4Harvesting for seedHarvesting cucumbers for seed and washing seed.
5DISEASE: Watermelon Fruit Bloch CROP: Watermelon, other cucurbits are hostsPATHOGEN: Acidovorax avenae subsp. CitrulliDISTRIBUTION: FL, SC, NC, MD, IN, LAPATHOGEN DESCRIPTION: BacteriumGram-negative, straight rod, motile, peritrichous flagella.
6Disease Symptoms Foliage Infected transplants- dark, water-soaked areas on the underside of cotyledons and first leaves.Necrotic lesions may appear on the foliage.Young seedlings may develop lesions on the hypocotyl, causing eventual collapse and death.Disease symptoms on foliage in the growing season may not be obvious or confused with other diseases.Symptoms on transplants can go away, and return with symptoms on fruit!!!
7Disease Symptoms Bacterial fruit blotch Caused by Acidovorax avenae subsp. citrulliInfected seedling
8Disease Symptoms and Signs FruitBegin as small, water-soaked areas (few millimeters in diameter), rapidly expand into larger lesions with irregular margins.The entire surface of the fruit may become covered with dark green, greasy-looking lesions.Older fruit lesions become necrotic and may crack.Whitish bacterial ooze may exude from the splits, later infected fruit will rot.
9Disease Symptoms Whitish ooze Bacterial fruit blotch Caused by Acidovorax avenae subsp. citrulli
11Disease DevelopmentIntroduced into fields with infested seed, infected transplants, natural spread via alternate host (wild cucurbits or volunteer watermelon).Infected transplants represent most important means of disease transmission – infected transplants may be asymptomatic – lead to high numbers entering a field.Warm, wet weather in May-June favors the bacterium and disease.Disease can develop quickly, 100% infection from just a few primary infection sites.
12Control of Fruit Blotch PreventionAvoid introduction of bacterium (pathogen-free seed)Inspection of seedlings and destroy suspicious flatsDecontaminate if contact is made with infected plantsChemicalStreptomycin (illegal, not labeled) is used in dire situations in the greenhouse to stop the spread of the pathogen
13Control of Fruit Blotch In the field:Culls and plant debris should be plowed underRotate to new areas away from contaminated fieldsChoose less susceptible varietiesThose with light green rinds = more susceptibleLight and dark green striped= more resistantSolid dark green varieties are most resistantBacterium moved by wind-driven rain or by mechanical means. Avoid contaminated fields when wet.Copper-based fungicides can reduce incidence of fruit symptoms.
15Disease Symptoms and Signs Crops affected are mainly cucumber and cantaloupe, but also squash and pumpkin to a limited extent. Watermelon is not affected.Foliage wilts suddenly, frequently on a single runner at first, followed by wilting of the entire plant.Wilt is permanent. Bacteria are abundant in the vascular tissue and exude in white droplets from vascular bundles on cut stems.The viscous bacterial mass will 'string-out' when the cut ends of the stem are touched together.
16Bacterial wilt of cucurbits Bacterial wilt of melonCaused by Erwinia tracheiphila
18Bacterial wilt of melon Caused by Erwinia tracheiphilaNote: Sticky strand test on cut stems with bacterial slime streaming from xylem tissues
19Conditions for Disease Development: The pathogen survives for extended periods in its cucumber beetle vectors. It is transmitted by the striped beetle, Acalymma sp. and the spotted beetle, Diabrotica sp.; therefore, conditions conducive to development of the vectors favor the occurrence of the disease.
20Striped cucumber beetle Acalymma vittatumAdult and larvae
22Control Measures:Rogue diseased plants to prevent secondary spread of the pathogen.Control cucumber beetles with insecticides.Some cultivars are more tolerant than others, if available they should be used.
24Pathogen Description: Fungus Cylindrical, hyaline conidia arc produced on lesions in pinkish masses in acervuli also bearing two to three septate, brown setae.
25Pathogen Description: Fungus Formation of appresoriumTwo-celled conidium
26Disease Symptoms and Signs The disease is particularly damaging to watermelon, cucumber, and cantaloupe, but also may occur on most other cucurbit crops.On cucumber and cantaloupe, leaf lesions are circular and brown up to 1 cm in diameter, while on watermelon the leaf lesions arc black and somewhat smaller.Petiole and stem lesions arc elliptical in shape and sunken.Fruit lesions appear at or near maturity as water-soaked spots that develop into sunken, circular lesions lined with dark fungal stroma bearing masses of pink spores.
27Anthracnose of cucurbits cucumberAnthracnose on cucurbitsCaused by Colletotrichum orbicularewatermelon
28Anthracnose of cucurbits (watermelon) Sunken lesions with pink/salmon colored sporulationAnthracnose on watermelonCaused by Colletotrichum orbiculare
29Disease Cycle Pathogen persists in crop debris, seedborne and may survive on volunteer plants or cucurbit weedsConidia are the main means of in-field spread and aredispersed by watersplash and wind blown rain.
30Control Cultural Use commercially produced, disease-free seed. 2. Rotate vine crops with unrelated crops in a three-year rotation.3. Practice good sanitation by plowing under fruits and vines at theend of the season.4. Choose anthracnose-resistant varieties if at all possible. Resistant cucumber slicers include Dasher II and Slicemaster. Many pickling cucumbers are tolerant or resistant, including Score and Premier. Resistant watermelon varieties include Charleston Gray, Crimson Sweet, and Dixie Lee.
31ControlFungicides Apply approved fungicides to the crop at regular intervals, more often if frequent rains occur.Among fungicides available are chlorothalonil (Bravo), benomyl (Benlate), and maneb and mancozeb formulations.An effective spray treatment has been the combination of Bravo with Benlate or mancozeb. If angular leaf spot should be a problem, substitute a copper compound for Benlate in the combination.
32Powdery MildewThis disease of cucurbits is caused by two powdery mildew fungi; Sphaerotheca fuliginea and Erysiphe cichoracearum. While fruit infection is possible, the greatest damage comes from decimation of the leaves leaving the fruit exposed for sunscald and decreasing the surface area available for photosynthesis. The end result is decreased quantity and quality of yield.
33Powdery MildewPathogen: Erysiphe cichoracearum, Sphaerotheca fuligineaCylindrical, hyaline conidia are produced in chains on conidiophores that arise from surface mycelial growth.
34Symptoms and Signs Powdery mildew Caused by Sphaerotheca fulginae and Erysiphe cichoracearumFungal growth on both surfaces of the leaves
35Signs of the PathogenThis is a close-up of a leaf showing the white fungal mycelium and spores that have covered the entire leaf surface.
36Symptoms and Signs: All cucurbits are susceptible to powdery mildew Symptoms appear first as pale yellow spots on leaves and stemsSporulation becomes evident as white powdery masses of conidia are produced over the lesion surfaceLeaves and stems become chlorotic, then turn brown and dry prematurely.
37Conditions for Disease Development The pathogens are obligate parasites and can persist on wild cucurbits or crop plantsDisease development can occur over a wide range of temperatures as long as there sufficient moisture for spore germination and infection.These conditions can be provided by high relative humidity or dew formation in the absence of rainfall.Inoculum is airborne for long distances
38Control Strategies Avoid crowding of plants Resistant cultivars of many crops available, pumpkin is exceptionFungicide sprays are available, but may not be cost effectiveSanitation and practices that avoid lush growth help to delay spread