Cercospora leaf spot is caused by the fungus Cercospora citrullina. The disease is most damaging to watermelon, other melons, and cucumber. The disease cycle begins when spores (conidia) are deposited onto leaves and petioles by wind or splashing water. Conidia germinate during moderate to warm (78 to 90ºF) temperatures in the presence of free moisture. New cycles of infection and sporulation occur every seven to 10 days during warm, wet weather. The pathogen is readily disseminated within and among fields by wind and splashing rain and irrigation water, and survives between cucurbit crops as a pathogen on weeds and in infested crop debris.
Cercospora leaf spot symptoms occur primarily on foliage, but petiole and stem lesions can develop when conditions are highly favorable for disease development. Fruit lesions are not known to occur. On older leaves, small, circular to irregular circular spots with tan to light brown lesions appear. The number and size of lesions increases, eventually coalescing and causing entire leaves to become diseased. On cucumber, squash, and melon the centers of lesions may grow thin and fall out. Lesion margins may appear dark purple or black, and may have yellow halos surrounding them. Severely infected leaves turn yellow, senesce, and fall off. On watermelon, lesions often form on younger rather than older foliage. Cercospora leaf spot can reduce fruit size and quality, but economic losses are rarely severe.
No biological control practices have been developed for Cercospora leaf spot.
Elimination of crop debris and cucurbit weed hosts is essential for Cercospora leaf spot management. Practice a two- to three-year rotation to nonhosts. No resistance to Cercospora leaf spot resistance has been identified in commercial cucurbit varieties.
Fungicide sprays are necessary for disease control in wet, humid weather but are not required in most years in the High Plains.
Product List for Cercospora Leaf Spot:
Pesticide |
Product per acre |
Application Frequency
|
Remarks |
Chlorothalonil and Chlorothalonil Mixtures |
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|
Bravo 720 |
|
|
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 |
EBDC, Copper/EBDC, and EBDC/Zoxamide Mixtures |
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|
Cuprofix MZ Disperss |
5-7.25 lb |
3-10 days |
Maximum of 63.1 pounds per season; 5 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 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 |
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, Cercospora Leaf Spot, Cucumber, Melon, Pumpkin, Squash, Zucchini
Date: 04/01/2007