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 watermelon 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.

Fungal Diseases in Watermelon

Downy Mildew in Watermelon

Downy mildew is caused by the fungal pathogen Pseudoperonospora cubensis.

Causes:

Infected plant debris and weeds are primary sources of the disease. Wind and rain splash spread spores to healthy plants. High soil moisture, cool, wet, and humid conditions (15-23°C) favor the disease.

Symptoms of Downy Mildew in Watermelon:

Yellowish angular spots appear on the upper leaves, starting at the edges and spreading inward. A white or grayish powdery growth appears on the underside when wet. These spots turn brown to black, and the leaves may wilt and die. The plant may become stunted, producing fewer and smaller fruits with a bitter taste in severe cases.

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
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

Powdery Mildew in Watermelon

Powdery mildew is caused by the fungal pathogens Erysiphe cichoracearum and Sphaerotheca fuliginea.

Causes:

Fungal spores overwinter in dormant buds, plant debris, or weeds. Wind spreads the disease, which favors dry conditions and rainfall.

Symptoms of Powdery Mildew in Watermelon:

White, powdery spots appear on leaves, stems, and young plant parts. Over time, the spots turn yellow or brown, and the leaves may curl or become distorted. Fruit may stop growing or become deformed, leading to premature defoliation.

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
Chemical Management
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

Anthracnose in Watermelon

Anthracnose is caused by Colletotrichum orbiculare and Colletotrichum lagenarium.

Causes:

Fungal spores overwinter in soil. Warm temperatures (24-30°C), high humidity, and leaf wetness favor its spread.

Symptoms of Anthracnose in Watermelon:

Circular or irregular dark brown to black spots appear on leaves, stems, and fruit. Spots have a water-soaked appearance, surrounded by a yellow halo. Infected fruit shows 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
Chemical Management
Taqat Fungicide	Hexaconazole 5% + Captan 70% WP	2 gm/lit water
Indofil M45 Fungicide	Mancozeb 75% WP	0.8 – 1 gm/lit water
Kocide Insecticide	Copper Hydroxide 53.8% DF	2 gm/lit water

Alternaria Leaf Spot in Watermelon

Alternaria leaf spot is caused by Alternaria cucumerina.

Causes:

The fungus overwinters in soil debris. Lack of proper fertilization, warm weather, and continuous wet conditions favor disease development.

Symptoms of Alternaria Leaf Spot in Watermelon:

Small, circular spots initially water-soaked, turning brown or black. The spots may merge and cause distortion and wilting of leaves. Infected fruit shows sunken lesions.

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
Amistar Top Fungicide	Azoxystrobin 18.2% + Difenoconazole 11.4% SC	1 ml/lit water
Nativo Fungicide	Tebuconazole + Trifloxystrobin 75 WG (50% +25% )	0.2 – 0.5 gm/lit water

Fusarium Wilt in Watermelon

Fusarium wilt is caused by Fusarium oxysporum.

Causes:

Infected soil, root wounds, and infected seeds are primary sources of spread. High soil temperature and moisture favor the disease.

Symptoms of Fusarium Wilt in Watermelon:

Stunted plant growth, yellowing of leaves, wilting, and brittle leaves. Vascular tissue may show brown discoloration, and the plant may eventually die.

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
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
Roko Fungicide	Thiophanate Methyl 70% WP	Foliar spray: 1 gm/lit water Drenching: 3 gm/lit water

Gummy Stem Blight in Watermelon

Gummy stem blight is caused by Didymella bryoniae.

Causes:

High humidity, rainfall, leaf wetness, overhead irrigation, and infected seeds favor disease development.

Symptoms of Gummy Stem Blight in Watermelon:

Brown to black lesions appear on stems and leaves, leading to wilting and defoliation. Gummy, reddish-brown substances develop on the lesions.

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
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
Splash Fungicide	Chlorothalonil 75% WP	2 gm/lit water

Bacterial Diseases in Watermelon

Bacterial Wilt in Watermelon

Bacterial wilt is caused by Erwinia tracheiphila, transmitted by cucumber beetles.

