DISEASES OF MAIZE
| DISEASES | CAUSAL ORGANISM |
| Downey mildew / Crazy top | Peronosclerospora sorghi, P.philipenensis |
| Charcoal rot | Macrophomina phaseolina |
| Head smut | Sphacelotheca reiliana |
| Leaf blight | Helminthosporium maydis |
| Rust | Puccinia sorghi |
1. DOWNY MILDEW OR CRAZY TOP- Peronosclerospora sorgi
Symptoms
The development of chlorotic streaks appears on the leaves and plants exhibit stunted and bushy appearance. White downy growth of the fungus can be seen on the lower surface of the leaf. Later browning of tissues and leaf shredding symptoms are noticed. Proliferation of axillary buds on the stalk of tassel and top [crazy top] takes place.
Mode of spread and survival
Air borne conidia help in the spread of the disease and the pathogen survives as Oospore in soil and infected seeds.
Epidemiology
Low temperature, high humidity and light drizzling encourages the disease
Management
- Deep ploughing
- Crop rotation with pulses
- Adjust the time of sowing
- Roguing and destruction of infected plant debris
- Treat the seeds with metalaxyl @ 4g/kg of seed
- Spray the crop with metalaxyl + mancozeb @ 2kg/ha on 20 DAS
- Grow resistant varieties like CO 1. Hybrids – CoH – 1, 2
2. CHARCOAL ROT – Macrophomina phaseolina
Symptoms
The fungus attack roots of seedlings and young plants [wilt symptom]. The stalk of infected plants becomes shredded and grayish black minute “sclerotia” develop on the vascular bundles. Finally disintegration of root system results in death of the plants.
Mode of spread
The primary infection takes place through the sclerotia present in the soil and the secondary spread is through wind borne pycnidiospores
Survival
The fungus survives as soil borne sclerotia
Epidemiology
High temperature, low soil moisture help in the disease development
Management
- Long crop rotation with non-host crops
- Balanced fertilizer application and collection and destruction of diseased plants
- Seed treatment with captan or carbendazim @ 2g/kg of seed
- grow resistant varieties like Ganga 5, 101, Amber, jawahar.
3. HEAD SMUT – Sphacelotheca reiliana
Symptoms
Large smut sori replace the entire tassal and the ear. Finally the tassal wholly gets converted in to smut sorus and floral bracts grow in to leaf-like structures / small shoots.
Mode of spread and Survival
The pathogen is externally seed and soil borne and survives in the infected seeds and plant debris
Epidemiology
High soil temperature and low moisture favour the disease development
Management
- Field sanitation
- Crop rotation with pulses
- Seed treatment with captan or thiram @ 4g/kg of seed
4. LEAF BLIGHT – Helminthosporium maydis
Symptoms
Small yellowish round to oval spots on leaves develops which latter turns grayish brown colour in the centre with dark brown margins. The surface is covered with olive green velvety masses of conidia and conidiophores
Mode of spread and survival
The pathogen is seed borne and survives infected plant debris
Epidemiology
Cool climate favours the disease
Management
- Seed treatment with captan or thiram @ 4g/kg of seed
- Spray mancozeb 1.25 kg/ha or captan @ 1kg/ha
- Grow resistant varieties like Jawahar, Pusa prakash. Hybrids – Ganga 5, Ranjit
5. RUST- Puccinia sorghi
Symptoms
Circular to oval elongated, brown powdery pustules can be seen scattered over both surfaces of leaves. Finally the pustules become as red uredospores to black teliospores
Mode of spread and survival
The fungus spreads through wind borne uredospores and survives in the alternate hosts
Epidemiology
Cool temperature and high RH encourages the disease
Management
- Remove alternate host
- Spray mancozeb @ 1.25kg / ha
- Grow resistant varieties like CM 105, 111, OH 43, 545 and N 28
