Alternaria blight, caused by the fungus Alternaria cucumerina, is a common disease of most cucurbits in warm, rainy weather. A similar cucurbit disease called Alternaria spot, caused by a related fungus (Alternaria alternata), is not known to occur in the High Plains. The Alternaria blight disease cycle begins when dormant mycelium in infested crop debris produce spores (conidia), which are disseminated by wind and splashing water to new plantings of susceptible cucurbit crops. Spores germinate in free moisture and penetrate their hosts through natural openings or wounds. Disease is most severe during extended periods of leaf wetness (8 to 24 hours) during moderate to warm (54 to 86ºF) temperatures. Frequent rainfall, especially during warm weather, is highly favorable to the pathogen and disease development. The pathogen survives between susceptible crops in infested crop debris up to two years.
Alternaria blight symptoms first appear on older leaves near the crown, appearing as small, yellow to brown spots with a light green to yellow halo. Lesions enlarge into brown necrotic areas and generally have concentric rings. As disease progresses, lesions merge and cause leaves to cup and die, exposing fruit to sunscald. Fruit lesions have been reported, but are rare. Alternaria blight reduces both fruit yield and quality.
No biological control practices have been developed for Alternaria blight or spot.
Practice a three-year or longer crop rotation to nonhosts such as a small grain, another vegetable, or corn. Deeply incorporate crop debris after harvest to reduce pathogen survival and primary inoculum that could incite future epidemics. Promote air movement within the canopy by planting rows parallel to prevailing wind direction, reducing plant population, and planting on wider row spacing. These practices will reduce the duration of leaf and soil wetness, and may help reduce Alternaria blight in semi-arid production areas. Avoid irrigating near dusk and overhead irrigation, if possible, to reduce periods of leaf wetness. Some melon types, such as some honeydew, are highly resistant to Alternaria blight, but little resistance is available in most commercially acceptable cucurbits. Leafminer feeding can increase the incidence and severity of Alternaria blight, and should be controlled.
Chemical controls are most effective when integrated with sound cultural control practices. The fungicide Procure is registered for powdery mildew control in cucurbits, but it may provide suppression or control of Alternaria blight as well.
Product List for Alternaria Blight and Spot:
Pesticide |
Product per acre |
Application Frequency
|
Remarks |
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 Weather Stik |
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. |
|
Cuprofix Disperss |
2.5 lb |
5-7 days |
|
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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 |
|
Kocide 4.5LF |
1-2 pts |
5-7 days |
May cause injury |
|
Kocide 3000 |
0.5-1.25 lb |
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 |
EBDC, Copper/EBDC, and EBDC/Zoxamide Mixtures |
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Cuprofix Disperss MZ |
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 |
Strobilurins and Strobilurin Mixtures |
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Cabrio |
12-16 oz |
7-14 days |
Maximum of 4 applications or 64 oz per season; Alternate Cabrio with fungicides with different modes of action; 0 day PHI |
|
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 |
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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, Alternaria Blight, Alternaria Spot, Cucumber, Melon, Pumpkin, Squash, Zucchini
Date: 04/10/2007