Causes:

The bacterium spreads through beetles feeding on leaves, transmitting the disease through wounds.

Symptoms of Bacterial Wilt in Watermelon:

Leaves wilt suddenly, turning dull green but remaining attached. The plant dies within days. Sticky, slimy exudates appear near the soil line, and the stem collapses.

Management of Bacterial Wilt in Watermelon:

Product name	Technical content	Dosage
Biological Management
Ajay Biotech Biosan	Pongamia Pinnata Extract	2-3gm/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

Management of Vector – Cucumber Beetle that transmits 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

Note: Apply insecticides with caution, as overuse can harm beneficial insects.

Bacterial Fruit Blotch in Watermelon

Bacterial fruit blotch is caused by Acidovorax citrulli.

Causes:

The disease spreads through infected seeds, plant debris, and weed hosts. Overhead irrigation and mechanical transmission by workers or equipment also contribute.

Symptoms of Bacterial Fruit Blotch in Watermelon:

Dark reddish-brown spots appear along leaf veins. Water-soaked spots on fruit lead to cracks, soft flesh, and a sour smell.

Management of Bacterial Fruit Blotch in Watermelon:

Product name	Technical content	Dosage
Biological Management
Ecoderma Bio Fungicide	Trichoderma viride	Seed treatment: 10gm/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
Crystocycline Bactericide Antibiotic	Streptomycin sulphate 90% + Tetracylin hydrocloride 10% SP	0.2 gm/lit water
Dhanuka Kasu B Fungicide	Kasugamacyin 3% SL	2 – 2.5 ml/lit water

Viral Diseases in Watermelon

Bud Necrosis Disease in Watermelon

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

Causes:

Transmitted by thrips, this disease is more common in dense plantings under hot, dry conditions.

Symptoms of Bud Necrosis Disease in Watermelon :

Yellowing or bronzing of young leaves, stunted growth, and necrotic spots on buds and fruit.

Cucumber Mosaic Virus (CMV) in Watermelon

CMV is transmitted by aphids.

Causes:

The virus spreads through aphids, infected seeds, and mechanical transmission.

Symptoms of Cucumber Mosaic Virus in Watermelon:

Leaves curl, show mottled discoloration, and may become brittle or necrotic. Fruit may become deformed or smaller.

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
Amruth Alestra Bio Insecticide	Verticillium lecanii	2 ml/lit water
Viro Raze Bio Viricide	Plant extracts	2 ml/lit water
Geolife No Virus	Fermented Organic manure	5 ml/ lit water
Chemical Management
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
Pegasus Insecticide	Diafenthiuron 50% WP	1 gm/lit water

Conclusion

Watermelon is susceptible to several diseases caused by fungi, bacteria, and viruses. Effective management includes proper irrigation, fertilization, and plant spacing. Field sanitation is essential to prevent disease spread, as many diseases are carried by over-wintering spores in debris. Applying chemicals at the right time and dosage can reduce yield loss. Implement these practices to protect your crop and maximize yields.

Frequently asked questions

What is the Economic Threshold Level (ETL) for watermelon diseases?

The ETL for diseases like Downy Mildew is often set by the number of affected leaves or the percentage of the crop showing symptoms. For example, for thrips, the ETL is 6 thrips per leaf or 10% of the crop affected. Monitoring and controlling at these levels helps reduce yield losses.

How does maintaining proper field sanitation help prevent watermelon diseases?

Field sanitation, including the removal of plant debris and weeds, helps reduce the overwintering of disease-causing spores. This is crucial for controlling fungal and bacterial diseases like Downy Mildew and Bacterial Wilt.

How do I know when to apply fungicides or bactericides in watermelon crops?

Timing is key in managing diseases. For most fungal and bacterial diseases, apply fungicides or bactericides as soon as symptoms appear or at the first sign of pest infestation. Follow the product's recommended dosage and application schedule for the best results.