Effectiveness of spraying herbicides in the centre compared to all over rosettes of Cirsium vulgare and Jacobaea vulgaris

摘要

Spot-spraying of weeds in pasture can often result in considerable damage to pasture plants adjacent to the sprayed weed. A glasshouse experiment was conducted to determine whether herbicides are just as effective if applied only to the centre of a weed rosette compared with over the complete plant for Cirsium vulgare and Jacobaea vulgaris. Two herbicides commonly used for spot spraying pasture weeds in New Zealand were used, i.e. metsulfuron and a triclopyr/picloram mixture. Herbicides were appliedeither to the centre of rosettes (about 5% of leaf area) or the whole rosette using a hand-held sprayer. A range of rates, each applied at 5 mL per plant either in the centre or over the complete rosette, and an untreated control was used for each herbicide to obtain dose-response curves. There was generally no significant difference between applying either metsulfuron or the triclopyr/ picloram mixture to the centre rather than all over C. vulgare or J. vulgaris rosettes. Thus, if farmers ensure they still apply the correct amount of active ingredient, applying it all to the centre of the weed should give the same level of control and presumably greatly reduce the area of pasture damaged around each weed.