Cucurbitaceous Vegetable Diseases

Downy mildew

Host range

• Musk melon, Sponge gourd and Bitter gourd etc.

Symptoms:

• Yellow, angular spots restricted by veins resembling mosaic mottling appear on upper surface of leaves
• The corresponding lower surface of these spots shows a purplish downy growth in moist weather
• The spots turn necrotic with age
• The diseased leaves become yellow and fall down
• Diseased plants get stunted and die
• Fruits produced may not mature and have a poor taste

Survival and spread:

• Primary: Oospores in soil and sporangia from perennial collateral weed hosts in the vicinity
• Secondary: Wind borne and rain splashed conidia (sporangia) or autonomous zoospores

Favourable conditions:

• Relative humidity > 90%
• High soil moisture
• Frequent rains

Powdery mildew

Host range:

• Pumpkins, bottle gourd, coccinia, cucumber, ridge gourd, Bitter gourd is less affected.

Symptoms:

• Whitish or dirty grey, powdery growth on foliage, stems and young growing parts
• The superficial growth ultimately covers the entire leaf area
• The diseased areas turn brown and dry leading to premature defoliation and death
• Fruits remain underdeveloped and are deformed

Survival and spread:

• Primary: Dormant mycelium or cleistothecia in infected plant debris or conidia from collateral hosts
• Secondary: Wind borne conidia

Favourable conditions:

• Morning relative humidity > 90%
• Cool and dry weather

Cucumber mosaic

Wide host range:

• Cucumber, Pumpkin, gourds, Cowpea, tomato, chilli, etc. Cucumovirus with spherical particles having ssRNA

Symptoms:

• Symptoms appear on the youngest and still expanding leaves when infection occurs at 6 – 8 leaves stage
• Typical mosaic pattern develops on young leaves
• Leaves curl downwards and become mottled, distorted, wrinkled and reduced in size
• Veins appear bunchy because of shortening of internodes
• When infection occurs at midseason previous growth remains normal and produces normal fruit
• Fruit set is very less if infection occurs early in crop growth
• Fruits are often misshapen, mottled, warty and reduced in size

Survival and spread:

• Primary: Virus particles on collateral and other weeds, ornamentals or crops Hosts: Banana, clover, corn, passion fruit, safflower, spinach, sugarbeet, wild cucumber, Commelina communis, C. diffusa, C. nudiflora, Solanum elaegnifolium, Phytolacca sp., periwinkle, Gladiolus sp., Impatiens sp. and Phlox
• Secondary: Virus particles transmitted by aphids (Aphis craccivora, Myzus persicae) and spotted and striped cucumber beetles

Cercospora leaf spot

Host range:

• Common on watermelon, muskmelon and cucumber

Symptoms:

• Minute water soaked spots or yellow specks develop initially on leaves
• Spots enlarge rapidly and becomes circular to irregular with pale brown, tan or white centers and purple to almost black margins
• Spots coalesce to form large blotches
• The leaf may dry and die presenting the leaf a scorched appearance
• Fruits are also occasionally attacked

Survival and spread:

• Primary: Dormant mycelium or conidia on infected plant debris or collateral hosts
• Secondary: Wind borne conidia

Fusarium wilt

Damage symptoms:

• The first symptom of the disease is clearing of the veinlets and chlorosis of the leaves.
• The younger leaves may die in succession and the entire may wilt and die in a course of few days.
• Soon the petiole and the leaves droop and wilt.
• In young trailing plant, symptom consists of clearing of veinlet and dropping of petioles. In field, yellowing of the lower leaves first and affected leaflets wilt and die.
• The symptoms continue in subsequent leaves. At later stage, browning of vascular system occurs. Plants become stunted and die.

Survival and spread:

• Soil and implements

Favourable conditions:

• Relatively high soil moisture and soil temperature

Diseases cycles

Downy mildew: Pseudoperonospora cubensis

Powdery mildew: Erysiphe cichoracearum DC, Sphaerotheca fuligena (Schltdl.) Pollacci

Cercospora leaf spot: Cercospora leaf spot C. citrullina, C. melonis, C. lagenarium

Fusarium wilt: Fusarium oxysporum Schlecht

IPM for Cucurbitaceous Vegetable

To know the IPM practices for Cucurbitaceous Vegetable, click here

Source: NIPHM, Directorate of Plant Protection, Quarantine & Storage