Effect of soil physical factors on methyl iodide and methyl bromide

Abstract

: Production and importation of methyl bromide is scheduled to be banned by 2001. Methyl iodide was evaluated as a possible replacement soil fumigant. The e †ects of soil moisture, temperature, soil texture and fumigation time on the efficacy of methyl iodide for the control of two common weeds, Abutilon theophrasti and L olium multiÑorum, were characterized and compared with those of methyl bromide. The optimal soil moisture for methyl iodide to kill both weed species in sandy soils was 14% water content (w/w). Greater efficacy was obtained when the temperature during fumigation was above 20¡C. Compared to methyl bromide, the efficacy of methyl iodide was more consistent in di †erent soils. Time to 100% mortality of weeds was 24 h for methyl iodide fumigation and 36 h for methyl bromide when 200 kM of fumigant was used. On a molar basis methyl iodide was consistently more e †ective than methyl bromide across the range of environmental factors tested. In terms of application technology and spectrum of activity, methyl bromide can be directly replaced by methyl iodide.1998 SCI ( Pestic. Sci., 53, 71È79 (1998)

Sources of iodine and iodine 129 in rivers

“…However, the small proportion left in soils may not reflect the proportion contributed to river water, since it may be in a soluble form and be preferentially leached, or may be returned seasonally and contribute a larger fraction of the total during the time of flood irrigation return flow. Methyl iodide has been proposed as an ozone‐safe alternative to methyl bromide, a soil fumigant often applied at the rate of a few tons/acre [ Ohr et al , 1996; Zhang et al , 1998]. However, to date, application of methyl iodide remains on an experimental scale.…”

Physical, chemical and environmental properties of selected chemical alternatives for the pre‐plant use of methyl bromide as soil fumigant

“…Under a range of soil moistures, temperatures, textures, and fumigation times, methyl iodide is consistently more effective than methyl bromide on a molar basis and its use as a direct replacement has been proposed 30. Independent trials conducted since 1998 by ARS have repeatedly found methyl iodide to be one of the most promising methyl bromide alternatives 31, 32.…”

Methyl Iodide

“…Such simulations can be used to obtain information on the effectiveness of application methods while ensuring that the soil fumigant distribution is not compromised and that efficacious dosages and biological control would be achieved. Zhang et al (1998) found that the optimal soil moisture for MeI to kill the weed species, Abutilon theophrasti and Lolium multiflorum, in sandy soils was 14% water content, and that greater efficacy was obtained when the temperature during fumigation was above 20°C. The same authors also noted that 100% mortality of weeds was achieved more rapidly with MeI (24 h), compared to MeBr (36 h).…”