Institute for Commercial Forestry Research ICFR

Pietermaritzburg, South Africa

Institute for Commercial Forestry Research ICFR

Pietermaritzburg, South Africa
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Poona N.K.,Stellenbosch University | Poona N.K.,Institute for Commercial Forestry Research ICFR | Van Niekerk A.,Stellenbosch University | Van Niekerk A.,University of Western Australia | And 2 more authors.
Applied Spectroscopy | Year: 2016

Hyperspectral data collected using a field spectroradiometer was used to model asymptomatic stress in Pinus radiata and Pinus patula seedlings infected with the pathogen Fusarium circinatum. Spectral data were analyzed using the random forest algorithm. To improve the classification accuracy of the model, subsets of wavebands were selected using three feature selection algorithms: (1) Boruta; (2) recursive feature elimination (RFE); and (3) area under the receiver operating characteristic curve of the random forest (AUC-RF). Results highlighted the robustness of the above feature selection methods when used in conjunction with the random forest algorithm for analyzing hyperspectral data. Overall, the Boruta feature selection algorithm provided the best results. When discriminating F. circinatum stress in Pinus radiata seedlings, Boruta selected wavebands (n = 69) yielded the best overall classification accuracies (training error of 17.00%, independent test error of 17.00% and an AUC value of 0.91). Classification results were, however, significantly lower for P. patula seedlings, with a training error of 24.00%, independent test error of 38.00%, and an AUC value of 0.65. A hybrid selection method that utilizes combinations of wavebands selected from the three feature selection algorithms was also tested. The hybrid method showed an improvement in classification accuracies for P. patula, and no improvement for P. radiata. The results of this study provide impetus towards implementing a hyperspectral framework for detecting stress within nursery environments. © Society for Applied Spectroscopy. © The Author(s) 2015.

Nadel R.L.,University of Pretoria | Nadel R.L.,Institute for Commercial Forestry Research ICFR | Wingfield M.J.,University of Pretoria | Scholes M.C.,University of Witwatersrand | And 3 more authors.
Journal of Pest Science | Year: 2014

Thaumastocoris peregrinus is a sap-sucking insect that infests non-native Eucalyptus plantations in Africa, New Zealand, South America and parts of Southern Europe, in addition to street trees in parts of its native range of Australia. In South Africa, pronounced fluctuations in the population densities have been observed. To characterise spatiotemporal variability in T. peregrinus abundance and the factors that might influence it, we monitored adult population densities at six sites in the main eucalypt growing regions of South Africa. At each site, twenty yellow sticky traps were monitored weekly for 30 months, together with climatic data. We also characterised the influence of temperature on growth and survival experimentally and used this to model how temperature may influence population dynamics. T. peregrinus was present throughout the year at all sites, with annual site-specific peaks in abundance. Peaks occurred during autumn (February-April) for the Pretoria site, summer (November-January) for the Zululand site and spring (August-October) for the Tzaneen, Sabie and Piet Retief monitoring sites. Temperature (both experimental and field-collected), humidity and rainfall were mostly weakly, or not at all, associated with population fluctuations. It is clear that a complex interaction of these and other factors (e.g. host quality) influence population fluctuations in an annual, site specific cycle. The results obtained not only provide insights into the biology of T. peregrinus, but will also be important for future planning of monitoring and control programs using semiochemicals, chemical insecticides or biological control agents. © 2014 Springer-Verlag Berlin Heidelberg.

