Root and stem rot English name: Durian root and stem rot Scientific name: Phytophthora palmivora Pest group: Fungi Order: Peronosporales Family: Pythiaceae Note: Durian root and stem rot is caused by the same fungus that also causes Durian fruit rot. They are discussed as two separate diseases as the symptoms and management practices are different. Signs and symptoms The disease attacks the root system. The Durian roots will rot and become brown in color. If rot is serious, the leaves which are at the tip of branches become yellow, stop their development and fall down. The leaves at the base of the branch fall down later than the leaves at the end of the branch. A clear symptom is the development of a juicy spot with water run off at the foot of the tree. When using a knife to cut this wound, water will gush out of it. The bark tissue and the core of the trunk change to be a dark brown color. If this symptom spreads around the entire foot of the tree, all leaves will fall down and eventually the tree will die. Under humid conditions with frequent rain, the fungus will spread to big branches where it will also cause juicy spots, change of tissue color and yellowing of leaves. Source and spread In soils which have poor drainage, root infecting and spreading to the foot of the tree is most common The disease will spread by the wind into leaves, branches and fruits and is most serious in rainy and humid conditions. Role of environmental factors humidity, rain, drainage Importance - plant compensation - physiological impact Natural enemies - antagonists Trichoderma harzianum can be applied to the soil surface to antagonize soil borne diseases. Management and control practices Prevention activities Make sure that trees are strong and healthy so they are better capable to fight and tolerate diseases. Apply fertilizer and lime to nourish the soil, to adjust pH and to optimize nutrition of the trees. Preferably apply organic manure or use green manure as this will improve soil quality and development of beneficial micro-organisms. Treat the soil surface with Trichoderma harzianum. This fungus, which is commercially available, antagonizes soil borne diseases. The disease prefers humid conditions. Pruning of branches will allow more air movement within the orchard, which will lower the humidity. Improve the drainage in the orchard to avoid flooding or too wet conditions of the soil. In a well drained soil the disease will cause less problems. Once an infection is present in the field Pruning of infested branches and fruits and destroy them as they form a source of infestation. Remove rotted fruits that fall on the ground and destroy (burn) them. They are a source of infestation. When pruning big branches or rotted parts of the trees, treat the wound with paint or a fungicide (metalaxyl) to protect it against the disease. If the disease is spreading, spray fungicide on infested tree trunks, branches and fruits. Fungicides containing metalaxyl (WHO class III) or mancozeb (WHO class III) can be used....verify effect on natural enemies Some farmers have been pouring fungicides (metalaxyl) into the soil to prevent root rot disease. This should not be done. It has only little effect in small trees and no effect at all in bigger trees, but it has a very negative impact on the quality of the soil. After harvesting, soak durian in Fosetyl Al, will decrease postharvest rotting. Using metalaxyl at the tree bole (tree foot) which was grated the bark to prevent the foot rot disease, it have a good effect.
Posted on: Thu, 25 Dec 2014 14:21:02 +0000
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