Derrick J. Wilson

Botanical survey of perennial ryegrass-based dairy pastures in three regions of New Zealand: implications for ryegrass persistence

A botanical survey of 24 commercial dairy pastures ranging in post-sowing age and perennial ryegrass type (mid-season diploid, late-season diploid, tetraploid) was undertaken in each of Waikato-Bay of Plenty (BoP), Taranaki and Canterbury during autumn/winter. The mean perennial ryegrass proportion (85% of total DM) and tiller density (3252 m−2) was greatest in Canterbury and the broadleaved weed proportion lowest (2%). Conversely, Waikato–BoP had the lowest ryegrass proportion (59%), tiller density (1817 m−2) and greatest proportion of broadleaved weeds (15%), with Taranaki intermediate. Tiller density was greater in pastures sown with diploid rather than tetraploids (averaging 3033 vs. 1784 m−2). Grass grub (Costelytra zealandica, 11 m−2) populations were lowest in the youngest age category pastures where nematode populations were highest (80 g−1 dry soil). The soil seedbank was dominated by unsown species (with total species emergence averaging 4594 seeds m−2), with negligible ryegrass emergence.

Verticillium dahliae and other pathogenic fungi in Cirsium arvense from New Zealand pastures: occurrence, pathogenicity and biological control potential

Abstract Cirsium arvense (Californian thistle) populations in pastures throughout New Zealand were surveyed in November–December 2005 (30 sites) and January–March 2006 (94 sites) to identify potential biological control agents for this weed. Fungi were isolated from healthy shoots and shoots showing leaf yellowing/browning, stunting or localized lesions. Verticillium dahliae was isolated most frequently, being detected at 30% of the sites in 2005 and at 51% in 2006. Other pathogenic/saprophytic fungi isolated included Sclerotinia sclerotiorum, Plectosphaerella cucumerina and species of Cylindrocarpon, Rhizoctonia and Phoma. Inoculating cut shoots of C. arvense with conidia of V. dahliae, or cutting shoots with a wetted blade previously used to cut infected shoots resulted in yellowing of leaves and shoot death. Spread of V. dahliae infection among plants facilitated by cutting when wet may explain the reported demise of C. arvense populations mown during rainfall and the fungus may have potential as a bioherbicide.

Testing a new low-labour method for detecting the presence of Phasmarhabditis spp. in slugs in New Zealand

Most studies on distribution of Phasmarhabditis spp. in slugs use dissection of individual slugs, which is time-consuming. Here we use a technique modified from that used to collect Pristionchus spp. nematodes from their beetle hosts. Slugs are decapitated and cadavers incubated for 1 week prior to examining for presence of adult nematodes. We compared the new technique with traditional dissection using field-collected untreated slugs, and slugs infected with Phasmarhabditis hermaphrodita in the laboratory. There was no difference in the efficacy of the two techniques. We also used the new technique to study prevalence of P. hermaphrodita at 22 New Zealand sites. We found P. hermaphrodita present at three sites and P. californica at two other sites suggesting Phasmarhabditis spp. are relatively common in New Zealand.

Implications of grass-clover interactions in dairy pastures for forage indexing systems. 4. Canterbury

ABSTRACT This paper describes how the core treatments in the national experimental design (all combinations of with/without clover and high/low nitrogen (N)) were implemented at an irrigated Canterbury site and monitored for three years. There was a consistent N × clover interaction, caused mainly by substantially lower yields in the Low N without clover treatment compared with all other treatments. At the phenotypic contrast level, the main effect of perennial ryegrass heading date on white clover content was significant in four of the nine seasonal data sets available: on these occasions, mixtures based on mid-season heading cultivars had higher clover content than later season-heading cultivars. However, this difference was not sufficient to cause any clover × cultivar interactions in herbage accumulation. Hence, the hypothesis that relative yield rankings of ryegrass cultivars do not differ when ryegrass is grown in monoculture or in mixture with white clover is supported.

Implications of grass–clover interactions in dairy pastures for forage value indexing systems. 5. Southland

ABSTRACT The implementation and monitoring of the treatments in the core experiment (eight perennial ryegrass cultivars grown under four combinations of plus/minus clover and high/low nitrogen (N)) at a dryland Waikato site is described. The N x clover interaction was significant in 10 of the 17 seasonal or total annual herbage accumulation (HA) data sets available, caused by substantially lower annual HA in the low N minus clover treatment compared with all other treatments. Five significant scaling-type clover × cultivar interactions in HA were evident. In all cases, HA was greater in plus clover than minus clover treatments, but more so for some cultivars than others. However, the interactions were not consistent across seasons, and different cultivars or phenotypic contrast groups were involved in many cases. The hypothesis that relative HA rankings of ryegrass cultivars do not differ when ryegrass is grown in monoculture versus mixtures with white clover is supported.

