Crop bromide concentrations following methyl bromide fumigation for pale cyst nematode in southeastern Idaho

Abstract

Methyl bromide (MeBr) is a sterilizing fumigant used to control quarantine pests that is restricted due to its detrimental atmospheric effects. The degradation of injected MeBr produces crop-available Br⁻. Up to five applications of MeBr were used in southeastern Idaho fields to combat the pale cyst nematode (Globodera pallida). Data regarding the uptake and partitioning of Br⁻ in crops following MeBr application in the region were unavailable. Research determined background concentrations of Br⁻ in alfalfa (Medicago sativa L.), barley (Hordeum vulgare L.), corn (Zea mays L.), potato (Solanum tuberosum L.), and wheat (Triticum aestivum L.) compared to MeBr-treated fields. Background Br⁻ concentrations ranged from nondetectable (ND) to 33.0 mg Br⁻ kg⁻¹; vegetative tissue concentrations were greater than reproductive, except corn where there was no difference. Nearly all crops grown in MeBr-treated fields had greater Br⁻ concentrations than background. Background-baled-alfalfa tissue Br⁻ concentration was 33.0 mg kg⁻¹ compared to 117.8 mg Br⁻ kg⁻¹ from a MeBr-treated field. Br⁻ concentration in green alfalfa decreased from 79.8 to 36.5 mg Br⁻ kg⁻¹ at the final cutting in a MeBr-treated field, where time after application decreased crop Br⁻ concentrations. Small grains had low Br⁻ concentrations in reproductive tissue (1.7 mg Br⁻ kg⁻¹) compared to vegetative tissue (106.5 mg Br⁻ kg⁻¹). Corn stover concentration (12.7 mg Br⁻ kg⁻¹) was low relative to small-grain straw, but corn ear (5.8 mg Br⁻ kg⁻¹) was greater than small-grain reproductive tissue in the MeBr-treated field. Crop selection following MeBr applications should consider the likelihood of elevated Br⁻ concentration for the plant fractions intended end use.