Diseases in sorghum are divided into four types:
- Foiler Diseases
- Stalk Diseases
- Ear head Diseases
- Viruses affecting Sorghum
Foiler Diseases:
Foiler diseases in Sorghum are classified into five different types which include
- Downy Mildew
- Crazy Top Downy Mildew
- Leaf Blight
- Rust
- Anthracnose
Now let us see about each of them individually.
1.Downy Mildew:
Downy Mildew
Whitish growth on the undersurface of the leaves.
The fungus invades the growing points of young plants and as the leaves unfold they show various types of symptoms. The first few leaves that show symptoms normally are only partially infected (the lower portion) with a lighter green or yellow coloration of the infected portion. Abundant downy white growth is produced on the under surfaces of infected portions of leaves during humid weather (Fig.).
Streaks of bleached leaves. Systemically infected plants show progressively more of a complete bleaching of the leaf tissue, sometimes in streaks or stripes (Left Fig.) and sometimes over the entire leaf surface (Bottom Fig.).
Leaf shredding As the infected bleached leaves mature they become necrotic and the interveinal tissues disintegrate to give the typical shredded leaf symptom (Fig.).
Management The eradication of wild hosts near sorghum fields. Removal of infected sorghum plants in the field. Destruction of plant debris by deep ploughing and other methods. Growing resistant varieties and hybrids like CSV5, CSV 6 etc.Seed treatment with Metalaxyl at 4 g/kg of seed or with Redomyl MZ @ 6 g/kg seed before sowing of sorghum. Foliar spray of Mancozeb 2.5 g/liter or Metalaxyl MZ at 2g/liter is recommended if standing crop is infested with downy mildew.
2.Crazy Top Downy Mildew:
Twisted and curled leaves
The symptoms vary considerably with the sorghum cultivar. Young sorghum plants may develop mottled leaves resembling mosaic virus infection and subsequently develop thick, stiff, twisted or curled leaves. Yellow occurs later. This disease will always be most noticeable in fields in low spots where water stands.
Leaf shredding characteristic of downy mildew does not occur with this disease. Infected plants tiller profusely, usually survive, but do not produce grain. Management Provide adequate field drainage as high soil moisture levels and flooding are required for disease development.
Long elliptical necrotic
lesions on leaves Seedlings could be infected with leaf blight. Typical symptoms are long elliptical necrotic lesions, straw colored in the centers with dark margins (Fig.). These spots later enlarge and join together leading to wilting of leaves and consequently seedlings may die.Leaf blight is widespread in many humid areas where sorghum is grown.
If leaf blight is established on susceptible cultivars before earhead emergence, grain yield losses may be up to 50%.
If infection is moderate or delayed until after the formation of the flower head (inflorescence), yield losses are minimal.
3.Leaf Blight:
Leaf blight is widespread in many humid areas where sorghum is grown.
If leaf blight is established on susceptible cultivars before earhead emergence, grain yield losses may be up to 50%. If infection is moderate or delayed until after the formation of the flower head (inflorescence), yield losses are minimal.
Management Rotation with nonsusceptible crops i.e., crops other than grassy crops like maize, rice, pearl millet etc., aids in the destruction of infected residue. Foliar application of fungicides may be needed in seed production fields but it is not economical in grain production fields.
4.Rust:
Rust flecks on leaves
Young plants are rarely affected by rust. The typical symptoms are seen in 1.5 to 3 months old plants. Scattered purple, red, or tan flecks appear on both surfaces of leaves (Fig.) and in resistant cultivars the symptoms develop no further.
Healthy leaf on left.
Rust affected leaf on the right In susceptible cultivars typical rust pustules develop, mainly on the lower leaf surfaces. When fingers are passed on such leaves reddish powder can be seen on the fingers. In highly susceptible cultivars the pustules occur so densely that almost the entire leaf tissue is destroyed (Fig.).
Pustules on
inflorescence stalks The pustules may also occur on leaf sheaths and on inflorescence stalks.
Management In areas where rust becomes economically important disease, growing less-susceptible or resistant cultivars like PSH 1, SPH 837, CSV 17 etc. is the only solution. Selective fungicides that suppress the disease are usually not economical.
5.Anthracnose:
Anthracnose spots
The symptoms vary with cultivar and the prevailing weather. The foliar phase may occur during any plant stage but usually appears on leaves of 30 to 40 days plants. Typical symptoms are small, circular, elliptical, or elongated spots (Fig.).
Anthracnose spots Under conditions of high humidity or high rainfall, the spots increase in number and join together to cover much of the leaf and kill large portions of the leaf (Fig.). In its severe form, anthracnose causes premature defoliation, thus reducing growth and delaying development of plants or even premature death of plants.
