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BACKGROUND: Fertiliser applications are well‐established tools in pasture‐based agricultural landscapes. This study focuses on the impact of phosphorus (P) fertiliser on grass grub (Costelytra giveni), a major pasture pest. This research investigates the interplay between P, plant growth, and grass grub fitness in Epichloë endophyte‐infected perennial ryegrass (Epichloë sp. LpTG‐3 strain AR37) and meadow fescue infected with E. uncinata (strain MaxR; AR1017), alongside their endophyte‐free counterparts. In a glasshouse trial, plants were grown in P‐enriched soil with varying Olsen P levels (9, 18, 28 or 78 mg L−1), and grass grubs were introduced. Their survival and weight gain, and plant performance were measured. In a bioassay, grass grubs were placed in specimen vials with P‐enriched soils (Olsen P levels 9, 18, 28 and 78 mg L−1) and provided with identical plant material to assess their diet consumption and weight gain. RESULTS: In the glasshouse trial, results highlighted a notable decrease in the survival of grass grub on plants infected with MaxR endophyte, but not with AR37, as well as increasing soil Olsen P levels in both plant species. While grass grub decreased plant performance at the low Olsen P level (9 mg L−1), this effect diminished with increasing P. Likewise, results from the bioassay showed a decrease in diet consumption with increasing soil Olsen P levels. In both trials increasing Olsen P levels correlated with diminished grass grub performance, revealing a nuanced relationship between soil fertility and pest dynamics. CONCLUSION: The study underscores the pivotal role of selected Epichloë endophyte–grass associations in mitigating grass grub damage across varying phosphorus levels. This study highlights the potential to integrate P applications for sustainable pest control against grass grub. Further field trials are required to validate these findings. © 2024 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Both adults and larvae of Listronotus bonariensis damage ryegrass (Lolium spp.), a dominant component of New Zealand pasture. Damage can be reduced by Epichloë festucae var. lolii, a biotrophic fungal symbiont of ryegrass, through the production of alkaloids with deterrent and/or toxic effects to insect herbivores including L. bonariensis. Here we report results from two pot trials and a field trial comparing endophyte strains with different alkaloid profiles that have been introduced to reduce or eliminate adverse effects on stock. Adult L. bonariensis feeding scars, number of eggs and the proportion of tillers with larval damage and the severity of that damage were recorded. Samples of pseudostem and leaf blades were analysed for alkaloids. AR1 endophyte reduced adult feeding, oviposition, and larval damage whereas AR37 had no effect on adults but was highly effective in reducing larval damage. Reduction in adult feeding and oviposition by different NEA strains was governed by concentrations of peramine and ergovaline. For plants infected with AR37, alkaloid concentrations that determined the extent of larval damage were influenced by host species and ploidy; tetraploid L. perenne was more severely damaged than its diploid equivalent; L. multiflorum cultivars were more susceptible than the L. hybridum and L. perenne cultivars. [ABSTRACT FROM AUTHOR]

New Zealand's economically vital exotic pastures are unique in their low complexity making them highly susceptible to invasive pest species such as the Argentine stem weevil Listronotus bonariensis. This field-based contribution further examined the ecology of the adult weevil and its parasitoid control agent Microctonus hyperodae. This included factors that affect field sampling accuracy, interpretation of population density and parasitism estimates. Compared to adult population estimates measured via turf flotation, suction sampling (G-vac) showed c.30% under-estimation of population densities while parasitism rates were over-estimated by c.26%. The bionomic implications of the sampling biases are discussed as they relate to the recently observed sharp declines in L. bonariensis parasitism. The weevil's field parasitism rates showed no relationship to population density again confirming the parasitoid's very high host searching efficiency. This study also coincided with meteorological conditions (>30°C) that resulted in a very large L. bonariensis 'swarming' event. The mass emigration from the experimental plots left only a low residual population of parasitised weevils that typically do not fly. Therefore, measured L. bonariensis populations and their M. hyperodae parasitism levels cannot always be presumed to be solely the result of population dynamics in situ. [ABSTRACT FROM AUTHOR]

Cerodontha australis Malloch (wheat sheath miner) is a leaf mining fly native to New Zealand and eastern Australia that feeds on grasses and cereals. It is thought to have limited economic impact despite being one of the most widespread and common insects in New Zealand pastures. In this study, data on C. australis were gathered over an 18‐month period from field plots of endophyte‐free Lolium perenne. Observations from pot trials on parasitism and other leaf miner species are also presented. Larval numbers were highest in late spring to early summer. One distinct peak per year of eggs and pupae indicated that this species may not be multivoltine, contradicting previous literature. Damage levels were high in spring/summer, with leaf mining in up to 53% of tillers sampled and, in mid‐summer, extending into the pseudostem in up to 41% of sampled tillers. Measurement of cephaloskeleton lengths confirmed that this species has three larval instars. Generally, only one larva per tiller survives to pupation, indicating density dependent regulation of populations, and larval/ pupal parasitism can reach high levels in summer. This study provides new information on the seasonal biology of C. australis, and its potential impact on L. perenne pastures in Waikato, New Zealand. [ABSTRACT FROM AUTHOR]

