An Ultimate Guide To Watermelon Diseases: Causes, Symptoms And Control Measures

Watermelon is an important fruit crop in India widely grown in summer season and has the potential to provide significant economic benefits to farmers. They are easy to grow, require relatively little maintenance and have short growing season. However, the crop is vulnerable to a number of fungal, bacterial and viral diseases that can cause significant yield losses and reduce the quality of the fruit. It can be difficult to control these diseases once they are established in the field. Early detection and prompt management using appropriate fungicides or bactericides can help to limit the spread of disease and minimize crop losses.  

Common types of Watermelon Diseases

Disease type	Diseases	Stage of occurrence
Fungal Diseases	Downy mildew	Vegetative stage
	Powdery mildew	Vegetative, fruiting stage
	Anthracnose	Vegetative, fruiting stage
	Alternaria leaf spot	Vegetative stage
	Fusarium wilt	Vegetative, fruiting stage
	Gummy stem blight	Vegetative, fruiting stage
Bacterial Diseases	Bacterial wilt	Vegetative stage
	Bacterial Fruit Blotch	Vegetative, fruiting stage
Viral Diseases	Bud necrosis disease	Vegetative stage
	Cucumber mosaic virus	Vegetative, fruiting stage

 

Fungal Diseases

1. Downy Mildew

Downy mildew in watermelon is caused by the fungal pathogen Pseudoperonospora cubensis. 

Causes:

Presence of infected plant debris and weed hosts cause the primary spread of the disease. Wind and rain splash causes the spread of spores to the healthy plants. High soil moisture, cool, wet and humid conditions and temperature (15 – 23°C) favours disease incidence. 

Symptoms:

• Yellowish angular spots appear on the upper surface of the leaves. The yellowing often starts at the edges of the leaves and then spreads towards the center.
• As the disease progresses, a white or grayish powdery fungal growth appears on the underside of the leaves when the leaves are wet.
• These spots later turn brown to black (necrosis). Later, the leaves may wilt and die.
• It can cause stunted growth of the plants. Affected plants may appear smaller than usual, with fewer fruits.
• In case of severe infection, the fruits produced may be smaller, misshapen or have bitter taste.

Management of Downy Mildew in Watermelon:

Product name	Technical content	Dosage
Biological Management
Downy Raze	Plant extracts	2.5 ml/lit water
Anant Dr Bacto’s Fluro	Pseudomonas fluorescence	2.5 ml/lit water
Chemical Management
Ridomil Gold	Metalaxyl 4% + Manconzeb 64% WP	1 – 1.5 gm/lit water
Melody Duo Fungicide	Iprovalicarb + Propineb 5.5% +61.25% WP	3 – 4 gm/lit water
Cabrio Top Fungicide	Metiram 55% + Pyraclostrobin 5% WG	1.2 – 1.4 gm/lit water
Zampro Fungicide	Ametoctradin 27% + Dimethomorph 20.27% SC	1.6 – 2 ml/lit water
Moximate Fungicide	Cymoxanil 8% + Mancozeb 64% WP	2 gm/lit water

 

2. Powdery Mildew

Powdery mildew is a common and destructive disease caused by the fungal pathogen Erysiphe cichoracearum / Sphaerotheca fuliginea. 

Causes:

Fungal spores overwintering in dormant buds, plant debris or weeds causes disease development. Wind currents spread the disease. Rainfall, morning dew, dry weather conditions favours disease incidence.   

Symptoms:

• White, powdery spots or patches on the leaves, stems and young growing parts of the plant. Later, it may spread rapidly and cover the entire leaf surface.
• The white powdery spots may gradually turn yellow or brown and become necrotic.
• The affected leaves may curl or become distorted and the fruit may stop growing or become deformed.
• Leads to premature defoliation and death of affected areas.

