Diseases Of Maize Plant – Study material

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DISEASES OF MAIZE

DISEASESCAUSAL ORGANISM
Downey mildew / Crazy topPeronosclerospora sorghi, P.philipenensis
Charcoal rotMacrophomina phaseolina
Head smutSphacelotheca reiliana
Leaf blightHelminthosporium maydis
RustPuccinia 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

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