Maydis leaf blight (MLB) – Bipolaris maydis
- 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.
- 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)
- 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.
- Resistant varieties – Comp. A-9, Indimyt 345, EH-43861, KH-526, AH-36.
Brown stripe downy mildew (Scleropthora rayssiae var. zeae)
- 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.
- Resistant varieties -Prabhat, Kohinoor, ICI-703, PAC-9401, PMZ-2, SEEDTEC-2331, BIO-9681 (Y) etc.
Brown spot (Physoderma maydis)
- 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.
- 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)
- 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.
- 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)
- 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.
- Planting crop on ridges. Avoid water logging and proper drainage
Charcoal stalk Rot (Macrophomina phaseolina)
- 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.
- 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)
- 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.
- 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