Sorghum

Disease Management

Introduction

  • More than 50 diseases have been reported to attack sorghum, of which 10 are of major importance. In general sorghum diseases cause less damage than insects. The important fungal diseases which affect the yield are grain mould, ergot, downy mildew, smut, rust and charcoal rot.

Stage of the crop
Disease
Common Name
Scientific Name
Seedling stage and Vegetative stage (10 – 60 days)
Downy mildew
Selerospora sorghi
Seedling to flowering stage
(10 – 80 days)
Leaf blight
Exerohilium turcicum
Vegetative phase
(30 – 60 days)
Rust
Puccinia purpuria
Flowering to grain maturation
(60 – 90 days)
Charcoal rot
Macrophomina phaseolina
Rectangular leaf spot
Cercospora sorghi
Anthracnose and red rot
Colletotrichum graminicolum
Ergot or Sugary disease
Sphacelia sorghi
Grain mould
Fusarium sp, Alternaria sp, Aspergillus sp.
Grain smut
Phoma sp
Loose smut
Sphacelotheca sorghi
  Long smut Sphacelotheca cruenta
  Head smut Tolyposporium ehrenbergii, Sphacelotheca reiliana

Top

Anthracnose and Red Rot (Colletotrichum graminicolum)

Seasonal Occurrence

  • The disease is more during rainy season and if the temperature is between 28-30°C.
  • High humidity enhances disease infection.

Disease Cycle

  • The disease spreads by means of seed-borne and air-borne conidia and also through the infected plant debris.

Nature And Symptoms Of Damage

  • The fungus causes both leaf spot (anthracnose) and stalk rot (red rot) in sorghum. The disease appears as small red coloured spots on both surfaces of the leaf. The centre of the spot is white in colour encircled by red, purple or brown margin.
  • Numerous small black dots are seen on the white surface of the lesions which are the fruiting bodies (acervuli).
  • Red rot can be characterized externally by the development of circular cankers, particularly in the inflorescence.
  • Infected stem when split open shows discoloration, which may be continuous over a large area or more generally discontinuous giving the stem a marbled appearance.

Management Practices

  • Treat the seeds with Captan or Thiram @ 4 g/kg.
  • Spray the crop with Mancozeb @ 1.25 kg/ha.
  • Use 500 litres of spray fluid/ha.

Top

Charcoal Rot (Macrophomina phaseolina)

Disease Cycle

  • The fungus is soil borne and survives saprophytically on crop residues. It invades crown via the roots and colonize in cortical tissue of the lower internode.

Nature And Symptoms Of Damage

  • The infected stalk splits longitudinally into a mass of fibres and tissues. Numerous black sclerotial bodies are seen on the infected tissues.
  • Losses in grain yield occur due to premature drying and lodging.
  • Stunted growth and smaller stalks due to infection results in loss of quality and quantity of fodder.

Management Practices

  • Crop rotation reduces charcoal rot.
  • Treat the seeds with Trichoderma viride @ 4 g/kg of seed.

Top

Downy Mildew (Sclerospora sorghi)

  • It occurs in all sorghum growing areas and causes severe damage when favourable conditions prevail.

Seasonal Occurrence

  • Disease incidence is more when humidity is high and when temperature is between 21-23°C. Light drizzling accompanied by cool weather is highly favourable.

Disease Cycle

  • The soil borne oospores are the source of primary infection and initiate primary infection, which later produce large number of conidia on leaf surface.
  • These conidia spread by wind and other agencies, to become the source of secondary infection. The spread of secondary infection is aggrevated by closer spacing, high humidity and favourable microclimate.
  • If two sorghum crops are grown successively in the same field disease incidence is higher.
  • The conidia are short lived and the oospores, the primary source of infection persist in the soil for several years.

Nature And Symptoms Of Damage

  • The disease starts as vivid green and white stripes on the under surface of leaves. Later this growth spreads to major portion of leaves, which appears yellowish through the upper surface.
  • As the disease advances, chlorotic streaks develop and turn brown. After oospore formation, the characteristic shredding of leaves occur and plants become stunted.
  • Infested plants usually fail to head. Even if heads are exerted, they are small, compact or club shaped and have little or no seed.

