Disease:Cordana Leaf Spot

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  • Yellow or pale brown oval shaped spots appear near the leaf margins of lower leaves.(Image1).
  • As the spots develop, the central necrotic area develops concentric zonation with surrounding yellow halo.(Image2).
  • Individual spots enlarge or several spots coalesce to form large infected areas.
  • When the leaf margins are infected, small concentric spots develop which is later converted into long stripes of pale brown necrotic tissues. The stripes sometimes extend upto midrib.(Image3)

Spread of Disease

Leaf wetness, dews on veins, temperature of 23-250C, rainy days, high relative humidity (more than 80%), poorly managed crops, poor and badly drained soils, close planting etc. help in the sudden outbreak of the disease.

Control Measures

  • Cut and burn all moderate to severe infected lower leaves in the case of yellow sigatoka. In the case of black sigatoka cut and remove the leaves as soon as the initial symptoms are observed.
  •   Grow resistant/less susceptible varieties such as BRS 1,BRS 2 and Manjeri Nendran 2.
  •   Spray 1 % Bordeaux mixture soon after the appearance of the initial symptoms of the disease along with stickers or 0.4 % mancozeb or heavy oils like Mobil oil A.F., Gas oil, White oil or mineral oil @ 3ml/L. However, in some varieties symptoms of oil phytotoxicity may occur which consist of varying levels of leaf flecking and general bronzing of leaves.
  • Spray carbendazim @0.05% or give alternate spraying of Tridimorph (0..1 % Calyxin) soon after the appearance of the initial symptom.
  • Tilt (propiconazole) 0.1% has become very popular for the management of these leaf infections. However, the continuous uses of systemic fungicide can result in the formation of resistant strain of the pathogen. This can be avoided by alternating the use of systemic fungicide with 1% Bordeaux mixture.
  • The number of sprays to be given depends on the severity of infection. When more than one spray is required follow a rational rotation of systemic and non systemic fungicides.
  • Spray bio agents such as Pseudomonas 20 g/L or Bacillus subtilis 5 g/L .