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Anthracnose
Colletotrichum lagenarium
Symptoms
 Older leaves show small, water-soaked or yellowish areas that
enlarge rapidly and turn tan to reddish brown
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Spots - often circular to angular
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Later, spots may merge, blighting large sections of the leaf
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Petioles and stems - Tan to black, elongated and form slightly
sunken streaks called cankers
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Attacks Watermelon, Cantaloupe, Cucumber
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Squash and pumpkin are almost immune
Older, and greatly enlarged lesions on a
melon leaf
Lesions on watermelon are irregular and
turn dark brown or black
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Immature fruit - turn black, shrivel, and die
Round, water-soaked spots develop on the older fruit
Spots turn dark green to brown with age and may become
sunken
Under wet conditions, pinkish-colored spore masses can be
seen oozing out of the sunken spots
Lesion on watermelon showing a
gelatinous mass of salmon colored
spores
Melon showing the blackened center of
the lesion and a hint of the pinkish spore
mass
Fungus
 Mycelium - septate, hyaline when young and dark when old
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Setae - brown, thick walled, 2-3 septate
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Conidia - hyaline, oblong and single celled
Whisker like setae and conidia
Mode of spread and survival
 Soil and seed borne
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Fungus overwinters in old cucurbit vines or in weeds for 5 yrs
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Anthracnose can appear anytime during the season, but
most damage occurs late in the season after the fruit is set
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Spread - running water, workers and the insect Pimelia sp.
Epidemiology
 Warm, wet conditions - favour rapid development and spread
of the disease
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Temp - 25oc, 100%RH
Management
 Field sanitation - destroy the plant debris
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Hot water treatment of seeds @ 57.2oc for 20 min
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Seed treatment - thiram or carbendazim or mancozeb @ 2g/kg
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Spraying at weekly intervals of
◦ Carbendazim 0.1 %
◦ Mancozeb 0.2%
◦ Difolaton 0.2%
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Fruit dip - 5 min in wash water containing 120 ppm of chlorine
helps to prevent infection of healthy fruits
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Resistant varieties in watermelon - Black Stone, Congo,
Diamond, Charleston
Gummy stem blight and black spot
Didymella bryoniae
• Leaf - water-soaked lesion, inter veinal
necrotic scorch
• Lesions - surrounded by a yellow halo, & when
spots dry up, they often crack
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Stems - water-soaked lesions and later
appear tan
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Stem lesions often cause gummy, reddish brown or black beads to exude
Black rot
 Affected area - brownish and water soaked
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Advanced stages - rind becomes black and deeply wrinkled
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Large irregular areas of the fruit become bronzed with distinct
concentric rings
Fungus
 Pycnidia are produced, giving rise to conidia, which serve as the
primary inoculum
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Young pycnidia appear light brown & as they age become black
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Conidia - short and cylindrical, with usually one septum near the
middle, or they may be unicellular
Pycnidia with prominent ostiole through
which conidia are released
Mode of spread and survival
 Seed and soil-borne
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Survives as dormant mycelium or as chlamydospores
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Under moist conditions, they are readily dispersed by
splashing water
Epidemiology
 RH - 85 %
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Optimal temperature
 Watermelon 23.9oc
 Muskmelon 39oc
Management
 Disease-free seed
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2-year crop rotation out of all cucurbits
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Field sanitation
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Fungicides - chlorothalanil, mancozeb and benomyl
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Cucumbers - precooled to 10oc or lower temp
Choanephora wet rot
Choanephora cucurbitarum
Symptoms
 Attacks the blossoms first and progresses into the developing
fruit causing a wet rot at the blossom end
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Fruit rot progresses rapidly and can affect entire fruit within one
or two days
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Sporulation by the fungus appears as spines with dark heads on
the surface of infected tissues
Fungus
 Produces both conidia and sporangiophores
 Conidiophores - unbranched and has a spherical head
 Sporangiophores - unbranched, recurved at the tip, bearing the
sporangium
Sporangia and fertile heads
Fertile head
Mode of spread and survival
 Attacks cauliflower, cotton, cucumber, pumpkin, radish and
squash
 Survive as a saprophyte - as chlamydospores and zygospores
 Spread - air, beetles and bees
Management
 Crop management practices
◦ Reduce soil moisture (raised beds)
◦ Prevent fruit injury
◦ Prevent soil contact with the soil (plastic mulches or trellising)
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Post harvest losses may be reduced by
◦ Harvesting fruits at proper stage of maturity
◦ Minimizing cucurbit fruit injuries at harvest
◦ Pre cooling fruit
◦ Maintaining relatively low storage temperature
Fruit rot
Pythium aphanidermatum
Symptoms
 Fruits in intimate contact with soil is affected
