Alopecurus myosuroides Huds. (black-grass) has become problematic globally due to its repeated evolution of herbicide resistance. Three incursions via contaminated seed lots have occurred in the past 20 years despite strict border biosecurity in New Zealand. However, it is not known if the black-grass populations linked to these incursions carried herbicide resistance. Enough seed was obtained from contaminated seed lots (ryegrass-linked population UK2007; linseed-linked population FR2021) for a dose–response assay to test resistance to a commercial herbicide product containing both iodosulfuron and mesosulfuron, used for black-grass control in Europe, but not enough for repetition of the experiment or to test multiple herbicides. Seed lot FR2021 showed a high level of resistance, requiring 250g ai/ha to achieve 90% control (LD90) more than ten times the label rate whereas seed lot UK2007 had an LD90 of 19.0 g ai/ha almost twice the label rate (10 g ai/ha). Acetohydroxyacid synthase (AHAS)-inhibitor herbicides should not be used against black-grass populations during incursion responses in New Zealand. Any future black-grass incursions will be increasingly likely to carry herbicide resistance traits. Strong border measures, certified seed use, avoiding seed sourced from infested areas and screening for resistance are critical for prevention and effective control of black-grass incursions.
Fuller’s rose weevil, Naupactus cervinus (Boheman) (Coleoptera, Curculionidae) adults are only available in the field for a short period of time each year. As field-collected insects are not of a known standardised quality or age, they are not suitable for experimental work. Our goal was to develop a laboratory rearing technique to enable access to all life stages of this insect year-round. This paper reports on life-cycle data for two generations of Naupactus cervinus reared on an artificial diet. Key life cycle parameters were determined, and a laboratory colony was successfully established. The life cycle parameters at 20°C and an 18-h photoperiod were as follows: the egg development period was approximately 30 days, the neonate-to-adult period was about 21 weeks, and the average generation time (egg to egg) was approximately 27 weeks. The diet and rearing technique enabled the year-round, laboratory rearing of standardised adult insects of known quality and age, with larvae fed artificial diet and adults fed mature citrus leaves for two successive generations.
Thorough field evaluation of local and imported microbial products under New Zealand growing conditions is needed to ensure growers can use these products with confidence. There are no uniform guidelines for evaluation of the diverse range and functions of microbial products containing live microorganisms, and trials must be designed to accommodate complex interactions among microorganisms, target pest and crop. Successful trial outcomes rely on: thorough assessment of prior knowledge of the target and microorganism; detailed pre-trial planning to minimise risk and ensure optimal trial design; well documented trial establishment and monitoring; appropriate statistical analysis of the data; and evaluation of trial outcomes.
Shade tolerance is a key factor determining which environmental weeds can invade and persist in intact forest, where light availability can be as low as 1% of full sunlight. Understanding which species can survive under such low light is critical for predicting future invasions. We examined growth responses and phenotypic plasticity of eight environmental weeds: three palms (Archontophoenix cunninghamiana, Phoenix canariensis, Trachycarpus fortunei), four trees (Acer negundo, Maytenus boaria, Pinus patula, Prunus lusitanica), and one vine (Actinidia chinensis). We used a shade-house experiment with four shade levels (53%, 93%, 97%, 99%) to assess seedling establishment, biomass, root:shoot ratio (R:S), and specific leaf area (SLA). Palms showed high shade tolerance, with minimal variation in establishment and small biomass reductions at the deepest shade, but little plasticity. Maytenus boaria and Prunus lusitanica were moderately shade tolerant, with stable establishment but larger biomass declines between 97% and 99% shade. Actinidia chinensis and Acer negundo were less tolerant, showing greater biomass and establishment declines under deep shade. Pinus patula was least tolerant, with no seedlings surviving at 99% shade and the greatest biomass reduction between 53% and 93% shade. Maytenus boaria and Actinidia chinensis showed the greatest plasticity, with declining R:S and increasing SLA with shade. Prunus lusitanica was plastic in SLA but not R:S, while Acer negundo and Pinus patula showed minimal plasticity. Results indicate that all species except for Pinus patula have potential to establish in deep shade. Further research to determine their ability to invade intact native forests would be valuable.
