1. POST HARVEST DISEASES
OF CUCURBITS

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
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

5. 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

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. Field sanitation - destroy the plant debris
Management
Field sanitation - destroy the plant debris
Hot water treatment of 57.2oc for 20 min
Seed treatment - thiram or carbendazim or 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
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

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. 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

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. 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

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 %
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. 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

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.