Management of Powdery Mildew in Watermelon:

Product name	Technical content	Dosage
Biological Management
Anant Dr Bacto’s Fluro	Pseudomonas fluorescence	2.5 ml/lit water
V-Kure	Eugenol, Thymol, potassium salts, cationic surface agent, sodium salts & preservatives	1.5 – 2 gm/lit water
Samrudhi Agro Pogon	Botanical extracts	1.5 – 2 ml/lit water
Chemical Management
Sarthak Fungicide	Kresoxim – Methyl 15 % + Chlorothalonil 56 % WG	1 – 2 gm/lit water
Katyayani Azoxy Fungicide	Azoxystrobin 23% SC	1 – 1.5 ml/lit water
Dhanustin Fungicide	Carbendazim 50% WP	0.5 – 0.8 gm/lit water
Contaf Fungicide	Hexaconazole 5 % EC	2 ml/lit water
Flick Super Fungicide	Dimethomorph 12 % + Pyraclostrobin 6.7 % WG	3 gm/lit water
Merivon Fungicide	Fluxapyroxad 250 G/L + Pyraclostrobin 250 G/L SC	0.4 ml/lit water

 

3. Anthracnose

Anthracnose is a fungal disease caused by the pathogen Colletotrichum orbiculare / Colletotrichum lagenarium affects all parts of the plant and reduces fruit quality. 

Causes:

Fungal spores over wintering in the soil causes disease development. Temperature (24 – 30°C), high humidity, leaf wetness favours anthracnose incidence in watermelon plants.  

Symptoms:

• Small, circular or irregularly shaped spots appear on leaves, stems and fruit that are dark brown or black in color.
• The spots may have a water-soaked appearance and may be surrounded by a yellow halo.
• In severe cases, the affected leaves drop prematurely.
• Lesions on the stem girdle the vascular tissues and causes wilting of wines.
• Infected fruit may show sunken lesions, cracks and rot.

Management of Anthracnose in Watermelon:

Product name	Technical content	Dosage
Biological Management
Fungo Raze	Botanical extracts	1 –2 ml/lit water
Terra Fungikill	Herbal formulation	2 ml/lit water
Sonkul Sun Bio Monus	Pseudomonas fluorescens	5 ml/lit water
Chemical Management
Kocide Insecticide	Copper Hydroxide 53.8% DF	2 gm/lit water
Taqat Fungicide	Hexaconazole 5% + Captan 70% WP	2 gm/lit water
Indofil M45 Fungicide	Mancozeb 75% WP	0.8 – 1 gm/lit water
Turf Fungicide	Carbendazim 12 % + Mancozeb 63 % WP	1.5 gm/lit water
Splash Fungicide	Chlorothalonil 75% WP	2 gm/lit water

 

4. Alternaria Leaf Spot / Alternaria Blight:

Alternaria leaf spot is a fungal disease caused by the pathogen Alternaria cucumerina. 

Causes:

Fungus overwintering in the soil debris causes primary spread of the disease. Weakened plants due to lack of proper fertilization, warm weather, continuous wet conditions favours disease development.  

Symptoms:

• Small, circular or irregularly shaped spots appear on leaves that are initially water-soaked, then turn brown or black as they dry out.
• The spots may have a yellow halo and may merge to form larger lesions.
• The infected leaves may become distorted, wilt, and eventually die.
• Affected fruits may have lesions on the surface that are sunken, brown, and dry.
• In severe cases, the disease can cause complete defoliation of vines and reduce fruit quality and yield.

Management of Alternaria Leaf Spot in Watermelon:

Product name	Technical content	Dosage
Biological Management
Anand dr Bacto’s Dermus	Trichoderma viride	2.5 ml/lit water
Ecomonas Bio Fungicide	Pseudomonas fluorescens	8 – 10 ml/lit water
Chemical Management
Tilt Fungicide	Propiconazole 25 % EC	1 ml/lit water
Avtar fungicide	Zineb 68% + Hexaconazole 4% WP	1 gm/lit water
Amistar Top Fungicide	Azoxystrobin 18.2% + Difenoconazole 11.4% SC	1 ml/lit water
Dithane M45 Fungicide	Mancozeb 75% WP	2 – 2.5 gm/lit water
Tata Ishaan Fungicide	Chlorothalonil 75% WP	2.5 gm/lit water
Nativo Fungicide	Tebuconazole + Trifloxystrobin 75 WG (50% +25% )	0.2 – 0.5 gm/lit water
Indofil Z78 Fungicide	Zineb 75% WP	2 – 2.5 gm/lit water

