POST HARVEST DISEASES OF CUCURBITS

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

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 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

Mycelium - septate, hyaline when young and dark when old 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

Field sanitation - destroy the plant debris 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 Leaf - water-soaked lesion, inter veinal necrotic scorch Lesions - surrounded by a yellow halo, & when spots dry up, they often crack Stems - water-soaked lesions and later appear tan Stem lesions often cause gummy, reddish - brown or black beads to exude

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

Young pycnidia appear light brown & as they age become black 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

Produces both conidia and sporangiophores Fungus Produces both conidia and sporangiophores Conidiophores - unbranched and has a spherical head Sporangiophores - unbranched, recurved at the tip, bearing the sporangium Fertile head Sporangia and fertile heads

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 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

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 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

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 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

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 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

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.

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

First indication of sporulation on the earlier water-soaked lesion 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.