MAJOR DISEASES IN SUGARCANE (Saccharum officinarum)

1.Red rot - Colletotrichum falcatum

Symptoms

• The first external symptom appears mostly on third or fourth leaf which withers away at the tips along the margins. 
• Typical symptoms of red rot are observed in the internodes of a stalk by splitting it longitudinally. These include the reddening of the internal tissues which are usually elongated at right angles to the long axis of the stalk. 
• The presence of cross-wise white patches are the important diagnostic character of the disease. The diseased cane also emits acidic-sour smell.
•  As the disease advances, the stalk becomes hollow and covered with white mycelial growth.
• Later the rind shrinks longitudinally with minute black, velvetty fruiting bodies protruding out of it. The pathogen also produces tiny reddish lesions on the upper surface of leaves with dark dots in the centre. 
• The lesions are initially blood red with dark margins and later on with straw coloured centres. Often the infected leaves may break at the lesions and hang down, with large number of minute black dots.

Favourable Conditions

• Monoculturing of sugarcane.
• Successive ratoon cropping.
• Water logged conditions and injuries caused by insects.

Management

• Adopt crop rotation by including rice and green manure crops.
• Select the setts from the disease free fields or disease free areas.
• Aviod ratooning of the diseased crop.
• Soak the setts in 0.1% Carbendazim or Triademefon 0.05% solution for 15 minutes before planting.
• Grow resistant varieties CO 62198, CO 7704 and moderately resistant varieties CO 8001, CO8201.
• Setts can be treated with aerated steam at 52 ˚C for 4 to 5 hours and by moist hot air at 54˚C for 2 hours.

2.Smut- Ustilago scitaminea

Symptoms

• It is a culmiculous smut. The affected plants are stunted and the central shoot is converted into a long whip-like, dusty black structure. 
• The length of the whip varies from few inches to several feet. In early stages, this structure is covered by a thin, white papery membrane. 
• The whip may be straight or slightly curved.
  On maturity it ruptures and millions of tiny black smut spores (teliospores) are liberated and disseminated by the wind. Affected plants are usually thin, stiff and remain at acute angle. 
• The whip like structure, representing the central shoot with its various leaves, may be produced by each one of the shoots/tillers arising from the clump.
• The smutted clumps also produce mummified arrows in which lower portion consisted of a normal inflorescence with typical flowers and the upper portion of the rachis is converted into a typical smut whip. Occasionally smut sori may develop on the leaves and stem.

Favourable Conditions

• Monoculturing of sugarcane.
• Continuous ratooning and dry weather during tillering stage.

Management

• Plant healthy setts taken from disease free area.
• Remove and destory the smutted clump (collect the whips in a thick cloth bag/polythene bag and immerse in boiling water for 1 hr to kill the spores).
• Discourage ratooning of the diseased crops having more than 10 per cent infection.
• Follow crop rotation with green manure crops or dry fallowing.
• Grow redgram as a companion crop between 2 rows of sugarcane.
• Grow resistant varieties like Co 7704 and moderately resistant varieties COC 85061 and COC 8201.
  

3. Settrot- Ceratocystis paradoxa

Symptoms

• The disease primarily affects the setts usually two to three weeks after planning. The fungus is soil-borne and enters through cut ends and proliferates rapidly in the parenchymatous tissues. 
• The affected tissues first develop a reddish colour which turns to brownish black in the later stages. The severely affected setts show internodal cavities covered with the mycelium and abundant spores. 
• A characteristic pineapple smell is associated with the rotting tissues. The setts may decay before the buds germinate or the shoots may die after reaching a height of about 6-12 inches. Infected shoots are stunted.

Favourable Conditions

• Poorly drained fields.
• Heavy clay soils.
• Temperature of 25-30o C.
• Prolonged rainfall after planting.

Management

• Soak the setts in 0.05% Carbendazim 15 minutes.
• Use long setts having 3 or 4 buds.
• Provide adequate drainage during rainy seasons.

4.Wilt - Cephalosporium sacchari

Symptoms

• The first symptom of the disease is visible in the canes of 4-5 month age. The canes may wither in groups. 
• The affected plants are stunted with yellowing and withering of crown leaves. The midribs of all leaves in a crown generally turn yellow, while the leaf lamina may remain green.
• The leaves dry up and stem develop hollowness in the core. The core shows the reddish discolouration with longitudinal red streaks passing from one internode to another. 
• In severe cases, spindle shaped cavities tapering towards the nodes develop in each internode. The canes emit a disagreeable odour, with lot of mycelial threads of the fungus cover the cavity.

Favourable Conditions

• High day temperature (30-35˚C).
• Low humidity (50-60%).
• Low soil moisture and alkaline soils.
• Excess doses of nitrogenous fertilizers.

Management

• Select the seed material from the disease-free plots.
• Avoid the practice of ratooning in diseased fields.
• Burn the trashes and stubbles in the field.
• Grow coriander or mustard as a companion crop in the early stages of crop.
• Dip the setts in 40ppm Boran or Manganese for 10 minutes or in 0.25% Emisan or 0.05% Carbendazim for 15 minutes.

