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.