Macadamia Industry Research Articles

Nut bush pesticide limits: urgent need for a comprehensive strategy to address current and emerging insect pests and insecticide options in the Australian macadamia industry.

In Australia, macadamia orchards are attacked by four main insect pest groups. Management and control of three of these key pests currently relies on broad-spectrum insecticides whose long-term future is questionable. Of the 23 insecticides registered for use in macadamia in Australia, 19 face issues affecting their availability and 12 are presently not approved in the EU, the USA or Canada. These international markets may refuse produce that does not adhere to their own insecticide use standards, hence Australian produce may be excluded from market access. Many of the potential replacement integrated pest management methods of pest control are generally considered less effective by the industry and have not been adopted. There are 17 insect pest groups identified by the industry, any of which have potential to become major problems if broad-spectrum insecticide options become unavailable. Thirteen pest groups need urgent attention as they are at risk of losing current effective control methods, and no replacement solutions have yet been developed. The lag period for research and development to identify new chemical and biological control solutions means there is now an urgent need for the macadamia industry to craft a strategy for sustainable pest management for each pest. Critically, this industry strategy needs to address the vulnerabilities identified in this paper, identify potential solutions for any cases of market failure and consider funding mechanisms to address these gaps. On economic and sustainability grounds, potential biological control options should be explored, especially in cases where insecticide control options are vulnerable. © 2024 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Seasonal dynamics of inoculum of Botryosphaeriaceae in macadamia orchards in Australia

AbstractMacadamia (Macadamia integrifolia and M. tetraphylla and their hybrids) is a tree nut crop affected by Botryosphaeria branch dieback. The disease results in branch and tree death in commercial orchards, so reducing the productivity of the Australian macadamia industry. There is a dearth of knowledge of the disease cycle in macadamia, which confounds disease management. This study investigated the dynamics of pathogen inoculum associated with Botryosphaeria branch dieback and the influence of environmental factors (temperature, rainfall and relative humidity) on the seasonal spore release within the orchards. Diseased and asymptomatic plant parts from macadamia trees were collected each season for 3 years in commercial orchards. Fungal structures (pycnidia and pseudothecia) mainly were (71%) observed on symptomatic wood samples. A comparison of the number of spores released from the fungal structures between summer and autumn revealed high concentrations of Lasiodiplodia pseudotheobromae from diseased wood (4.8 × 104 conidia/cm2) and Neofusicoccum luteum from blighted leaves (2.1 × 103 conidia/cm2). The peak airborne conidia dispersal period, quantified using microscopy and quantitative PCR assays, was consistently detected after rainfall and strongly associated with relative humidity over 70% and temperatures between 20 and 27°C during summer and autumn. Botryosphaeriaceae isolates obtained from the pycnidia on the macadamia trees caused severe branch dieback symptoms when inoculated on detached macadamia twigs, which suggests both airborne and rain‐splashed spores from fungal structures on the trees contribute to the disease in macadamia orchards.

Bats and birds control tortricid pest moths in South African macadamia orchards

The global macadamia industry is growing rapidly, and the world's biggest macadamia nut producer, South Africa, is continuously expanding its production. Insect pest mitigation and research are mainly focused on the damage caused by heteropteran pest species, whereas the damage associated with lepidopteran tortricid moths in South African macadamia orchards is understudied. Here we explore the potential biocontrol of tortricid moths by natural predators through full exclosure of bats and birds, daytime only exclosure (birds), night exclosure (bats and possibly nocturnal birds), and control treatments. The exclusion experiment showed that bats and birds are effective natural predators, which can reduce tortricid moth damage by more than 35%. Impacts of biocontrol are higher at natural orchard edges next to natural or semi-natural vegetation, compared to human-modified edges (12.4% damage decrease in 2017, 10.6% in 2018). At the full exclosure, there was no difference in damage between natural orchard edges and human-modified edges, in both years of our study (56.5% vs. 56.6% in 2017, 19% vs. 18.5% in 2018). We recommend increased preservation efforts of more heterogeneity with semi-natural vegetation in agricultural landscapes to ensure the conservation of biocontrol services, as their loss can be expected to result in significant negative impact on macadamia production. This biological pest control can be used as part of integrated pest management to reduce the reliance on chemical pesticides, so decreasing sustainability challenges.

