Caused by the same fungus Phytophthora palmivora, the disease is known by various names depending on the plant organ that is affected.This is the most feared disease which affects different parts of durian in all stages of development. It is responsible for the death of many durian trees in the orchards located in several countries.
Root rot affects the root which results to the weakening of the tree and, ultimately, death.
Patch canker or stem canker starts with a gum-like substance that exudes from lesion on the bark of the stem. This lesion enlarges and when it is able to surround the entire trunk, the branches start to die back. Eventually, the tree defoliates and die. This disease commonly infects mature trees during the wet season. Infection starts from wounds, cracks, or entry holes of shot-hole borers on the stem.
Fruit rot infects both immature and mature fruits. Damage symptoms are characterized by watery patches on the rind of the fruit which later become dry and change in color to dark brown and black. Whitish, cottony mycelia and sporangia are found on the lesions. Affected fruits that are immature drop.
Foliar blight or leaf blight commonly affects durian plants in the nursery. The disease is characterized by water-soaked spots on the leaves which turn black and develop into large necrotic areas. Infected leaves are blighted, drop prematurely, and the seedling begins to die back.
Common insect pests attacking durian are the fruit borers (Tonica lagaropis and Conogethes punctiferalis), shot-hole borer, and psyllids.
Although it is only the fruit borer that has a significant contribution in directly reducing durian yield, the other insect pests can play an indirect role in increasing the incidence of Phytophthora infection either by creating entryways for the fungal pathogen or by decreasing the resistance of the trees against the disease.
External symptoms of fruit borer infestation are visible on the durian fruit. These include brownish feces and holes on the rind of the fruits. The holes are made by the caterpillars which bore into the fruit. The caterpillars are hatched from eggs laid on the rind by the female moth.
Other host plants of the durian fruit borer are cacao, chico, citrus, jackfruit, papaya, rambutan, and eggplant.
The shot-hole borer (Xyleborus sp.) is a tiny black or brown beetle which bore holes in the bark and feed on the cambium layer. It is of particular significance to the subject of disease control in durian because it is associated with Phytophthora. Control management strategies include maintenance of the vigor of durian trees and scraping of infested portion followed by the application of insecticides.
The psyllids (Allocarsidara incognita)
lay eggs on the unopened leaves. The nymphs have body coverings that
appear cottony white. They suck the young leaves causing yellowish spots
and, if not controlled, severe infestation may cause dying of the tree.
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