maize
April 3, 2018 Sruthi PK

Major diseases of maize

Maydis leaf blight (MLB) – Bipolaris maydis

Symptoms

  • Young lesions are small and diamond shaped.
  • As they mature, they elongate. Lesions may coalesce, producing a complete “burning” of large areas of the leaves.
  • They vary in size and shape among inbreds and hybrids with different genetic background.
  • Race ‘O’ produced tan, elongated (2-6x 3-22 mm) lesion between the veins with limited margins, with buff to brown borders, usually attacks only leaves.

Control

  • Resistant varieties  – Deccan, VL 42, Prabhat, KH-5901, PRO-324, PRO-339, ICI-701, F-7013, F-7012, PEMH 1, PEMH 2, PEMH 3, Paras, Sartaj, Deccan 109.
  • Two applications of  captafol

Sorghum downy mildew (Peronosclerospora sorghi)

Symptoms

  • The chlorotic area of leaf always includes the base of the blade, and transverse margins usually sharply defined between the diseased and healthy tissues
  • A white, downy growth may appear on both surface of infected leaves. Sometimes tassels of diseased plant may exhibit phyllody.
  • Tolerant plant may show symptoms of systemic infection but have normal seed production.

Control

  • Resistant varieties – Comp. A-9, Indimyt 345, EH-43861, KH-526, AH-36.

Brown stripe downy mildew  (Scleropthora rayssiae var. zeae)

Symptoms

  • Lesions start developing on lower leaves as narrow chlorosis or yellow stripes,3-7 mm wide,with well defined margin and are delimited by the veins.
  • The stripes later become reddish to purple.Lateral development of lesions causes sever striping and blotching.
  • Seed development may be suppressed,and plant may die prematurely if blotching occurs prior to flowering.
  • Sporangia on the leaves appear as a downy whitish to wooly growth on both surface of the lesions.
  • Floral or vegetative parts are not malformed, and the leaves do not shred.

Control

  • Resistant varieties -Prabhat, Kohinoor, ICI-703, PAC-9401, PMZ-2, SEEDTEC-2331, BIO-9681 (Y) etc.

Brown spot (Physoderma maydis)

Symptoms

  • The first noticeable symptoms develop on leaf blades and consist of small chlorotic spots, arranged as alternate bands of diseased and healthy tissue. Free water and high temperatures(23-300C) is favorable for this disease.
  • Spots on the mid-ribs are circular and dark brown, while lesions on the laminae continue as chlorotic spots.  Nodes and internodes also show brown lesions.
  • In severe infections, these may coalesce and induce stalk rotting and lodging.

Control

  • Planting corn early allows to escape infection.
  • Removing of Saccharum spontaneoum grass growing around the crop, can minimise the diease.
  • Systemic fungicides mainly based on  acylalamines such as, metalaxyl (Ridomil 25 WP, Apron 35 SD, Apron 35 FN)
  • Resistant varieties – Ganga 11,Deccan, Deccan 103,Composite Suwan1, F-9572 A, JKMH-178-4, FH-3113

Pythium stalk rot (Pythium aphanidermatum)

Symptoms

  • Usually the basal internodes become soft, dark brown water soaked, causing the plants lodge.
  • Damaged internodes commonly twist before the plants lodge.  Diseased plants can remain alive until all vascular bundles become affected.
  • Isolations in culture media are necessary to differentiate Pythium from Erwinia stalk rots.

Control

  • Planting time between 10 & 20 July in Northern India.
  • Maintain plant population around 50,000/ha.
  • Good field drainage.
  • Removal of previous crop debris.
  • Resistant varieties – Ganga,  Safed 2

Bacterial stalk rot (Erwinia chrysanthemi pv zeae)

Symptoms

  • The stalk near the ground become water-soaked with brownish discolouration and are easily breakable.
  • The rotting tissues emit a putrid smell.
  • Infected plants show dark colour and water soaking at the base of the stalk.  Plants die shortly after tasseling.
  • The bacterial decomposition produces an unpleasant odor.

Control

  • Planting crop on ridges. Avoid water logging and proper drainage

Charcoal stalk Rot (Macrophomina phaseolina)

Symptoms

  • Disease appears 1-2 weeks after the flowering.  The outside of the lower internode becomes straw coloured.
  • The pith becomes badly disintegrated.
  • The pathogen invades seedling roots.  When plants approach maturity, the internal parts of stems show a black discolouration and shredding of the vascular bundles.
  • This occurs mainly in lower stalk internodes.  Careful examination of rind and vascular bundles of infected plants easily reveals small black sclerotia which can overwinter and infect next crop.
  • Fungus may infect kernels which cause them blacken completely.
  • Disease favoured by high soil temperature 30-42o C and low soil moisture.

Control

  • Avoiding water stress at flowering time can reduce disease incidence,
  • Apply Trichoderma in furrows after mixing with FYM @ 1kg/100kg  FYM/acre (mix 10 days before use in field)

Fusarium stalk rot (Fusarium moniliforme)

Symptoms

  • Affected plant wilt,leaves change from light to dull green, and the lower stalks become straw coloured.
  • Reddish discoloration occurs inside the infected stalk.
  • The internal pith tissue disintegrates, leaving only the vascular bundles.
  • Fungus enter through roots and grow up in to lower stem.
  • If infection occurs just after flowering, husks appear bleached and straw coloured.

Control

  • Seed from infected areas should not be planted.
  • Rotation with other crops.
  • Resistant varieties – Ranjit and Ganga 5
  • Single Cross – CM 103 x CM 104, CM 400 x CM 300
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