The Use Of Chlorine Dioxide Gas To Control Diseases On Ornamental Bulb Crops

This is a quotation taken from page 6 of the paper titled "Update On New Fungicides And The Use Of Chlorine Dioxide Gas To Control Diseases On Ornamental Bulb Crops", by Dr. Gary Chastagner, Plant Pathologist at Washington State University: www.biocidasargentina.com/pdf/FungicidasAndClO2BulbCrops.pdf

Background Information Relating to Chlorine Dioxide

Inoculum of a number of ornamental bulb crop pathogens can be carried on the surface of bulbs, contributing to the spread and buildup of diseases during storage and production. Management of these diseases is generally based on a combination of cultural practices, environmental manipulations, and the application of fungicides. Recently there has been an increased interest in using general biocides or disinfectants for the control of diseases in ornamental production systems. This is particularly true where recirculating water systems are used. Most fungicides only inhibit spore germination or growth of fungi, whereas disinfectants can kill cells upon contact and thus are well suited for reducing inoculum levels and the carryover of disease organisms from one crop or one source to the next.

There are several types of disinfectants being used to kill inoculum of various pathogens in the food processing industry and various agricultural production systems. Chlorine dioxide (ClO2) is being used increasingly as a replacement for chlorine to kill microorganisms in drinking water and various meat and fruit/vegetable processing facilities. It is also used as a general water disinfectant in many industrial applications. Chlorine dioxide is replacing use of hypochlorites because it is less affected by pH, less reactive to organic and inorganic materials (e.g. ammonium, chloramines, bromines, etc.), removes phenolic tastes and odors, and produces fewer to no toxic or carcinogenic by-products (e.g. trihalomethanes and haloorganics). In addition, ClO2 has a higher biocidal activity on a ppm basis than sodium hypochlorite, iodine, quaternary ammonium compounds, glutaraldehyde, and phenol. 

Working with several postharvest pathogens of tree fruits, Roberts and Reymond (1994) showed that spores of Cryptosporiopsis perennans were killed when exposed to 1 µg ClO2/ml for 30 seconds.  Spores of Mucor piriformis were killed after a 4 minute exposure at 1 µg ClO2/ml or 30 second exposure at 3 µg ClO2/ml and spores of Penicillium expansum are killed after a 2 minute exposure at 3 µg ClO2/ml or a 30 second exposure at 5 µg ClO2/ml.  Spores of Botrytis cinerea were killed after a 2 minute exposure at 5 µg ClO2/ml. These researchers concluded that a concentration of about 3 to 5 µg ClO2/ml chlorine dioxide in the dump tank water should provide an effective control of spores and thus reduce the potential for various postharvest diseases.

Mebalds et al. (1996) reported that ClO2 was highly effective against a range of plant pathogens, including Fusarium oxysporum, Alternaria zinniae, Colletotrichum capsici, and Phytophthora cinnamomi. They found that an exposure of 8 minutes at 3 µg ClO2/ml was required to control waterborne fungal pathogens. In addition they showed that higher concentrations were required when impurities were present in the water.