The tolerance of newly emerged broadleaved tree seedlings to the herbicides clopyralid, cycloxydim and metazachlor

Abstract

Summary In direct-seeded woodlands and nursery seed-beds, weeds can rapidly invade newly sown areas, leading to death or suppression of tree seedlings. Hand weeding is usually expensive, and the safe use of broad-spectrum contact herbicides is seldom possible. Hence in the work reported here, the tolerance of young tree seedlings to the potentially more selective, post-emergence herbicides clopyralid, cycloxydim and metazachlor, was tested. Seedlings of Fraxinus excelsior L. (ash) with two to four expanded true leaves (2 – 4 ETL), Fagus sylvatica L. (beech) (2 – 4 ETL), Acer pseudoplatanus L. (sycamore) (4 – 6 ETL), Prunus avium L. (cherry) (6 – 8 ETL) and Quercus robur L. (oak) (6 – 8 ETL) appeared to tolerate applications of cycloxydim at a rate of 0.45 kg a.i. ha − 1 . Applications of 0.2 kg a.i. ha − 1 clopyralid or 1.25 kg a.i. ha − 1 metazachlor also appeared to be generally tolerated, but did cause some suppression of annual growth increment in Q. robur , P. avium , F. sylvatica and A. pseudoplatanus , particularly where repeat applications were made to the earliest growth stages. Seedling survival was unaffected by any herbicide treatment. Mixtures of all three herbicides were no more damaging than the same herbicides applied separately. Therefore, depending on tree species and growth stage, it appears that clopyralid could potentially be safely used to control a range of herbaceous weed species, metazachlor a variety of seedling or germinating weeds and cycloxydim a range of established grass weed species, in direct sown woodlands or nursery seed-beds, although further research is advisable to confi rm crop safety.