Disease Management in Maize: Part 2

Head Smut : Sphacelotheca reiliana

Occurrence

Reported from Tamilnadu, Andhra Pradesh, Karnataka, Madhya Pradesh, Uttar Pradesh and Punjab

Epidemiology

The fungus survives in the soil. Soil temparature of 21-28° C with moderate to low soil moisture (15-25%) are optimal for seedling infection.

Symptoms

Head smut appears when ears and tassels are formed. Floral structures may be partially or completely converted to sori containing masses of brownish black teliospores.

Tassel infection may be confined to individual spikelets. In such cases floral bracts grow out in to leafy structures, some times in to small shoots.

Ears infected plants may be smutted or aborted with leafy buds replacing normal ears. Such plants donot produce pollen. Infected plants are dwarf with increased tillering.

Control measures

Seed treatment with Thiram or Captan 3g/kg seed.

Field sanitation, crop rotations

Maydis Leaf Blight : Helminthosporium maydis

Occurrence

The disease is prevalent in Northern states. It is not a major disease in Andhra Pradesh.

Symptoms

Leaves show greyish, tan, parallel straight sided or diamond shaped 1-4 cm long, lesions with buff or brown borders or with prominent colour banding or irregular zonation.

Symptoms may be confined to leaves or may develop on sheaths, stalks, husks, ears and cobs.

The lesions longitudinally elongated typically limited to a single inter vascular region, often coalescing to form more extensive dead portions.

Control measures

Growing resistant hybrids DHM 103, and DHM 1.

Use protective fungicides of Carbamate or Mancozeb group.

Maize Mosaic

Symptoms

Symptoms appear as Chlorotic spots, short lines and broken to nearly continuous Chlorotic stripes covering entire leaf blade.

Chlorotic stripes and spots can also develop leaf sheaths, stalks and husks. Moderate to severe rosetting of new growth is observed.

Size of stalk, leaf blades and tassel tend to be normal in late infection.

Maize mosaic virus is transmitted by Leaf hopper : Peregrinus maidis

Control

Destroy the alternate hosts

Spray systemic insecticides like Monocrotophos 1.5 ml/l or Dimethoate 2 ml/l for the control of vector.

Maize Dwarf Mosaic: Maize Dwarf Mosaic Virus(MDMV)

Symptoms

Symptoms first appear on the youngest leaves as irregular, light and dark-green mottle or mosaic.

Later they develop into narrow sreaks along veins that appear as dark green islands on a clorotic back ground.

Plants are stunted, with excessive tillering multiple ear shoots and poor seed set.

The virus is transmitted by AphidsRhopolosiphum maidis Myzus persicae,Schizaphis graminicum.

Control

Destruction of Johnson grass or other wintering reservoir hosts

Spray systemic insecticides like Monocrotophos 1.5 ml or Dimethoate 2 ml/l for the control of vector.

Turcicum Leaf Blight : Helminthosporium turcicum

This disease has a world wide distribution. In India the disease is prevalent in the Himalayan region, Peninsular India and the State of Bihar.

The hot spots being Mandya in Karnataka, Kolhapur in Maharashtra, Karimnagar in Andhra Pradesh and Dholi in Bihar.

In Andhra Pradesh principal maize growing areas like Warangal, Karimnagar, Medak, Nizambad, Adilabad and Ranga Reddy had recorded more disease in the rabi season.

Occurrence

This disease is prevalent in the areas where maize is planted in the high lands (more than 1000m altitude), where temperate conditions prevail and in winter plantings in the plain as the cool/moderate conditions favour disease development.

Epidemiology

The occurrence and damage is severe in areas with heave dew and rainfall with temperature of 18 to 27° C

Symptoms

Turcicum leaf blight (Northern corn leaf blight) on maize is characterized by long elliptical, grayish green or tan lesions on the leaves measuring 2.5 to 25 cm in length and 4 cm in width.

Lesions first appear on the lower leaves and increase in size and number until very little living leaf tissue is left. Spores produced on the under surface are arranged in concentric zones resembling a target like pattern when observed against light.

Crop debris is the usual source of primary inoculum. Once the infection takes place it spreads through wind currents.

Control measures

Use of resistance varieties like CM 104, CM 118, CM 121 and DHM 1 is the most effective and economical method of reducing the losses.

Chemical control as general practice is not recommended to the farmers. However the protection of precious material either experimental or seed production, spraying with Mancozeb @ 0.25 to 0.4% when made at 8-10 days interval is effective.

Smut : Ustilago maydis

Disease cycle

The sporidia, produced by germination of teleutospores which infect the soil, cause shoot infection.

Dikaryotization though not essential for growth in host tissue is however, essential for gall formation.

The successive generations of teleutospores cause secondary local infections.

Epidemiology

Disease development is favoured by dry conditions and temparatures between 26-34° C. High nitrogen and injuries increase the potential for smut infection.

Symptoms

Ground parts are suceptable, particularly young, actively growing meristematic tissues.

Galls are formed on the ears, axillary buds, tassels, stalks and some times on the leaves ears, axillary buds, tassels, stalks and some times on the leaves causes smut disease in ears and tassels by which they are partially transformed to galls.

Galls are first covered with a glistening, greenish to silvery white tissue. The interior of these galls darkens and turns into masses of powdery, dark olive brown to black spores, except for galls on leaves.

Plants with galls on lower stalks may be barren and produce small ears. Galls on young seedlings may result in stunting or death of the plants.

Control

Crop rotation

Avoiding mechanical injury to plants during cultivation.

Avoid applying of higher doses of nitrogen.

Uproot the smut-effected plants.

Seed treatment with Thiram or Captan 3g/kg seed

Seed Rots and Seedling Disease

These are incited by species of Fusarium, Rhizoctonia, Aspergillus, Pythium, Cephalosporium etc.

Occurrence

These occur mainly in areas where the soil temperature are low (cooler areas in the Himalayas and in the hill regions of Southern Rajasthan.)

Epidemiology

The problem becomes severe with the use of old seeds stored under high temperature and humidity and sown during winter.

Symptoms

Infected seeds when sown, produce thin stands of the crop with gaps, pre-emergence seed rot, post emergence damping off, brown sunken lesions on mesocotyl, collar rot, wilting, toppling of collapsed of seedlings.

Control Measures

Mechanical sieving or winnowing of seed lots meant for sowing eliminates lightweight, chaffy injured or infected seeds.

Seed should be treated with the fungicide Thiram or Captan 2 to 2.5 gm/kg of seed by vigorously shaking in a closed metal drum or earthen vessel before sowing.

Use certified seed.

Avoid planting in cold, wet or water logged soil.

Virus (MDMV)

Symptoms

Symptoms first appear on the youngest leaves as irregular, light and dark-green mottle or mosaic.

Later they develop into narrow sreaks along veins that appear as dark green islands on a clorotic back ground.

Plants are stunted, with excessive tillering multiple ear shoots and poor seed set.

The virus is transmitted by AphidsRhopolosiphum maidis Myzus persicae,Schizaphis graminicum.

Control

Destruction of Johnson grass or other wintering reservoir hosts

Spray systemic insecticides like Monocrotophos 1.5 ml or Dimethoate 2 ml/l for the control of vector.

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