Kiwifruit (Actinidia spp.) is an important horticultural crop, but unmanaged self-propagation results in ‘wild kiwifruit’, a serious environmental weed that can harbour pests and diseases, threatening New Zealand’s kiwifruit industry. Seed is the main dispersal mechanism for wild kiwifruit, and its longevity impacts weed-management planning. To determine the persistence of wild kiwifruit seed in a seed bank, we buried 800 kiwifruit seeds (A. chinensis var. deliciosa ‘Hayward’) in fine-mesh bags at a single depth (5–10 cm) in well-draining sandy loam under simulated field conditions. Bags were retrieved annually for three years and seed germination rates assessed in the last two years. Germination declined markedly between 24 and 36 months: seeds buried for 24 months showed high germination (80%), whereas those buried for 36 months exhibited very low germination (1%). This sharp decline indicates that wild green kiwifruit forms a short-lived seedbank, with most seeds losing viability between two and three years. These findings support the practical feasibility of eradicating wild kiwifruit populations following plant removal, provided seed rain is prevented. Also, these findings reinforce the importance of continued vigilance by industry and land managers, in covering fruit bins, using bird netting, and removing or mulching old vines, to minimise seed escape and reinvasion risk. Our results strengthen confidence that local eradication of wild kiwifruit is achievable with sustained management.
Herbicides are a vital tool to reducing weed competition during the establishment phase of revegetation plantings. However, there is limited information on herbicide tolerances of native species, hindering the ability to develop effective weed-management plans. In a pilot study, tolerances of five New Zealand native species (Coprosma propinqua, Griselinia littoralis, Hoheria angustifolia, Prumnopitys taxifolia, and Cyperus ustulatus) were tested against the herbicides clopyralid, haloxyfop-P-methyl, triclopyr, glufosinate-ammonium and glyphosate at label rates, and to a dilute glyphosate treatment used to simulate drift from spraying around native plants. Treatments were sprayed directly onto plants, with survival and growth over four months compared to a control group. Clopyralid caused significant damage to H. angustifolia and G. littoralis, but increased growth in Cyperus ustulatus. Haloxyfop-P-methyl did not damage any species. While glyphosate and glufosinate-ammonium at label rates caused significant mortality, a low dose of glyphosate did not damage any species except Coprosma propinqua. Triclopyr also caused significant mortality or damage even in non-dicotyledonous plants, possibly due to small plant sizes. These results identify broader than expected susceptibility to triclopyr and clopyralid, suggesting additional caution with these herbicides may be required. The findings from this study also indicate that spraying glyphosate carefully around these species is unlikely to cause harm, except to Coprosma propinqua.
HIGHLIGHTS: Invasive alien species are increasingly recognised for their negative impact on economic, environmental, social and cultural assets and values throughout the world, including Aotearoa New Zealand. Here we briefly describe New Zealand’s biosecurity system, and place this in the context of the many challenges it faces in an ever-changing world. This paper then summarises and assesses information on the magnitude of the biosecurity challenge for New Zealand’s plant systems in terms of: (1) assets to be protected; (2) current impacts from invasive species found in New Zealand; (3) potential impacts from invasive species not yet found in New Zealand; (4) investment in defensive biosecurity activities; and (5) attempts to determine the return on investment for biosecurity operations and research. Our findings indicate that the economic impacts of established invasive species and potential impacts from non-established invasive species are in the billions of dollars, and that there are sizable benefit-cost ratios for investment in mitigating these impacts, including investment in research. This information can inform policy development and provide the basis for developing an economic or value framework for investment in biosecurity, and especially for plant border biosecurity.
Exporting agricultural produce is vital for the economy of Aotearoa New Zealand, and pest management, typically reliant on pesticides, ensures high productivity and quality. However, due to human health and environmental risks, pesticide use is increasingly regulated internationally and influenced by consumer attitudes. This paper summarises the recommendations from a workshop held in Auckland, New Zealand in April 2023 within the context of the topic at the time of publication. The workshop involved members of regional and national government, researchers and various commercial sectors, and aimed to identify challenges related to pesticide risk assessment and management in New Zealand. Key recommendations to strengthen government policies and reduce risks included establishing secure national data-sharing systems for pesticide use, modernising the regulatory framework with time-bound approvals, and introducing incentives for agricultural pesticide users to transition to more sustainable practices. Increased government funding would enable timely pesticide (re)assessments and more targeted pesticide monitoring in the environment.