The wheat sheath miner, Cerodontha australis Malloch (Diptera: Agromyzidae), is a small leaf‐ and stem‐mining fly that is native to New Zealand and eastern Australia where it feeds on grasses and cereals. Although not considered to be a major insect pest of pastures in New Zealand, it can be abundant during spring and summer in Waikato, New Zealand, and infests tillers of the introduced pasture plant, perennial ryegrass, Lolium perenne L. (Poaceae). Cerodontha australis is not deterred from feeding on L. perenne infected with commercially available strains of the fungal endophyte Epichloë festucae var. lolii, which have been shown to provide protection from a range of other insect pests. In this study, three‐pot trials and periodic examination over 18 months of field‐collected L. perenne tillers showed that two Epichloë endophyte strains, AR47 and AR48, reduced the survival and feeding damage by C. australis larvae, but there was no evidence of an effect on adult female feeding or oviposition. Compared to other strains of E. festucae var. lolii endophytes tested, plants infected with AR47 and AR48 had fewer and smaller larvae and less larval mining. The number of tillers with mining was reduced in AR47 relative to endophyte‐free (Nil) by 57.1% (ranging from 25.0 to 92.5% across trials) and in AR48 by 67.1% (26.3–100%). Larvae in AR47 and AR48 were found further from the base of the tiller where they were less likely to damage the meristem and cause tiller death. The number of larvae and pupae in pseudostems was reduced in AR47 and AR48 compared with Nil by 78.4 and 82.0%, respectively, in the field trial. Very few larvae survived to pupation in AR47 and AR48 plants, with a reduction compared to Nil of over 81.5% in AR47 and over 97% in AR48 in each of the four trials presented here. [ABSTRACT FROM AUTHOR]

Grasses have developed a wide range of morphological and physiological mechanisms to resist herbivory. For instance, they accumulate silicon (Si) in tissue, as physical defence, and associate symbiotically with foliar Epichloë‐endophytes that provide chemical defence via antiherbivore alkaloids. Recent evidence showed that some Epichloë‐endophytes increase foliar Si in forage grasses; however, whether this impacts insect herbivores is unknown. Furthermore, while Si is primarily a physical defence, it also affects production of plant defensive secondary metabolites; Si supply might therefore affect Epichloë‐alkaloids, although this remains untested.We grew endophyte‐free (Nil) and Epichloë‐infected tall fescue and perennial ryegrass in a factorial combination with or without Si supplementation, in the absence or presence of Helicoverpa armigera. Epichloë‐endophyte strains were AR584 for tall fescue, and AR37, AR1 or Wild‐type (WT) for perennial ryegrass. We assessed how Si supply and Epichloë‐endophytes in interaction with herbivory affected foliar Si and mutualist‐derived alkaloid concentrations. Subsequently, their effects on H. armigera relative growth rates (RGRs) were evaluated.Endophytes generally increased Si concentrations in Si‐supplied plants. In tall fescue AR584 and perennial ryegrass AR37, endophytes increased constitutive (herbivore‐free) and induced (herbivore‐inoculated) Si concentrations by at least 25%; in contrast, in perennial ryegrass, the AR1 endophyte only increased constitutive levels. Si supply did not affect alkaloids produced by AR584 or AR1/WT endophytes; however, in the presence of herbivory, Si supply decreased the induction of alkaloids produced by AR37 endophytes by 33%. For tall fescue, Si supply reduced H. armigera RGR by at least 76%, regardless of endophytic status, whereas, endophyte‐alkaloids played a secondary role only reducing herbivore growth in the absence of Si supply. Conversely, in perennial ryegrass, both Si and endophyte‐alkaloids (regardless of Si supply) reduced herbivore RGR although not synergised.Novel interactions between constitutive and induced Si‐ and alkaloid‐based antiherbivore defences in grasses were observed. Overall, Si had a greater effect on the folivore than endophytes in both grasses. Endophyte defences contributed more to herbivore resistance in perennial ryegrass than tall fescue. We demonstrate that Si and endophytes were not antagonistic and highlight that the protective nature of their interaction varies with the grass‐endophyte species tested. A free Plain Language Summary can be found within the Supporting Information of this article. [ABSTRACT FROM AUTHOR]

