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. 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
|