Management Practices

  • Treat the seeds with Metalaxyl @ 4 gm/ kg of seeds.
    Remove and destroy infected plants upto 45 days after sowing.
  • Spray any one of the following fungicides. Use 500 litres of spray fluid/ha.
  • Metalaxyl 500 gm/ha.
  • Mancozeb 1 kg/ha.
  • Ziram 1 kg/ha.
  • Zineb 1 kg/ha.

Top

Ergot Or Sugary Disease (Sphacelia sorghi)

Seasonal Occurrence

  • Diseases incidence is more during high rainfall and high humidity period (September- October).
  • Cool night temperature and cloudy weather aggravate the disease.

Disease Cycle

  • The infection is mainly through air-borne conidia which come to rest in the spikelet.
  • The fungus can perpetuate through sclerotial bodies in soil. The secondary spread takes place through air and insect borne conidia.

Nature And Symptoms Of Damage

  • The disease is confined to individual spikelets.
  • Honey dew the creamy sticky liquid ooze out from the spikelets.
  • Under favourable condition long, straight or curved, creamy to light brown hard sclerotia develop.
  • Seed setting is severely affected.

Management Practices

  • Sowing period to be adjusted so as to prevent heading during rainy season and severe winter.
  • Spray any one of the following fungicides at earhead emergence (5-10% flowering) followed by a spray at 50% flowering and repeat the spray after a week if necessary. Use 500 litres of spray fluid/ha.
  • Mancozeb 1 kg/ha.
  • Ziram 1 kg/ha.
  • Zineb 1 kg/ha.

Top

Grain Mold

  • More than thirty genera of fungi are reported to infect the earheads and cause mold growth. The frequently occurring genera are Fusarium, Alternaria, Aspergillus and Phoma.

Seasonal Occurrence

  • The disease incidence was more during wet weather condition. Prolonged monsoon and excessive rainfall at seed maturity cause heavy grain mold infestation.

Disease Cycle

  • The fungi survive as parasites as well as saprophytes in the infected plant debris.
  • They spread through air-born conidia.

Nature And Symptoms Of Damage

  • The infection results in discolouration of grains.
  • The grains infected with Fusarium semitectum and F. moniliforme have fluffy white or pinkish colouration. Curvularia lunata infection results in black colouration.
  • If the infection is severe the grain weight is reduced leading to yield loss.
  • The germination and nutritive value of seed are also affected.
  • Toxins produced by the fungi are harmful to animals fed with infected grains.

Management Practices

  • Adjust the sowing time to avoid flowering during rainy season.
  • Delay in harvesting matured grains have to be avoided.
  • Spray any one of the following fungicides in the case of intermittant rainfall during earhead.
  • emergence and a week later. Use 500 litres of spray fluid/ha.
  • Mancozeb 1 kg/ha.
  • Captan 1 kg/ha + Aureofungin -sol 100 g/ha.
  • Zineb 1 kg/ha.

Top

Leaf Blight (Exerohilum turcicum)

Seasonal Occurrence

  • The disease occurrence is more during cool moist weather. High humidity and high rainfall is conducive for disease development.

Disease Cycle

  • The fungus is found to persist in the infected plant debris. Seed borne conidia are responsible for seedling infection.
  • The secondary spread of the disease is through wind borne conidia.

Nature And Symptoms Of Damage

  • The fungus also causes seed rot and seedling blight.
  • The disease appears in the form of small narrow elongated spots in the initial stage. But in due course they extend along with the length of the leaf and become bigger.
  • On older plants, the typical symptoms are long elliptical necrotic lesions, straw coloured in the centre with dark margins. The straw coloured centre become darker during sporulation.
  • The lesions can be several centimeters long and wide. Many lesions may develop and coalesce on the leaves, destroying large areas of leaf tissue, giving the crop a distinctly burnt or blasted appearance.

Management Practices

  • Use disease-free seeds.
  • Treat the seeds with Captan or Thiram at 4 g/kg.
  • Spray Mancozeb 1.25 kg or Captafol 1 kg/ha.
  • Use 500 litres of spray fluid/ha.

