is 0 days. 12-hr reentry.
- Tebuzol 3.6F at 4 to 6 fl oz/A on 7- to 14-day intervals. Do not apply within 7 days of harvest. 12-hr reentry.
- Fontelis (Group 7) at 12 to 16 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 1 day. 12-hr reentry.
- Oils are labeled to control powdery mildew. 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.
- JMS Stylet-Oil at 3 to 6 quarts/100 gal water. 4-hr reentry. O
- Trilogy at 0.5% to 1%. Not labeled for use in Oregon. 4-hr reentry. O
- OSO 5% SC (Group 19) at 3.75 to 13 fl oz/A on 7- to 14-day intervals. Can be applied the day of harvest. 4-hr reentry. O
- Quintec (Group 13) at 4 to 6 fl oz/A on 10- to 14-day intervals. Do not apply more than two (2) applications before alternating to a labeled 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 fungicides (Group 11) are labeled for use. 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.
- Cabrio EG at 12 to 16 oz/A. Preharvest interval is 0 days. 12-hr reentry.
- Evito 480 SC at 3.0 to 5.7 fl oz/A. Preharvest interval is 1 day. 12-hr reentry.
- Flint Extra at 2 to 3.8 fl oz/A. Preharvest interval is 7 days. 12-hr reentry.
- Heritage at 0.08 to 0.18 oz/1000 sq. ft for transplant production only. Preharvest interval is 1 day. 4-hr reentry.
- Quadris Flowable at 11 to 15.5 fl oz/A. Preharvest interval is 1 day. 4-hr reentry.
- Sulfur is registered. 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. Do not apply if temperature will exceed 90°F within 3 days after application. Do not use within 2 weeks of an oil treatment. Although sulfur reduces sporulation of established infections, it is primarily a protectant and must be applied before infection.
- Microthiol Disperss at 5 to 10 lb/A. 24-hr reentry. O
- Topsin M WSB (Group 1) at 0.5 lb/A for ground applications. 24-hr reentry.
- Torino (Group U6) at 3.4 fl oz/A on no shorter than 7-day intervals. Preharvest interval is 0 days. 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 14-day intervals. May be applied the day of harvest. 12-hr reentry.
- Inspire Super (Group 3 + 9) is registered for powdery mildew of cantaloupe but is not recommended due the fact that the Group 9 chemistry is only suppressive to powdery mildew at best. 12-hr reentry.
- ManKocide (Group M1 + M3) at 2 to 3 lb/A on 7- to 10-day intervals. Under moderate to severe disease pressure use the higher rate on 5- to 7-day intervals. Do not apply within 5 days of harvest. 48-hr reentry.
- Merivon Xemium (Group 7 + 11) at 4 to 5.5 fl oz/A on 7- to 14-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 14-day intervals. Preharvest interval is 1 day. 12-hr reentry.
- Orondis Opti (Group M5 + 49) at 1.75 to 2.5 pints/A on 7- to 14-day intervals. May be applied the day of harvest. 12-hr reentry.
- Pristine (Group 7 + 11) at 12.5 to 18.5 oz/A. Preharvest interval is 0 days. 12-hr reentry.
- Quadris Top (Group 11 + 3) at 10 to 14 fl oz/A. Preharvest interval is 1 day. 12-hr reentry.
- Switch 62.5WG (Group 12 + 9) at 11 to 14 oz/A on 7- to 10-day intervals. Do not apply within 1 day of harvest. 12-hr reentry.
Biological control
- Ecoswing at 1.5 to 2 pints/A. Preharvest interval is 0 days. 4-hr reentry. O
- LifeGard WG (Group P6) at 1 to 4.5 oz/A on 7- to 14-day intervals for activating plant resistance. Refer to label for appropriate rate per application volume. Preharvest interval is 0 days. 4-hr reentry. O
- Romeo at 0.45 lb/A on 7- to 10-day intervals starting prior to infection. Preharvest interval is 0 days. 4-hr reentry. O
- Serenade Opti (Group BM02) at 14 to 20 oz/A on 7- to 14-day intervals. Applications can be made up to and the day of harvest. 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