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Diseases of Cucurbits

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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. – PowerPoint PPT presentation

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Title: Diseases of Cucurbits


1
Diseases of Cucurbits
  • Types of Cucurbits
  • Those grown in IL
  • Production facts
  • Etc.

2
Diseases Covered
  • Watermelon fruit blotch
  • Bacterial wilt
  • Anthracnose
  • Powdery mildew

3
Production of squash seed
4
Harvesting for seed
5
DISEASE Watermelon Fruit Bloch
  • CROP Watermelon, other cucurbits are hosts
  • PATHOGEN Acidovorax avenae subsp. Citrulli
  • DISTRIBUTION FL, SC, NC, MD, IN, LA
  • PATHOGEN DESCRIPTION Bacterium
  • Gram-negative, straight rod, motile, peritrichous
    flagella.

6
Disease 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!!!

7
Disease Symptoms
8
Disease Symptoms and Signs
  • Fruit
  • Begin 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.

9
Disease Symptoms
10
Disease Cycle
11
Disease Development
  • 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.

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 Str
eptomycin (illegal, not labeled) is used in dire
situations in the greenhouse to stop the spread
of the pathogen
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.
14
DISEASE Bacterial Wilt
  • CROP Cucurbits
  • PATHOGEN Erwinia tracheiphila
  • DISTRIBUTION North America, Europe, Asia, Africa
  • PATHOGEN DESCRIPTION Bacterium
  • Gram-negative, straight rod, motile, peritrichous
    flagella.

15
Disease 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.

16
Bacterial wilt of cucurbits
17
Bacterial wilt of cucurbits (pumpkin)
18
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19
Conditions 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.

20
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21
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22
Control 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.

23
DISEASE Anthracnose
  • CROP Cucurbits
  • PATHOGEN Colletotrichum lagenarium (imperfect
    (asexual) stage) Glomerella cingulata var.
    orbiculare (sexual stage)
  • DISTRIBUTION Worldwide

24
Pathogen Description Fungus
  • Cylindrical, hyaline conidia arc produced on
    lesions in pinkish masses in acervuli also
    bearing two to three septate, brown setae.

25
Pathogen Description Fungus
Formation of appresorium
Two-celled conidium
26
Disease 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.

27
Anthracnose of cucurbits
cucumber
watermelon
28
Anthracnose of cucurbits (watermelon)
Sunken lesions with pink/salmon colored
sporulation
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.
30
Control
  • 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 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.

31
Control
FungicidesApply 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.
32
Powdery Mildew
33
Powdery Mildew
  • Pathogen Erysiphe cichoracearum, Sphaerotheca
    fuliginea
  • Cylindrical, hyaline conidia are produced in
    chains on conidiophores that arise from surface
    mycelial growth.

34
Symptoms and Signs
35
Signs of the Pathogen
36
Symptoms and Signs
  • All cucurbits are susceptible to powdery mildew
  • Symptoms appear first as pale yellow spots on
    leaves and stems
  • Sporulation becomes evident as white powdery
    masses of conidia are produced over the lesion
    surface
  • Leaves and stems become chlorotic, then turn
    brown and dry prematurely.

37
Conditions for Disease Development
  • The pathogens are obligate parasites and can
    persist on wild cucurbits or crop plants
  • Disease 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

38
Control Strategies
  • Avoid crowding of plants
  • Resistant cultivars of many crops available,
    pumpkin is exception
  • Fungicide sprays are available, but may not be
    cost effective
  • Sanitation and practices that avoid lush growth
    help to delay spread
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