Top

Rectangular Leaf Spot (Cercospora sorghi)

Seasonal Occurrence

  • Disease occurrence is more if the weather is cool and moist with high humidity. Excess rainfall is favourable for disease development.

Disease Cycle

  • The conidia survive upto 5 months. The disease spreads through air-borne and seed-borne conidia.

Nature And Symptoms Of Damage

  • The symptoms appear as small leaf spots which enlarge to become rectangular lesions (which can be 5-15 mm long by 2 - 5 mm wide) on the leaf and leaf sheath. Usually the lower leaves are first attacked.
  • The lesions are typical dark red to purplish with some what lighter centres. The lesions are mostly isolated and limited by veins.
  • Severe spotting results in premature drying of leaves. The colour of the spots vary from red, purple, brown or dark depending upon the variety.

Management Practices

  • Use disease-free seeds.
  • Treat the seed with following fungicides.
    1. 1. Captan @ 4 g/kg or
      2. Thiram @ 4 g/kg
  • Spray Mancozeb @ 1.2 kg or Captafol @ 1 kg/ha
  • Use 500 litres of spray fluid/ha.

Top

Rust (Puccinia purpurea)

Seasonal Occurrence

  • Low temperature of 10 to 12°C favours spore germination and a spell of rainy weather is conducive for onset of disease.

Disease Cycle

  • This fungus is known as a long cycle rust with Oxalis corniculata as alternate host of the aecial and pycnial stage.
  • The uredospores infect the host in the usual manner for rusts, forming appresoria and infective hyphae which enter the host through stomata, producing uredosori in about 10 days. The uredo stage occurs on many cultivated and wild species of sorghum.

Nature And Symptoms Of Damage

  • All stages of the plants are affected but more often the infection starts when the plants are two months old.
  • The rust pustules usually appear first on the both surfaces of lower leaves. As the disease advances infection spreads to younger leaves.
  • The pustules will be round to elliptical with purple tan or red colour and lie between and parallel with leaf veins.
  • The older leaves dry prematurely and the plants become stunted.

Management Practices

  • Use disease free seeds.
  • Adopt crop rotation.
  • Spray Mancozeb @ 1 kg/ha when disease reaches grade 3. Repeat the spraying after 10 days. Use 500 litres of water/ha

Top

Smut Diseases

  • There are four types of smut disease caused by different fungal pathogens.

Nature And Symptoms Of Damage

Grain Smut (Sphacelotheca sorghi)

  • The individual grains are replaced by smut sori which can be localized at a particular part of the head or occur over the entire inflorescence.
  • The sori are oval or cylindrical and are covered with a tough white cream to light brown skin (peridium) which often persists unbroken upto threshing.

Loose Smut (Sphacelotheca cruenta)

  • The affected plants are shorter about a foot than the healthy plants and have thinner stalks.
  • Affected plants tiller excessively.
  • The ears come out much earlier than the healthy.
  • The glumes are hypertrophied and the earhead gives a loose appearance than healthy.
  • The sorus is covered by a thin membrane which ruptures very early, exposing the spores even as the head emerges from the sheath.

Long Smut (Tolyposporium ehrenbergii)

  • This disease is normally restricted to a relatively small proportion of the florets which are scattered on a head.
  • The sori are long, more or less cylindrical, elongated, slightly curved with a relatively thick creamy-brown covering membrane (peridium).
  • The peridium splits at the apex to release black mass of spores among which are found several darkbrown filaments which represent the vascular bundles of the infected ovary.

Head Smut (Sphacelotheca reiliana)

  • The head is completely replaced by a large gall (sorus).
  • The galls are at first covered by a whitish grey membrane of fungal tissue, which ruptures, often before the head emerges from the boot leaf, to expose a mass of brown - black powder (smutspores). They are embedded with long, thin, dark coloured filaments which are the vascular bundles of the infected head.
  • Sometimes smaller sori develop on the leaves and lower part of the peduncle.

Management Practices

  • Treat the seed with Captan or Thiram @ 4 g/kg.
  • Use disease-free seeds.
  • Follow crop rotation.
  • Collect the smutted ear heads in cloth bags and dip in boiling water.

Top

Tamilnadu