Non-native conifers are some of the most invasive weeds in Aotearoa New Zealand (A-NZ). One species, Pinus contorta, has undergone known reproductive trait shifts since its introduction to A-NZ that increase the number of seeds produced per cone compared to its native range. Seed potential is partially determined by the number of fertile cone scales, however prior studies in A-NZ have only considered the number of cone scales rather than their fertility. This preliminary study investigates cone scale fertility across two A-NZ sites known to differ in their seed potential (Lake Pukaki and Craigieburn). As expected, cones from Craigieburn contained four times fewer filled seeds than cones from Lake Pukaki but, surprisingly there was no difference in the proportion of fertile scales between the two sites. Notably, the number of fertile scales at both A-NZ sites was almost double that reported in the native range. Further work is required to understand whether this finding is consistent across A-NZ or influenced by within- or between- tree factors (e.g. cone location in the crown), and comparisons with data from the native range are required to understand whether the higher cone scale fertility in A-NZ represents a trade-off against cone-defences (e.g. scale thickness).
Plant-parasitic nematodes threaten horticultural crops, causing damage by feeding on plant roots, reducing yields, and affecting global food security. We present preliminary results on nematode genera found in soil around two varieties of grapevine (Sauvignon blanc and Pinot noir) with different rootstocks (101-14, SO4, 5C, Riparia Gloire, 3309, Schwarzmann) in ten vineyards located in Blenheim, part of the largest grape-growing area in New Zealand. Soil samples were collected, and nematodes were extracted using a modified centrifugal-flotation technique. Nematode counting and morphological identification to genus level was conducted based on characteristics such as stylet size and overall body shape. Soil texture analysis was performed, and the influences of grape variety and rootstock as well as soil type on nematode diversity were assessed. Four genera of plant-parasitic nematodes, including Pratylenchus, Paratylenchus, Helicotylenchus, and Criconomella, were recovered from the vineyard soils and a snapshot of relative abundance was determined. Differences in the nematode genera and their relative abundance among varieties and rootstocks were found, which suggests potential interactions between nematode genera and grapevine rootstocks/scions. This preliminary survey provides updated information on nematodes since the last survey conducted 20 years ago in New Zealand. This work indicates the presence of various genera of plant-parasitic nematodes in soils around grapevines grown around Blenheim, New Zealand. These findings highlight the need for further research to understand the interactions between nematodes, grape varieties, and rootstocks. The importance of addressing this knowledge gap for biosecurity measures and potential implications on grapevine growth and vineyard productivity is discussed.
Samara morphology, including weight, size, and wing-to-seed ratios, is an important precursor to seed dispersal, and therefore a primary driver in large-scale alien conifer invasions. Prior studies have not reported morphological differences between samaras of different cones within a tree possibly because cone position at differing crown heights has not been examined. This preliminary study investigated whether cones from different crown heights of three lodgepole pine (Pinus contorta Douglas) trees differ in the morphological characteristics of their samaras. Samaras from the lower tree crown were 17% heavier on average than those from the upper crown, without any significant differences in wing loading. Cones in the upper crown produced more seeds than in the lower crown, although this was inconsistent across the small sample size. These results suggest the effects on primary seed-dispersal are negligible, but further research is needed to determine the effect on secondary seed-dispersal. Larger seeds from the lower crown are better adapted to survive in a competitive environment near other trees, while cones in the upper crown may produce more, but smaller, seeds which could infer a bet-hedging strategy when dispersing into heterogeneous environments. These results suggest canopy-height should be considered when accounting for inter-cone variation in conifers.
This study examines differences in extraction efficiency of three methods for extracting root-lesion nematodes (Pratylenchus spp.) from maize roots. The Baermann funnel, Whitehead & Hemming tray, and centrifugal-sugar flotation methods were evaluated for efficiency and clarity using microscopic observation. Statistical analysis confirmed significant differences among the methods. The centrifugal-sugar flotation method yielded the highest nematode count (1874±76 per 5 g of roots) but the clarity of the observation field under the microscope was lower due to root residues compared to the other two tested methods. The Baermann funnel method yielded 35.9% extraction efficiency (672±46 per 5 g of roots) compared to the centrifugal-sugar flotation method with higher clarity of the observation field than other tested methods. The Whitehead & Hemming tray presented a moderate level of observation field clarity compared to other tested methods with a nematode extraction efficiency of 60.8% (1140±53 per 5 g of roots) compared to the centrifugal-sugar flotation method. The results suggest that the Whitehead & Hemming tray could be a viable choice for nematode extraction, especially when both nematode numbers and microscopic clarity are important considerations. Understanding the restrictions of each methodology enhances the accuracy of nematode quantification leading to improved and updated data for maize producers in New Zealand.
