Maize is known in many countries as corn or mielie/mealie. It is grown in a wide range of environments, extending from extreme semi-arid to sub-humid and humid regions. it’s also a crop very popular in the low- and mid-hill areas of the western and northeastern regions. Broadly, maize cultivation can be classified into two production environments: (1) traditional maize growing areas, including Bihar, Madhya Pradesh, Rajasthan, and Uttar Pradesh (BIMARU), and (2) non-traditional maize areas, including Karnataka and Andhra Pradesh (KAP). In traditional areas, the crop is often grown in marginal eco-regions, primarily as a subsistence crop to meet food needs.
In contrast, maize in non-traditional areas is grown for commercial purposes – i.e., mainly to meet the feed requirements of the booming poultry sector. The main objective of this article is to provide the best knowledge of maize diseases and how to manage them so that maize production can be improved.
1. Bacterial Stalk Rot
Causal organism: Erwinia carotovora, Erwinia chrysanthemi
- The basal internodes develop soft rot and give a water-soaked appearance. A mild sweet fermenting odour accompanies such rotting.
- Leaves sometimes show signs of wilting or water loss and affected plants within a few days of infection lodge or topple down.
- Ears and shanks may also show rot. They fail to develop further and the ears hang down simply from the plant
- Use of disease-resistant varieties, i.e. Hybrids Ganga Safed-2, DHM 103, show significantly less disease incidence than other hybrids.
- Avoid waterlogging and poor drainage.
2. Black Bundle Disease and Late Wilt
Causal organism: Cephalosporium maydis, Caphalosporium acremonium
- The disease kills the plant prematurely after flowering. Infected plants do not show symptoms until they reach tasseling.
- Wilting generally starts from the top leaves, Leaves become dull green, eventually lose colour and become dry.
- In advanced stages the stalk loses its healthy green colour, lower portions become dry, shrunken with or without wrinklings, hardens and turn purple to dark brown which is more prominent on lower internodes.
- When split open diseased stalks, show brown vascular bundles starting in the underground portion of the roots.
- Diseased plants produce only ears with undeveloped shrunken kernels.
- In severe cases affected plants remain abortive causing 100 per cent loss.
- Cephalosporium maydis is primarily soil-borne and may infect young maize plants more readily than other plants through roots or mesocotyl. In the case of C. acremonium, only vascular bundles get blackened.
- Use of resistant varieties like Ganga Safed 2.
- Crop sanitation, crop rotations.
- Avoiding water stress at flowering.
- Seed treatment with Thiram or Captan 3g/kg seed.
Causal organism: Macrophamina phaseolina
- The characteristic symptoms of the disease become apparent as the plants approach maturity. The disease generally appears early after flowering.
- Plants affected by M. phaseolina show evidence of pre-mature ripening. The outsides of lower internodes become straw-coloured. The pith becomes badly disintegrated.
- The infected stalks may split longitudinally into a mass of fibres.
- A distinguishing characteristic of the disease is the presence of the small black sclerotia in the pith of the affected stalks. Roots are also invaded and show black sclerotia in the disorganised tissue.
- Regular irrigations, particularly during flowering time, should be provided.
- Use resistant varieties like DHM 103, Ganga Safed – 2 and avoid sowing of susceptible varieties like DHM 105.
- Seed treatment with Carbendazim or Thiram 3g/kg seed is effective.
- Field sanitation and crop rotation should be followed.
4. Common Rust
Causal organism: Puccinia sorghi
- Circular to elongate golden brown or cinnamon brown, powdery, erumpent pustules appear on both leaf surfaces
- As the crop matures brownish-black pustules containing dark thick-walled two-celled teliospores develop. In severe cases, the infection spreads to sheaths and other plant parts.
- Plant hybrids like Deccan, Ganga-5, Deccan Hybrid Makka-103 and DHM – 1 which are resistant to this disease to minimise the disease intensity.
- Spray Mancozeb 2.5g/lit or Dithane M-45 spray can be taken (0.4%) as soon as first symptoms are observed and it can be repeated at 10 days interval till flowering.
5. Downy Mildews
a) Sorghum downy mildew
Causal organism: Perenosclerospora sorghi.
- Early maize crops escape infection because by the time conidia are produced they develop resistance to the collateral host susceptibility occurs only up to about 15 days of age.
- In susceptible seedling plants, less than 4 weeks after seedling infection becomes systemic in all growth, subsequent to downward growth of mycelium and colonization of shoot apex (growing point). All Peronosclerospora spp. induce both local and systemic infection.
- Malformation of tassels in infected plants.
- Chlorosis, white stripes, stunting with downy fungal growth on both leaf surfaces are the characteristic symptoms.
b) Brown stripe Downy mildew
Causal organism: Sclerophthora rayssiae.
- Disease symptoms have been observed only on leaves. They are vein limited.
- Wilting generally starts from the top leaves; Leaves become dull green, eventually lose colour and become dry.
- Chlorotic stripes, 3-7 mm wide will develop and they further extend in a parallel fashion and may in severe cases cover the entire leaf lamina.
- Severe infection also incites blotching. The stripes in the advanced stage become necrotic with purple or reddish colour and present a burnt appearance.
c) Crazy top downy mildew
Causal organism: Sclerophthora macrospora
- Disease symptoms first appear as rolling and twisting of upper leaves before malformation of tassel.
- The important symptoms of the disease are the partial or complete malformation of the tassel which continues until the tassel resembles a mass of narrow, twisted, leafy structures.
- Affected plants show excessive tillering, stunted with chlorotic stripes on leaves.
d) Sugarcane Downey mildew
Causal organism: Peronosclerospora sacchari
- Downey growth is seen on both leaf surfaces. Plants may be distorted with small, poorly filled ears with misshapen tassels
- Characterized by local lesions and systemic infection. Initial lesions are small, round, chlorotic spots on the leaves.
- Systemic symptoms appear as pale yellow to white stripes or streaks at the base of the 3rd to 6th oldest leaves.
- Several streaks may develop on leaf and may extend on the entire leaf.
Control Measures for Downy Mildew Diseases
- The eradication of collateral and wild hosts near the maize field and rouging of infected maize plants have been recommended.
- Destruction of plant debris by deep ploughing and other methods.
- Seed treatment with Metalaxyl at 4 g/kg and foliar spray of Mancozeb 2.5 g/l or Metalaxyl MZ at 2g/l is recommended.
- Use of resistant varieties like DMR 1, DMR 5 and Ganga 11.