White Root Disease of Mangoes

Disease Identification

• The white root rot disease is also referred to as dematophora root rot and is caused by Rosellinia necatrix or Dematophora necatrix. The fungus infects nearly 170 different plant species of deciduous fruit trees. Subtropical fruits like mango and avocado, and crops such as tea and coffee, are among the favored hosts. White root rot is considered a serious disease of avocadoes.

Symptoms

• Earliest symptoms of the disease include yellowing leaves, lack of new growth and shriveled fruit. Inspection of roots reveals decay and white, threadlike fungal growth called mycelia covering the smaller feeder roots. This mycelia gradually starts to grow upward through the soil and appears on soil surface around the tree. Lower trunk areas starts to decay. As mycelia matures, it turns gray to black. Trees are dead within one to three years of initial symptoms.

Favorable Conditions

• The causal agent of the white root rot is a soilborne fungus that can persist for extended periods in the soil. Planting trees in sites with known prior cases of the disease is a frequent cause of infection in new plants. It is therefore not recommended to plant trees in infected soil unless the soil has been disinfected by solarization first, suggests The University of California Extension in "Integrated Pest Management for Avocadoes."

Management

• There are no chemical control options to cure trees once an infection occurs. The best strategy is to minimize the spread of infection to other trees. Once infection is confirmed, remove the mango tree entirely from root and dispose. Also remove any other close-by mango trees that are likely to be infected with the soilborne fungus. Remove all pieces of roots from the areas. Create trenches around infected sites in order to break root grafts and prevent runoff water from the infected site from reaching healthy trees.