📈 Diseases of Cucurbits

Cucurbits (family Cucurbitaceae) include cucumber, melon, watermelon, pumpkin, squash, bottle gourd, bitter gourd, and ridge gourd. These warm-season vegetables are affected by numerous fungal, bacterial, and viral diseases.

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Downy Mildew

Causal Organism: Pseudoperonospora cubensis (Berk. & Curtis) Rostovzev — an Oomycete

Symptoms

• Angular, yellow to brown spots on the upper leaf surface, limited by leaf veins
• Purplish-grey, downy sporulation on the lower leaf surface
• Leaves become necrotic and curl upward; severe infections cause rapid defoliation
• Cucumber and muskmelon are the most susceptible cucurbit hosts

Favourable Conditions

Cool nights (15-20 degrees C), warm days, and persistent leaf wetness promote the disease. Morning dew and fog are particularly conducive.

Management

• Spray Metalaxyl + Mancozeb (Ridomil MZ, 0.25%) or Cymoxanil + Mancozeb preventively
• Use resistant varieties where available
• Avoid dense planting and overhead irrigation
• Destroy crop debris promptly after harvest

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Powdery Mildew

Causal Organism: Podosphaera xanthii (syn. Sphaerotheca fuliginea) and Golovinomyces cichoracearum (syn. Erysiphe cichoracearum)

Symptoms

• White, powdery fungal colonies on both surfaces of leaves, petioles, and stems
• Severely affected leaves turn yellow and desiccate
• Premature defoliation reduces fruit size and sugar content in melons

Management

Fungicide	Dosage	Type
Wettable Sulphur	0.2%	Contact
Dinocap (Karathane)	0.1%	Contact
Hexaconazole	0.05%	Systemic
Myclobutanil	0.1%	Systemic

• Alternate contact and systemic fungicides to prevent resistance development
• Grow resistant varieties such as Pusa Sanyog (cucumber) and Arka Rajhans (watermelon)

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Anthracnose

Causal Organism: Colletotrichum orbiculare (syn. C. lagenarium)

Symptoms

• Circular to angular, water-soaked spots on leaves that become brown with a yellow halo
• On fruits, sunken, dark, circular lesions with pink, gelatinous spore masses in the centre
• Stems and petioles develop elongated, sunken lesions

Management

• Use certified disease-free seed or treat seed with Thiram (3 g/kg)
• Spray Carbendazim (0.1%) or Chlorothalonil (0.2%) during the cropping season
• Practice crop rotation for 2-3 years
• Avoid working in the field when foliage is wet

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Mosaic Viruses

Several viruses cause mosaic symptoms in cucurbits.

Cucumber Mosaic Virus (CMV)

• Symptoms: Green and yellow mosaic on leaves, leaf distortion, stunting, and warty fruits
• Vector: Aphids (non-persistent transmission by Aphis gossypii)
• Management: Control aphids, use reflective mulches to repel aphids, rogue infected plants

Watermelon Mosaic Virus (WMV) and Zucchini Yellow Mosaic Virus (ZYMV)

• Cause severe leaf mosaic, fruit distortion, and knobby fruits
• Aphid-transmitted in a non-persistent manner
• Use resistant cultivars and control aphid populations

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Fusarium Wilt

Causal Organism: Fusarium oxysporum (various formae speciales specific to each cucurbit host)

• Wilting, yellowing, and death of vines; brown discolouration of vascular tissue
• Practice crop rotation, use resistant varieties, and apply Trichoderma viride to the soil
• Grafting susceptible scions onto resistant rootstocks (e.g., bottle gourd rootstock) is an effective strategy

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Summary Cheat Sheet

Disease	Causal Organism	Hallmark Symptom	Core Management
Downy mildew	Pseudoperonospora cubensis	Angular yellow-brown lesions and lower sporulation	Preventive anti-oomycete sprays + field aeration
Powdery mildew	Podosphaera/Golovinomyces	White powdery colonies on foliage	Alternate contact/systemic fungicides
Anthracnose	Colletotrichum orbiculare	Sunken fruit lesions with pink spore masses	Clean seed + fungicide protection
Mosaic viruses	CMV/WMV/ZYMV	Mosaic, distortion, malformed fruits	Aphid management + rogueing
Fusarium wilt	Fusarium oxysporum spp.	Vascular browning and vine wilt	Rotation + resistant rootstock + biocontrol

References

2 sources • [1] [2]

[1]

Indian Council of Agricultural Research (ICAR)

Official

[2]

CABI Crop Protection Compendium

Website