Cucurbits Diseases, Symptoms,
Etiology, Disease cycle and
Their Management.
1. Downy mildew
2. Powdery
mildew
3. wilt
4. Angular leaf
spot
5. Mosaic
6. TOSPO virus
: Pseudoperonospora cubensis
: Erysiphe
cichoracearum,
Sphaerotheca fuligena
: Fusarium oxysporum
f.sp. niveum
: Pseudomonas syringae
pv. lachrymans
:Cucumber mosaic virus
: Tomato spotted wilt
virus (TSWV)
1.Downy mildew :
Pseudoperonospora
cubensis
Host Members of Cucurbitaceae, the gourd family,
including cucumber (Cucumis sativus), squash (Cucurbita
spp.), melon (Cucumis melo) and watermelon (Citrullus
lanatus).
 Symptoms:
Cucumber, squash and pumpkin
Downy mildew symptoms first appear as small yellow spots or water-
soaked lesions on the topside of older leaves.
 The centre of the lesion eventually turns tan or brown and dies.
 The yellow spots sometimes take on a "greasy" appearance and do not
have a distinct border.
During prolonged wet periods, the disease may move onto the upper crop
canopy.
This is the earliest symptom produced by the disease, but will disappear as
moisture dissipates.
Early lesions are light green in appearance and become chlorotic and
finally necrotic as host plant cells die.
Severe infection results in leaves that are completely dead and curled up.
This symptom has been described as “wildfire” as the leaves appear to be
burned.
A greater proportion of mishapen fruit (especially in cucumber)
Watermelon and cantaloupe.
Symptoms on watermelon and cantaloupe are typically irregular shaped
lesions on the foliage that turn brown rapidly.
Infected leaves may experience an upward leaf curl
In cantaloupe crops, the lesions appear irregular shaped, whereas the
lesions are smaller and rounder on infected watermelon leaves.
As the disease progresses, the lesions expand and multiply, causing
the
field to take on a brown and "crispy" appearance.
Etiology:
P. cubensis is an obligate parasite . The mycelium is coenocytic
and intracellular with small finger like haustoria. 1-5 sporangiophores
arise through stomata. Spore bearing tip are subacute. Sporangia are
grayish to olivaceous purple. Ovoid to ellipsoidal, thin walled with
distal papilla & 21-39 µm X 14-23µm. Zoospore are 10-30µm in dia.
Oospore are not common.
Disease cycle :
P.I: Collateral hosts or fungus surviving in plant debris
S.I: Wind borne sporangia or splashing rain water
Management
 Destruction of cucurbitaceous weeds around field
Avoid excess overhead irrigation.
Wider spacing and planting sites with good drainage.
Seed treatment with Apron at 2 g/kg.
Spray metalaxyl@0.2% or chlorothalonil@0.2%
 Spray zineb@0.3% at 10 days interval
2. Powdery mildew : Erysiphe cichoracearum or Sphaerotheca
fuligena
 Symptoms :
Powdery mildew forms obvious patches of whitish mycelium
(resembling talc) on upper and lower leaf surfaces, petioles, and
stems.
First noted on the older leaves, powdery mildew appears as pale
yellow spots on stems, petioles, and leaves.
These spots enlarge as the white, fluffy mycelium grows over plant
surfaces and produces spores, which give the lesions a powdery
appearance.
Affected leaves become dull, chlorotic, and may show some degree
of wilting in the afternoon heat; eventually they become brown and
papery.
The diseased areas turn brown and dry. This leads to premature
defoliation and death
Fruits remain undeveloped and are deformed
Etiology:
E. Cichoracearum the conidia measure 63.8 X 31.9 µm. The
clestothecia are globose 80-100 µm in dia., containnig 10-15 asci,
which are 58-90 µm in size.each ascus contains two ascospores and
are oval or sub cylindrical.
S. fulinginea occasionaly brownish when old. Conidia are in
chains with fibrisin bodies, ellipsoid to barrel-shaped and 25-37 X
14-25 µm. Conidial germ tubes mostly forked perithecia
are round,
66-98 µm in dia. Asci are broadly elliptic and are 50-80 X 30-
60 µm. In each ascus 8ellipsoid ascospores are found.