Midrib Infection Midrib infection often occurs and is seen as elongate-elliptical red or purple lesions (Fig.). If midrib and foliar infection occur together, leaf damage, defoliation, and reduction of yield may be greater.
Management
Clean cultivation, elimination of weed hosts, removal of crop residues will help in controlling this disease. A 2-year crop rotation with crops other than sorghum. Growing resistant cultivars like SPV 462, CSV 17 etc.
Stalk Diseases:
Stalk Diseases are of two types.They include
- Anthracnose Stalk Rot
- Charcoal Rot
1.Anthracnose Stalk Rot:
Anthracnose disease infestation occurs on foliage, sorghum stalks and also on earheads.
The stalk rot occurs after leaves are infested. Foliar phase of Anthracnose is more common in humid areas , and later, plants develop stalk and earhead symptoms. Stalk rot can be economically important even late in the growing season.
Anthracnose stalk rot can be recognized by circular cankers, particularly in the inflorescence (early stage of earhead). Infected stems when split open show discoloration (depending on cultivar) which may be continuous over a large area, or more marbled appearance (Fig.)
Management Clean cultivation, elimination of weed hosts, removal of crop residues will help in controlling this disease. A 2-year crop rotation with crops other than sorghum. Growing resistant cultivars like SPV 462, CSV 17 etc.
2.Charcoal Rot:
Charcoal rot is a major disease in the dry sorghum-growing regions.
It is particularly destructive on high-yielding sorghums that mature during hot and dry weather if the vigorously growing crop is subjected to moisture stress during the pre-flowering period. Post-flowering stress may be substantially increased by the presence of leaf diseases, droughts, and heavy application of fertilizers, root and shoot damage by insects. Yield losses vary, depending on the weather and the growth stage of the cultivars at the time of infection by the fungi causing this disease. In general, charcoal rot becomes conspicuous near crop maturity. In some fields, particularly of hybrid sorghums, more than 50% of the plants may break at the base and lodge.
Infected Roots The charcoal rot fungi infects roots of plants growing under adverse environmental conditions, particularly moisture stress and high temperature. Infected roots show water-soaked lesions that turn brown or black (Fig.)
Sorghum lodging due
to Charcoal Rot Affected stalks are soft or spongy at the base and tend to lodge. Lodging is the most apparent symptom of charcoal rot (Fig.).
Disintegration of
stalk tissues. If lodged plant is split open and examined, the pith of the stalk may be found in various stages of rotting of the tissues (Fig.).
Management Maintaining soil moisture through irrigation, if possible, during the post- flowering period can minimize charcoal rot infestation. A balanced fertilizer program is beneficial as with high levels of nitrogen application with low levels of potassium may lead to charcoal rot.High plant population should be avoided. Best plant density based on moisture availability need to adopted. Growing of drought tolerant, lodging resistant, and no senescing types of sorghum like CSV 17, SPV 462 etc. can reduce yield losses from charcoal rot infestations.
Ear head Diseases:
These are also classified into two types:
1.Grain Mild
2.Ergot
1.Grain Mild:
Grain mold is a major yield-reducing disease especially in early-maturing sorghum cultivars, and in areas where the crop flowers and matures under high humidity due to continuous rains, and warm conditions.
Cultivars with white grain are particularly affected by this disease.Grain mold drastically reduces both quantity and quality of sorghum grain and affects germination of seeds. Yield losses range from 30 to 100% depending on cultivar type, time of flowering, maturity and soil.Molded grain may contain certain mycotoxins. So, consumption of molded grain may produce symptoms that include body ache, fever, general body heating, eye burning, and loss of appetite.
The symptoms of grain mold depend on the fungus, and the time and severity of infection. There are 3 types of infected grain:
- Severely infected grain fully covered with mold,
- Normal-looking grain with slight discoloration,
- Apparently normal grain with no external symptoms.
The molded grain show pink, orange, gray, white, or black discoloration depending on the fungus involved.
Another symptom associated with grain mold complex is small seed. These seeds fail to mature properly and shrink after drying.
Management Avoidance of the disease is one of the most important control strategies. Avoidance can be practiced either by delaying sowing dates or by growing medium to late maturing cultivars such that the grain filling and maturity stages occur after end of the rains. Sowing date adjustments may require irrigation, which is not always available to resource-poor farmers. Reduction in mold damage is possible if the crop is harvested at physiological maturity. (Click on the word “physiological maturity “ for information) Chemical control appears to provide some protection against grain mold, but it is neither practical nor economical except for saving valuable sorghum seed in small fields.
