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A. Diseases 

B. Pests  

DISEASES:

1. Purple Blotch  (Alternaria  porri)

Symptoms :

On leaves eye shaped, purple colour spots develop which are surrounded by a broad chlorotic margin.  These spots are very prominent on the flower stalk.  Lesions may girdle leaves and stalks, which drop after 2-3 weeks.

  

Management:  Follow clean cultivation, good drainage and use drip irrigation.

Foliar sprays of Mancozeb   @ 0.25%, Tricyclazole @ 0.1% and Hexaconazole @ 0.1% at 30, 45 and 60 days resp. after transplanting helps in checking disease incidence.

2. Stemphylium leaf blight (Stemphylium vesicarium)

 Symptoms :

Small yellow to orange flecks or streaks develop in the middle of the leaf which soon develop into elongated, spindle shaped to ovate elongate diffused spots surrounded by characteristic pinkish margin.  The spots progress from the tip to the base of the leaves.   The spots coalesce into extended patches, blighting the leaves and gradually the entire foliage.

 Management :  Follow crop rotation and clean cultivation.

Three sprays of Mancozeb   @ 0.25%, Tricyclazole @ 0.1% and Hexaconazole @ 0.1% at 30, 45 and 60 days resp. after transplanting helps in checking disease incidence.

3. Anthracnose/Twister Disease (Colletotrichum gleosporioides)

Symptoms :

 The characteristic symptoms are curling, twisting, chlorosis of the leaves, and abnormal elongation of neck (false stem). Initially pale yellow water soaked oval sunken lesions appears on leaf blades. Numerous black coloured slightly raised structures (acervuli) are produced in the central portion, which may be arranged in concentric rings.  The affected leaves shrivel, droop down and finally wither.

Management:  since this disease is prevalent in Kharif season, growing of onion should be done on raised beds, which assures good drainage.

Clean cultivation, removal of debris from previous crop with longer crop rotation helps to minimize inoculums load in soil.

Application of benomyl @ 0.2% as soil treatment is recommended. Foliar sprays as mentioned under purple blotch.

4. Fusarium or Basal Plate Rot (Fusarium oxysporum f. sp. cepae)

Symptoms :

The roots may turn pink and gradually decay until the entire root disappears.  A semi watery decay affecting the fleshy scales starts from the base and progresses upward and with early infection and may be almost complete by harvest time.  White mycelium appears on the stem plate.  Infected stem plate may show a brown discoloration.

Management:  Good drainage, deep ploughing in hot summer, avoiding injury during cultural practices reduces the disease incidence. Crop rotation of 4-5 years with non-host crop has been found effective in eliminating the disease. Mixed cropping with tobacco and sorghum is effective.

Seed treatment with Trichoderma viride and Pseudomonas fluorescence reduced onion basal rot incidence. Dipping onion sets in Carbendazim @ 0.2% provide protection to basal rot. Spraying of Carbendazim @ 0.1% before harvest minimizes the storage loss due to this disease.

5. Pink Root (Pyrenochaeta terrestris)

Symptoms :

The affected roots turn yellow, shrivel and die, meanwhile taking on a distinct pink colour. The affected plants are commonly not killed but development of bulbs retarded.

Management: Soil solarization reduce pink root incidence. Long rotations with non-host crop should be followed.

6.  Damping Off

Symptoms :

Seedlings topple over after they emerge from the soil.  It usually occurs at or below the ground level and infected tissues appears soft and water soaked.

Management :  Seed treatment with Thiram or Captan @ 0.3%. Drenching the nursery beds by captan or thiram @ 0.2% or carbendazim @ 0.1% or copper oxychloride @ 0.3%.

   

7. White Rot or Sclerotial rot  (Sclerotium cepivorum)

Symptoms :

Yellowing and dying back of leaf tips. Roots are normally destroyed. Superficial white fluffy mycelium may present on decaying scales. Brown or black sclerotia develop on surface or within tissue.

Management :  Crop rotation should be followed, infected plant may be destroyed and the soil around these plant spot should be treated.  Solarization of soil at high temperature reduces the disease incidence. 

Carbendazim @ 0.1% may be applied for controlling the disease.

  

8. Black Mould (Aspergillus spp.)

Symptoms :

Bulbs show black discoloration at the neck and streaks of black mycelium and conidia beneath the outer dry scales.  In advanced stages all scales are infected and the onion shrivels.

Management:  After proper drying onion should be stored at 1-15oC.  Bruising should be avoided when bulbs are harvested, stored or transported.

         

9. Iris Yellow Spot Virus

Symptoms :

Iris yellow spot symptoms first appear as straw-coloured, dry, tan, spindle or diamond-shaped lesions, with or without distinct green centers with yellow or tan borders on leaves. The symptoms are more pronounced on flower stalks. Infected leaves and stalks lodge during the latter part of the growing season.

Management:  Plant high quality transplants free from thrips and Iris yellow spot virus. Practice three year or longer rotation between onion crops. Eliminate volunteers, culls, and weeds in and around onion fields. Avoid crop stress. Thrips control may provide some reduction in iris yellow spot, but thrips control alone is not sufficient to economically control the disease.

10. Onion Yellow  Dwarf  Virus

Symptoms :

Onion yellow dwarf virus (OYDV) is the major viral pathogen of garlic crop and is reported to occur worldwide. OYDV is a member of family Potyviridae, genus potyvirus, characterized by monopartile, single-strang positive sense RNA genome encapsulated in flexuous filamentous particle. OYDV transmitted by Myzes persicae in a non-persistent manner or mechanically to garlic. It produces symptoms of mold chlorotic stripes to bright yellow stripes depending on the virus isolates and cultivars.

Management:  Use of virus-free planting material is only viable solution available at present.

PESTS:

1. Thrips (Thrips tabaci)

 Symptoms :

If infestation is in the early stages of the growth, plants show curling and twisting of leaves

Small white silvery patches are seen all over the leaves which shine in the sun

In severe infestation, whole plant looks blemished and turn white

Management:  Plant barrier of 2 rows of maize or inner row of wheat and outer row of maize atleast 30days before onion planting

Spray insecticides like profenofos, carbosulfan, dimethoate, methomyl 40% SP.

Refer IPM package for further details.

2. Eriophyid Mites

 Symptoms :

Leaves do not open completely. Whole plant shoe curling

Yellow mottling is seen mostly on the edges of the leaves

Management: Spray dicofol (2 ml/l) as soon as the symptoms appear in the field. Repeat the spray if necessary after 15 days.

         

3. Red Spider Mites

 Symptoms :

In garlic webbing on leaves is seen. Small patches along with faeces, eggs, larvae and adults are seen.

Webbing encircles onion umbels.

Management:  Spray dicofol (2 ml/l) as soon as the symptoms are noticed.

 

Last Updated on Monday, 06 April 2015 09:07
 

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