Disease cycle:
P.I: Collateral hosts or through Cleistothecia
S.I: Wind borne conidia
Management
Plant resistant varieties where available.
Choose planting sites with good air movement and free of shade.
Spray Calixin 0.1% or Karathane @0.2%
3.
Wilt
: Fusarium oxysporum f.sp.
niveum
 Symptoms:
 Symptoms can occur at any stage of growth
On young seedlings, a hypocotyl rot and damping-off may occur. In
older plants, there is marginal yellowing progressing to a general
yellowing of the older leaves, and wilting of one or more runners.
In some cases, sudden collapse occurs without any yellowing of the
foliage.
On stems near the crown of the plant, a linear, necrotic lesion may
develop, extending up the plant and usually on one side of the vine.
One runner on a plant may wilt and collapse, with the rest of the
runners remaining healthy.
In a wet weather , a white or pinkish fungus growth develops on the
surface of dead stems.
Vascular discoloration should be evident and is very diagnostic.
Mature plants often wilt severely (collapse) late in the season because
of the fruit load stress.
Etiology :
The fungus produces three types of spores, small colourless,
oval to narrowly elliptical, non-septate microconidia, lagre sickle
shaped, septate macro-conidia and thick walled Chlamydospores.
DISEASE CYCLE OF WILT
The fungus can survive in soil as saprophyte for many years
and chlamydospores act as resting spores. The pathogen is both
externally and internally seed-borne. The primary infection is
mainly from dormant hyphae and chlamydospores in the soil. The
secondary spread is through conidia and chlamydospores
which are disseminated by wind
and irrigation water.
MANAGEMENT
Treat the seeds with Carboxin or Carbendazim at 2 g/kg.
Apply increased doses of potash with a balanced dose
of nitrogenous and phosphatic fertilizers.
organic
Apply heavy doses of farm yard manure or
other manures. Follow mixed cropping with non-host
plants.
Use resistant varieties.
 Maintaining a pH of 6.5 to 7.0.
4. Angular leaf spot:
Pseudomonas syringae pv.
lachrymans
 Symptoms:
Small, round water-soaked spots appear on leaf tissue, and expand until
they are confined by veins, giving them the characteristic angular look.
Under moist conditions a milky white exudates containing bacterial cells
may ooze out of the lesion on the lower leaf surface.
These wet-looking spots will dry out and turn yellow-brown or the dead
tissue may fall out leaving a “shot-hole” appearance.
Yellowing of the leaf between lesions may occur where disease severity is
high.
Similarly, water-soaked spots may appear on stems and petioles, drying
out to form a whitish crust.
Spots can also appear on fruit, where they are tiny and water-soaked but
dry to form whitish, chalky, spots.
These spots cause internal decay of fruit, and fruit that is infected early
may be deformed. Affected plants will grow poorly, produce less fruit, and
affected fruit is unmarketable.
Etiology :
The bacterium is gram negative, aerobic and rod shaped motile with 1-5
polar flagella & 0.8-1.2 µm in length.
It forms capsule and green fluorescent pigment in culture.
Disease cycle:
The Pseudomonas bacterium is a seed
borne pathogen. In addition, the
pathogen can overwinter in infested crop residues. The secodary
spread through irrigation water.
Management
Plant certified, pathogen-free seed produced in arid western
locations.
Resistant cucumber varieties are available.
Do not grow cucurbits in the same field more than once every three or four
years and avoid excessive nitrogen fertilization.
Limit the use of overhead irrigation and avoid cultivating, harvesting, or
otherwise handling plants when they are wet.
Where ever feasible, cleanly plow under or collect and burn crop debris
immediately after harvest.
Apply a recommended bactericide at first sign of
disease. (Streptocycline/Streptomycine). Spray 400ppm Streptomycin
sulphate.
Tank-mix the recommended bactericide with effective fungicides to protect
the plants against fungal diseases.
5. Cucumber Mosaic: Cucumber mosaic
virus
Symptoms
Symptoms of CMV in cucurbits generally manifest as severe stunting,
prominent yellow foliar mosaic, plant and leaf malformation, and stunting
due to drastic reduction of leaf size and stem internodes.
When the virus becomes systemic, leaves prominently curl downward,
develop a mosaic pattern, and remain small.
Flowers develop abnormalities and have greenish petals.