Pomovirus solani (common name: potato mop-top virus, PMTV) was first recorded in New Zealand on 11 September 2018. In contrast, Spongospora subterranea, the vector of PMTV, was first recorded in New Zealand in 1909, and is widespread causing important diseases of potato. PMTV causes distortion on potato leaves, shoots and tubers, and was designated at the time of first record as an Unwanted Organism by the New Zealand Ministry for Primary Industries. Spongospora subterranea and PMTV can survive for long periods in soil and in alternative hosts, so multi-year non-potato crop rotations are important for limiting the diseases caused by these pathogens. Both pathogens can also survive in wastes from potato processing factories, so disposal of processing effluent should be avoided on paddocks likely to be used for potato crops. The first observation and timely reporting of PMTV symptoms by a potato processing company instigated an official biosecurity response to the virus ‘incursion’, although PMTV may have been present 1 or 2 years prior to this first record. Rapid establishment of a PMTV Technical Advisory Group, including relevant international expertise, and the advice it provided, effectively directed the prompt response to the PMTV ‘incursion’, and the Ministry for Primary Industries and Potatoes New Zealand (Inc.) swiftly and effectively developed capability for monitoring and management of the ‘incursion’. Efforts since then by the New Zealand potato industry have reduced potential impacts of PMTV in this country, as demonstrated by low incidence of the virus in seed potato crops in 2019/20 and 2020/21. This low incidence indicates that PMTV is not adversely affecting potato productivity in New Zealand, and that management of the virus ‘incursion’ has been effective.
Phytophthora agathidicida is responsible for a devastating dieback disease that threatens the survival of Agathis australis (kauri), an ancient conifer species endemic to New Zealand. To develop durable control strategies against kauri dieback disease, a better understanding of the host metabolites necessary for the growth and survival of P. agathidicida during in planta growth, particularly during colonisation of the apoplastic environment, where early contact between host and pathogen cells is made, is required. As a starting point to address this knowledge gap, we investigated changes in the metabolite profile of apoplastic washing fluid (AWF) samples harvested from kauri leaves following either mock inoculation or inoculation with P. agathidicida. AWF was extracted from leaves of kauri saplings and inoculated with P. agathidicida on cellophane membranes or cellophane membranes without the pathogen as a control. The metabolite profile of the AWF samples was then analysed via proton nuclear magnetic resonance (1H NMR) spectroscopy at 24 hours and 10 days post-inoculation, and changes investigated relative to the control. Some changes in the metabolite profile of kauri AWF samples following P. agathidicida inoculation were observed using 1H NMR spectroscopy, including a decrease in sucrose and an increase in glucose resulting from the breakdown of more complex carbohydrates. Our results suggest that P. agathidicida modifies or utilises metabolites present in the leaf apoplast of kauri, including carbohydrates that serve as a source of nutrition. These results provide possible new insights into the nutritional requirements of P. agathidicida during apoplastic colonisation of kauri.
Vine decline and trunk diseases have been observed in New Zealand kiwifruit orchards since the year 2000. In 2019, a block of Actinidia chinensis var. deliciosa ‘Hayward’ vines that were being re-grafted was noted to have differences in colouration of the internal wood of the cut trunks, with dark cores often corresponding with less vigorous vines and/or vines with trunk disorders. Cross-sections of 10 symptomatic and 10 externally asymptomatic trunks were taken from 1–1.5 m above the soil and fungal isolations made across the width of the trunks. Fungi found within the symptomatic vines included Neobulgaria alba, Ilyonectria spp., Neonectria microconidia, Gliomastix murorum, Clonostachys sp. and Penicillium sp. There was a wide variety of symptoms and fungal profiles seen. However, Neobulgaria alba often closely matched the stained areas seen in the wood and was not recovered from the asymptomatic vines. The most common fungus in the asymptomatic vines was Chaetomium sp. These isolations revealed a group of fungal genera that were associated with diseased trunks of kiwifruit at this site. Pathogenicity testing is needed to confirm which of these fungi are secondary invaders and which are primary pathogens of this host.
Biological control of pathogens can be an important tool for long-term management of diseases. Species in the fungal genus Trichoderma have been used for a broad range of agricultural functions including biological control. Here we tested if isolates and mixes of Trichoderma spp. could be effective in reducing symptoms of dothistroma needle blight, caused by the foliar pathogen Dothistroma septosporum, on Pinus radiata. Pot trials with natural and artificial D. septosporum infection and field trials were undertaken. The majority of Trichoderma treatments were not significantly different from the control. However, in one experiment, the Trichoderma treatments significantly reduced disease symptoms in one seedlot but not in the other seedlot tested. Conversely, in the field trial, one Trichoderma treatment significantly increased symptoms in comparison to the control. PCR analysis indicated that Trichoderma can persist over time, 16 months after inoculation, in the soil P. radiata seedlings were grown in, however, further investigation is required. Overall, the results from our trials showed that the Trichoderma isolates and mixes tested were unable to control dothistroma needle blight in P. radiata and are not suitable as biological control agents.
