Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 1/8/2004
Publication Date: 9/1/2004
Citation: Ibekwe, A.M. 2004. Effects of fumigants on non-target organisms in soils. In: Sparks, D.L., editor. Advances in Agronomy. Vol. 83. San Diego, CA:Academic Press. p. 1-35.
Interpretive Summary: Application of fumigants to agricultural soils before planting of high value cash crops has been the mainstay for the control of nematodes, soil-borne pathogens, and weeds for many years. But under an international agreement to phase out ozone depleting chemicals, methyl bromide will be banned in 2005. Currently, only four registered fumigants are available in the Unites States: 1,3-dichloropropene, methyl isothiocyanate, chloropicrin, and methyl bromide. Methyl iodide is another fumigant yet to be registered that is considered being a promising alternative to methyl bromide for soil-borne pest control in high value cash crops. Since the international agreement, many studies have been reported on the environmental toxicology, chemistry, and air pollution potentials of alternative fumigants, but the effects of these fumigants on soil microbes has received very little attention. In this review, we examined the effects of approved fumigants on soil microbial diversity under different experimental conditions and methodologies. Methyl bromide strongly inhibited the growth of bacteria immediately after application, and its impact continues to decrease with time resulting in the emergence of new microbial communities from the treated soils. The fumigant with the least effect on soil bacteria has been shown to be 1,3-dichloropropene (Telone). The effects of metham sodium and chloropicrin were found to be intermediate. The results from this review has provided the basic information that Telone may be the best alternative to methyl bromide in terms of sustaining stable microbial populations for healthy agricultural soils, but no single registered fumigant is as effective as methyl bromide in controlling soil-borne pathogens.
Technical Abstract: Soil fumigants are extensively used to control plant-parasitic nematodes, weeds, fungi, and Insects for planting of high value cash crops. The ideal pesticide should be toxic only to the target organisms, however, fumigants are a class of pesticide with broad biocidal activity and effect many non-target soil organisms. Soil microorganisms play one of the most critical roles in sustaining the health of natural and agricultural soil systems. The ability of soil microorganisms to recover after treatment with pesticide is critical for the development of healthy soils. In the southwestern United States, fumigation is used to control pathogens such as Verticillium dahliae, Pythium, Rhizoctonia, or Cylindrocarpon spp. In addition to pathogen control, fumigation can also result in enhanced growth response of the plant by reducing weed pressure. The continued use of fumigants in agriculture will require more investigations of the different types of fumigants, soils, environmental conditions and biological/ microbial communities to establish both the effectiveness on target organisms and safety to the general public.