 

5. Fusarium Wilt

Fusarium Wilt is a fungal disease caused by the pathogen Fusarium oxysporum that can cause severe yield loss, if not managed at right time. 

Causes:

Infected soil, wounds in roots and infected seeds causes fungal spread. Secondary spread occurs through wind, tools or equipments. High soil temperature and soil moisture favours disease infection.  

Symptoms:

• Stunted growth of the plant and yellowing of leaves, especially older leaves.
• Leaves may wilt and become brittle, eventually die.
• Vascular tissue (xylem) of the stem and roots may show brown discoloration and the stems may develop cracks.
• In severe cases, the plant may die.
• Wilting symptoms during maturity stage can cause premature fruit drops, reduced yield and quality.

Management of Fusarium Wilt in Watermelon:

Product name	Technical content	Dosage
Biological Management
Amruth Almonas Bio Fungicide	Pseudomonas sp	2ml/lit water
Terra Fungikill	Herbal formulation	2 ml/lit water
Ecoderma Bio Fungicide	Trichoderma viride	Seed treatment: 10 gm/lit water Soil application: 2 – 3 kg Ecoderma +150 – 200 kg FYM
Chemical management
Benmain Fungicide	Carbendazim 50% DF	Soil drenching: 2 gm/lit water
Amistar Fungicide	Azoxystrobin 23% SC	Spraying: 0.5 – 1 ml/lit water
Ridomil Gold Fungicide	Metalaxyl 4% + Manconzeb 64% WP	Soil application: 1 – 1.5 gm/lit water
Taqat Fungicide	Hexaconazole 5% + Captan 70% WP	Drenching: 2 gm/lit water
Roko Fungicide	Thiophanate Methyl 70% WP	Foliar spray: 1 gm/lit water Drenching: 3 gm/lit water

 

6. Gummy Stem Blight

Gummy stem blight is a serious fungal disease caused by the pathogen Didymella bryoniae. 

Causes:

Humidity (>85%), rainfall, longer period of leaf wetness, overhead irrigation and infected seeds/transplant materials may cause disease development. The optimum temperature for the disease incidence is about 24°C. Presence of wounds, feeding activity of cucumber beetle and aphids, along with powdery mildew incidence may induce development of gummy stem blight infection. 

Symptoms:

• Brown to black, circular water-soaked lesions appear on stems which later become dry and wilt
• Irregular tan to brown blotches appears on the leaves which may lead to wilting and blight of foliage.
• The development of a gummy, reddish brown substance on the surface of the lesions, which gives the disease its name.
• Premature senescence and defoliation of the plants.

Management of Gummy Stem Blight in Watermelon:

Product Name	Technical Content	Dosage
Biological Management
Multiplex Bio-Jodi	Pseudomonas fluorescence & Bacillus subtilis	5 – 10 gm/lit water
Chemical Management
Amistar Fungicide	Azoxystrobin 23%SC	0.5 – 1 ml/lit water
Custodia Fungicide	Azoxystrobin 11% + Tebuconazole 18.3% SC	1.5 ml/lit water
Master Fungicide	Metalaxyl 8% + Mancozeb 64% WP	1.5 – 2.5 gm/lit water
Krilaxyl 35% WS Power Fungicide	Metalaxyl 35% WS	Seed treatment: 6 – 7 gm/kg seed
Splash Fungicide	Chlorothalonil 75% WP	2 gm/lit water

 

Bacterial Diseases

7. Bacterial wilt

Bacterial wilt is a destructive disease caused by the bacterium Erwinia tracheiphila.  