First report of Neofusicoccum parvum causing leaf spot disease on Macadamia integrifolia in China.

The macadamia industry is developing rapidly in China. A brown leaf spot disease was noted in six Macadamia integrifolia plantations in Lincang, Yunnan, in October 2021. Over 60% of trees sampled had brown leaf spot symptoms, among approx.15,000 trees planted in these areas. Lesions (3 to 5 mm dia.) were small round brown spots with yellow edges. Lesions on severely infected leaves were darker and larger, with irregular shape (8 to 10 mm long, 3 to 6 mm wide). About 10% of diseased leaves had lesions characterized by a shot hole surrounded by a yellow halo. Potential pathogens were isolated from four randomly-selected symptomatic leaves from each of the six plantations by cutting lesion edges into small pieces. The pieces were surface sterilized, placed onto water agar containing 100 ppm aureomycin and incubated for 5 days at 24°C in the dark. Subculturing microbial growth on potato dextrose agar produced single-hyphal isolates with white fluffy aerial mycelia that turned pale olivaceous gray after 4 to 5 days. In four randomly-selected cultures, conidia were single celled, hyaline, spindle shaped to oval, and measured 10.9 to 16.3 µm long and 4.0 to 6.2 µm wide (n = 50). These characteristics matched those of Neofusicoccum parvum (Pavlic et al. 2009). Isolate LC013 was randomly selected as a representative individual for molecular identification. Internal transcribed spacer (ITS; ITS1/ITS4 primers; White et al. 1990), beta-tubulin gene (tub2; BT2A/BT2B primers; Glass and Donaldson 1995) and translation elongation factor 1-alpha gene (tef1-α; EF1-728F/EF2 primers; Carbone and Kohn 1999; O'Donnell et al. 1998) regions were PCR amplified from genomic DNA. Sequences of the products were used to BLAST probe the type specimen nucleotide sequences in GenBank. The LC013 sequences (GenBank accessions OM392021 (ITS); OM453641 (tub2); OM567656 (tef1-α)) had >99% sequence identity with analogous sequences from the type specimen of N. parvum CBS 138823 (accessions AY236943 (ITS); AY236917 (tub2); AY236888 (tef1-α)). Isolate LC013 was sister to N. parvum type strain in a maximum-likelihood (ML) tree constructed from analogous concatenated ITS, tef1-α, and tub2 sequences of 27 species that are phylogenetically closely-related to LC013 based on the ITS single locus ML tree. Koch's postulates were tested twice with two isolates by wounding leaves of four 14-month-old M. integrifolia seedlings with a sterile needle and placing a 5-mm-diameter agar plug containing N. parvum on the wound site. PDA plugs alone were used as uninoculated controls. Leaves were covered with sealed bags to maintain >90% humidity for 24 hours. All plants were kept in the same glasshouse under natural conditions. Leaves of inoculated plants began to discolor at 5 days post-inoculation (dpi). Brown spot symptoms were observed at 9 dpi. Control plants were symptomless. N. parvum was re-isolated from leaf lesions of the infected plants, but not from control plants, thus fulfilling Koch's postulates. N. parvum is an aggressive pathogen that causes severe disease on important tree and woody species, including M. integrifolia (Liddle et al. 2019). In China, it has been reported to cause leaf spot disease on 26 plant species (Farr and Rossman 2022), but this is the first report of N. parvum causing leaf spot disease on M. integrifolia. Further investigation is required to estimate the importance of this pathogen to the macadamia industry in China.

Evaluation of In-Field Inoculation Methods for Characterization of Macadamia Germplasm to Husk Spot Incidence and Severity.

