Cucurbit diseases


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  • Production of squash seed
  • Harvesting cucumbers for seed and washing seed.
  • 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.
  • Cucurbit diseases

    1. 1. Diseases of Cucurbits <ul><li>Types of Cucurbits </li></ul><ul><li>Those grown in IL </li></ul><ul><li>Production facts </li></ul><ul><li>Etc. </li></ul>Muhammad Asif Pakistan
    2. 2. Diseases Covered <ul><li>Watermelon fruit blotch </li></ul><ul><li>Bacterial wilt </li></ul><ul><li>Anthracnose </li></ul><ul><li>Powdery mildew </li></ul>Muhammad Asif Pakistan
    3. 3. Production of squash seed Muhammad Asif Pakistan
    4. 4. Harvesting for seed Muhammad Asif Pakistan
    5. 5. DISEASE: Watermelon Fruit Bloch <ul><li>CROP: Watermelon, other cucurbits are hosts </li></ul><ul><li>PATHOGEN: Acidovorax avenae subsp. Citrulli </li></ul><ul><li>DISTRIBUTION: FL, SC, NC, MD, IN, LA </li></ul><ul><li>PATHOGEN DESCRIPTION: Bacterium </li></ul><ul><li>Gram-negative, straight rod, motile, peritrichous flagella. </li></ul>Muhammad Asif Pakistan
    6. 6. Disease Symptoms <ul><li>Foliage </li></ul><ul><li>Infected transplants- dark, water-soaked areas on the underside of cotyledons and first leaves. </li></ul><ul><li>Necrotic lesions may appear on the foliage. </li></ul><ul><li>Young seedlings may develop lesions on the hypocotyl, causing eventual collapse and death. </li></ul><ul><li>Disease symptoms on foliage in the growing season may not be obvious or confused with other diseases. </li></ul><ul><li>Symptoms on transplants can go away, and return with symptoms on fruit!!! </li></ul>Muhammad Asif Pakistan
    7. 7. Disease Symptoms Muhammad Asif Pakistan
    8. 8. <ul><li>Fruit </li></ul><ul><li>Begin as small, water-soaked areas (few millimeters in diameter), rapidly expand into larger lesions with irregular margins. </li></ul><ul><li>The entire surface of the fruit may become covered with dark green, greasy-looking lesions. </li></ul><ul><li>Older fruit lesions become necrotic and may crack. </li></ul><ul><li>Whitish bacterial ooze may exude from the splits, later infected fruit will rot. </li></ul>Disease Symptoms and Signs Muhammad Asif Pakistan
    9. 9. Disease Symptoms Muhammad Asif Pakistan Whitish ooze
    10. 10. Disease Cycle Muhammad Asif Pakistan
    11. 11. Disease Development <ul><li>Introduced into fields with infested seed, infected transplants, natural spread via alternate host (wild cucurbits or volunteer watermelon). </li></ul><ul><li>Infected transplants represent most important means of disease transmission – infected transplants may be asymptomatic – lead to high numbers entering a field. </li></ul><ul><li>Warm, wet weather in May-June favors the bacterium and disease. </li></ul><ul><li>Disease can develop quickly, 100% infection from just a few primary infection sites. </li></ul>Muhammad Asif Pakistan
    12. 12. 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
    13. 13. 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
    14. 14. DISEASE: Bacterial Wilt <ul><li>CROP: Cucurbits </li></ul><ul><li>PATHOGEN: Erwinia tracheiphila </li></ul><ul><li>DISTRIBUTION: North America, Europe, Asia, Africa </li></ul><ul><li>PATHOGEN DESCRIPTION: Bacterium </li></ul><ul><li>Gram-negative, straight rod, motile, peritrichous flagella. </li></ul>Muhammad Asif Pakistan
    15. 15. Disease Symptoms and Signs <ul><li>Crops affected are mainly cucumber and cantaloupe, but also squash and pumpkin to a limited extent. Watermelon is not affected. </li></ul><ul><li>Foliage wilts suddenly, frequently on a single runner at first, followed by wilting of the entire plant. </li></ul><ul><li>Wilt is permanent. Bacteria are abundant in the vascular tissue and exude in white droplets from vascular bundles on cut stems. </li></ul><ul><li>The viscous bacterial mass will 'string-out' when the cut ends of the stem are touched together. </li></ul>Muhammad Asif Pakistan
    16. 16. Bacterial wilt of cucurbits Muhammad Asif Pakistan
