Issue
In crop fields in New Zealand, a control approach has been to sow a competing crop to restrict the development of A. millefolium (Kannangara and Field, 1985a). One of the species used is Pisum sativum, which limits the seedling and plant development by reducing the light availability to the soil, and suppressing seedling development by root competition. In New Zealand, Hordeum vulgare (barley) has also been used to control the growth of A. millefollium on crop lands. H. vulgare reduces the growth rate of A. millefolium by reducing seedling and rhizome production because of low irradiance at soil level (Bourdot et al., 1985). Farhad et al. (1999) also report that the addition of nitrogen fertilizer to fields reduces the density of some weeds, A. milleifolium included, due to strong competition by the crop species.