Foliar and flower symptom intensity varies with species and cultivar:
symptoms are most severe in summer squash, some pumpkins, and many
melons and less severe in cucumber, winter squash, and watermelon.
Infected fruit are often distorted and discolored, remain small, and, when
severely infected, produce a negligible amount of seeds.
Survival and spread
 Survive on weeds, ornamentals or other crops
 Transmitted by aphids (Aphis craccivora, Myzus persicae) and spotted
and
striped cucumber beetles
Collateral hosts: Banana, clover, corn, passion fruit, safflower, spinach,
sugarbeet, wild cucumber, Commelina communis, C. diffusa, C. nudiflora,
Solanum elaegnifolium, Phytolacca sp., periwinkle, Gladiolus sp., Impatiens
sp. and Phlox
Management
Rogue out infected plants
Eliminate perennial weed hosts
Vector control by spraying monochrotophos or
phosphamidon,
1.5 ml per liter of water
3. TOSPO virus : Tomato spotted wilt virus (TSWV)
 Symptoms:
Cucurbits infected with tospovirus exhibit a variety of symptoms.
Leaves can show bronzing to severe systemic chlorotic spotting.
Other symptoms include leaf deformation, mosaic, die-back and
overall plant stunting.
Fruit symptoms can range from chlorotic ring spots on young fruit
to necrotic lesions on older fruit.
Fruit cracking may also be observe
Etiology:
Tospo virus spp. possess a tripartite single-stranded RNA genome with
a negative or ambisense expression strategy.
Genomic RNAs are encapsidated by nucleocapsid proteins (N) and
enveloped by a lipoprotein membrane
Transmission:
Western flower thrips (Frankliniella occidentalis), Tobacco thrips (F.
fusca),
Melon thrips (Thrips palmi).
Management
In protected culture and transplant nurseries, utilize mesh screening
(minimum 72 mesh /192 microns) and phytosanitary measures to minimize
tospovirus infection by excluding thrips.
Avoid planting near or downwind of ornamentals or older crops, which
can serve as reservoirs for thrips and tospovirus.
 Control weeds and cucurbit volunteers.
Implement a comprehensive insecticide program beginning prior to
sowing or transplanting to manage thrips early larval stages and limit
secondary tospovirus spread.
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cucurbitsdiseasespath-365-210427070106.pptx

  • 1. Cucurbits Diseases, Symptoms, Etiology, Disease cycle and Their Management. 1. Downy mildew 2. Powdery mildew 3. wilt 4. Angular leaf spot 5. Mosaic 6. TOSPO virus : Pseudoperonospora cubensis : Erysiphe cichoracearum, Sphaerotheca fuligena : Fusarium oxysporum f.sp. niveum : Pseudomonas syringae pv. lachrymans :Cucumber mosaic virus : Tomato spotted wilt virus (TSWV)
  • 2. 1.Downy mildew : Pseudoperonospora cubensis Host Members of Cucurbitaceae, the gourd family, including cucumber (Cucumis sativus), squash (Cucurbita spp.), melon (Cucumis melo) and watermelon (Citrullus lanatus).  Symptoms: Cucumber, squash and pumpkin Downy mildew symptoms first appear as small yellow spots or water- soaked lesions on the topside of older leaves.  The centre of the lesion eventually turns tan or brown and dies.  The yellow spots sometimes take on a "greasy" appearance and do not have a distinct border. During prolonged wet periods, the disease may move onto the upper crop canopy. This is the earliest symptom produced by the disease, but will disappear as moisture dissipates. Early lesions are light green in appearance and become chlorotic and finally necrotic as host plant cells die. Severe infection results in leaves that are completely dead and curled up. This symptom has been described as “wildfire” as the leaves appear to be burned. A greater proportion of mishapen fruit (especially in cucumber)
  • 3. Watermelon and cantaloupe. Symptoms on watermelon and cantaloupe are typically irregular shaped lesions on the foliage that turn brown rapidly. Infected leaves may experience an upward leaf curl In cantaloupe crops, the lesions appear irregular shaped, whereas the lesions are smaller and rounder on infected watermelon leaves. As the disease progresses, the lesions expand and multiply, causing the field to take on a brown and "crispy" appearance.
