Downy mildew of cucurbits is caused by the fungus-like pathogen Pseudoperonospora cubensis. The pathogen can attack all cucurbits and cause economic damage to field and greenhouse-grown crops. The disease cycle requires living hosts since the pathogen cannot survive on dead plant material or in the soil. It is thought that the inoculum that initiates epidemics in the High Plains originates from diseased plants produced in greenhouses or windblown sporangia from very distant cucurbit plantings. Cool to moderate (59-68ºF) temperatures and leaf wetness are essential for sporulation and infection. Repeating cycles of sporulation and infection can occur in as little as four days under conditions favorable for disease.
Downy mildew symptoms first appear on leaves as small, dull to bright yellow areas on the upper surfaces of leaves. Lesions develop first on the oldest leaves near crowns and move progressively up the plant as new leaves expand. Lesion margins are irregular on must cucurbits, but are angular on cucumber and bounded by leaf veins. When humidity is high and temperatures are cool to moderate, the bottom sides of leaves have a light gray to deep purple downy appearance from abundant sporulation from the pathogen. As lesions enlarge, large areas of leaves may collapse, eventually defoliating the entire plant. As leaves drop, the fruit is exposed to sunscald. Downy mildew can reduce fruit yield, size, quality, and marketability. Downy mildew can be very damaging to most cucurbits under favorable conditions for the pathogen.
No biological control strategies have been developed for downy mildew of cucurbits.
Several cucumber and melon varieties possess some degree of resistance to downy mildew and should be planted if suitable for your production and marketing needs. Squash and pumpkin are resistant to some strains of the pathogen, but are highly susceptible to other strains. Promote air movement within the plant canopy and rapid leaf drying by avoiding dense plantings, narrow row spacings, and excess and overhead irrigation. Orientating rows parallel to the prevailing wind direction can also help to reduce periods of leaf wetness in semi-arid environments.
Chemical controls should be integrated with sound cultural practices to be most effective. Resistance to some fungicides has been reported in the downy mildew pathogen.
Product List for Downy Mildew:
Pesticide |
Product per acre |
Application Frequency
|
Remarks |
Captan |
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Captan 4F |
4 pt |
5-7 days |
4 day REI |
|
Captan 50 |
4 lb |
5-7 days |
4 day REI |
Chlorothalonil and Chlorothalonil Mixtures |
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Bravo 720 |
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Do not graze or feed debris to livestock; 7 day PHI |
|
Bravo Ultrex |
1.4-1.8 lb |
7-10 days |
Maximum of 16.5 pounds per season; 0 day PHI |
|
Bravo WeatherStik |
1.5-2.0 pt |
7-10 days |
Maximum of 20 pints per season; 0 day PHI |
|
Echo 720 |
1.5-2.0 pt |
7-10 days |
Maximum of 2.5 gallons per season; 7 day PHI |
|
Echo 90DF |
1.2-1.6 lb |
7-10 days |
Maximum of 16.67 pounds per season; 7 day PHI |
|
Echo Zn |
2.2 to 2.8 pt |
7-10 days |
Maximum of 3.6 gallons per season; 7 day PHI |
|
Ridomil/Bravo |
1-2 lb |
7-14 days |
7 day PHI |
Copper Fungicides |
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Champ Dry Prill |
1.33 lb |
5-7 days |
|
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Champ Formula 2 |
1.33 pt |
5-7 days |
|
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Copper-Count-N |
4-6 pt |
7 days |
Mid-harvest. |
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Kocide 101 |
1.5-3 lbs |
5-7 days |
May cause injury |
|
Kocide DF |
1.5-3 lbs |
5-7 days |
May cause injury |
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Kocide 4.5LF |
1-2 pts |
5-7 days |
May cause injury |
|
Nordox |
1.5-2.0 lb |
7-10 days |
|
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Tri Basic Copper |
