Cucurbit Diseases

1
Cucurbit Diseases

• Belly Rot - Rhizoctonia solani
• Anthracnose - Colletotrichum lagenarium
• Scab - Cladosporium cucumerinum
• Phytophthora Blight - Phytophthora capsici
• Black Rot, Gummy Stem Blight - Didymella bryoniae
• Powdery Mildew Erysiphe cichoracearum,
• Sphaerotheca fuliginea
• Downey Mildew - Pseudoperonospora cubensis
• Alternaria Leaf Blight - Alternaria cucumerina
• Fusarium Wilt
• Fusarium oxysporum f. sp. cucumerinum (cucumber)
• Fusarium oxysporum f. sp. melonis (muskmelon)
• Fusarium oxysporum f. sp. niveum (watermelon)

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Cucurbit Diseases

• Angular Leaf Spot - Pseudomonas syringae pv.
  lachrymans
• Bacterial Wilt - Erwinia tracheiphila

• Cucumber Mosaic Virus
• Squash Mosaic Virus
• Watermelon Mosaic Virus
• Zucchini Yellow Mosaic

• Root Knot Nematode - Meloidogyne hapla

• Blossom End Rot
• Juglone Toxicity
• Windburn

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Angular Leaf Spot
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Angular Leaf Spot Fruit Infection
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Angular Leaf Spot Internal Fruit Infection
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Cucurbit Diseases - Angular Leaf Spot Key Points

• Pathogen Pseudomonas syringae pv. lachrymans
• Symptoms
• Leaf lesions bounded by veins - angular
  appearance
• Lesions dry, turn tan, and drop out - tattered
  leaves
• Fruit lesions small, circular, water-soaked spots
• Extensive internal rot of fruit may also be
  present
• Favored by warm, humid conditions
• May be seed-borne
• Spread via rain splash, insects, human activity
  and farm machinery
• May overwinter in infected crop residues

7
Cucurbit Diseases - Angular Leaf Spot Control
Strategies

• Use pathogen-free seed
• Rotate crops - 2 year minimum between cucurbit
  crops
• Irrigation to avoid prolonged wetting of foliage
  and fruit
• Avoid fields when foliage is wet
• Season ending sanitation

8
Belly Rot
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Cucurbit Diseases - Belly Rot Key Points

• Pathogen Rhizoctonia solani
• Symptoms
• Water-soaked, tan to brown lesions on undersides
  and blossom ends of fruit
• Lesions become cratered as they enlarge
• Favored by 80o F and high relative humidity
• Inoculum survives in soil for many years
• All cucurbits are susceptible
• Cucumber is the most susceptible

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Cucurbit Diseases - Belly Rot Control Strategies

• Deep tillage before planting buries inoculum
• Mulching provides physical barrier between fruit
  and soil-borne inoculum
• Long-term rotation may help
• Soil-applied fungicides provide some benefit

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Anthracnose - Cucumber
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Anthracnose - Cucumber
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Anthracnose - Cucumber
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Anthracnose - Muskmelon
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Anthracnose Acorn Squash
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Anthracnose - Gourd
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Cucurbit Diseases - Anthracnose Key Points

• Pathogen Colletotrichum lagenarium
• Symptoms
• Leaf lesions are more or less circular start
  near veins
• Infection points on the fruit are circular,
  sunken
• Fruit lesions on acorn squash are black and large
• Spread favored by splashing rain and warm
  temperatures
• Infected leaves serve as inoculum source for
  fruit
• Pathogen overwinters on infected plant residue

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Cucurbit Diseases - Anthracnose Control
Strategies

• Deep tillage immediately after harvest
• Plant only pathogen-free seed
• Crop rotation - At least 2 years between
  cucurbits
• Protectant and systemic fungicides at label rates

19
Scab - Cucumber
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Cucurbit Diseases - Scab Key Points

• Pathogen Cladosporium cucumerinum
• Symptoms
• Pale green water-soaked lesions on leaves
• Lesions turn gray or white spots drop out of
  leaves
• Spots on fruit are small and sunken, resemble
  insect injury
• Watery, then gummy exudate from fruit lesions
• Dark green velvety fungal growth on fruit lesions
  in moist conditions
• Pathogen may be seed-borne
• Transported by insects and humans
• Disease progresses more rapidly at 63o than 70o
  with 100 RH
• Broad host range in cucurbit family, but most
  likely on susceptible cucumber cultivars

