2. Anthracnose
Colletotrichum lagenarium
Symptoms
Older leaves show small, water-soaked or yellowish areas that
enlarge rapidly and turn tan to reddish brown
Spots - often circular to angular
Later, spots may merge, blighting large sections of the leaf
Petioles and stems - Tan to black, elongated and form slightly
sunken streaks called cankers
Attacks Watermelon, Cantaloupe, Cucumber
Squash and pumpkin are almost immune
3. Older, and greatly enlarged lesions on a
melon leaf
Lesions on watermelon are irregular and
turn dark brown or black
4. 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
Melon showing the blackened center of
the lesion and a hint of the pinkish spore
mass
Lesion on watermelon showing a
gelatinous mass of salmon colored
spores
5. Fungus
Mycelium - septate, hyaline when young and dark when old
Setae - brown, thick walled, 2-3 septate
Conidia - hyaline, oblong and single celled
Whisker like setae and conidia
6. Mode of spread and survival
Soil and seed borne
Fungus overwinters in old cucurbit vines or in weeds for 5 yrs
Anthracnose can appear anytime during the season, but
most damage occurs late in the season after the fruit is set
Spread - running water, workers and the insect Pimelia sp.
Epidemiology
Warm, wet conditions - favour rapid development and spread
of the disease
Temp - 25oc, 100%RH
7. Management
Field sanitation - destroy the plant debris
Hot water treatment of seeds @ 57.2oc for 20 min
Seed treatment - thiram or carbendazim or mancozeb @ 2g/kg
Spraying at weekly intervals of
◦ Carbendazim 0.1 %
◦ Mancozeb 0.2%
◦ Difolaton 0.2%
Fruit dip - 5 min in wash water containing 120 ppm of chlorine
helps to prevent infection of healthy fruits
Resistant varieties in watermelon - Black Stone, Congo,
Diamond, Charleston
8. Gummy stem blight and black spot
Didymella bryoniae
Stems - water-soaked lesions and later
appear tan
Stem lesions often cause gummy, reddish -
brown or black beads to exude
• Leaf - water-soaked lesion, inter veinal
necrotic scorch
• Lesions - surrounded by a yellow halo, & when
spots dry up, they often crack
9. Black rot
Affected area - brownish and water soaked
Advanced stages - rind becomes black and deeply wrinkled
Large irregular areas of the fruit become bronzed with distinct
concentric rings
10. Fungus
Pycnidia are produced, giving rise to conidia, which serve as the
primary inoculum
Young pycnidia appear light brown & as they age become black
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
11. Mode of spread and survival
Seed and soil-borne
Survives as dormant mycelium or as chlamydospores
Under moist conditions, they are readily dispersed by
splashing water
Epidemiology
RH - 85 %
Optimal temperature
Watermelon 23.9oc
Muskmelon 39oc
12. Management
Disease-free seed
2-year crop rotation out of all cucurbits
Field sanitation
Fungicides - chlorothalanil, mancozeb and benomyl
Cucumbers - precooled to 10oc or lower temp
13. Choanephora wet rot
Choanephora cucurbitarum
Symptoms
Attacks the blossoms first and progresses into the developing
fruit causing a wet rot at the blossom end
Fruit rot progresses rapidly and can affect entire fruit within one
or two days
Sporulation by the fungus appears as spines with dark heads on
the surface of infected tissues
14. 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
15. 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)
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
16. Fruit rot
Pythium aphanidermatum
Symptoms
Fruits in intimate contact with soil is affected
Forms a luxuriant wooly mycelial mat on the affected fruits
Skin of the friut shows soft, dark green, water soaked lesions
Interior tissue become watery and soft and decaying matter
emits a bad odour
17. Fungus
Mycelium - intra-cellular, hyaline and coenocytic
Oogonia - smooth and spherical
Antheridia - broadly clavate, terminal or intercallary
Spreads among the fruits during the storage and transit
High moisture and temperature - favours the growth
Management
Soil drenching with copperoxychloride - 0.25%
Fruits should be kept away from soil
18. Belly rot
Rhizoctonia solani
Dark brown water-soaked decay on the side of the fruit in
contact with the soil
Followed by a yellowish-brown discolouration of the fruit surface
Entire fruit rot within few days
Water-soaked lesions
19. 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
Holding the fruit at 10°C (50°F) will retard disease
development during transit and storage
20. 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
21. Mode of survival - conidia
Mode of spread - wind, farm implements, insects
Management
Scratches and bruises must be avoided
Pre cooling after harvest
Harvest fruits with long stems
Cut ends painted with a fungicide paste - copper sulphate
22. Curvularia fruit rot - Curvularia ovoidae
Rot is characterised by brown to black irregular lesions
Later covered with dense velvety, black conidial mass of the
pathogen
Fungus
Mycelium - dark coloured
Conidia – septate, inner cells deep brown and outer cells light
brown in colour
23. Aspergillus fruit rot - Aspergillus flavus and Aspergillus nidulans
Water soaked lesions developed on the fruit surface
Covered by greenish or blackish fungal growth at later stage
Geotrichum fruit rot - Geotrichum candidum
Rot appears as water soaked lesion on fruit surface
Fruit skin becomes soft, sometimes shows cracks on the lesion
and emit bad colour
Fruit skin - small, black, sunken spots are produced
24. Bacterial soft rot
Erwinia carotovora
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
25. Bacterial Fruit Rot
Xanthomonas campestris pv.cucurbitae
Fruit - small, slightly sunken, circular spots with a tan center and
dark brown border
Epidermis may split, spots enlarge, and become sunken
Bacteria can penetrate into the flesh causing fruit rot and other
secondary bacteria may invade
Pathogen – seed borne
Disease is common high and occurs frequently after heavy
rainfall.
26. Management
Seed treatments with hot water (50˚ C for twenty minutes) or
10 % Chlorox
Avoid overhead irrigation and working the fields when they
are wet
Rotate out of cucurbits for two years
Repeated applications of copper fungicides as a protectant
may be helpful
27. 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
28. Management
Rotation with non-host crops is recommended.
Other hosts are pepper, tomato, eggplant, cocoa, and
macadamia.
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.
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.