DAMPING OFF (Rotting of young plants at soil level)
There are several fungi species causing damping off. These include Pythium, Rhizoctonia, Phytophthora and Sclerotium. This type of disease is common in seedlings and is a serious nursery problem. Older plants are rarely killed by this group of diseases, however their growth may be considerably retarded by root damage.
Symptoms: Seeds can rot before germination, shoots from freshly germinated seeds can rot before they emerge from the growing media, or young seedlings rot at the base after they have emerged and collapse. On older trees, root and stem lesions and root rots may occur.
Control: Hygiene and good drainage are very important, particularly in warm, humid situations, such as greenhouses. Provide good ventilation (don't plant seedlings too close together). If possible use sterilised seed raising and potting mixes when growing your own plants. Dust your seeds prior to sowing with thiram or zineb. Potting mixes using composted tree barks (eg. pine bark) instead of soil, significantly reduce the incidence of damping off. Benomyl drenches and sprays and copper oxychloride sprays give general control of these fungi, however some benomyl resistant strains of some of these fungi occur. Other fungicides can be more effective on particular fungi (eg. Fongarid on Phytophthora, Ridomil on Phytophthora, Ziram on Pythium).
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