DETERIORATION OF LECITHIN-ADHERED ZINC PHOSPHIDE BAITS IN ALFALFA

A 2 . 00 (+/-0 . 36)% zinc phosphide (Zn3P2, CAS no. 1314-84-7) steam- rolled-oat (SRO) greats bait containing 1 . 04% lecithin vehicle was b roadcast in alfalfa (Medicago sativa). Samples of bait were collected immediately after broadcast, and 1, 7 and 14 days after exposure to ex istent agronomic and climatological conditions. Analyses of respective samples yielded 1 . 80 (+/-0 . 36)%, 1 . 18 (+/-0 . 04)%, 1 . 20 (+/- 0 . Il)%, and less than or equal to 0 . 26 (+/-0 . 05)% Zn3P2. A simil ar to 10% loss of Zn3P2 occurred immediately due to mechanical broadca st; similar to 33% loss was noted 1-7 days after exposure to pH 6 . 0 soil and 0 . 05 cm rainfall; and greater than or equal to 87% loss of Zn3P2 occurred by day 14 following an additional 0 . 96 cm rainfall. M echanical, precipitation and soil-acidity factors are viewed to reduce the concentration of Zn3P2-grain baits in crop situations. Lecithin-a dhered Zn3P2 baits showed a relatively rapid decline in concentration of active ingredient (A.I.) after broadcast and exposure to slight moi sture - a useful attribute of these baits in areas where hazards to no ntarget wildlife are of concern.