Husk spot, a fungal disease of macadamia pericarps (Pseudocercospora macadamiae), induces premature abscission in several major commercial cultivars. Breeding for resistance to husk spot is a priority of the Australian macadamia industry. Due to the large tree size of macadamia and high numbers of progeny in breeding populations, inoculating for resistance screening is laborious and time consuming. Previously utilized methods included direct applications of P. macadamiae suspensions and the hanging of bags of diseased husks above developing fruit in tree canopies. In this study, both methods were modified to allow for efficient application in large-scale breeding populations, and their efficacy was evaluated. Two quantities of diseased husk per bag, 'large' (75 g) and 'small' (30 g), and two concentrations of sprayed P. macadamiae suspensions, 'stock' (5 × 105 propagules/ml) and 'dilute' (2.5 × 105 propagules/ml), were tested across two fruiting seasons. Treatments were compared against a control (sterile water) in commercial cultivars A38 and A4. Husk spot incidence and severity produced by small bags were significantly affected by season. A significant season effect was less common for other treatments. All four treatments infected over 50% of target fruit in each season, but the highest husk spot incidence across both seasons (≥85%) was produced from large bags. Overall, the large bags were the most reliable method for infection of target fruit. Results also demonstrate the importance of considering the effect of season when selecting husk spot inoculation methods.

Biology and ecology of insect pests in macadamia: a review of the current status of IPM strategies in Australia

Abstract Macadamia spp. are native to Australia and have significant commercial value worldwide for their edible nuts. Integrated pest management (IPM) can be challenging in Australia because macadamia is a native plant cultivated commercially in its native range alongside its native insect pests and their natural enemies. Attaining viable commercial yields of macadamia in Australia has historically relied heavily upon the use of chemical insecticides, including organophosphates, and a shift away from reliance on these practices has not yet happened. Amblypelta spp. have historically been the pests of greatest concern to the Australian macadamia industry and that has not changed, but the make-up of the other major and minor pests has changed over time. More recently, the more southern-growing regions have experienced increases in Cercotingis decoris, Proteatingis howardi, and Kuschelorhynchus macadamiae, and there are currently no long-term viable control options for these species. The Australian macadamia pests, Cryptophlebia ombrodelta and Acanthococcus ironsidei, not necessarily of major concern in Australia, have spread to macadamias in other countries and have become significant pests as they do not have the corresponding native natural enemies. There are critical gaps in the identification of macadamia pest species and their natural enemies, as well as an understanding of their biology and ecology, distribution, host preferences, and movement. The identified knowledge gaps need to be addressed to support IPM in macadamia, both in Australia and internationally.

Natural Vegetation Edges Promote Bat Activity in Macadamia Orchards in Northeastern South Africa

Agricultural intensification can result in extremely fragmented landscapes with typically only small natural areas remaining. The South African macadamia industry is expanding dramatically, with over 5000 ha planted per year. Remaining natural vegetation around macadamia orchards will be key to retain important ecosystem services such as biological pest control of insects provided by, amongst others, insectivorous bats. We evaluated how the activity of bat species on macadamia farms within different land-use mosaics is related to general insect abundance and what role the phenological stages of macadamias play. Recordings of bat echolocation and insect light trap collections were conducted (July 2019 – March 2020) at different edges of land-use types on two macadamia farms in Hazyview, South Africa. Results showed that edge type significantly influenced bat activity and insect abundance with natural vegetation edges recording the highest bat activity (n = 3153) and insect abundance (n = 16 524). River edges (bat n = 1635, insect n = 11 284) presented lower activity and abundance than natural edges but still double that of road edges (bat n = 695, insect n = 3743). Bat activity was also higher during developing-nut and mature phenology stages when pest insects peak. Bats from all foraging guilds were recorded during the study, which points towards a more intact bat assemblage within the study area compared to other macadamia areas in South Africa. Our study highlights the importance of retaining natural vegetation within an agricultural land-use mosaic to maintain biological pest control.

Genetic diversity of the two-spotted stink bug Bathycoelia distincta (Pentatomidae) associated with macadamia orchards in South Africa.

