Etiology and control of the following Sugarcane diseases: Red rot, Smut
Red Rot of Sugarcane:-
Pathogen:- Glomerella tucumanensis. (Older name = Colletotrichum falcatum)
Symptoms:-
> The affected canes exhibit leaf colour change, from green to orange and then to yellow in the third or fourth leaf. Then the leaves start drying from bottom to top.
> If the fungal spores enter the leaf sheath through the leaf midrib, then reddish spots can be seen on the back side of the leaf midrib also.
> The external symptoms appear only after16 - 21 days after infection and drying of entire cane takes another 10 days time.
> When the affected cane is split opened, the inner region is reddish in colour with intermittent white tinges across the cane length.
> Sometimes, the pith inside the cane is filled with blackish brown liquid and exhibited alchohol odour.
Management:-
i. Cultural method:-
> The best way to control red rot is to select setts for planting from healthy plants in a disease- free area.
> The red rot affected field must be rotated with rice for one season and other crops for two seasons.
> Growing of recommended resistant and moderately resistant varieties viz., Co 86032, Co 86249, CoSi 95071, CoG 93076, CoC 22, CoSi 6 and CoG 5.
ii. Physical method:-
> Removal of the affected clumps at an early stage and soil drenching with Carbendazim 50 WP (1 gm in 1 litre of water).
> The cut ends and entire setts should be dipped in a fungicide solution, such as one per cent Bordeaux mixture.
> If the disease is noticed in the field, the leaves and canes should be collected and destroyed by burning.
iii. Chemical method:-
> Adopt sett treatment with Carbendazim before planting (Carbendazim 50 WP (0.5 gm in 1 litre of water) or Carbendazim 25 DS (1gm in 1 litre of water) along with 2.5 kg of Urea in 250 litre of water.
> Use fungitoxic chemicals like Bavistan, Benomyl, Topsin and Aretan at 0.1 per cent for 18 min. at 52ºC for dipping setts which gave almost complete elimination of rot infection.
Smut of Sugarcane:-
Pathogen:- Ustilago scitaminea
Symptoms:-
> Production of whip like structure ( 25 – 150 cm) from the growing point of the canes.
> Whip covered by translucent silvery membrane enclosing mass of black powdery spores.
> Initial thin canes with elongated internodes later become reduced in length.
> Profuse sprouting of lateral buds with narrow, erect leaves especially in ratoon crop.
Management:-
i. Cultural method:-
> Growing of resistant and moderately resistant varieties viz., Co 86249, CoG 93076, CoC 22, CoSi 6 and CoG 5.
> Discourage ratooning of the diseased crops having more than 10 per cent infection.
> Cajanus cajan can be grown as a companion crop between rows of sugarcane, and the secondary spread of the disease is substantially reduced.
ii. Physical method:-
> Treating the seed setts with Areated Steam Therapy (AST) at 50 ºC for 1 hour or in hot water at 50 ºC for 30 minutes or at 52 ºC for 18 minutes.
> Roguing of smut whips with gunny bags/polythene bag and dipped in boiling water for 1 hour, and diseased clums must be uprooted and burnt.
iii. Chemical method:-
> Sett treatment with fungicides viz., Triadimefon @ 1gm in 1 litre of water or Carbendazim @ 1gm in 1 litre of water for 10 minutes.
> Spray on infected stools with a small amount of a 10% solution of roundup, using a small hand held sprayer.
> In severe cases spray the entire block with glyphosate (360 G/L) at 5-7 lit/ha.