Effect of native weevils (Coleoptera: Curculionidae) on white clover establishment and yield in tussock grassland

Seed coating with insecticide to improve oversown white clover(Trifolium repensL.) establishment in tussock grassland

“…The densities of these weevils in the vicinity of the trial measured in October, November, and December 1987 were 31, 24, and 23 per m 2 respectively. This is very similar to the density of 26.3 per m 2 found in the previous season at this site, but is high in comparison with the mean of 10.9 per m 2 for 20 sites sampled in the area (Barratt et al 1992). This may have contributed to the low seedling densities and yields of white clover at this site.…”

“…This was close to the average density of 13.5 + 2.2 for the 12 sites for the years 1983-86, so expected damage from broadnosed weevils in this trial would be similar to that reported by Barratt et al (1992).…”

“…The data indicate that there were considerable seedling losses during the summer and early autumn, which may have reduced the magnitude of the differences evident between treatments earlier in the season. The yields were, however, very low compared with 5-year averages recorded in this locality which in similar trials for 1982-3 to 1986-7 were 100 kg/ha at the end of the first season's growth (Barratt et al 1992), compared with the equivalent of 1.1 kg/ha in this trial. Although data on rainfall are unavailable for the site, the 1987-88 season was extremely low throughout eastern New Zealand.…”

“…In field trials, insecticides tended to have their greatest effect in the first 6 weeks after sowing as expected, but previous work has shown that damage during the cotyledon stage can have longer-term effects (Barratt et al 1992), the benefits of which were demonstrated particularly well in these trials in the commercial furathiocarb seed coat evaluation. While insecticide seed treatment can increase seedling establishment and dry matter production, the economics of seed treatment need to be assessed in relation to potential gain.…”

“…Received 10 February 1995; accepted 13 July 1995 establishment and production of white clover {Trifolium repens L.) oversown in tussock grassland (Barratt et al 1992). Weevils damage and destroy cotyledon stage white clover seedlings, causing direct seedling mortality, reduced nodulation success, and reduced yields of surviving plants (Barratt 1982(Barratt , 1985.…”