Decline in Phytotoxicity of Benzyl Isothiocyanate Formulated as Granules

Abstract

Benzyl isothiocyanate (BITC) was formulated in dry granules with tung oil and calcareous loess to facilitate safe handling of the water-sensitive lachrymator. Crop and weed seeds were exposed to granular BITC at 40 mg ai/kg (w/w) substrate on moist sand for 2 days. When the pretreated seeds were washed with water and placed on BITC-free sand in a germination chamber for 15 days, germination in comparison to untreated seeds was 0 to 8% for pitted morningglory (Ipomoea lacunosa L. # IPOLA), sicklepod (Cassia obtusifolia L. # CASOB), milo [Sorghum bicolor (L.) Moench. ‘Funks G-522DR’], and red rice (Oryza sativa L. # ORYSA) seeds; 15 or 16% for velvetleaf (Abutilon theophrasti Medic. # ABUTH) and johnsongrass [Sorghum halepense (L.) Pers. # SORHA]; and 39% for barnyardgrass [Echinochloa crus-galli (L.) Beauv. # ECHCG]. Subjecting milo seeds to moist sand medium that contained BITC granules at 10, 20, and 40 mg ai/kg substrate reduced germination of milo by 78, 97, and 100%, respectively. However, BITC granules applied to the growth medium 2 to 4 days prior to sowing seeds had little effect on germination and growth of milo or sicklepod. Thus, BITC-treated soil soon became safe for newly sown seeds, but seeds present in soil when the toxin granules were applied failed to recover from exposure to BITC and deteriorated within 15 days.