Important diseases of maize, symptoms of damage and there management aspects are as follows:
1. Sorghum Downy Mildew (Peronosclerospora Sorghi):
Symptoms:
Infected plant chlorotic and sometime stunted, white-striped leaves & abnormal seed set. 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 the surface of infected leaves. Sometimes tassels of diseased plant may exhibit phyllode. Tolerant plants may show symptoms of systemic infection but have normal seed production.
Management:
Seed treatment with Acylalanine fungicide metalaxyl @ 6.0 g/kg. Rogue out infected plants at early stage. Seed treatment with Apron 35 WP, @ 2.5 g/kg. Grow resistant varieties viz., CoH (M) 5 Comp. A-9, Indimyt 345, EH-43861, KH-526, AH-36. Spray with Metalaxyl 1g/lit or Metalaxyl + Mancozeb @ 2.5 g/lit.
2. 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 severe striping and blotching.
Seed development may be suppressed, 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 shed.
Management:
Grow resistant varieties – Prabhat, Kohinoor, ICI-703, PAC-9401, PMZ- 2 etc. Seed treatment with Acylalanine fungicide metalaxyl @ 6.0 g/kg- Rogue out infected plants at early stage. Apply Apron 35 WP, @ 2.5 g/kg as seed treatment. Spray with metalaxyl 1g/l or metalaxyl + mancozeb @ 2.5 g/l of water.
3. Charcoal Stalk Rot (Macropliomina Phaseolina):
Symptoms:
Disease appears 1-2 week 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 reveals small black sclerotia which can overwinter and infect next crop. Fungus may infect kernels which cause them blacken completely. Disease is favoured by high soil temperature 30-42°C and low soil moisture.
Management:
Avoiding water stress at flowering time to reduce disease incidence. Apply Trichoderma in furrows after mixing with FYM @ 2.5 kgAa FYM/acre (mix 10 days before use in field).
4. Turcicum Leaf Blight-TLB (Exserohilum Turcicum):
Symptoms:
It causes significant economic damage when infection takes place at silking stage and conditions are optimum. In early stages slightly oval, water soaked, small spots produced on leaves. These grow into elongated, spindle-shaped necrotic lesions They appear first on the lower leaves and continue increasing in size and number as plant develops, until the complete ‘burning’ of foliage is conspicuous. These spots are long, elliptical, grayish-green or tan lesions ranging from 2.5 to 15 cm in length.
Management:
Spray with Mancozeb @ 2.0 g/lit. Grow resistant varieties such as Sartaj, Deccan 105, Trishulata, Deccan 109, JH-1267.
5. Maydis Leaf Blight (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 inbreeds and hybrids with different genetic background.
Management:
Spray with Mancozeb @ 2 g/lit of water. Grow resistant varieties such as Deccan, VL 42, Prabhat, PRO-339, ICI-701, PEMH 1, PEMH 2, PEMH 3, Paras, Sartaj, and Deccan 109.
6. Curvularia Leaf Spot (Curvularia Pallescens, Curvularia Lunata):
Symptoms:
The disease appears in the form of flecking which later develops into larger lesions. The lesions in general are round to oval, separate or coalescent, 1-6 mm in diameter. The centre of each lesion is straw coloured to light brown, which is surrounded by a dark brown margin.
Management:
Seed treatment with Thiram and Captan @ 2g Ag reduce seed infection.
Two applications of Captafol @2g/lit of water.
7. Brown Spot (Physoderma Maydis):
Symptoms:
The first noticeable symptoms develop on leaf blades and consists of small chlorotic spots, arranged as alternate bands of diseased and healthy tissue. Spots on the midribs 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.
Management:
Planting corn early allow to escape infection. Removing of Saccharum spontaneoum grass growing around the crop, can minimise the disease. Systemic fungicides mainly based on acylalamines such as, metalaxyl. Grow resistant varieties such as Ganga 11, Deccan, Deccan 103, Composite Suwan 1, JKMH-178-4, FH-3113.
8. Pythium Stalk Rrot (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.
Management:
Planting time is between 10 & 20 July in Northern India. Maintain plant population around 50,000/ha. Good field drainage. Remove of previous crop debris. Soil drench with Captan at basal internode (5-7week growth stage) @ 1g/lit of water. Grow resistant varieties like Ganga safed 2.
9. Bacterial Stalk Rot (Erwinia Chrysanthemi Pvzeae):
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.
Management:
Application of bleaching powder containing 33% chlorine @ 10 kg/ha as soil drench at pre-flowering stage. Plant crop on ridges. Avoid water logging and ensure proper drainage in the field.
10. Fusarium Stalk Rot (Fusarium Moniliforme):
Symptoms:
Affected plant wilts, 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 enters through roots and grows up in to lower stem. If infection occurs just after flowering, husks appear bleached and straw coloured.
Management:
Application of potassic fertilizers reduces infection. Seed from infected areas should not be planted. Rotation with other crops. Grow resistant varieties like Ranjit and Ganga 5.