Cause The fungi, Golovinomyces cucurbitacearum (formerly G. cichoracearum and Erysiphe cichoracearum), Podosphaera xanthii (formerly P. fuliginea and Sphaerotheca fuliginea), and Leveillula taurica (anamorph = Oidiopsis taurica) can all infect the cucurbits, including cucumber but G. cucurbitacearum has a lower optimum temperature while P. xanthii appears to more aggressive on cucurbits and causes disease during the warmer summer months. Infection can occur between 50°F and 90°F with 68°F to 81°F being optimum; temperatures above 100°F are reported to halt disease.
The sexual stage (chasmothecium) that these powdery mildew fungi can produce is rarely observed in the Pacific Northwest and its role in initiating powdery mildew outbreaks is unclear. However, these fungi all readily produce conidia, which can be dispersed from infected plants in greenhouses or in the field. Conidia can remain viable for a week and may be moved by wind across long distances. Warm temperatures and dew formation in summer favor disease development; high relative humidity favors infection while drier conditions promote colony growth as well as production and dispersal of conidia. In 3 to 7 days after infection, colonies are visible. Dense plantings and low light conditions promote disease.
Cultural control
- A 2-year rotation out of cucurbits is helpful.
- According to a Cornell University factsheet web site on powdery mildew (https://www.vegetables.cornell.edu/pest-management/disease-factsheets/cu...), the following pickle varieties are resistant to powdery mildew: Action 411 F1, Adam Gherkin F1 (European), Alibi F1, Arkansas Little Leaf, Bella, Boston Pickling/Pickler, Bush Pickle F1, Calypso F1, Carolina F1, Citadel F1, Country Fair F1, Cross Country F1, Emiliano 410, Eureka F1, Excelsior F1, Fancipak F1, Gherking F1, Jackson Supreme F1, Little Leaf, Little Tyke F1, Manny F1, Max Pack F1, Mcpick F1, Mercury F1, Parisian Gherkin F1, Picklebush, Pioneer F1, Puccini F1, Regal F1, Ronda F1, Salt & Pepper, Sassy F1, SMR 58, Supremo F1, Suhyo Long (Asian Heirloom), Vlasstar F1, and Zapata.
- According to a Cornell University factsheet web site on powdery mildew (https://www.vegetables.cornell.edu/pest-management/disease-factsheets/cu...), the following cucumber slicer varieties are resistant to powdery mildew: Alcazar F1, Ashley, Bristol F1, Camaro F1, Centella F1, Cobra F1, Cool Breeze F1, Corinto F1, Cutter F1, Darlington F1, Dasher II F1, Diamondback, Diomede F1, Diva F1, Dominator F1, Fanfare F1, Garden Sweet Burpless F1, Gateway F1, General Lee F1, Green Finger F1 (European), Hybrid 177, Impact F1, Intimidator F1, Iznik F1, Katrina F1, Lancer 152, La-ser 160, Lisboa, Mamba, Marketmore 76, Marketmore 97, Martini, Mini Munch F1, Mongoose F1, Olympian F1, Paraiso F1, Pepinex F1, Perseus, Picolino F1 (European), Poinsett 76, Proximus, Python, Rockingham F1, Salad Bush F1, Saladmore Bush F1, Silver Slicer, Sir Crunch A Lot, Slice More F1, Socrates F1 (European), Southern Delight F1, Speedway F1, Stonewall F1, Straight Eight Elite F1, Summer Dance F1 (Japanese), Summer Top F1 (Japanese), Superior F1, SV3462CS, SV4719CS F1, Sweet Slice F1, Sweeter Yet F1, Talladega F1, Tasty Green F1 (Japanese), Tasty Jade F1 (Japanese), Taurus F1 (Japanese), Thunder F1, Thunderbird F1, Torneo 143, Turbo F1, Tyria F1 (European), Vitaly F1, and Unistar F1.
- Avoid establishment of plants where shaded by tall plants or structures.
- Avoid planting too dense of stands.
Chemical control Usually the disease is not severe enough to warrant a spray program.
- Actigard 50WG at 0.5 to 1 oz/A on 7-day intervals applied preventatively prior to disease development. Use of an adjuvant is recommended. It can be tank-mixed with other fungicides. May be applied the day of harvest. 12-hr reentry.
- Bicarbonates are registered to control powdery mildew. Thorough coverage is essential.
- Bi-Carb 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 the day of harvest. 1-hr reentry. H O
- Chlorothalonil (Group M5) formulations are labeled.
- Bonide Fung-onil (Group M5) is available for home gardens. H
- Echo 720 (Group M5) at 2 to 3 pints/A on 7-day intervals. Preharvest interval is 0 days. 12-hr reentry.
- Copper products (Group M1) are not recommended as stand-alone materials.
- Badge SC at 0.5 to 2.5 pints/A on 5- to 7-day intervals. Preharvest interval is 0 days. 24-hr reentry for greenhouse use; 48-hr reentry for all other applications.
- 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.
- Orius 3.6F at 4 to 6 fl oz/A on 10- to 14-day intervals. Do not apply within 7 days 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 on 7- to 14-day intervals. 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.
- Topguard at 10 to 14 fl oz/A on 7-day intervals. Preharvest interval is 0 days. 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. Thorough coverage is essential. Cannot be used with or close to sulfur applications. Do not spray if temperature is below 50°F or above 90°F or when plants are wet or under heat or moisture stress. Do not use when foliage is wet as good coverage is essential. Some of the formulations registered for use include the following:
- JMS Stylet-Oil at 3 to 6 quarts/100 gal water. 4-hr reentry. O
- Neem oil 70% at 0.5% to 1% or Neem Oil RTU on 7- to 14-day intervals. H O
- Trilogy at 0.5% to 1%. Not labeled for use in Oregon. 4-hr reentry. O
- Vergol at 2% on 7- to 14-day intervals. 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
- 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.
- Quadris Flowable at 11.0 to 15.4 fl oz/A. Preharvest interval is 1 day. 4-hr reentry.
- Sulfur is registered and is fungitoxic in its vapor phase. 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 2 to 4 lb/A. 24-hr reentry. O
- Thiolux at 4 to 6 lb/A on 10- to 14-day intervals. 24-hr reentry.
- Topsin M WSB (Group 1) at 0.5 lb/A on 7- to 14-day intervals. Preharvest interval is 1 day. 24-hr reentry.
- Torino (Group U6) at 3.4 fl oz/A on no shorter than 7-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 14-day intervals. May be applied the day of harvest. 12-hr reentry.
- Dexter Xcel (Group M3 + 11 + 3) at 64 fl oz/A on 7- to 10-day intervals. Preharvest interval is 7 days. 24-hr reentry.
- Inspire Super (Group 3 + 9) is registered for powdery mildew of cucumber but is not recommended due the fact that the Group 9 chemistry that 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 Opti (Group 11 + M5) at 3.2 pints/A or Quadris Top (Group 11 + 3) at 12 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-day intervals. Do not apply within 1 day of harvest. 12-hr reentry.
Biological control Efficacy in the Pacific Northwest is unknown.
- Actinovate Lawn & Garden at 0.5 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
- 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 10-day intervals. Can rotate with other fungicides. 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
- Taegro 2 at 2.6 to 5.2 oz/A applied as a drench, in-furrow at planting or through drip irrigation. 4-hr reentry.