Submitted to: Annual Horticulture Field Day Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 9/30/2003
Publication Date: 10/5/2003
Citation: Copes, W.E. 2003. Disinfectants - The Rate Matters. Proc 31th Annual Horticulture Field Day. 31:27. Interpretive Summary: The objective of this research was to define if one or multiple rates were required to effectively kill plant pathogens on the common materials from which production surfaces are made. Results demonstrate for the six disinfestants that dose should be selected based on the substrate being disinfested of B. cinerea conidia.As an example, lower and higher rates were required to disinfest galvanized metal and pressure treated wood surfaces, respectively, of plant pathogens. This information will help research scientists, extension agents, and wholesale and retail ornamental plant producers reduce pathogen survival and dispersal to healthy plants.
Technical Abstract: Lethal dose curves were calculated for six disinfestants (chlorazene hydrosol, hydrogen dioxide, hydrogen peroxide, iodine, quaternary ammonium chloride, sodium hypochlorite) when applied on seven substrates (galvanized metal, stainless steel, polyethylene ground fabric, polyethylene pot plastic, pressure-treated pine, exterior latex-painted pine, raw pine,) that had been inoculated with a water suspension of Botyrtis cinerea conidia. Mortality was determined by percentage of ungerminated versus germinated conidia that had been rubbed off of a substrate on to half-strength potato dextrose agar (hPDA) 16 to 24 hr previously. A significant difference in mortality was attributed to substrate with a mortality of 7 to 60% for raw pine to stainless steel, respectively. The effect due to substrate was subtracted to produce an adjusted mortality (Madj). A log10 transformed Madj was tested by probit analysis and back-transformed to calculate lethal doses. Based on overlapping confidence limits (95% C.L.) of the lethal doses resulting in 90 and 50% mortality (LD90 and LD50, respectively) and significance of slopes, differences occurred between substrates with all six disinfestants. LD90 values ranged from 0.21 to 4.54 g a.i. l-1 for chlorazene hydrosol, 4.99 to 40.3 g a.i. l-1 for hydrogen dioxide, 63.0 to 233.1 g a.i. l-1 for hydrogen peroxide, 0.42 to 2.45 g a.i. l-1 for iodine, 0.64 to 6.46 for g a.i. l-1 for quaternary ammonium chloride, and 0.87 to 6.84 g a.i. l-1 for sodium hypochlorite. For hydrogen dioxide and quaternary ammonium chloride (labeled for use in plant production systems) and sodium hypochlorite (approved Reregistration Eligibility Document (738-F-91-108)), a Binomial Lethal Dose Response (LDb) was calculated by inoculating substrate pieces with 5,000 B. cinerea conidia, spraying the substrates with doses of the disinfestants that ranged from near the LD50 value to greater than the LD99 value, plating the inverted substrates on hPDA, then recording the presence or absence of B. cinerea mycelial growth over 7 days. Lethal doses resulting in 100% mortality or absence of mycelial growth (LDb100) were equal to or greater than the LD90 values for most disinfestants and substrates. Results demonstrate for the six disinfestants that dose should be selected based on the substrate being disinfested of B. cinerea conidia.