Bacterial fruit blotch Caused by Acidovorax avenae subsp. citrulli Infected seedling
Bacterial fruit blotch Caused by Acidovorax avenae subsp. citrulli
Bacterial wilt of melon Caused by Erwinia tracheiphila
Bacterial wilt of melon Caused by Erwinia tracheiphila Note: Sticky strand test on cut stems with bacterial slime streaming from xylem tissues
Striped cucumber beetle Acalymma vittatum Adult and larvae
Anthracnose on cucurbits Caused by Colletotrichum orbiculare
Anthracnose on watermelon Caused by Colletotrichum orbiculare
This 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.
Powdery mildew Caused by Sphaerotheca fulginae and Erysiphe cichoracearum Fungal growth on both surfaces of the leaves
This is a close-up of a leaf showing the white fungal mycelium and spores that have covered the entire leaf surface.
Introduced 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.
Muhammad Asif Pakistan
Control of Fruit Blotch Prevention Avoid introduction of bacterium (pathogen-free seed) Inspection of seedlings and destroy suspicious flats Decontaminate if contact is made with infected plants Chemical Streptomycin (illegal, not labeled) is used in dire situations in the greenhouse to stop the spread of the pathogen Muhammad Asif Pakistan
Control of Fruit Blotch In the field: Culls and plant debris should be plowed under Rotate to new areas away from contaminated fields Choose less susceptible varieties Those with light green rinds = more susceptible Light and dark green striped= more resistant Solid dark green varieties are most resistant Bacterium moved by wind-driven rain or by mechanical means. Avoid contaminated fields when wet. Copper-based fungicides can reduce incidence of fruit symptoms. Muhammad Asif Pakistan
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.
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.
Disease Symptoms and Signs Muhammad Asif Pakistan
Anthracnose of cucurbits cucumber watermelon Muhammad Asif Pakistan
Anthracnose of cucurbits (watermelon) Sunken lesions with pink/salmon colored sporulation Muhammad Asif Pakistan
Disease Cycle Pathogen persists in crop debris, seedborne and may survive on volunteer plants or cucurbit weeds Conidia are the main means of in-field spread and are dispersed by watersplash and wind blown rain. Muhammad Asif Pakistan
2. Rotate vine crops with unrelated crops in a three-year rotation.
3. Practice good sanitation by plowing under fruits and vines at the
end 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.
Muhammad Asif Pakistan
Control Fungicides 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. Muhammad Asif Pakistan