    17. 17. Bacterial wilt of cucurbits (pumpkin) Muhammad Asif Pakistan
    18. 18. Muhammad Asif Pakistan
    19. 19. Conditions for Disease Development: <ul><li>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. </li></ul>Muhammad Asif Pakistan
    20. 20. Muhammad Asif Pakistan
    21. 21. Muhammad Asif Pakistan
    22. 22. Control Measures: <ul><li>Rogue diseased plants to prevent secondary spread of the pathogen. </li></ul><ul><li>Control cucumber beetles with insecticides. </li></ul><ul><li>Some cultivars are more tolerant than others, if available they should be used. </li></ul>Muhammad Asif Pakistan
    23. 23. DISEASE: Anthracnose <ul><li>CROP: Cucurbits </li></ul><ul><li>PATHOGEN: Colletotrichum lagenarium (imperfect (asexual) stage): Glomerella cingulata var. orbiculare (sexual stage) </li></ul><ul><li>DISTRIBUTION: Worldwide </li></ul>Muhammad Asif Pakistan
    24. 24. Pathogen Description: Fungus <ul><li>Cylindrical, hyaline conidia arc produced on lesions in pinkish masses in acervuli also bearing two to three septate, brown setae. </li></ul>Muhammad Asif Pakistan
    25. 25. Pathogen Description: Fungus Two-celled conidium Formation of appresorium Muhammad Asif Pakistan
    26. 26. <ul><li>The disease is particularly damaging to watermelon, cucumber, and cantaloupe, but also may occur on most other cucurbit crops. </li></ul><ul><li>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. </li></ul><ul><li>Petiole and stem lesions arc elliptical in shape and sunken. </li></ul><ul><li>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. </li></ul>Disease Symptoms and Signs Muhammad Asif Pakistan
    27. 27. Anthracnose of cucurbits cucumber watermelon Muhammad Asif Pakistan
    28. 28. Anthracnose of cucurbits (watermelon) Sunken lesions with pink/salmon colored sporulation Muhammad Asif Pakistan
    29. 29. 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
    30. 30. Control <ul><li>Cultural </li></ul><ul><li>Use commercially produced, disease-free seed. </li></ul><ul><li>2. Rotate vine crops with unrelated crops in a three-year rotation. </li></ul><ul><li>3. Practice good sanitation by plowing under fruits and vines at the </li></ul><ul><li>end of the season. </li></ul><ul><li>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. </li></ul>Muhammad Asif Pakistan
    31. 31. 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
    32. 32. Powdery Mildew Muhammad Asif Pakistan
    33. 33. Powdery Mildew <ul><li>Pathogen: Erysiphe cichoracearum, Sphaerotheca fuliginea </li></ul><ul><li>Cylindrical, hyaline conidia are produced in chains on conidiophores that arise from surface mycelial growth. </li></ul>Muhammad Asif Pakistan
    34. 34. Symptoms and Signs Muhammad Asif Pakistan
    35. 35. Signs of the Pathogen Muhammad Asif Pakistan
    36. 36. <ul><li>All cucurbits are susceptible to powdery mildew </li></ul><ul><li>Symptoms appear first as pale yellow spots on leaves and stems </li></ul><ul><li>Sporulation becomes evident as white powdery masses of conidia are produced over the lesion surface </li></ul><ul><li>Leaves and stems become chlorotic, then turn brown and dry prematurely. </li></ul>Symptoms and Signs: Muhammad Asif Pakistan
    37. 37. Conditions for Disease Development <ul><li>The pathogens are obligate parasites and can persist on wild cucurbits or crop plants </li></ul><ul><li>Disease development can occur over a wide range of temperatures as long as there sufficient moisture for spore germination and infection. </li></ul><ul><li>These conditions can be provided by high relative humidity or dew formation in the absence of rainfall. </li></ul><ul><li>Inoculum is airborne for long distances </li></ul>Muhammad Asif Pakistan
    38. 38. Control Strategies <ul><li>Avoid crowding of plants </li></ul><ul><li>Resistant cultivars of many crops available, pumpkin is exception </li></ul><ul><li>Fungicide sprays are available, but may not be cost effective </li></ul><ul><li>Sanitation and practices that avoid lush growth help to delay spread </li></ul>Muhammad Asif Pakistan