2-4 pt |
7-10 days |
1 day PHI |
|
Dimethomorph |
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Forum |
6 oz |
5-7 days |
Maximum of 5 applications and 30 oz/are per season; tank mix with another fungicide class that has a different mode of action, 0 day PHI |
EBDC, Copper/EBDC, and EBDC/Zoxamide Mixtures |
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Cuprofix MZ Disperss |
4-7.25 lb |
3-10 days |
Maximum of 63.1 pounds per season; 5-14 day PHI |
|
Dithane |
2-3 lb |
7-10 days |
Maximum of 25.6 pounds per season; 5 day PHI; use a non-ionic surfactant to improve performance |
|
Gavel 75DF |
1.5-2.0 lb |
7-10 days |
Maximum 16 pounds per season; 5 day PHI; include a nonionic surfactant to improve performance |
|
Maneb 75 DF |
1.5-2.0 lb |
7-10 days |
Maximum of 17.1 pounds per season; 5 day PHI |
|
Manex 80W |
1.5-2.0 lb |
7-10 days |
Maximum of 16.0 pounds per season; 5 day PHI |
|
Manex |
2.4-3.2 pt |
7-10 days |
Maximum of 25 pints per season; 5 day PHI |
|
ManKocide |
2.0-2.5 lb |
7-10 days |
Maximum of 128 pounds per season; 5 day PHI |
|
Penncozeb 80W |
1.5-3.0 lb |
7-10 days |
Maximum of 24.0 pounds per season; 5 day PHI |
|
Penncozeb 75DF |
1.5-3.0 lb |
7-10 days |
Maximum of 25.6 pounds per season; 5 day PHI |
Mefenoxam Mixtures |
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Ridomil/Bravo |
1-2 lb |
7-14 days |
Maximum of four applications; 5 day PHI |
|
Ridomil/Copper |
1.5-2.0 lb |
7-14 days |
Maximum of four applications; 5 day PHI |
|
Ridomil MZ |
2.0-2.5 lb |
7-14 days |
Maximum of four applications; 5 day PHI |
Strobilurins and Strobilurin Mixtures |
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Cabrio |
8-16 oz |
7-14 days |
Maximum of 4 applications or 64 oz per season; Alternate with different modes of action; 0 day PHI |
|
Flint |
4 oz |
7-14 days |
Suppression only; Maximum of 4 applications or 16 ounces per seaon; 0 day PHI; rotate with fungicides with different modes of action |
|
Quadris |
11.0-15.4 fl oz |
5-14 days |
Maximum of 4 applications or 2.88 quarts per season; Alternate Quadris with fungicides with different modes of action; 1 day PHI |
|
Tanos |
8 oz |
5-7 days |
Rotate with fungicides with a different mode of action, such as chlorothalonil or mancozeb; Maximum of 48 ounces per season; 3 day PHI |
Thiophanate Methyl |
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Topsin M 70WP |
0.5 lb |
7-14 days |
Maximum of 3 lb per season; Alternate fungicide sprays or tank-mix with fungicides with a different mode of action; 1 day PHI |
|
Topsin 4.5 FL |
10 fl oz |
7 days |
Maximum of 60 fl oz per season; Alternate fungicide sprays or tank-mix with fungicides with a different mode of action; 1 day PHI |
|
Topsin WSB |
0.5 lb |
7-14 days |
Maximum of 3 lb per season; Alternate fungicide sprays or tank-mix with fungicides with a different mode of action; 1 day PHI |
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The information herein is supplied with the understanding that no discrimination is intended and that listing of commercial products, necessary to this guide, implies no endorsement by the authors or the Extension Services of Nebraska, Colorado, Wyoming or Montana. Criticism of products or equipment not listed is neither implied nor intended. Due to constantly changing labels, laws and regulations, the Extension Services can assume no liability for the suggested use of chemicals contained herein. Pesticides must be applied legally complying with all label directions and precautions on the pesticide container and any supplemental labeling and rules of state and federal pesticide regulatory agencies. State rules and regulations and special pesticide use allowances may vary from state to state: contact your State Department of Agriculture for the rules, regulations and allowances applicable in your state and locality. |
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Categories: Cucurbits, Disease, Downy Mildew, Cucumber, Melon, Pumpkin, Squash, Zucchini
Date: 04/01/2007