The South African macadamia industry is severely affected by a complex of stink bugs, dominated by the two-spotted stink bug, Bathycoelia distincta Distant (Pentatomidae). This species was first discovered during the spring of 1984 in the Limpopo province. Although considerable effort has been spent trying to manage this pest, it continues to be a pest of concern for the macadamia industry. Information on the genetic diversity of this species is lacking, despite the potential relevance of such information for management strategies. The present study aimed to characterise the genetic diversity of B. distincta populations in South Africa. The Cytochrome c Oxidase Subunit 1 (COI) and cytochrome b (Cytb) gene regions were sequenced from individuals collected from the three main regions of macadamia production over three different seasons (2018-2020). An overall high haplotype diversity (COI = 0.744, Cytb = 0.549 and COI+Cytb = 0.875) was observed. Pairwise mean genetic distance between populations from each region varied from 0.2-0.4% in both datasets, which suggests the absence of cryptic species. The median joining network for both datasets consisted of one or two central haplotypes shared between the regions in addition to unique haplotypes observed in each region. Finally, low genetic differentiation (FST < 0.1), high gene flow (Nm > 1) and the absence of a correlation between genetic and geographic distance were estimated among populations. Overall, these results suggest that the B. distincta populations are not structured among the areas of macadamia production in South Africa. This might be due to its ability to feed and reproduce on various plants and its high dispersal (airborne) between the different growing regions of the country along with the rapid expansion of macadamia plantations in South Africa.

Discovery of Single Nucleotide Polymorphisms for Resistance to Abnormal Vertical Growth in Macadamia.

Abnormal vertical growth (AVG) syndrome is a serious threat to the Australian macadamia industry as it decreases the yield of nuts by as much as 70% per annum. A lack of information on the cause of AVG has hindered the development of an effective disease management strategy. Discovery of genetic markers associated with disease resistance can be used as tool for rapid selection of elite cultivars, hence helps in efficient disease management. Differences in field susceptibility of macadamia cultivars provide an opportunity for discovery of genetic markers that are associated with host resistance. REML mixed model analysis was performed to estimate the AVG rating of 51 cultivars from multiple origins using phenotypic data from 359 trees planted in four sites. Most of the Hawaiian cultivars were found as susceptible, while selections from the Australian macadamia industry breeding program were predominantly resistant. All the cultivars were genotyped for 13,221 DArTseq-based single nucleotide polymorphism (SNP) markers. A bulked sample analysis was performed using 20 genotypes each at the extremes of AVG phenotypic ratings. Ten SNP markers were predicted to be associated with AVG resistance and two arbitrarily selected SNP markers were validated using PCR and Sanger sequencing. Our findings suggest that AVG resistance in the commercial cultivars may be derived from the genomic introgression of Macadamia tetraphylla through interspecific hybridization. The results may support marker-assisted selection for macadamia germplasm with AVG resistance.

Using choice analysis of growers’ preferences to prioritize breeding traits in horticultural tree crops: A macadamia case study

This paper evaluates a novel approach in horticulture of using quantitative survey methodology to inform horticultural tree crop breeding objectives. Using the Australian macadamia breeding program as a case study, the aim was to elicit Australian macadamia industry stakeholder preferences for economical equivalent trait improvements, estimate preference heterogeneity, and identify associations with stakeholder characteristics. A total of 19 respondents participated in the survey, representing 20% of the Australian macadamia industry. Respondents displayed a high willingness to use pairwise comparison implemented in the 1000minds software. Respondents exhibited a wide variability in preferences, however, variation in average preference among trait improvement levels was not large, suggesting on average preferences were consistent with economic values of unit of trait change derived from an industry developed bio-economic model. Observed heterogeneity in preferences were not associated with respondents’ role in industry, orchard size, or growing region.

Macadamia Orchard Planting Year and Area Estimation at a National Scale

Accurate estimates of tree crop orchard age and historical crop area are important to develop yield prediction algorithms, and facilitate improving accuracy in ongoing crop forecasts. This is particularly relevant for the increasingly productive macadamia industry in Australia, where knowledge of tree age, as well as total planted area, are important predictors of productivity, and the area devoted to macadamia orchards is rapidly increasing. We developed a technique to aggregate more than 30 years of historical imagery, generate summary tables from the data, and search multiple combinations of parameters to find the most accurate planting year prediction algorithm. This made use of known planting dates of more than 90 macadamia blocks spread across multiple growing regions. The selected algorithm achieved a planting year mean absolute error of 1.7 years. The algorithm was then applied to all macadamia features in east Australia, as defined in an recent Australian tree crops map, to determine the area planted per year and the total cumulative area of macadamia orchards in Australia. The area estimates were refined by improving the resolution of the mapped macadamia features, by removing non-productive areas based on an optimal vegetation index threshold.

