WHITE ROOT DISEASE
Channel: MUHAMMAD HASNUL HAZIM MOHD FIAN
Date: 2023-01-26

White root disease is caused by a fungus named Rigidoporous lignosus.  It is white in colour. The rhizomorphs are firmly attached to the root, and it is threadlike rounded structures, but become flattened towards the end. After some time, the colour changes to reddish-brown. The fruit body is usually found growing at the base of a diseased-dead tree or decaying stump. The upper surface of the fruit body bracket is orange-yellow, while the underside is reddish or brownish in colour. This disease is very common in young rubber. It is the most dangerous because it spreads very fast.
 The symptoms occurred by fungus penetrating the roots and causing damage to the vascular bundle tissues and the first above-ground symptom is the general discoloration of the foliage. This is followed by leaf fall and dieback of branches and death of the tree. Immature trees show the disease symptoms in a few months, but mature trees could survive longer, and this depends to a great extent on the disease severity and the root system. When the roots of plants showing characteristic foliar symptoms are exposed, typical thick, ramifying white mycelial strands, known as rhizomorphs, are clearly seen on the affected roots.
 Prevention of these diseases can be implemented by removing all the root diseases source before clearing an old rubber area for replanting. Clearing methods such as uprooting and poisoning are able to reduce root disease incidence in replanting. Even if the trees are manually felled by cutting, the stumps must be poisoned, and the cut surfaces painted. Establishing and maintaining legume cover crops can also reduce root diseases as they cause roots and stumps to rot faster. During the transplanting of rubber, sulfur should be incorporated into the planting hole to promote the growth of fungi that are antagonistic to the root disease fungi. Painting of collar protectant chemicals to the collar region of the plant can also prevent root disease infection for two years. Open wounds on any part of the tree should not be left untreated. Suitable fungicidal wound dressing should be applied immediately to avoid root disease spores enter the tree through such wounds. An isolation trench is dug between the infected and healthy trees to prevent spread.
 Method of treatment can be applied by locating and identifying by foliage inspection of the infected tree at three-monthly intervals, beginning from six-month-old plants. Trees with unhealthy and deformed leaves should be suspected as root diseased. This is confirmed by collar inspection. The collar region of the infected plant is exposed by digging a cavity around the base of the plant; the depth of opening should be about 5 cm for a year old to about 20 cm for a four-year-old plant when a diseased tree is found, the neighbouring trees in the row must also be collar-inspected, although they may have been passed during foliage inspection. They may have been infected but have not shown symptoms on the leaves.
 All dead roots are removed including the dead portion of the tap root and the debris collected. Any soil found attached to the roots must be removed. When the root surfaces have dried, a suitable collar protectant is painted over the exposed tap root and 15 cm of the lateral roots. For white root disease, use Shell Collar Protectant. The treated tree is marked with the name of the disease and the date of treatment. The treated tree is reinspected after two years. Treatment of white root disease by chemical drenching plants can be practiced in their initial stages by drenching the collar region with fungicides such as Bayleton 25WP (10 g + 1-liter water). This method of treatment is only effective where the infection is at the initial stage, that is before the fungus penetrates the wood tissues of the root.