Argentine stem weevil effects on Nui and Ruanui ryegrasses grown with two levels of nitrogen/water nutrition

Abstract

Monoculture plots of 'Grasslands Ruanui' and 'Grasslands Nui' perennial ryegrasses were established with high and low nitrogen/water treatments. Twice-weekly examinations of tagged rye grass tillers showed Ruanui with high N/water (RH) to be more severely damaged by Argentine stem weevil larvae than Ruanui with low N/water (RL) or Nui with either treatment (NL and NH). More stem weevil larvae were found in Ruanui plots, and in plots with high N/water. Peak larval densities in RH plots were 1500 larvae/m 2 or one per 4.8 tillers. Although RH plots sustained higher rates of stem weevil damage, no similar cultivar x nutrition interaction was detected for larval density. Net growth rates for RH plots were reduced because of high rates of herbage and tiller death during January and February when stem weevil damage was greatest. High rates of tillering in RH plots during April were associated with a recovery of both tiller density and growth rate. It is suggested that studies concerning stem weevil susceptibility should allow for nutritional effects.

Oversowing of five grass species and white clover on a Taupo hill country pumice soil

“…White clover establishment was assessed visually in January 1984. Numbers oftagged grass plants suffering Argentine stem weevil damage to tillers (Hunt & Gaynor 1982) were recorded in December 1983, andin January andMarch 1984. To quantify the effects of sward treatment, point analysis of pasture composition (50 first hits per plot) was conducted on seven occasions from sowing to 6 months after sowing. The presence of A. lolii endophyte in tagged ryegrass plants was determined by the light microscope technique (Latch et al 1984) on tillers harvested in autumn 1985.…”

Nitrogen cycling through senescent leaves and litter in swards of Ruanui and Nui ryegrass with high and low nitrogen inputs

“…1) varied seasonally, fluctuating from low winter to peak summer values. Peak leaf death rates were associated with a period of Argentine stem weevil infestation (Listronotus bonariensis Kuschel) during summer 1978-79 (Hunt & Gaynor 1982). Stem weevil larvae caused premature death of many leaves and tillers, and even though growth was active, accumulation of green herbage in Ruanui-high nutrition plots (RH) was severely depressed.…”

“…Low nutrition plots were not irrigated and received 6-monthly maintenance N fertiliser dressing that included 250 kg/ha calcium ammonium nitrate (Hunt & Gaynor 1982). High nutrition treatments were designed to provide N in excess of anticipated growth requirements.…”

Planting depth effects on overdrilled seedling survival in summer

“…This was detected in root length measurements made on 2-month-old seedlings here, although the 20 mm difference is likely to be an overestimate of the difference in maximum root length at this time because the shoot base of ryegrass (where nodal roots are initiated) is located just below the soil surface (Yates & Jacques 1952), whereas hypocotyl extension in red clover raises the shoot base just above the surface in seedlings (Wellington 1970). Poorer survival of ryegrass relative to red clover may have reflected the difference in root morphology, but probably involved additional factors, such as Argentine stem weevil damage (Hunt & Gaynor 1982), which can be pronounced at this time of year.…”