Spinach: Diseases and Symptoms

Downy mildew

• The initial stage: Dull to bright yellow spots that form on cotyledons and leaves of all ages.
• The late stage: Enlarged spots and become browning and dry. Close inspection of the underside of the leaf often reveals the purple growth of the fungus.
• If disease development is extensive, leaves appear curled and distorted and may take on a blighted effect as a result of numerous infection sites.

Host range: Spinach, Chenopodium weed, Beta sp.

• Fungus survives in disease plant debris or in soil in form of resting spore.
• Primary: The heavy canopy of densely planted spinach retains much moisture and creates ideal conditions for infection and disease development.
• Secondary: Spores (sporangia/zoospores) are dispersed in the air from plant to plant and field to field by winds and splashing water.

• Heavy canopy of densely plantations, relative humidity > 90%, high soil moisture and frequent rains favour the development of diseases.

Anthracnose

• In initial stage: Small, circular, water - soaked lesions on both young and old leaves.
• In late stage: Lesion turns brown to brownish in color, and become thin and papery.
• Tiny black fruiting bodies (acervuli) form profusely in diseased tissue and are a characteristic feature of the disease.

Host range: Cowpea (Vigna unguiculata), bean (Phaseolus vulgaris) and betel vine (Piper sp)

• Fungus survives in plant debris or soil.
• Primary: Seed borne inoculum and dormant mycelium in infected plant debris.
• Secondary: Spores are spread from plant – to - plants by splashing water from rains or sprinklers

• Relative humidity > 90%, High soil moisture and frequent rains favour the development of disease.

Cladosporium Leaf spot

• Round, brownish leaf spots that rarely exceed 0.2 inch in diameter.
• Dark green spores and mycelium later develop in the centers of the spots.
• The presence of dark green sporulation distinguishes Cladosporium leaf spot from anthracnose and Stemphylium leaf spot diseases, both of which also form circular lesions.

Leaves showing disease symptoms

• Pathogen survives in seeds and these seeds are source of primary inoculums. The secondary spread occurs by means of conidia.

• Heavy rain in spring favours the development of diseases.

Stemphylium leaf spot

• Initial stage: Small (0.1 to 0.2 inch diameter), circular to oval, gray-green leaf spots.
• Late stage: Leaf spots enlarge, remain circular to oval in shape, and turn brownish in color. Older spots coalesce, dry up, and become papery in texture.                                                         Leaves showing disease symptoms

• Visual signs of fungal growth are generally absent from the spots; hence this symptoms is readily differentiated from foliar diseases in which purple growth (downy mildew), green spores ( Cladosporium leaf spot), or acervuli (anthracnose) develop within circular lesions.
• Overall, symptoms resemble the brownish, circular spots caused by pesticide or fertilizer toxicity.

• Fungus survives in seeds and infected seeds are the source of primary inoculums. Secondary infection occurs by means of conidia.

• High humidity and moisture conditions favour the development of disease.

Damping off and root rot

• Symptoms of damping-off and root rot consist of poor seed germination, pre-emergence death of seedlings, post emergence death of newly emerged seedlings, stunted plants, yellowed lower leaves, general poor growth, wilting, and eventual collapse and death of older plants.
• Roots of infected plants can appear water-soaked or brown to black in color. The upper taproot may be girdled by a necrotic lesion, or the tip of the taproot may be necrotic. In severe cases, nearly all roots may be girdled or rotted off.
• Severity is influenced by cultivar, soil texture, irrigation, and pathogen populations. Severe damping- off is associated with clay or poorly draining soils with a history of frequent spinach production. While all stages of spinach can be infected by root rot organisms, newly emerging plants and young seedlings are very susceptible.

• The fungus survives in soil and inoculum present in the soil is source of primary infection. Secondary infection occurs by means of conidia through rain splash or wind.

• High humidity, high soil moisture, cloudiness and low temperatures below 24°C for few days are ideal for infection and development of disease.
• Crowded seedlings, dampness due to high rainfall, poor drainage and excess of soil solutes hamper plant growth and increase the pathogenic damping-off.

IPM for Spinach

To know the IPM practices for Spinach, click here.

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