5.Rust- Puccinia erianthi (Syn: P. melanocephala and
P. kuehnii)

Minute, elongated, yellow spots (uredia), usually
2-10 x 1-3 mm appear on both the surfaces of young leaves. The pustules turn to brown on maturity. Late in the season, dark brown to black telia appear on the lower surface of leaves. In severse cases, the uredia also appear on the leaf sheath and the entire foliage looks brownish from a distance.

Favourable Conditions

• Temperature of 30˚C.
• Rumidity between 70 and 90 per cent.
• High wind velocity and continuous cloudiness.

Management

• Remove the collateral hosts.
• Spray  Tridemorph 1 kg or Mancozeb 2 kg/ha.

6.Gummosis - Xanthomonas axonopodis pv. vasculorum

 

Symptoms

• The bacterium produces two distinct types of symptoms. On the mature leaves, longitudinal stripes or streaks, 3-7mm in width and several cm in length, appear around the affected veins, near the tip. 
• Initially these stripes are pale yellow in colour, later turn to brown. The affected tissues slowly dry up.The infected canes are stunted with short internodes, giving a bushy appearance. 
• When such canes are cut transversely or split open longitudinally, a dull yellow bacterial ooze comes out from the cut ends and bacterial pockets are seen inside the slitted cane. 
• The fibro vasuclar bundles are deep red and internodal cavities formed in the severe cases are filled with yellow coloured bacterial gums.

Management

• Remove and burn the affected clumps and the stubbles in the field. Select setts from disease free areas.
• Avoid growing collateral hosts like maize, sorghum and pearlmillet near the sugarcane fields.

7.Redstripe- Pseudomonas rubrilineans

Symptoms

• The disease first makes it appearance on the basal part of the young leaves. The stripes appear as water soaked, long, narrow chlorotic streaks and become reddish brown in few days. 
• These stripes are 0.5 to 1 mm in width and 5-100 mm in length, run parallel to the midrib. 
• The stripes remain confined to lower half of the leaf lamina and whitish flakes spreads to growing points of the shoot and yellowish stripes develop, which later turn reddish brown. 
• The rotting may commence from the tip of the shoot and spreads downwards. 
• The core is discoloured to reddish brown and shrivelled and form cavity in the centre. In badly affected fields, a foul and nauseating smell appears.

Favourable Conditions

• Continuous ratooning and prolonged rainy weather with low temperature (25℃).

Management

• Whenever the disease is noticed; the affected plants should be removed and burnt.
• Growing resistant varieties Select setts from the healthy fields.
• Avoid growing collateral hosts near the sugarcane fields.

8.Sugarcane Mosaic- Sugarcane mosaic poty virus 

Symptoms

The disease appears more prominently on the basal portion of the younger foliage as chlorotic or yellowish stripes alternate with normal green portion of the leaf. As infection becomes severe, yellow stripes appear on the leaf sheath and stalks.  Elongated necrotic lesions are produced on the stalks and stem splitting occurs. The necrotic lesions also develop on the internodes and the entire plant becomes stunted and chlorotic.      

Management

• Roguing of infected plants and use of disease free planting material.
• Chemical sprays to manage the insect vector population in early crop stage.
• Grow mosaic-resistant or, at least, tolerant varieties.
• Breeding mosaic-resistant varieties is needed.
•  Saccharum spontaneum L. and S. barberi (Jesweit) carry resistance to mosaic and so varieties with this background must be preferred.
• Rogue out the diseased clumps periodically. Select setts from the healthy fields as the virus is sett-borne Aerated Steam Therapy (AST) at 56˚C for 3 hrs, for setts before planting is advised.

9.Grassy shoot - Phytoplasma

Symptoms

• The disease appears nearly two months after planting. The disease is characterised by the production of numerous lanky tillers from the base of the affected shoots. 
• Leaves become pale yellow to completely chlorotic, thin and narrow. The plants appear bushy and ‘grass-like’ due to reduction in the length of internodes premature and continuous tillering. 
• The affected clumps are stunted with premature proliferation of auxillary buds. Cane formation rarely occurs in the affected clumps, if formed, thin with shorter internodes having aerial roots at the lower nodes. 
• The buds on such canes usually papery and abnormally elongated.

Management

• Eradication of diseased parts as soon as symptoms are seen.
• Avoid selection of setts from diseased area.
• Pre-treating the healthy setts with hot water at 52°C for 1 hour before planting.
• Treating them with hot air at 54°C for 8 hours.
• Spraying the crop twice a month with insecticides.

10.Ratoon stunting - Clavibacter xyli sub sp. xyli (Rickettsia Like Organism - RLO)

Symptoms

Diseased clumps usually display stunted growth, reduced tillering, thin stalks with shortened internodes and yellowish foliage. Orange-red vascular bundles in shades of yellow at the nodes are seen in the infected canes.

Management

• Select the setts from disease free fields or from disease free commercial nursery.
• Remove and burn the clumps showing the disease incidence.
• Treat the setts before planting, as specified for grassy shoot disease.