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Cucurbit Diseases - ScabControl Strategies

• Use scab-resistant cultivars of cucumber
• Rotation out of cucurbit crops for minimum of 3
  years
• Careful irrigation to avoid long periods of leaf
  wetting
• Protectant fungicide sprays

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Phytophthora Fruit Rot
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Phytophthora Fruit Rot
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Phytophthora Fruit Rot - Pumpkin
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Cucurbit Diseases - Phytophthora Fruit RotKey
Points

• Pathogen Phytophthora capsici
• Symptoms
• Rapid wilting of individual plants, vascular
  browning
• Watersoaked areas on fruit
• Rapid enlargement of fruit lesions
• White fungal growth covers fruit lesion
• Rapid collapse of affected fruit
• Favored by warm and wet conditions
• Spread by rain splash, insects, workers
• May overwinter in crop debris and in soil

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Cucurbit Diseases - Phytophthora Fruit
RotControl Strategies

• Pathogen-free seed
• Crop rotation minimum of 3 years
• Plant in well-drained sites
• Avoid over-irrigation
• Do not enter fields with wet foliage
• Prompt tillage of infected debris at season end
• No known resistance
• Fungicide controls being evaluated

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Black Rot - Pumpkin
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Black Rot - Pumpkin
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Black Rot - Pumpkin
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Black Rot - Pumpkin
31
Cucurbit Diseases - Black Rot, Gummy Stem Blight
- Key Points

• Pathogen Didymella bryoniae
• Symptoms
• Infected seedlings can die quickly
• On older plants, leaf lesions often begin at leaf
  margin as wilt
• Infected stems develop cankers with brownish red
  gummy fluid
• Tiny black fruit bodies with infected tissue
• On fruit, lesions first appear as small
  watersoaked spots
• Fruit lesions rapidly enlarge on mature fruit
• Pumpkin fruit lesions are large and black rapid
  fruit decay
• Favored by moderate temperatures and wet weather
• Spread by splashing rain, workers and equipment
• Soilborne, overwinters in crop debris

32
Cucurbit Diseases - Black Rot, Gummy Stem Blight
- Control Strategies

• Crop rotation minimum of 3 years
• Careful irrigation - avoid overwatering
• Avoid working in wet fields
• Removal of infected plants and plant debris
• Resistant cultivars not yet available
• Fungicide program with protectant/systemic
  materials effective

33
Powdery Mildew
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Powdery Mildew
35
Cucurbit Diseases - Powdery MildewKey Points

• Pathogen Erysiphe cichoracearum, Sphaerotheca
  fuliginea
• Symptoms / Signs
• Talcumlike powdery growth on leaves, stems
• Infected leaves and stems wither and die
• Appearance most likely with cool nights and heavy
  dews
• Free water not necessary for infection
• Inoculum is airborne for long distances

36
Cucurbit Diseases - Powdery Mildew 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

37
Downy Mildew
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Downy Mildew
39
Cucurbit Diseases - Downy MildewKey Points

• Pathogen Pseudoperonospora cubensis
• Symptoms
• Mottling and yellow spotting
• Coalescence of small lesions
• Fine grayish white fungus growth on lower leaf
  surface
• Infected leaves die, but remain erect
• Favored by warm and humid conditions
• Fog, dew and rain highly favorable for infection
  and development
• Spores can be transported by wind over large
  distances

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Cucurbit Diseases - Downy Mildew Control
Strategies

• Resistant varieties available for some crops
• Avoid overirrigation
• Avoid overcrowding of plantings
• Fungicide sprays effective for control on
  susceptible varieties

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Alternaria Blight
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Cucurbit Diseases - Alternaria Leaf BlightKey
Points

• Pathogen Alternaria cucumerina
• Symptoms
• Circular tan spots on leaves
• Leaf lesions have concentric rings
• Yellow halo surrounding lesions
• Infection of foliage leads to defoliation
• Favored by warm humid conditions
• Heavy irrigation or rain contributes to spread
  and losses
• Plants deficient in nitrogen most susceptible

43
Cucurbit Diseases - Alternaria Leaf Blight
Control Strategies

• Crop rotation - minimum of three years out of
  cucurbit crop
• Balanced crop nutrition program
• Avoid crop stress
• Timely irrigation, but not overirrigation
• Crop sanitation between cropping seasons

44
Fusarium Wilt
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Fusarium Wilt
46
Cucurbit Diseases - Fusarium WiltKey Points