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Forms a luxuriant wooly mycelial mat on the affected fruits
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Skin of the friut shows soft, dark green, water soaked lesions
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Interior tissue become watery and soft and decaying matter
emits a bad odour
Fungus
 Mycelium - intra-cellular, hyaline and coenocytic
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Oogonia - smooth and spherical
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Antheridia - broadly clavate, terminal or intercallary
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Spreads among the fruits during the storage and transit
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High moisture and temperature - favours the growth
Management
 Soil drenching with copperoxychloride - 0.25%
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Fruits should be kept away from soil
Belly rot
Rhizoctonia solani
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Dark brown water-soaked decay on the side of the fruit in
contact with the soil
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Followed by a yellowish-brown discolouration of the fruit surface
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Entire fruit rot within few days
Water-soaked lesions
Fungus
 Produces pycnidia and sclerotia
 Pycnidiospores - hyaline, single celled, ovate to ellipsoid
Mode of spread and survival
 R. solani overwinters in soils as mycelia on plant debris and
as dark brown sclerotia that remain in soil for long periods
Management
 Pre-harvest sprays of the fungicides
◦ Azoxystrobin
◦ Chlorothalonil
◦ Thiophanate-methyl
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Holding the fruit at 10°C (50°F) will retard disease
development during transit and storage
Diplodia fruit rot of watermelon and cucumber
Diplodia natalensis
Symptoms
 Stems and leaves - blight and wilting
 Fruit - decay appears around the stem
 Rind becomes slightly darkened, water soaked and light brown
later
 Centre of the spots turn black, cracks and wrinkles
Fungus
 Pycnidia - black and large
 When young - colourless, thick walled and one celled
 When mature - dark brown, rough walled and two celled
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Mode of survival - conidia
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Mode of spread - wind, farm implements, insects
Management
 Scratches and bruises must be avoided
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Pre cooling after harvest
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Harvest fruits with long stems
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Cut ends painted with a fungicide paste - copper sulphate
Curvularia fruit rot - Curvularia ovoidae
 Rot is characterised by brown to black irregular lesions
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Later covered with dense velvety, black conidial mass of the
pathogen
Fungus
 Mycelium - dark coloured
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Conidia – septate, inner cells deep brown and outer cells light
brown in colour
Aspergillus fruit rot - Aspergillus flavus and Aspergillus nidulans
 Water soaked lesions developed on the fruit surface
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Covered by greenish or blackish fungal growth at later stage
Geotrichum fruit rot - Geotrichum candidum
 Rot appears as water soaked lesion on fruit surface
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Fruit skin becomes soft, sometimes shows cracks on the lesion
and emit bad colour
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Fruit skin - small, black, sunken spots are produced
Bacterial soft rot
Erwinia carotovora
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Infects the fruit via cracks or wounds in the skin
Soft rot rapidly disintegrates the flesh, turning it into a soft
mass of leaky tissue
Infected fruits typically have a foul odour
Management
 Avoid injury to the skin
 Use properly sanitized (i.e. 150 ppm hypochlorous acid) wash
water
Bacterial Fruit Rot
Xanthomonas campestris pv.cucurbitae
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Fruit - small, slightly sunken, circular spots with a tan center and
dark brown border
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Epidermis may split, spots enlarge, and become sunken
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Bacteria can penetrate into the flesh causing fruit rot and other
secondary bacteria may invade
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Pathogen – seed borne
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Disease is common high and occurs frequently after heavy
rainfall.
Management
 Seed treatments with hot water (50˚ C for twenty minutes) or
10 % Chlorox
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Avoid overhead irrigation and working the fields when they
are wet
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Rotate out of cucurbits for two years
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Repeated applications of copper fungicides as a protectant
may be helpful
Phytophthora Fruit Rot (Phytophthora capsici
 Fruit rot of processing pumpkin caused by P. capsici:
 Lesions appear on fruit surface;
 Fruit rot developed on the side contacting the soil;
 Fruit rot as a result of falling an infected leaf on fruit
 Severely infected fruits are collapsed.
First indication of sporulation on the earlier water-soaked lesion
Management
 Rotation with non-host crops is recommended.
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Other hosts are pepper, tomato, eggplant, cocoa, and
macadamia.
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Manage soil moisture by selecting well-drained fields,
avoiding low-lying areas, subsoiling, preparing dome-shaped
raised beds for non-vining crops, and not over irrigating.
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Movement in soil on equipment is probably an important
means by which Phytophthora has been spread between
fields and may account for disease occurrence in fields with
no history of susceptible crops.