Symptom Identification and Control Methods of Orchid Root Rot

This disease is also a devastating disease inorchids, and it can infectorchids at all stages of growth. There are many types it affects, mainly including: Cattleya, Oncidium, Paphiopedilum, Cypripedium, Dendrobium, Phalaenopsis, Vanda, and Cymbidium, among multiple genera oforchids. The pathogen of this disease is Rhizoctonia solani. Root rot is caused by the infection of seedling roots and rhizomes by the fungal hyphae and sclerotia (dormant bodies). If left uncontrolled, the rot can spread to the stem and lower leaves. During infection, a ring of brown rot forms around the plant, first causing seedling wilt and ultimately death. When mature plants are affected, they gradually weaken. Usually the rot is mostly confined to the roots, causing root damage, but sometimes the rot can also extend to the rhizome and enter part of the pseudobulb. Plants with root rot decline and may eventually die. Leaves and pseudobulbs turn yellow, shrink, become thin and weak, and distort. Orchids are most commonly affected when grown in used or water-saturated bark or other potting mixes, but newly repotted plants can also develop the disease even with proper drainage. For control, generally remove the roots and all rotted parts of diseased plants, and drench with Benlate at 1000 times dilution; if Pythium ultimum or Phytophthora cactorum is also present, use a mixture of azole and Toclofos-methyl compound prepared as a solution to drench the plants, also at 1000 times dilution. In addition, there is a type of severe rot caused by Pellicularia filamentosa (Thanatephorus cucumeris), a brown fungus that infects roots and the lower part of pseudobulbs. It can destroy seedlings in a very short time and can cause mature plants to wilt, turn yellow, and die "without visible cause." Infected plants should be soaked in a 1:2000 solution of sodium orthophenylphenate; every 10 L of water add 20 g of thiram, or every 10 L of water containing 25 g of 80% wettable powder zineb. The treatment must be repeated every 4 to 7 days. (Liu Zhongjian)