Strychnine Uptake by Cereals and Legumes Grown in the Glasshouse and Field

Strychnine‐coated wheat grain was used as bait in broad‐acre agriculture in Australia to control severe mouse damage during 1993 to 1995. To establish whether plants could take up strychnine, glasshouse experiments were conducted on wheat ( Triticum aestivum L.), barley ( Hordeum vulgare L), lupine ( Lupinus angustifolius L.), pea ( Pisum sativum L.) and faba‐bean ( Vicia faba L.). Strychnine uptake was also determined by growing plants from germinated baits. In the glasshouse experiments strychnine was detected in lupine grain (<80–2500 µg kg −1 ) and in straw from wheat, barley, pea, faba‐bean, and lupine (<40–390 µg kg −1 ) when these plants were grown adjacent to 1 or 3 baits, equivalent to 36 to 107 times the recommended field rate, respectively. Strychnine was also detected in straw from the germinated baits (<40–2233 µg kg −1 ). Field experiments were then conducted to study strychnine uptake by wheat, barley, lupine, chickpea ( Cicer arietinum L), pea, and canola ( Brassica napus var. napus ) under more realistic conditions. In the field strychnine was detected in only 3 samples of pea straw (10, 24, and 58 µg kg −1 ) where the bait was applied after flowering at eight times the recommended rate. This is probably due to bait lodging in the pea straw rather than from plant uptake of strychnine. The study has shown potential plant uptake of strychnine, but at the recommended rate of application under field conditions (3 baits m −2 ) it is unlikely that strychnine concentrations in the crops studied will exceed the detection limits (10–50 µg kg −1 ). Nevertheless, the existing programs monitoring strychnine levels in crops treated with baits should be maintained.