DURIAN (Durio zibethinus) subject to various pests and diseases throughout the year. Attacked of pests and diseases on durian tree started from seedling stage to harvesting stage that cause serious damage if not properly controlled. Durian diseases divided to Seedling and root diseases,Trunk and branch diseases, Foliar diseases and Fruit diseases. This article I would like to share my knowledge about the durian diseases based on various study in Malaysia, Thailand, Indonesia and other growing durian countries. Few technical durian book from various researcher and extension bulletin are use as references in this article.
2) TRUNK AND BRANCH DISEASES
2.1 DURIAN PATCH CANKER
Patch Canker of durian or known as Stem Canker together with root rot and dieback are serius disease of durian. The main cause of this disease are Phythopthora palmivora. The first sypmtom of this disease is the appearance of of wet lession on the trunk surface usually near the crotch region. Bark necrosis is accompanied by discoloration of the bark and exudation of a reddish brown resinuos substances. The infection sometimes deep into the wood and when we knocked with hard object it sounds hollow. As the lesion expands, I always saw the tree exhibits the sign of stress with the foliage wilt and began to dry up followed by branch dieback. The entire tree may defoliate and die where the entire bark become riddled with pin-holed made by pin-bole boring beetle (Platipus capulatus). The root underground infected with necrosis and decayed. This disease are the mos serious disease of durian tree and must use a multi-pronged approach to control. The combination of various chemical, environmental and biological measure should apply.
Environmental Control. This disease are easily appear under moist conditions. Wider planting distance, removal of thick weed undergrowth, pruning of low branch are practical. This will improve the air circulation and humidity level. The young tree should trained to pruning minimum 2 meter from the ground. Adequate agronomic practices such as fertilising, irrigation and spraying of chemical especially during drought season are advisable. The long dry spell reported to hasten the death of the durian tree. Death tree should be uprooted, removed and burned. The vacant hole should be drenched with appropriate fungicide and treated with sulphur to get rid of unwanted antagonistic soil microflora.
Chemical Control. This method by scraped away the infected durian bark and painted with fungicide. Fungicide such as copper fungicide, captafol, fentin acetate, maneb, etridiazole and mancozeb are suitable. This will followed by other fungicide such as metalaxyl, fosetyl aluminium, milfuram or cyprofuram. Another chemical approach is by drenching to the soil periodically around the infected and adjacent tree. The painting infected trunk and soil drencing are the best combination technique to control patch canker. Injecting the infested tree at the trunk with metalayxl, fosetyl aluminium and phosphorus acid are reported to be practical from the studies. Possible vectors that able to spread this disease such as snails and insects can be controlled with chemicals.
Biological Control. The use of antagonistic soil fungi are potential means to control this disease. The sporangia of and chlamydospores of P. palmivora can be aggressively parasitised and killed by an antagonistic soil fungus.
Resistant Cultivars. This is the best method of growing resistant durian varieties to durian patch canker. Select the certified seedling durian variety with less attack of this disease from the recommendation of various experts. .
2.2 PINK DISEASE
The Pink Disease caused by basidiomyceae fungus known as Corticum salmonicolor. The disease attacks the twigs and smaller branches of durian trees causing wilting and dieback. Four years and above old durian tree are subject to this attack due to bushy canopies. Those area with heavy rainfall especially on inland area are recorded high occurrence of this disease such as at Peninsular Malaysia, Sabah, Sarawak and Southern Thailand. The silky white mycelia threads appear on the bark of small branches or twigs. This mycelial threads later change appearance to pink color as the bark dies. The infected wood turns dark brown and their leaves yellow foliage in which it drops. The branch dies and finally the disease results wilting and death of foliage on the infected twig or branch. The whole tree is not killed.
The diagnose stage of the infection determine the success of control measure. As canker disease, I advise that tho control measure should combine with all effort from environmental, chemical and agronomic practices. Wider planting distance for durian tree are able to provide more air-ventilation thar reduce the incidence of pink disease. Remove and burn the infected pink disease twig or branch. The use of chemical such as Copper oxide, Copper oxychloride, copper hydroxide, triadimefen, tridemorph (calixin), oxycarboxin and other systemic fungicide are practical.
2.3 VELVET FELT FUNGUS INFESTATION
This disease caused by a type of basidiomycete fungus known as Septobacidium spp. As the records, this disease found only at Malaysia and Southern Thailand. It commonly found encircling portions of twigs and small branch of durian and other fruit tree. Infestation increase during rainy periods. As I observed, we may misidentified with pink disease symptom, this velvet fungus are not pathogenic to durian. It does not injured but detracts from the tree's normal appearance. The spongy, felt-like, violet or violet-grey fungus appearance are visible on twigs and small branch. The encrustation can easily removed as the fungus stroma do not penetrate in the bark of durian. Although this disease does not harm the tree, the appearance cause unsightly effect. The control of scale insect with malathion or white oil may reduce the infestation.
2.4 LICHEN INFESTATION
Lichen usually occur on the surfaces of the leaves as I usually examine. It may appear on the twigs and branch or durian bark of the durian trunk. This lichen are not parasitic to the tree but the appearance on the leaves reduces the photosynthesis activity such as transpiration and respiration. To eradicate the lichens we spray chemical such as copper or oil base to the infected parts. The effective method is by spraying during the lichen are dry.
2.5 MASS INFESTATION
The moss normally found on the bark of the durian trunk. It will form a large green velvety cushion on the bark if not controlled. Mosses also found on the leaves as I observed. They tend to proliferate on the upper side of sloping branches that face the prevailing winds and received the great amount of rain and run-off. The old durian tree with less foliage are more often of appearance. This moss does not injure the tree but rather manufacture their own food by photosynthesis. The removal of infected parts and spraying of sodium chloride able to control the moss. The use of salt water also a significant techniques.
Those five disease of fungus attack durian are the most common problem in durian establishment. More than 110,000 hectare durian tree was grown in Malaysia. Durian is a very sensitive tree that was susceptible from the attack of pest and disease if not properly maintained. The basic agronomic practices such as pruning, fertilizing weed control, irrigation (in certain area) and other agronomic practices must according to durian package technology. Sayonara!
(1 January 2013)