Scab, also known as gummosis, is caused by the fungus Cladosporium cucumerinum. The disease begins when fungal spores (conidia) are deposited onto aerial plant parts and invade by direct penetration or through natural openings and wounds. Lesions develop within 3 days after infection, and new spores are produced about 24 hours later. Wet weather and temperatures near or below 70ºF are highly favorable for disease development. Conidia are disseminated within and among fields on contaminated equipment, workers, insects, and long-distance in moist air. The pathogen survives between susceptible crops in and on infested crop debris, and in the soil as a weak saprophyte. C. cucumerinum may be seedborne.
Scab symptoms can be present on all aboveground plant parts, including leaves, petioles, stems, and fruit. Leaf lesions begin as pale green, water-soaked areas that gradually turn gray to white. Yellow halos often surround lesions. Lesions sometimes develop a shot-hole appearance as the centers fall out. During severe epidemics, young leaves become deformed and runners of young plants can be killed.
Fruit can be severely damaged from scab. Fruit symptoms vary depending on the host, but generally appear as small, sunken areas about 0.1 to 0/2 inches in diameter. Sticky exudates may ooze from infected areas on fleshy fruit. Infected fruit are often attacked by secondary soft-rotting bacteria that completely rot the fruit. On pumpkins, lesions may appear as sunken craters; infected areas of fruit are often misshapen. Watermelon is more resistant to scab and lesions appear as raised or superficial blisters.
No biological control strategies have been developed for scab.
Plant high quality seed free from the scab pathogen. Scab resistant varieties of cucumber are available and effectively control the disease, but resistance is not available in most other cucurbit crops. Practice a two-year or longer rotation to nonhosts. Carefully select fields with well-drained soils that allow for rapid leaf drying. 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 used in combination with cultural controls to be most effective.
Product List for Scab:
Pesticide |
Product peracre |
Application Frequency
|
Remarks |
|
Chlorothalonil and Chlorothalonil Mixtures |
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|
Bravo 720 |
1.5-2 pt |
7 days |
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 |
|
Nordox |
1.5-2.0 lb |
7-10 days |
|
|
Ridomil/Bravo |
1-2 lb |
7-14 days |
7 day PHI |
|
Tri Basic Copper |
2-4 pt |
7-10 days |
1 day PHI |
|
EBDC and Copper/EBDC |
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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 |
|
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 |
|
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, Scab, Cucumber, Melon, Pumpkin, Squash, Zucchini
Date: 04/01/2007