Performance of fogged disinfectants to inactivate conidia of Penicillium digitatum within citrus degreening rooms

Abstract

Fogging with formaldehyde of citrus packinghouses when the fruit are absent is a practice to control conidia of Penicillium digitatum (Pers.) Sacc., the cause of citrus green mold. Replacements for formaldehyde in these facilities are needed because of worker and environmental health issues. To evaluate the effectiveness of candidate sanitizers, craft wood sticks with conidia of P. digitatum were attached throughout commercial citrus ethylene degreening rooms and either water alone or the sanitizers were applied. The rooms were 20±2°C and humidified to 85–90% relative humidity. Aldehydes, peroxygen compounds, sodium hypochlorite, chlorine dioxide, quaternary ammonium, alcohols, one phenolic compound, and one organic acid were applied with a compressed air assisted atomizer or fan atomizer in a volume of approximately 6L per 100m3 of room volume dispensed over a 3h period. Rates applied were expressed as active ingredient per m3 of room volume. All were compared to formaldehyde applied at 1.98gm−3 of room volume. After 24h, the craft wood sticks were retrieved, and germination of the conidia assessed. Five sanitizers reduced germination of conidia by more than 95% and equaled formaldehyde in effectiveness. They were (effective rates): (1) glutaraldehyde (0.1gm−3); (2) hydrogen peroxide (4.4gm−3); (3) Citrisol (1.0gm−3), a proprietary mineral oxychloride oxidizer; (4) acetic acid (5.3gm−3); and (5) peracetic acid (2.4gm−3). The toxicity of effective sanitizers was determined by exposure of P. digitatum conidia for 10min to concentrations of each and the proportion of survivors used to estimate EC50 and EC99 concentrations. The toxicity of the sanitizers in this assay did not predict their effectiveness when applied by fogging, probably because other factors, such as distribution, persistence, droplet size, or vapor pressure also influenced their effectiveness.