Download - POST HARVEST DISEASES OF CUCURBITS
AnthracnoseColletotrichum 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
Older, and greatly enlarged lesions on a melon leaf
Lesions on watermelon are irregular and turn dark brown or black
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
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
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
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
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
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
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
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
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
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
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)
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 rotPythium 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
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
Belly rotRhizoctonia 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
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
Diplodia fruit rot of watermelon and cucumberDiplodia fruit rot of watermelon and cucumberDiplodia natalensisDiplodia 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
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
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
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
Bacterial soft rotErwinia 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
Bacterial Fruit RotXanthomonas 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.
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
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.
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.