Implications of grass–clover interactions in dairy pastures for forage indexing systems. 3. Manawatu

ABSTRACT The implementation and monitoring of the treatments in the core experiment (eight perennial ryegrass cultivars grown under four combinations of plus/minus clover and high/low nitrogen (N)) at a dryland Manawatu site are described. Herbage accumulation (HA) was significantly greater for high N than for low N in 14 out of 21 annual and seasonal totals. There were no significant main effects of clover and there were no interactions between clover and N level. With the exception of autumn 2016, there were significant differences among ryegrass cultivars in all seasons, but no clover × cultivar or N × cultivar interactions for HA or nutritive value (NV). With the caveat that successive droughts reduced the proportion of white clover to low levels, the hypothesis that relative HA or NV rankings of ryegrass cultivars do not differ when ryegrass is grown in monoculture or in mixtures with white clover is supported.

Pasture renewal on Bay of Plenty and Waikato dairy farms: impacts on pasture performance post-establishment

To determine the impact of pasture renewal on dairy pasture performance, a total of 24 renewed and unrenewed pastures were monitored in Bay of Plenty and Waikato for 5 years. Renewed pastures produced an additional 1.5, 1.8 and 1.9 t dry matter (DM) ha−1 in the first, second and third years of monitoring, respectively, compared with unrenewed pastures. There was a greater contribution of clover, sown grasses and unsown grasses and a smaller contribution of broadleaf weeds in renewed than unrenewed pastures in some years (% of total DM). The sown grass DM content (kg DM ha−1), perennial ryegrass tiller densities and endophyte infection frequencies were similar in renewed and unrenewed pastures. The abundance of invertebrate pests and total nematodes was lower in renewed than unrenewed pastures in some years. The greater clover content, fewer weeds and fewer insect pests, contributed to the greater herbage production of renewed pastures.

Effects of including forage herbs in grass–legume mixtures on persistence of intensively managed pastures sampled across three age categories and five regions

ABSTRACT To test the hypothesis that the inclusion of the forage herbs chicory (Cichorium intybus L.) or plantain (Plantago lanceolata L.) or both in a grass–legume pasture mix improves persistence of sown vegetation and reduces weed and invertebrate pest ingress, a study was undertaken in 31–44 intensively managed pastures in each of five regions in New Zealand (Northland, Waikato, Bay of Plenty, Taranaki and Canterbury). The regions were stratified according to farm type (dairy or sheep and beef), pasture type (sown with grasses, legumes and herbs or grasses and legumes) and pasture age (young: 1–2 years old; medium: 3–4 years old; and old: 5+ years since sowing, n = 171). Sown species ground cover and emergence from the soil seed bank was greater, and unsown species ground cover and emergence lower, in sheep and beef pastures sown with herbs than without herbs (78% vs 68% ground cover, respectively, averaged over all pasture ages), but there was no difference between pasture types on dairy farms. Invertebrate predator and parasitoid abundance was 65% greater under pastures sown with herbs than without herbs. The number and % dry matter contribution of sown species decreased, and that of unsown species increased, as pastures aged. Unsown species comprised 90% (sheep and beef) and 98% (dairy) of total seedling emergence. The inclusion of forage herbs increased persistence of sown species and reduced weed ingress, but only on sheep and beef farms.

Dispersal of the Invasive Pasture Pest Heteronychus arator into Areas of Low Population Density: Effects of Sex and Season, and Implications for Pest Management

African black beetle, Heteronychus arator (Scarabaeidae), is an exotic pest of pastures in northern New Zealand. Both adults and larvae feed on pasture grasses. Adults disperse by walking (short range) or flying (long range). Dispersal flights are triggered by warm night temperatures in spring and autumn. Short range adult dispersal in search of mates, food or oviposition sites is poorly understood. This study investigated walking activity of H. arator adults over three seasons in New Zealand pastures. Adult walking activity was monitored using pitfall traps along fence lines and in pasture plots on a dairy farm in Waikato, New Zealand, in spring 2013, spring 2014, and autumn 2015. Beetle populations were reduced by application of a biopesticide bait to compare walking activity between treated and control plots for up to 26 days post-treatment. Marked beetles were released into the pasture plots to measure the distance traveled by recaptured individuals. Trap catches along the fence lines were correlated with air temperatures in 2013. Trap catches were male biased in spring 2014 compared with autumn 2015. Trap numbers in the control plots were nearly double that of treated plots in both seasons. More beetles were caught in the pitfall traps at the edges of the treated plots than in the center. Trap catches were consistent throughout the control plot in spring 2014, but in autumn 2015 more beetles were caught in the center of the control plot than at the edges. Few marked beetles were recaptured with dispersal rates estimated as <0.5 m per day. Warmer temperatures encouraged short range dispersal in H. arator. Males were more active than females during the spring mating season. Edge effects were strong and should be considered in the design of field experiments.