Sunday, July 3, 2011

Ginger - Diseases and Pests

Soft rot or rhizome rot

Soft rot is the most destructive disease of ginger which results in total loss of affected clumps. The disease is soil-borne and is caused by Pythium aphanidermatum. P. vexans and P. myriotylum are also reported to be associated with the disease. The fungus multiplies with build up of soil moisture with the onset of south west monsoon.Younger sprouts are the most susceptible to the pathogen.

  • The infection starts at the collar region of the pseudostems and progresses upwards as well as downwards. The collar region of the affected pseudostem becomes water soaked and the rotting spreads to the rhizome resulting in soft rot.
  • At a later stage root infection is also noticed.  
  • Foliar symptoms appear as light yellowing of the tips of lower leaves which gradually spreads to the leaf blades.
  • In early stages of the disease, the middle portion of the leaves remain green while the margins become yellow. The yellowing spreads to all leaves of the plant from the lower region upwards and is followed by drooping, withering and drying of pseudostems. 
  • Treatment of seed rhizomes with mancozeb 0.3% for 30 minutes before storage and once again before planting reduces the incidence of the disease.
  • Cultural practices such as selection of well drained soils for planting is important for managing the disease, since stagnation of water predisposes the plant to infection.
  • Seed rhizomes are to be selected from disease free gardens, since the disease is also seed borne.
  • Application of Trichoderma harzionum along with neem cake @ 1kg/bed helps in preventing the disease.
  • Once the disease is located in the field, removal of affected clumps and drenching the affected and surrounding beds with mancozeb 0.3% checks the spread of the disease. 

Bacterial wilt

Bacterial wilt caused by Ralstonia solanacearum is also a soil and seed borne disease that occurs during south west monsoon when the crop is young.
  • Water soaked spots appear at the collar region of the pseudostem and progresses upwards and downwards.
  • The first conspicuous symptom is mild drooping and curling of leaf margins of the lower leaves which spreads upwards.
  • Yellowing starts from the lowermost leaves and gradually progresses to the upper leaves. In the advanced stage, the plants exhibit severe yellowing and wilting symptoms. 
  • The vascular tissues of the affected pseudostems shows dark streaks. The affected pseudostem and rhizome when pressed gently extrudes a milky ooze from the vascular strands.
The cultural practices adopted for managing soft rot are also to be adopted for bacterial wilt.
  • The seed rhizomes may be treated with Streptocycline 200 ppm for 30 minutes and shade dried before planting.
  • Once the disease is noticed in the field all beds should be drenched with Bordeaux mixture 1% or copper oxychloride 0.2%.

Leaf spot

Leaf spot is caused by Phyllosticta zingiberi  and the disease is noticed on the leaves from July to October.

  • The disease starts as a water soaked spot and later turns as a white spot surrounded by dark brown margins and yellow halo. 
  • The lesions enlarge and adjacent lesions coalesce to form necrotic areas.
  • The disease spreads through rain splashes during intermittent showers.
  • The incidence of the disease is severe in ginger grown under exposed conditions.
  • The disease can be controlled by spraying Bordeaux mixture 1% or mancozeb 0.2%.

Nematode pests

Root knot (Meloidogyne spp.), burrowing (Radopholus similis) and lesion (Pratylenchus spp.) nematodes are important nematode pests of ginger.

  • Stunting, chlorosis, poor tillering and necrosis of leaves are the common aerial symptoms.
  • Characteristic root galls and lesions that lead to rotting are generally seen in roots.
  • The infested rhizomes have brown, water soaked areas in the outer tissues.
  • Nematode infestation aggravates rhizome rot disease.
  • The nematodes can be controlled by treating infested rhizomes with hot water (50�C) for 10 minutes, using nematode free seed rhizomes and solarizing ginger beds for 40 days.

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