Mapping the condition of macadamia tree crops using multi-spectral UAV and WorldView-3 imagery

Australia is one of the world’s largest producers of macadamia nuts. As macadamia trees can take up to 15 years to mature and produce maximum yield, it is important to optimize tree condition. Field based assessment of macadamia tree condition is time-consuming and often inconsistent. Using remotely sensed imagery may allow for faster, more extensive, and more consistent assessment of macadamia tree condition. To identify individual macadamia tree crowns, high spatial resolution imagery is required. Hence, the objective of this work was to develop and test an approach to map the condition of individual macadamia tree crowns using both multi-spectral Unmanned Aerial Vehicle (UAV) and WorldView-3 imagery for different macadamia varieties and three different sites located near Bundaberg, Australia. A random forest classifier, based on all available spectral bands and selected vegetation indices was used to predict five condition categories, ranging from excellent (category 1) to poor (category 5). Various combinations of the developed models were tested between the three sites and over time. The results showed that the multi-spectral WorldView-3 imagery produced the lowest out of bag (OOB) classification errors in most cases. However, for both the UAV and the WorldView-3 imagery, more than 98.5% of predicted macadamia condition categories were either correctly mapped or offset by a single category out of the five condition categories (excellent, good, moderate, fair and poor) for trees of the same variety and at one point in time. Multi-temporally, the WorldView-3 imagery performed better than the UAV data for predicting the condition of the same macadamia tree variety. Applying a model from one site to another site with the same macadamia tree variety produced OOB classification between 31.20 and 42.74%, but with >98.63% of trees predicted within a single condition category. Importantly, models trained based on one type of macadamia tree variety could not be successfully applied to a site with another variety. The developed classification models may be used as a decision and management support tool for the macadamia industry to inform management practices and improve on-demand irrigation, fertilization, and pest inspection at the individual tree level.

Maximising recombination across macadamia populations to generate linkage maps for genome anchoring

The Proteaceae genus Macadamia has a recent history of domestication as a commercial nut crop. We aimed to establish the first sequence-based haploid-correlated reference genetic linkage maps for this primarily outcrossing perennial tree crop, with marker density suitable for genome anchoring. Four first generation populations were used to maximise the segregation patterns available within full-sib, biparental and self-pollinated progeny. This allowed us to combine segregation data from overlapping subsets of >4,000 informative sequence-tagged markers to increase the effective coverage of the karyotype represented by the recombinant crossover events detected. All maps had 14 linkage groups, corresponding to the Macadamia haploid chromosome number, and enabled the anchoring and orientation of sequence scaffolds to construct a pseudo-chromosomal genome assembly for macadamia. Comparison of individual maps indicated a high level of congruence, with minor discrepancies satisfactorily resolved within the integrated maps. The combined set of maps significantly improved marker density and the proportion (70%) of the genome sequence assembly anchored. Overall, increasing our understanding of the genetic landscape and genome for this nut crop represents a substantial advance in macadamia genetics and genomics. The set of maps, large number of sequence-based markers and the reconstructed genome provide a toolkit to underpin future breeding that should help to extend the macadamia industry as well as provide resources for the long term conservation of natural populations in eastern Australia of this unique genus.