Species of root-lesion nematode (Pratylenchus spp.) are associated with significant reductions in wheat yield in wheat-growing regions around the world. Of these, Pratylenchus thornei and P. neglectus are known to cause the highest damage to the Australasian wheat industry. New Zealand is known to produce high wheat yields on a per-hectare basis yet little research has been conducted to date to determine the effects of Pratylenchus spp. on the production of wheat in New Zealand. Therefore, as the first step towards filling this knowledge gap, the current research focused on conducting surveys to determine the population densities and distribution of Pratylenchus spp. in wheat-growing regions in Canterbury, South Island, New Zealand. Surveys were conducted at ten selected sites that were geographically distinct from each other. At six of the ten sites, lesion nematode populations were reported to be above the recorded Australian threshold of 2000 nematodes per kg of soil. In Australia, it’s been recorded that around 50% yield reductions can occur in intolerant wheat varieties when population densities reaches this number. Differences in population density within each location was also observed indicating the uneven distribution of lesion nematodes within a field. Morphological measurements of the nematodes collected from multiple sites during this study confirmed the presence of P. thornei and P. neglectus in Canterbury wheat-producing areas indicating a potential threat to the New Zealand wheat industry by root-lesion nematodes. Further studies need to be conducted to fully understand the situation and to develop management strategies to mitigate threats from nematodes.
This editorial summarises the first 75 years of the New Zealand Plant Protection Society. The structure of the Society and approaches to plant protection have changed over the years but the essence of the original vision to bring together industry, government, and university researchers, to ‘pool and exchange information’, is still relevant today.
Ripgut brome (Bromus diandrus) is a significant weed in arable systems with cereals being negatively impacted through yield reduction and contamination of harvested grain. There are limited herbicide options for its control, and reduction of the weed seed bank is a key part of its management. Ripgut brome seeds were incubated in three soils known to harbour a range of plant pathogens, and a range of fungi were subsequently isolated from ungerminated seeds. The most prevalent putative fungal pathogens isolated were Fusarium spp. and Marasmius sp. Selected isolates were cultured on artificial media and tested for their ability to inhibit germination of ripgut brome seeds in a series of in vitro assays, with many isolates completely inhibiting germination. When isolates were tested for their activity against non-target arable species in plant assays, three of five Fusarium spp. isolates significantly inhibited germination of oats and barley while a Marasmius sp. isolate had no effect on germination of these species. Further plant assays using four Marasmius sp. isolates against a wider range of plant species (oats, barley, ryegrass, brome, cocksfoot, and prairie grass) indicated some variability between Marasmius sp. isolates, with two isolates slightly inhibiting germination of some plant species, while two isolates (W14, W17) had no adverse effects. Sequencing of the ITS region of the Marasmius sp. isolates indicated that they were closely related but distinct from M. graminum, which is known to have some phytopathogenic activity and M. oreades which has not yet been reported as a plant pathogen. Further investigation of the Marasmius isolates as potential biocontrol agents for ripgut brome seed is warranted.
Costelytra giveni is a serious pasture pest in New Zealand and accurate estimates of population densities are important to inform control measures. This species generally has a one-year life cycle so populations should either remain stable after eggs have hatched or decline due to larval mortality. Larval counts were obtained using a simple, standard and widely used sampling method from a series of soil cores collected from ryegrass research plots in Canterbury, New Zealand between 27 January and 16 June 2021 and a significant increase in population was recorded. Measurements on 27 January, 19 March and 5 May, represented only c. 8%, 25% and 63% of the mean densities measured on 16 June, respectively. The apparent increase in larvae is attributed to failure to find small 1st and 2nd instar individuals within the soil samples. Larvae increased in size as they transitioned from 1st to 3rd instar and later instar specimens were more easily discovered. An equation to describe the observed results provided date-related correction factors to allow a more realistic prediction of C. giveni larval densities in the winter following empirical larval counts. Larval counts measured on 27 January, 19 March, and 5 May, would need to be multiplied by 13, 4 and 1.6, respectively, to accurately estimate the larval density found on 16 June. This study showed that summer-autumn sampling using the current method can significantly underestimate winter C. giveni larval densities, potentially leading to unanticipated pasture production losses. Similar results were also found in 2022. While the equation provides a guide to population estimates, the caveat is that region and environment will influence population trends in any particular year.