Vector – Cucumber beetle 

Causes:

The bacterium responsible for bacterial wilt is transmitted by the striped or spotted cucumber beetle, which feeds on the leaves of the plant and then transfers the bacteria to the stem. Presence of plant debris or alternate host, wounds in root system, high temperature, high humidity and soil moisture and alkaline pH of soil favours disease incidence. Heavy soils that can retain soil moisture for long duration are highly vulnerable to the disease.  

Symptoms:

• Sudden wilting of leaves which later turn dull green but remain attached to the stem.
• Wilting of the entire plant, which progresses from the point of bacterial entry through vascular tissue towards the main stem.
• Death of the plant within a few days of infection.
• Sticky or slimy exudates on the surface of the stem near the soil line.
• Collapse of the stem when the plant is cut at or above the soil line.

Management of Bacterial Wilt in Watermelon:

Product name	Technical content	Dosage
Biological Management
Ajay Biotech Biosan	Pongamia Pinnata Extract	2-3gm/lit water
V-Kure	Eugenol, Thymol, potassium salts, cationic surface agent, sodium salts & preservatives	1.5 – 2 gm/lit water
Chemical Management
Dhanuka Kasu B Fungicide	Kasugamacyin 3% SL	2 – 2.5 ml/lit water
Blitox Fungicide	Copper Oxychloride 50% WP	2 – 3 gm/lit water
Conika Fungicide	Kasugamycin 5% + Copper Oxychloride 45% WP	2 gm/lit water
Ridomil Gold Fungicide	Metalaxyl 4% + Manconzeb 64% WP	1.5 gm/lit water

 

Management of Vector – Cucumber Beetle that transmit Bacterial Wilt:

Product name	Technical content	Dosage
Biological Management
Econeem Azadirachtin 3000 PPM	Azadirachtin 0.3% EC	2.5 – 3 ml/lit water
Chemical Management
Karate Insecticide	Lambdacyhalothrin 5% EC	1.5 – 1.65 ml/lit water
Danitol Insecticide	Fenpropathrin 10% EC	1.5 – 2 ml/lit water
Anshul Ikon Insecticide	Acetamiprid 20% SP	0.5 gm/lit water

 

8. Bacterial Fruit Blotch

Bacterial fruit blotch is a bacterial disease caused by the pathogen Acidovorax citrulli. 

Causes:

Seeds from infected fruit, plant debris in the soil, presence of weed hosts causes bacterial fruit blotch infection. Infected seeds are the primary source of this disease spread. While over-head irrigation, mechanical transmission through workers’ hands and tools or equipment acts as secondary source of infection. High temperature (>32°C) and high humidity also favours disease incidence. 

Symptoms:

• Dark reddish-brown spots may develop along the leaf veins.
• Dark green to brown, water-soaked spots on the fruit, which can appear in a circular pattern or as a long streak. It can cause the development of distinctive cracks on the fruit surface.
• The flesh underneath the spots may become soft, watery and discolored.
• Infected fruit may develop a sour smell and ooze a sticky, tan-colored substance.
• Stunting and reduced yield of the plant.

Management of Bacterial Fruit Blotch in Watermelon:

Product name	Technical content	Dosage
Biological Management
Ecoderma Bio Fungicide	Trichoderma viride	Seed treatment: 10gm/lit water
V-Kure	Eugenol, Thymol, potassium salts, cationic surface agent, sodium salts & preservatives	1.5 – 2 gm/lit water
Geolife Geomycin	Consortium Plant Extracts	0.5 – 1 gm/lit water
Chemical Management
Blue Copper Fungicide	Copper Oxychloride 50% WP	2.5 gm/lit water
Dhanuka Kasu B Fungicide	Kasugamacyin 3% SL	2 – 2.5 ml/lit water
Borogold Fungicide	Combination of Nano Silver Particles & Peroxy Acid Forming complex	1.5 gm/lit water
Conika Fungicide	Kasugamycin 5% + Copper Oxychloride 45% WP	1.5 – 2 gm/lit water
Kocide Fungicide	Copper Hydroxide 53.8% DF	2 gm/lit water
Crystocycline Bactericide Antibiotic	Streptomycin sulphate 90% + Tetracylin hydrocloride 10% SP	0.2 gm/lit water