Improved crop forecasts for the Australian macadamia industry from ensemble models

Annual forecasts for the Australian macadamia crop have been issued since 2001, with varying (and not always improving) degrees of accuracy. Regression models using climate variables have formed the basis for these forecasts, with general linear model (GLM) ensembles being adopted more recently. This has proven to be a challenging task, as there are only a small number of observations (18) combined with a large number (90+) of independent variables – these being different climate measures for different times of the year (representing ‘key physiological periods for macadamia trees’). Also, these ‘assumedly-independent’ variables contain various degrees of correlation. This study uses cross-validation, with the most recent data for the two dominant production regions of Australia (Lismore and Bundaberg), to investigate the relative performance of alternate modelling methods. These modelling methods were GLMs, partial least squares (PLS) regression and LASSO (least absolute shrinkage and selection operator) penalised regression. Model ensembles, which have been shown to be beneficial in many alternate disciplines, are used to advantage. Both GLMs and PLS produced quite-disappointing results, failing to meet the project's benchmarked accuracy of ±10% error. The optimal LASSO models performed notably better, with a further improvement when ensembles were incorporated. The lowest mean absolute error (MAE) rates here were 9.0% for Lismore and 5.9% for Bundaberg. Hence LASSO ensembles will be adopted for future forecasts of the Australian macadamia crop.

Breeding New Cultivars for the Australian Macadamia Industry

In 2017, five new cultivars specifically selected for Australian conditions were released. These were developed from an improvement program initiated by Commonwealth Scientific and Industrial Research Organisation in the early 1990s. Progeny seeds were produced by crossing industry standard cultivars with other cultivars with elite kernel production per unit projected canopy area. Seedlings were planted at two densities (2 m and 4 m along rows) in field trials at Bundaberg in 1997 and 1998, and Northern New South Wales in late 1997, along with replicated plants of parents grafted onto seedling rootstocks. Trials were assessed for commencement of flowering, growth, yield, kernel recovery, and components of kernel quality over 8 years. Best linear unbiased predictions of clonal values were obtained for each individual progeny using a pedigree-based mixed linear model. A bio-economic model was used to estimate economic weights for a selection index of clonal values to identify elite candidates. Final approval of 20 candidates for second-stage assessment was made by an industry committee using selection index rankings and observations of tree field performance and kernel quality.

Rhizosphere Processes and Nutrient Management for Improving Nutrient-use Efficiency in Macadamia Production

Macadamia (Macadamia spp.) has been widely planted in southern China and has been now developed into an important industry. China has the largest area of macadamia plantation in the world but provides only 3% production of the world. Current farming systems have a fertilizer surplus of about 73 g of nitrogen (N), 103 g of phosphorus (P), and 24 g of potassium (K) per macadamia plant per year in southern China. Optimizing fertilization recommended for macadamia improves production by about 5 kg per plant. Macadamia develops cluster roots (i.e., proteoid roots) in a P-starvation environment. Overuse of P fertilizers restrains the development of cluster roots as well as rhizosphere processes, thus decreasing the P-use efficiency. Excessive fertilization, especially P fertilization, is one of the major limiting factors in China macadamia production. This study is the first to analyze current management practices and then discuss approaches of improving nutrient management based on the specific root biology of macadamia. For a sustainable macadamia industry, it is imperative to develop appropriate nutrient management by integrating root-zone soil nutrient supply, fertilizer application, and rhizosphere processes.

Pollen-parent affects fruit, nut and kernel development of Macadamia

The genotype of the pollen that fertilizes the ovule is known to affect the characteristics of fruits and nuts for many species, a phenomenom known as the xenia effect. Cross-pollination increases fruit set, nut mass, kernel mass and kernel recovery of macadamia nuts at maturity when compared with self-pollination. However there is limited information on the xenic effects of different macadamia cultivars used as cross pollen-parents on the fruit components and fruit development. The aim of this study was to clarify in what nut components and at what developmental stages xenic effects occurred. Two large-seeded macadamia cultivars, ‘HAES 246’ and ‘HV A16’, were used as maternal trees and pollen-parents were ‘HAES 246’, ‘HV A16’ and ‘HAES 814’, a small-seeded cultivar. Pollen-parents affected the mass of both the syngamous tissue of the kernel (embryo) and the tissues of maternal origin; i.e. the husk (pericarp) and shell (testa). Xenic effects were detected in the endosperm 6 weeks after pollination and in fruit, nut and kernel size and mass from 10 weeks after pollination until maturity. Nut mass, kernel mass and kernel recovery of macadamia were increased significantly by a different pollen-parent. The HV A16 pollen on HAES 246 flowers produced an increase of 11% nut mass compared with HV 814 pollen on HAES 246 flowers. This would increase the gross margin of a farm producing 4.5 t/ha of nuts by $2574/ha at typical 2018 prices. Macadamia growers and the macadamia industry would benefit from identification and use of the most beneficial cross-pollen sources available.

