Illinois State Florists' Association
Quite often it is desirable to reuse plastic pots, flats and other plastic containers. Clay pots and certain kinds of plastic can be steamed, but most plastic materials used in plant production become soft and distorted when steam ed or heated above 80°C (176°F). Chemical treatments can also be used to treat plastic and clay pots. Of the chemicals tested by Nichols and Joden (2), only formalin eliminated seven common plant pathogens from clay or plastic pots. Formaldehyde fumes from formalin are irritating to people and thus formalin is not popular. Although sodium trichlorophenate solutions might be effective and possibly suitable for use in treating plastic containers, all traces of the chemical must be removed by repeated washing to eliminate the possibility of residues that could damage plants. Soil can be freed of all plant pathogens by heating at 160°F for 30 minutes. This treatment time takes into ac count practical considerations such as heat penetration in to clods, plant residues, etc. The actual time to kill fungus structures such as sclerotia, spores and mycelia at 160°F can be a matter of seconds. For instance, sclerotia of Macrophomina phaseoli, a fungus that attacks crop plants under high temperatures and drought conditions, are killed by an exposure of 60 seconds at 60°C (140°F) (1). Spores and mycelia of the geranium rust fungus are killed by exposure in hot water at 122°F for 90 se conds (3). To determine if short exposures in hot water would kill two common soil inhabiting plant pathogenic fungi (Pythium ultimum and Rhizoctonia solani), dill seeds (Anethum graveolens) were sterilized and colonized with the two fungi. Ten such seeds were placed in small cot ton cheesecloth bags and immersed in hot water for 1, 2 and 3 minutes at 60°, 65°, 70°, 75°, and 80°C. Both fungi were killed in all hot water treatments, and neither was killed by a cold water dip.
Source: • Illinois State Florists' Association Bulletin # 354
Keywords: plant pathogenic fungi Pythium ultimum Rhizoctonia solani Sclerotia Mycelia