• Pathogen
• Fusarium oxysporum f. sp. cucumerinum (cucumber)
• Fusarium oxysporum f. sp. melonis (muskmelon)
• Fusarium oxysporum f. sp. niveum (watermelon)
• Symptoms
• Progressive wilting of affected plants
• Eventual debilitation of plants and plant death
• Discoloration of vascular tissue
• Mostly a problem on muskmelon and watermelon
• Fungus enters plant through roots
• Pathogen spread by wind-blown soil, equipment

47
Cucurbit Diseases - Fusarium Wilt Control
Strategies

• Crop rotation as long as possible between
  plantings
• Sanitation, prompt removal of symptomatic plants
• Plant wilt resistant cultivars

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Bacterial Wilt
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Bacterial Wilt
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Cucurbit Diseases - Bacterial WiltKey Points

• Pathogen Erwinia tracheiphila
• Symptoms
• Sudden wilting of individual runners or whole
  plants
• Wilted plants do not recover with watering
• Bacterial streaming (sticky strings) from cut
  ends of wilted stems
• Pathogen overwinters in cucumber beetles
• Pathogen spreads from plant to plant through
  beetle feeding

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Cucurbit Diseases - Bacterial Wilt Control
Strategies

• Eliminate wild cucurbit plants surrounding
  planting area
• Control the beetle vectors
• Tolerant cucumber varieties available
• No resistance in muskmelon
• Other cucurbits less susceptible
• Sanitation - removal of symptomatic plants

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Blossom End Rot
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Blossom End Rot
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Cucurbit Diseases - Blossom End RotKey Points

• Cause Primarily physiological, deficiency of
  calcium
• Symptoms
• Collapse of fruit at blossom end
• Most common on first set fruit and when
  fluctuating moisture

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Cucurbit Diseases - Blossom End Rot Control
Strategies

• Irrigation that meets but does not exceed plant
  needs
• Mulching
• Balanced soil fertility including calcium
  nutrition

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Root Knot Nematode
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Root Knot Nematode
58
Cucurbit Diseases - Root Knot NematodeKey Points

• Pathogen Meloidogyne hapla
• Symptoms
• Poor growth, yellow foliage
• Wilt during dry periods
• Galls on roots
• Pathogen soil-borne
• Spread by movement of soil and plant debris

59
Cucurbit Diseases - Root Knot Nematode Control
Strategies

• Crop rotation
• Deep tillage to bury inoculum
• Soil fumigation

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Cucumber Mosaic Virus
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Cucumber Mosaic Virus
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Squash Mosaic Virus
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Squash Ringspot
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Ringspot on Watermelon
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Watermelon Mosaic Virus
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Watermelon Mosaic Virus I
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Cucurbit Diseases - Virus DiseasesKey Points

• Pathogen
• Cucumber Mosaic Virus
• Squash Mosaic Virus
• Watermelon Mosaic Virus
• Zucchini Yellow Mosaic
• Symptoms
• Mosaic symptoms on foliage and fruit
• Stunted growth, distortion of new growth
• Zucchini yellow mosaic leads to severe
  malformation of fruit
• Aphid spread from plant to plant for CMV, WMV and
  ZYMV
• Beetle and grasshopper spread of SMV
• SMV is seed transmitted

68
Cucurbit Diseases - Virus Diseases Control
Strategies

• Purchase pathogen free seed (for SMV)
• Control insect vectors
• Control wild cucurbit plants that may harbor
  virus pathogens
• Prompt removal of symptomatic plants may reduce
  losses

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Juglone Toxicity
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Cucurbit Diseases - Juglone ToxicityKey Points

• Cause
• Toxic action of Juglone produced by walnut and
  butternut trees
• Symptoms
• Stunted growth
• Plant wilt and death
• Symptomatic plants within drip edge of walnut or
  butternut trees

71
Cucurbit Diseases - Juglone Toxicity Control
Strategies

• Avoid planting deep rooted plants within drip
  edge of walnut or butternut trees
• Do not mulch plants with leaves or nuts of walnut
  or butternut

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Windburn
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Cucurbit Diseases - WindburnKey Points

• Cause Exposure to intense sunlight and drying
  wind
• Symptoms
• Interveinal bleaching, drying and death of leaf
  tissues
• Death of succulent plants

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Cucurbit Diseases - Windburn Control Strategies

• Avoid exposure of unhardened plant tissues to
  unshaded sunlight and drying winds