  • 4. Etiology: P. cubensis is an obligate parasite . The mycelium is coenocytic and intracellular with small finger like haustoria. 1-5 sporangiophores arise through stomata. Spore bearing tip are subacute. Sporangia are grayish to olivaceous purple. Ovoid to ellipsoidal, thin walled with distal papilla & 21-39 µm X 14-23µm. Zoospore are 10-30µm in dia. Oospore are not common. Disease cycle : P.I: Collateral hosts or fungus surviving in plant debris S.I: Wind borne sporangia or splashing rain water Management  Destruction of cucurbitaceous weeds around field Avoid excess overhead irrigation. Wider spacing and planting sites with good drainage. Seed treatment with Apron at 2 g/kg. Spray [email protected]% or [email protected]%  Spray [email protected]% at 10 days interval
  • 5. 2. Powdery mildew : Erysiphe cichoracearum or Sphaerotheca fuligena  Symptoms : Powdery mildew forms obvious patches of whitish mycelium (resembling talc) on upper and lower leaf surfaces, petioles, and stems. First noted on the older leaves, powdery mildew appears as pale yellow spots on stems, petioles, and leaves. These spots enlarge as the white, fluffy mycelium grows over plant surfaces and produces spores, which give the lesions a powdery appearance. Affected leaves become dull, chlorotic, and may show some degree of wilting in the afternoon heat; eventually they become brown and papery. The diseased areas turn brown and dry. This leads to premature defoliation and death Fruits remain undeveloped and are deformed
  • 6. Etiology: E. Cichoracearum the conidia measure 63.8 X 31.9 µm. The clestothecia are globose 80-100 µm in dia., containnig 10-15 asci, which are 58-90 µm in size.each ascus contains two ascospores and are oval or sub cylindrical. S. fulinginea occasionaly brownish when old. Conidia are in chains with fibrisin bodies, ellipsoid to barrel-shaped and 25-37 X 14-25 µm. Conidial germ tubes mostly forked perithecia are round, 66-98 µm in dia. Asci are broadly elliptic and are 50-80 X 30- 60 µm. In each ascus 8ellipsoid ascospores are found.
  • 7. Disease cycle: P.I: Collateral hosts or through Cleistothecia S.I: Wind borne conidia Management Plant resistant varieties where available. Choose planting sites with good air movement and free of shade. Spray Calixin 0.1% or Karathane @0.2%
  • 8. 3. Wilt : Fusarium oxysporum f.sp. niveum  Symptoms:  Symptoms can occur at any stage of growth On young seedlings, a hypocotyl rot and damping-off may occur. In older plants, there is marginal yellowing progressing to a general yellowing of the older leaves, and wilting of one or more runners. In some cases, sudden collapse occurs without any yellowing of the foliage. On stems near the crown of the plant, a linear, necrotic lesion may develop, extending up the plant and usually on one side of the vine. One runner on a plant may wilt and collapse, with the rest of the runners remaining healthy. In a wet weather , a white or pinkish fungus growth develops on the surface of dead stems. Vascular discoloration should be evident and is very diagnostic. Mature plants often wilt severely (collapse) late in the season because of the fruit load stress.
  • 9. Etiology : The fungus produces three types of spores, small colourless, oval to narrowly elliptical, non-septate microconidia, lagre sickle shaped, septate macro-conidia and thick walled Chlamydospores.
  • 10. DISEASE CYCLE OF WILT The fungus can survive in soil as saprophyte for many years and chlamydospores act as resting spores. The pathogen is both externally and internally seed-borne. The primary infection is mainly from dormant hyphae and chlamydospores in the soil. The secondary spread is through conidia and chlamydospores which are disseminated by wind and irrigation water. MANAGEMENT Treat the seeds with Carboxin or Carbendazim at 2 g/kg. Apply increased doses of potash with a balanced dose of nitrogenous and phosphatic fertilizers. organic Apply heavy doses of farm yard manure or other manures. Follow mixed cropping with non-host plants. Use resistant varieties.  Maintaining a pH of 6.5 to 7.0.
