Diseases of Fruit Plantation Medicinal and Aromatic Crops

Phytophthora crown rot,collar rot and root tot disease

Phytophthora crown rot, collar rot and root rot disease

Causal organisms: Phytopthora spp.

• Collar rot affects the scion portion of the tree, crown rot affects rootstock portion of the tree where as root rot affects the root system away from the crown region.
Dissemination

• Pathogen survives in soil for several years as spores, especially in old orchard soils.
  
• It also enters the orchard through infected nursery stock.
Symptoms

• Cankers may be seen at or below the ground level which may extend from original site of infection to the root system or up the trunk to the bud union level and above it if the scion is also susceptible.
  
• Infected bark is brown and often slimy when wet. When the bark is pulled out, the cambium and phloem show an orange, reddish brown color.
  
• The cankers caused by the fungus girdle the tree, resulting in their poor vegetative growth and chlorotic foliage that may turn purple in the autumn.
  
• A severely infected tree may die. Trees may be killed in one growing season or may linger for a number of growing seasons.
Disease cycle

• The fungus survives in the soil as thick-walled spores (oospores) that are resistant to drought and relatively resistant to chemical treatment.
  
• The fungus may also be brought in through infected nursery stock and contaminated irrigation water.
  
• Mobile spores (zoospores) originating from the oospores move to the tree and colonize pear bark tissues.
  
• The fungus may build up to high levels in the soil in a short period under favourable conditions - i.e. during wet, cool periods after harvest and in spring.



Management

• The best time or key time to manage Phytopthora diseases is during the initial stages of orchard establishment. viz., selecting the orchard site, planting, site preparation and rootstock selection. While there are some fungicides registered for controlling Phytopthora disease, management is best achieved through cultural methods.
• Cultural Control
• While planting a new orchard, select the site and rootstocks carefully. Be sure the orchard site has adequate drainage system throughout the year. When irrigating orchard, do not saturate the soil for prolonged period.Use rootstocks resistant to infection by the disease. Scion cultivars may also be chosen for resistance.
• Chemical Method
• Spray Bordeaux mixture (1%) or Copper oxychloride (0.03%) or Mancozeb (0.25%)