 

Viral Diseases

9. Bud Necrosis Disease

Bud necrosis is caused by Tomato Spotted Wilt Virus (TOSPO virus) 

Vector – Thrips 

Causes:

Main source of transmitting this virus in watermelon is thrips. Presence of alternate hosts, dense planting, hot and dry weather favors thrips population which increases the spread of the disease.  

Symptoms:

• Yellowing or bronzing of leaves, especially younger leaves.
• Small, dark brown or black spots or rings may develop on the leaves.
• The new growth or buds may become stunted and show brown or black necrotic spots and hence the disease name ‘Bud necrosis’. It results in decay of floral structures.
• The fruit surface may also showring spots and may become deformed or discolored.
• In severe cases, the plant may become stunted and eventually die.

10. Cucumber Mosaic Virus (CMV)

Vector – Aphids 

Causes:

The virus is carried and transmitted through vector aphids. Other means of transmission include infected seeds and grafts, weeds, mechanical transmission through tools or equipments and farm workers hands. 

Symptoms:

• Leaves may curl downward and show mottled or streaked discoloration, usually with a yellow-green color.
• Leaves may also show puckering or distortion and may become brittle or necrotic.
• Veins of the affected leaves appear bushy due to shortening of internodes.
• The fruit may show a yellow or green mosaic pattern and may become deformed or small.
• The plant may become stunted or distorted, and in severe cases, may die.
• The virus can also reduce the overall yield and quality of the fruit.

Management of Aphids and Thrips in Watermelon:

Product name	Technical name	Dosage
Mechanical Management
Barrix Magic Sticker Chromatic trap yellow sheet	Chromatic trap	10 sheets/acre
Biological Management
Eco neem plus	Azadiractin 10000 PPM	2.5 ml/lit water
Amruth Alestra Bio Insecticide	Verticillium lecanii	2 ml/lit water
Viro Raze Bio Viricide	Plant extracts	2 ml/lit water
Geolife No Virus		5 ml/ lit water
Chemical Management
Benevia Insecticide	Cyantraniliprole 10.26% OD	2.0 ml/lit water
Anant Insecticide	Thiamethoxam 25 % WG	0.5 gm/lit water
Katyayani Acepro Insecticide	Acetamiprid 20% SP	0.5 gm/lit water
Confidor Insecticide	Imidacloprid 17.8% SL	0.75 ml/lit water
Alika Insecticide	Thiamethoxam 12.6% + Lambda-cyhalothrin 9.5% ZC	0.5 ml/lit water
Police Insecticide	Fipronil 40% + Imidacloprid 40% WG	0.2 gm/lit water
Pegasus Insecticide	Diafenthiuron 50% WP	1 gm/lit water
Starthene Insecticide	Acephate 75 % SP	2.5 gm/lit water

 

NOTE:  

• Refer to the product’s label before use to find the right time of application.
• Bio-fungicide and chemical fungicide are incompatible., therefore they should not be mixed together.
• It is advised to spray Bio-fungicides during early morning or evening hours when the temperature is relatively cool to get best results.

Conclusion

Watermelon is susceptible to several diseases caused by fungi, bacteria, and viruses. To manage these diseases, it is important to implement good cultural practices such as crop rotation, proper irrigation, fertilization and spacing of plants. In addition, maintaining proper field sanitation can be effective in preventing or controlling disease outbreaks since most of the diseases are spread through over wintering spores in crop debris. Right time and right dose of application of chemicals to control diseases and disease-causing vectors can help to reduce yield loss. By implementing these measures, you can protect your watermelon crop and achieve maximum yields.