  • 11. 4. Angular leaf spot: Pseudomonas syringae pv. lachrymans  Symptoms: Small, round water-soaked spots appear on leaf tissue, and expand until they are confined by veins, giving them the characteristic angular look. Under moist conditions a milky white exudates containing bacterial cells may ooze out of the lesion on the lower leaf surface. These wet-looking spots will dry out and turn yellow-brown or the dead tissue may fall out leaving a “shot-hole” appearance. Yellowing of the leaf between lesions may occur where disease severity is high. Similarly, water-soaked spots may appear on stems and petioles, drying out to form a whitish crust. Spots can also appear on fruit, where they are tiny and water-soaked but dry to form whitish, chalky, spots. These spots cause internal decay of fruit, and fruit that is infected early may be deformed. Affected plants will grow poorly, produce less fruit, and affected fruit is unmarketable.
  • 12. Etiology : The bacterium is gram negative, aerobic and rod shaped motile with 1-5 polar flagella & 0.8-1.2 µm in length. It forms capsule and green fluorescent pigment in culture.
  • 13. Disease cycle: The Pseudomonas bacterium is a seed borne pathogen. In addition, the pathogen can overwinter in infested crop residues. The secodary spread through irrigation water. Management Plant certified, pathogen-free seed produced in arid western locations. Resistant cucumber varieties are available. Do not grow cucurbits in the same field more than once every three or four years and avoid excessive nitrogen fertilization. Limit the use of overhead irrigation and avoid cultivating, harvesting, or otherwise handling plants when they are wet. Where ever feasible, cleanly plow under or collect and burn crop debris immediately after harvest. Apply a recommended bactericide at first sign of disease. (Streptocycline/Streptomycine). Spray 400ppm Streptomycin sulphate. Tank-mix the recommended bactericide with effective fungicides to protect the plants against fungal diseases.
  • 14. 5. Cucumber Mosaic: Cucumber mosaic virus Symptoms Symptoms of CMV in cucurbits generally manifest as severe stunting, prominent yellow foliar mosaic, plant and leaf malformation, and stunting due to drastic reduction of leaf size and stem internodes. When the virus becomes systemic, leaves prominently curl downward, develop a mosaic pattern, and remain small. Flowers develop abnormalities and have greenish petals. Foliar and flower symptom intensity varies with species and cultivar: symptoms are most severe in summer squash, some pumpkins, and many melons and less severe in cucumber, winter squash, and watermelon. Infected fruit are often distorted and discolored, remain small, and, when severely infected, produce a negligible amount of seeds. Survival and spread  Survive on weeds, ornamentals or other crops  Transmitted by aphids (Aphis craccivora, Myzus persicae) and spotted and striped cucumber beetles Collateral hosts: Banana, clover, corn, passion fruit, safflower, spinach, sugarbeet, wild cucumber, Commelina communis, C. diffusa, C. nudiflora, Solanum elaegnifolium, Phytolacca sp., periwinkle, Gladiolus sp., Impatiens sp. and Phlox
  • 15. Management Rogue out infected plants Eliminate perennial weed hosts Vector control by spraying monochrotophos or phosphamidon, 1.5 ml per liter of water
  • 16. 3. TOSPO virus : Tomato spotted wilt virus (TSWV)  Symptoms: Cucurbits infected with tospovirus exhibit a variety of symptoms. Leaves can show bronzing to severe systemic chlorotic spotting. Other symptoms include leaf deformation, mosaic, die-back and overall plant stunting. Fruit symptoms can range from chlorotic ring spots on young fruit to necrotic lesions on older fruit. Fruit cracking may also be observe
  • 17. Etiology: Tospo virus spp. possess a tripartite single-stranded RNA genome with a negative or ambisense expression strategy. Genomic RNAs are encapsidated by nucleocapsid proteins (N) and enveloped by a lipoprotein membrane Transmission: Western flower thrips (Frankliniella occidentalis), Tobacco thrips (F. fusca), Melon thrips (Thrips palmi). Management In protected culture and transplant nurseries, utilize mesh screening (minimum 72 mesh /192 microns) and phytosanitary measures to minimize tospovirus infection by excluding thrips. Avoid planting near or downwind of ornamentals or older crops, which can serve as reservoirs for thrips and tospovirus.  Control weeds and cucurbit volunteers. Implement a comprehensive insecticide program beginning prior to sowing or transplanting to manage thrips early larval stages and limit secondary tospovirus spread.