Diseases Of Maize
1. Downy mildew / Crazy top
Causal organism: Peranosclerospora sorghi
Symptoms: Chlorotic streaks appear on the leaf and white fungus growth is seen on both the surfaces of leaf. Affected plants become stunted and exhibit bushy appearance due to shortening of internodes. Sometimes leafy growths in the tassel and proliferation of axillary buds on the stalk of the tassel are noticed.
Favourable Conditions : Low temperature (21-33˚C);High relative humidity (90 per cent) and drizzling;Young plants are highly susceptible.
2.Rust
Causal organism: Puccinia sorghi
Symptoms: On both the surfaces of the leaf, brown pustules are seen. These represent the uredosori of the fungus. The alternate host is Oxalis corniunlata. Cool temperature and high relative humidity favours the disease.
3. Leaf Blight
Causal organism: Exserohilum turcicum & Helminthosporium maydis
Turcicum Leaf Blight Symptoms: The fungus affects the crop at young stage. Early symptoms are oval, water-soaked spots on leaves. Mature symptoms are characteristic cigar shaped lesions that are 3 to 15cm long. Lesions are elliptical and tan in color, developing distinct dark areas as they mature that are associated with fungal sporulation. Lesions typically first appear on lower leaves, spreading to upper leaves and the ear sheaths as the crop matures. Under severe infection, lesions may coalesce, blighting the entire leaf.
Maydis Leaf Blight Symptoms: Small yellowish round or oval spots appear on the leaves. These spots enlarge become elliptical and the center becomes straw coloured with a reddish brown margin. Conidia and conidiophores are formed in the center.
Favourable Conditions : Optimum temperature for the germination of conidia is 8 to 27˚C provided with freewater on the leaf;Infection takes place early in the wet season.
4.Charcoal rot
Causal organism: Macrophomina phaseolina
Symptoms: The pathogen affects the plant mostly after flowering and the disease is named as Post Flowering Stalk Rot (PFSR). The stalk of the infected plants can be recognized by greyish streak. The pith becomes shredded and greyish black minute sclerotia develop on the vascular bundles. Shredding of the interior of the stalk often causes stalks to break in the region of the crown. The crown region of the infected plant becomes dark in colour. Shredding of root bark and disintegration of root system are the common features. High temperature and low soil moisture (drought) favours the disease.
5.Bacterial Stalk rot
Causal organism: Erwinia dissolvens
Symptoms: The basal internodes develop soft rot and give a water soaked appearance. A mild sweet fermenting odour accompanies such rotting. Leaves some time show signs of wilting and affected plants topple down in few days. Ears and shank may also show rot. They fail to develop further and the ears hang down simply from the plant.
Disease Management
1.Seed treatment: Carbendazim @ 2 g/kg or Thiram @ 4g/kg or Metalaxyl @ 3g/kg of seed
2. Downy mildew or Crazy top
Use resistant TNAU maize hybrid CO-6 Rogue out affected plants. Spray Metalaxyl+ Mancozeb @ 1000g, Mancozeb 1000g/ha at 20 days after Sowing
3.Leaf blights
Spray Mancozeb or Zineb @2 -4 g/litre at 10 days interval after first appearance of the disease.
4.Post Flowering Stalk rot
Follow crop rotation Avoid water stress at flowering time reduced disease incidence Avoid nutrient stress. Apply potash @ 80 kg/ha in endemic areas Soil application of P. fluorescens (or) T. viride @ 2.5 kg / ha + 50 kg of well decomposed FYM or sand at 30 days after sowing.
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