Diseases of Vegetable, Ornamental and Spice Crops

DISEASES

1. WILT:

Losses from this disease range from 5-60 per cent.

Symptoms:

• The characteristic symptoms of the disease are drooping of leaf tips leading to mortality of the plants.
• Later in the season, the colour of the leaves changes from green to yellow, beginning from the oldest leaf and extending upward to the younger ones resulting in the wilting of the entire plant and if a part of the stem is affected resulting in partial wilting.
• If infection occurs at flowering stage, no seed formation takes place and if formed they are small and shrivelled.
• Internal symptom: brown vascular discoloration is common

Pathogen:

• The disease is caused by Fusarium oxysporum f.sp. cumini (Schlechet.) Prasad & Patel.
• The fungus produces micro and macro conidia as asexual spores on sporodochium and vegetative spores are chalamydospores.

Disease cycle and epidemiology:

• The pathogen is soil borne.
• It perpetuates in the form of chlamydospore in the soil.

Management:

i) Follow long crop rotation.
ii) Use healthy seed.
iii) Two to three summer ploughing and application of decomposable organic matter like cakes (castor and mustard) and poultry manure (2.5 t/ha) reduces disease.
iv) Use resistant cvs./lines like UC-33, MC-43, UC-62 and UC-90.
v) Seed treatment with carbendazim (0.2%) followed by sprays with the same chemical (0.1%) have been found effective in reducing the wilt incidence.

2. BLIGHT:

The disease was first reported from Kaira districts of Gujrat and since then it has been recorded from all cumin growing areas of the country.

Symptoms:

• The symptoms of the disease appear as minute necrotic areas on all above ground parts of the plants which turn purple in advanced stages and later turn brown and black.
• The affected parts of the plants become blighted.
• Severely affected plants bear no seeds or shriveled seeds.

Pathogen:

• The disease is caused by Alternaria burnsii Uppal, patel & Kamat.
• Mycelium consist of septate, branched light brown hyphae.
• Conidiophores are dark in colour bear conidia which are dark septate having transverse and longitudinal septa.

Disease cycle and epidemiology:

• The pathogen is both seed and soil borne in the form of infected plant debris.
• Cloudy and humid weather aggravates the severity of the blight.
• A temperature range of 23 – 28^o C is optimum for the development of the blight.

Management

• Collect and destroy the infected plant debris.
• Use healthy seed and treat the seed with captan (0.3%).
• With the initiation of the disease, spray the crop with fungicides like mancozeb (0.25%) or propiconazole (0.03%)
• Use tolerant lines like MC-43, Gujrat Cumin-1, RZ-19 and Gujrat Cumin-2.

3. POWDERY MILDEW:

The disease is widespread in most of the cumin growing areas of the country and may cause losses upto 50 per cent during the years of epiphytotics.

Symptoms:

• The disease appears as greyish specks on the lower leaves which enlarge and cover the leaf surface.
• Stem, flowers, umbels and fruits are also covered with fungal growth.
• The infected plants bear few, shriveled, light weight seeds.

Pathogen:

• The disease is caused by Erysiphe polygoni DC.
• The fungus is ectoparasitic, spreading on the surface of the host and sending haustoria into the epidermal cells to draw out nourishment.
• The fungus hyphae are hyaline and septate and conidiophores arise from it vertically bearing conidia either singly or in short chains.
• Conidia are ellipsoid to ovoid, mature conidia fall off and get dispersed by wind.
• Later in the season, cleistothecia (sexual stage) appear as dark coloured, round, minute bodies scattered in the mycelial web.

Disease cycle and epidemiology:

• Wherever cleistothecia are formed they explain the disease cycle, otherwise it survives on the weed/ cultivated hosts as conidia.
• Optimum temperature for disease spread is 26.7 to 35^o C.

Management:

• The disease can be effectively controlled by spraying fungicides like dinocap (0.05%), carbendazim (0.1%) or hexaconazole (0.05%) and repeat at 10- 14 days interval.

4. WITCHES BROOM

• The disease was first observed in Rajasthan where it caused upto 31 per cent yield losses.
• It is caused by a phytoplasma and tetracycline hydrochloride has been found effective in suppressing it.