Understanding grower demographics, motivations and management practices to improve engagement, extension and industry resilience: a case study of the macadamia industry in the Northern Rivers, Australia

ABSTRACTResearch and development programs for improved productivity and profitability in horticulture have focused largely on understanding biophysical factors and production and harvest technologies. By contrast, relatively few studies focus upon the existing status of a rural community in terms of demographics, rationales and motivations underlying current farm management practices. Understanding such factors is increasingly important as pressures from climate change, globalised market forces, land-use competition and ageing workforces intersect on farms and for farmers. This paper explores experiences among macadamia growers in the Northern Rivers region of New South Wales, Australia, with the aim to better understand and improve the targeting of development programs to meet grower needs and aspirations, for improved industry resilience. Results suggest that growers are a diverse, ageing demographic who came into the industry with a variety of skill sets. Noting a lack of previous farming experience for many growers, we highlight the need to consider information transfer and succession planning, along with aspirations to consolidate properties and skills. New engagement approaches are recommended, with tailored extension to different grower groups. To aid with this process, a classification tree was developed for the purposes of separating growers into groups with different support needs.

Economic value of bat predation services – A review and new estimates from macadamia orchards

The economic value of natural regulation of agricultural pests by bats has been estimated both by avoided cost models and by experimental predator-exclusion approaches. We review published studies globally from both complementary approaches. We further present an economic model for the avoided cost of bat predation on stinkbugs, the major economic pest of macadamias in South Africa, currently the world’s largest macadamia producer. We calculated both the direct (reduced stinkbug damage due to bat predation) and indirect (reduced pesticide use) avoided costs. We estimated the density of bats in a macadamia-growing region of South Africa to be 7.5–22.5 bats/ha, based on opportunistic data from the Merlin DeTEct (Inc.) avian-avoidance radar system. Current economic parameters for macadamia production, stinkbug injury coefficients and life history were obtained from the literature and from the Southern African Macadamia Association (SAMAC).We estimated the level of bat predation on pest stinkbugs in macadamia orchards from published dietary studies combined with both high and low published values for insect consumption rates relative to bat body mass. We found that the protected yield due to bat predation of stink bugs amounted to 0.53% (low consumption rates) to 1.29% (high consumption rates) of annual macadamia production in South Africa for 2015. Based on current macadamia prices, the approximate avoided cost values of these combined direct and indirect bat predation services varied between 9% and 23% of the current annual estimated cost of damage caused by stinkbugs to South African macadamia orchards (US$613/ha). Losing bats to disease epidemics, wind farms, human persecution or excessive or highly toxic pesticide applications could therefore significantly increase annual losses to the macadamia industry in South Africa caused by stinkbugs.

Using Intact Nuts and Near Infrared Spectroscopy to Classify Macadamia Cultivars

Macadamia nut industry is increasingly gaining more space in the food market and the success of the industry and the quality are largely due to the selection of cultivars through macadamia nut breeding programs. Thus, the objective of this study was to investigate the feasibility NIRS coupled to chemometric classification methods, to build a rapid and non-invasive analytical procedure to classify different macadamia cultivars based on intact nuts. Intact nuts of five different macadamia cultivars (HAES 246, IAC 4-20, IAC 2-23, IAC 5-10, and IAC 8-17) were harvested in 2017. Two NIR reflectance spectra were collected per nut, and the mean spectra were used to chemometrics analysis. Principal component analysis-linear discriminant analysis (PCA-LDA) and genetic algorithm-linear discriminant analysis (GA-LDA) were used to develop the classifications models. The GA-LDA approach resulted in accuracy higher than 94.44%, with spectra preprocessed with Savitzky-Golay smoothing. Thus, this approach can be implemented in the macadamia industry, allowing the selection of cultivars based on intact nuts. However, it is recommended that more experimentation to include more data variability in order to increase the classification accuracy to 100%.