Grain Mold
Resistant Cultivar Management Growing available tolerant / resistant cultivars like CSH 5, CSH 6, SPV 462, CSV 4, PVK 801 etc. will help to overcome the grain mold.
2.Ergot:
Ergot can be an economically devastating problem.
In seed production fields, yield losses ranging between 10 to 80% due to ergot disease have been reported in India. Although yield losses associated with ergot infection can be significant, indirect losses may be even more important. Harvesting grain from ergot-infected fields can be difficult. Ergot contamination reduces grain quality and limits its use as a feedstock.
Ergot infested panicle Ergot or sugary disease results from the ergot fungus infects the florets in the earhead (panicle) and prevents seed set in such florets (Fig.).
Honeydew exuding
from florets The first symptom is droplets of liquid honeydew exude from between the glumes of infected florets (Fig.). Honeydew may range from colorless to start with to yellow, brown or white with a thin to viscous consistency.
Ergot infested
earhead If honeydew exudation is profuse, it may drip down and smear the whole earhead, sometimes dripping down onto the soil. If the exudates is plentiful, the earhead appears with blackened grain (Fig.).
Management Sowing of ergot free seed. Soaking seeds with 5% salt solution will aid to remove ergot infested seeds, as ergot infested seeds will float in the salt solution. Seed treatment with fungicides such as Captan or Thiram.Control of ergot with fungicides such as Propiconazole or Tebuconazole has proved to be cost effective in seed production plots. Multiple sprayings at 5-7 days interval from flag leaf stage till end of an thesis are recommended to accommodate the variation in flowering within a field.
The grain on the left
is physiologically mature;
the one on the right is not. The best stage to harvest sorghum is when the plants reach the physiological maturity. Physiological maturity can be determined by the black (dark) spot at the bottom of the grain as shown in the Fig.
Ergot can be an economically devastating problem.
In seed production fields, yield losses ranging between 10 to 80% due to ergot disease have been reported in India. Although yield losses associated with ergot infection can be significant, indirect losses may be even more important. Harvesting grain from ergot-infected fields can be difficult. Ergot contamination reduces grain quality and limits its use as a feedstock.
Ergot infested panicle Ergot or sugary disease results from the ergot fungus infects the florets in the earhead (panicle) and prevents seed set in such florets (Fig.).
Honeydew exuding
from florets The first symptom is droplets of liquid honeydew exude from between the glumes of infected florets (Fig.). Honeydew may range from colorless to start with to yellow, brown or white with a thin to viscous consistency.
Ergot infested
earhead If honeydew exudation is profuse, it may drip down and smear the whole earhead, sometimes dripping down onto the soil. If the exudates is plentiful, the earhead appears with blackened grain (Fig.).
Management Sowing of ergot free seed. Soaking seeds with 5% salt solution will aid to remove ergot infested seeds, as ergot infested seeds will float in the salt solution. Seed treatment with fungicides such as Captan or Thiram.Control of ergot with fungicides such as Propiconazole or Tebuconazole has proved to be cost effective in seed production plots. Multiple sprayings at 5-7 days interval from flag leaf stage till end of an thesis are recommended to accommodate the variation in flowering within a field.
The grain on the left
is physiologically mature;
the one on the right is not. The best stage to harvest sorghum is when the plants reach the physiological maturity. Physiological maturity can be determined by the black (dark) spot at the bottom of the grain as shown in the Fig.
Virus Affecting Sorghum:
Maize Dwarf Mosaic (MDM) and Sugarcane Mosaic (SCM) are diseases caused by viruses, the symptoms of which are highly similar on sorghum.
The earlier the infection, the more severe will be the symptoms. In the most severe cases the plants may die, or growth may be stunted, flowering delayed, and the plants may fail to head or set seed.
The mosaic symptom is normally most prominent on the upper 2 or 3 leaves as an irregular mottling of dark and light green, often interspersed with longitudinal white or yellow streaks
In red-pigmented cultivars a “red-leaf” symptom may occur with elongated red stripes which develop necrotic centers and red margins (Fig.).
Management Johnson grass (Fig.) is a perennial weed found in and around sorghum growing fields. This weed is alternate host to these viruses. Aphids are the vectors for these viruses. When Johnson grass is controlled, this disease incidence will be more on sorghum crop due to the moment of aphids to sorghum.Control of alternate hosts (Johnson grass), control of aphid vectors and use of resistant cultivars are the recommended measure for Maize Dwarf Mosaic. Use of resistant cultivars is the only measure for Sugarcane Mosaic.
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