The invertebrate pests most commonly affecting New Zealand's pastoral-based production in 'average' years cause losses of between $1.7B and $2.3B p.a. of which up to $0.9B occur on sheep and beef farms and $1.4B on dairy farms. The native scarab grass grub is the most costly pest causing losses of $140-380 M on dairy farms and $75-205 M on sheep and beef farms annually. The exotic scarab, black beetle, although only affecting approximately 1 M ha, costs dairy farmers up to $223 M and sheep and beef farmers up to $19 M annually. Porina cause losses up to $84 M and $88 M respectively. Pasture nematodes are estimated to cost up to $274 M p.a. for dairy farmers and $326 M p.a. for sheep and beef farmers. Two exotic pests, Argentine stem weevil (ASW) and clover root weevil (CRW) are causing damage estimated at up to $200 M p.a. and $235 M p.a. respectively in dairy and sheep and beef pastures. While CRW is subject to successful biological control management it still causes considerable losses. Lesser pests also contribute to lost production, particularly as they often coexist with more major pests. However, their economic cost to New Zealand is difficult to calculate due to the variable nature of infestations on both temporal and spatial scales. At farm and paddock level, it is abundantly clear that substantial savings could be made if pest management is achieved. It is equally clear that in many instances the tools to do so are limited but if developed would contribute substantially to farm profitability. [ABSTRACT FROM AUTHOR]

This experiment, implemented at a Southland site representative of the lower South Island, New Zealand, and monitored for three full years from 2012/2013 to 2015/2016, was one of four throughout New Zealand that investigated the yield and nutritive value rankings of perennial ryegrass cultivars sown with or without white clover and with high (225 kg N/ha/annum) or low (50 kg N/ha/annum) application rates of nitrogen fertiliser. High inputs of nitrogen (N) fertiliser increased annual total dry matter (DM) yields and seasonal yield in 12 out of 18 measurement occasions. Adding white clover increased both annual dry matter yield and seasonal yield in 7 out of 18 measurement occasions. An interaction between clover and N input occurred on 10 occasions. Over time, the low N minus clover treatment became progressively lower yielding compared with the other three treatments. Ryegrass cultivar by clover interactions occurred in the latter half of the experiment. When analysed using ryegrass characteristics, early- and late-heading ryegrass cultivars produced similar yields when sown without clover, but late-heading ryegrass cultivars had a higher yield than early-heading pastures when sown with white clover (P < .001). Tetraploid ryegrasses had lower yields than diploid ryegrasses when sown without clover (P = .001). This difference was reduced when white clover was included. There was no significant interaction with ryegrass morphology when sown with white clover, as dense ryegrass cultivars always had a higher yield than open ryegrass cultivars (P = .005). Interactions occurred between N input levels and ryegrass cultivar. These occurred in early spring or late spring of each year. Analysis by ryegrass characteristics identified consistent interactions. Ryegrass cultivars with a late-heading date were higher yielding than early-heading cultivars at low N inputs (P = .029), but they were not different at high N inputs. Diploid and tetraploid ryegrass cultivars were similar with low N inputs, but diploid cultivars out-yielded tetraploid cultivars at high N inputs (P = .005). Significant interactions between N inputs and white clover addition affected herbage nutritive value but this did not extend to consistent interactions with ryegrass cultivar. Invertebrate pest numbers were generally low and unlikely to have influenced clover/ryegrass interactions or cultivar ranking. Results from this site suggest that ranking of ryegrass cultivars needs to account for both the inclusion of clover and variation in N fertiliser input. [ABSTRACT FROM AUTHOR]

The development of economic indexing systems for ranking cultivars of forage species requires new knowledge of factors that may influence the scaling of agronomic data collected in controlled, small-plot evaluation trials to whole farm systems. In the case of perennial ryegrass indexing, one such knowledge gap is the effect of growing clover with ryegrass on the relative rankings of different ryegrass cultivars. The objective of the investigation reported in this series was to test whether the relative yield rankings of perennial ryegrass (Lolium perenne L.) cultivars representing the range in phenotypes now available to New Zealand farmers as a result of recent breeding differed when those cultivars were grown in monocultures (as per standard protocols for cultivar yield trialling systems such as the National Forage Variety Trials) versus mixtures of grass and clover. This paper presents the rationale for the investigation by reviewing developments in perennial ryegrass breeding and evaluation in the context of grass-clover relationships in grazed pasture systems. The papers that follow report results from a multi-year, multi-site investigation comparing the yield, nutritive value and other productivity-related variables of eight perennial ryegrass cultivars grown with or without white clover (monoculture versus mixture respectively) at two levels of nitrogen fertiliser. Key considerations in the design of the experiment on which the investigation was based are discussed. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]