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Major diseases of fodder crops and their management
Pradeep Saxena, Principal Scientist (Plant Pathalogy)

What is Disease?
Any alteration in the physiological processes of a plant, caused by living organisms or nonliving agents, which negatively affects the plant.
OR
Abnormal conditions in plants that interfere with their normal appearance, growth, structure, or function.

Why disease management?
Pathogens feed on the crop plants to complete their life cycle or to obtain their nourishment, making them as an integral part of energy flow of the natural system. But their presence cause damage to the crops and in turn may cause economic damage to the human beings.

Cost of Plant Diseases
Approx. 4 billion dollars a year in Global crop losses. Commercial growers now average $4 for every $1 invested in managing plant diseases.

How much losses

Our knowledge of crop losses due to diseases is very limited.

There are few attempts to estimate global crop losses. Among these, the efforts of Cramer (1967) and Oerke et al. (1994) deserve recognition. Oerke in 2006 update his estimates

Losses in Forages
In forages, the pest losses are not only in terms of green or dry forage yield and or grain (seed) yield, but also quality factors, which affect the regrowth period and canopy structure.

How pathogens affect Host
Principal Process in plants which can be affected by growth reducing factors

Diseases of Sorghum

Downy mildew (Peronosclerospora sorghi):

The source of primary infection is mostly through oospores, which are carried on the seed surface or are present in soil. The more prevalent secondary infection is through asexually produced conidia. The conidia after germination produce local lesions as well as systemic infection. The oospores are produced sexually and have dormancy period of 15 months and can survive for 5 years. These oospores are not formed under cool humid environment.

Abundant local rectangular chlorotic lesions appear which later coalesce to give the leaf a blighted appearance.

Uproot infected plants before shredding starts. Seed treatment with Ridomil @ 4g/kg, metalaxyl @1g/kg. Spray Dithane M-45 @2G/L of water.

Rust (Puccinia purpurea):
The disease-causing agent is a macro-cyclic heterocious fungus, producing uredia and telia. The disease spreads through uredospores, which are released from the sori as brown powder. The spore dusts is blown by wind and infect other plants. Oxalis corniculata is the alternative host plant where teliospores germinate. The uredospores produced can infect the crop at all stages of growth and sori are formed 10 days after infection.

Appears first on lower leaves as pustules on distal half of the lower side. Bright purplish-red spots appear on the leaf.
Early sowing.

Use resistant varieties.

Sulphur dusting @ 15-20 kg/ha.

Anthracnose (Colletotrichum graminicola)
The disease infects sorghum at all stages of crop growth. The falcate, fusiform conidia are produced on the infected leaves. These later lodges on to other leave and infection takes place through epidermal cells and ultimately spots are produced. Under favourable conditions acervuli appears at the centre of the spot. In the stem, the hyphae spread in the parenchyma and the fungus grows in the plant upward to infect the earhead making the pathogen to become seed borne. The optimum temperature for the disease is between 30 to 32 °C.

Appears first on laminae of lower leaves as small circular spots later spreading to upper leaves. The colour of the spots may vary from red, purple to brown depending on variety. These symptoms may be found on stems also.

Use resistant varieties.

Seed treatment with Thiram @3g/kg.

Spray Carbendazim @5g/l of water.

Charcoal rot (Macrophomina phaseolina)
The fungus is widely distributed among nearly 300 crop plants including sorghum. The sclerotia, the main propogules for the disease spread, survive in the soil. The disease becomes apparent when soil temperature increases and soil moisture declines. The mycelium spreads fast in the stem and make the pith shredded and filled with black, smooth sclerotia. This causes stem to become hollow that can lodge easily and break. These sclerotia can survives in the plant stubble's or soil for years. The secondary infection is through asexually produced conidia.

Blight is the typical symptom on young plants while mature plants show stalk rot. The collar region becomes shrunken and discoloured. The stem have a blackened appearance.

Use of resistant varieties.

Seed treatment with Thiram and Bavistine @0.25g/kg

Sooty stripe (Ramulispora sorghi)
The disease initiates through sclerotia, which survives with plant debris in the soil. The asexually produced conidia formed in pink gelatinous mass are 3-8 septate. Under humid conditions the round to oval, black sclerotia, which are loosely attached to stomata, are globose and black. The sclerotia emerge through both the leaf surfaces. The optimum temperature for disease spread is 28 °C. The pathogen is seed and soil borne which survives in soil along with fallen leaves.

On the leaves elongate, elliptical lesions with straw coloured centers and purplish to tan margins appear. These may coalesce to cover large area which become necrotic.

Use resistant varieties.

Seed treatment with Thiram @3g/kg. Spray Carbendazim @5g.l water.

Zonate leaf spot (Gloeocercospora sorghi)
This is a common disease of Kharif season. The disease is a soil and seed borne which spreads by sporodochia, that are formed between guard cells or above stomata on well defined stalk. These bear short conidiophores, which produce conidia. The hyaline conidia are 1-7 septate. Black sclerotia are formed in the necrotic regions of the leaf.

On the leaf lamina, semi-circulars to circular spots with alternating bands of dark purple or straw colour are formed. These may enlarge, become dark red and tend to elongate parallel with leaf veins and form characteristic zonations. Glumes may also be affected.

Destroy plant debris by burning.

Suitable crop rotation.

Seed treatment with Thiram @3g/kg. Spray Bavistine @0.1%.

Rough leaf spot (Ascochyta sorghina)

The disease is most damaging particularly at the seedling stage during the rainy season. The pycnidia produced above the leaf surface gives a characteristically rough feel. The pathogen remains in the soil on crop residue. The secondary infection is through conidia, which are spread by wind and rainfall.

Light coloured circulars to oval lesions with darker margins develop on the leaves. These may coalesce to form blotches.

Crop sanitation. Use resistant varieties.

Seed treatment with Thiram + Bavistine and Carbofuran @0.25g/kg.

Brown spot	Northern leaf blight (Setosphaeria turcica (Luttrell) Leonard et Suggs	Gray leaf spot Cercospora zea-maydis Tehon & E. Y. Daniels

Sheath blight Rhizoctonia solani Kuhn	Smuts	Leaf Blight