Persistence of residual herbicides in maize silage fields

Abstract

Annual ryegrass (Lolium perenne) is typically grown in the winter following maize (Zea mays) silage but alternative crops such as oats (Avena sativa) and triticale (x Triticosecale) are being investigated The persistence of residual herbicides used in maize silage crops was investigated in three field trials located in Waikato (55 organic carbon) Taranaki (84 OC) and Canterbury (37 OC) planted on 3 5 and 16 October 2008 respectively Herbicides investigated included atrazine and acetochlor applied preemergence and mesotrione and nicosulfuron applied 612 weeks after planting Broadleaf weeds in control plots were removed with the nonresidual herbicide bromoxynil Soil samples (10 cm depth) were collected about the time of silage harvest and herbicide residues determined by glasshouse bioassay using oats and mustard (Brassica nigra) Detection limits ranged from 00101 mg/kg for atrazine and acetochlor 0005002 mg/kg for mesotrione and 0002001 mg/kg for nicosulfuron Using oats no residues were detected at any of the sites but the mustard bioassay found about 0005 mg/kg nicosulfuron at the Taranaki site which was the last site treated post emergence and with the least rainfall (180 mm) between application and sampling (215 mm for Waikato; 350 mm for Canterbury)