Nadel R.L.,University of Pretoria | Nadel R.L.,Institute for Commercial Forestry Research ICFR | Wingfield M.J.,University of Pretoria | Scholes M.C.,University of Witwatersrand | And 2 more authors.
Annals of Forest Science | Year: 2012

• Context Southern Hemisphere plantation forestry has grown substantially over the past few decades and will play an increasing role in fibre production and carbon sequestration in future. The sustainability of these plantations is, however, increasingly under pressure from introduced pests. This pressure requires an urgent and matching increase in the speed and efficiency at which tools are developed to monitor and control these pests. • Aim To consider the potential role of semiochemicals to address the need for more efficient pest control in Southern Hemisphere plantations, particularly by drawing from research in other parts of the world. • Results Semiochemical research in forestry has grown exponentially over the last 40 years but has been almost exclusively focussed on Northern Hemisphere forests. In these forests, semiochemicals have played an important role to enhance the efficiency of integrated pest management programmes. An analysis of semiochemical research from 1970 to 2010 showed a rapid increase over time. It also indicated that pheromones have been the most extensively studied type of semiochemical in forestry, contributing to 92% of the semiochemical literature over this period, compared with research on plant kairomones. This research has led to numerous applications in detection of new invasions, monitoring population levels and spread, in addition to controlling pests by mass trapping or disrupting of aggregation and mating signals. • Conclusion The value of semiochemicals as an environmentally benign and efficient approach to managing forest plantation pests in the Southern Hemisphere seems obvious. There is, however, a lack of research capacity and focus to optimally capture this opportunity. Given the pressure from increasing numbers of pests and reduced opportunities to use pesticides, there is some urgency to develop semiochemical research capacity. © INRA / Springer-Verlag France 2012.

Nadel R.L.,University of Pretoria | Nadel R.L.,Institute for Commercial Forestry Research ICFR | Wingfield M.J.,University of Pretoria | Scholes M.C.,University of Witwatersrand | And 4 more authors.
BioControl | Year: 2012

Thaumastocoris peregrinus Carpintero and Dellapé (Hemiptera: Thaumastocoridae) is a native Australian Eucalyptus sap-feeding insect that has become invasive and seriously damaging to commercially grown Eucalyptus in the Southern Hemisphere. Cleruchoides noackae Lin and Huber (Hymenoptera: Mymaridae) was recently discovered as an egg parasitoid of the Thaumastocoridae in Australia. Mitochondrial DNA (mtDNA; cytochrome c oxidase subunit I, COI) sequence diversity amongst 104 individuals from these native C. noackae populations revealed 24 sequence haplotypes. The COI haplotypes of individuals collected from the Sydney and Southeast Queensland clustered in distinct groups, indicating limited spread of the insect between the regions. Individuals collected from Perth in Western Australia were represented by four COI haplotypes. Although this population is geographically more isolated from other populations, two COI haplotypes were identical to haplotypes found in the Sydney region. The results suggest that C. noackae has recently been introduced into Perth, possibly from the Sydney area. The high mtDNA diversity and limited spread that is suggested for C. noackae is in contrast to the lack of geographic associated mtDNA diversity and extensive spread of T. peregrinus. If implemented as a biological control agent, this factor will need to be considered in collecting and releasing C. noackae. © 2011 International Organization for Biological Control (IOBC).

Roux J.,University of Pretoria | Germishuizen I.,Institute for Commercial Forestry Research ICFR | Nadel R.,Institute for Commercial Forestry Research ICFR | Lee D.J.,University of The Sunshine Coast | And 2 more authors.
Plant Pathology | Year: 2015

Puccinia psidii, the causal agent of myrtle rust, was first recorded from Latin America more than 100 years ago. It occurs on many native species of Myrtaceae in Latin America and also infects non-native plantation-grown Eucalyptus species in the region. The pathogen has gradually spread to new areas including Australia and most recently South Africa. The aim of this study was to consider the susceptibility of selected Eucalyptus genotypes, particularly those of interest to South African forestry, to infection by P. psidii. In addition, risk maps were compiled based on suitable climatic conditions and the occurrence of potential susceptible tree species. This made it possible to identify the season when P. psidii would be most likely to infect and to define the geographic areas where the rust disease would be most likely to establish in South Africa. As expected, variation in susceptibility was observed between eucalypt genotypes tested. Importantly, species commonly planted in South Africa show good potential for yielding disease-tolerant material for future planting. Myrtle rust is predicted to be more common in spring and summer. Coastal areas, as well as areas in South Africa with subtropical climates, are more conducive to outbreaks of the pathogen. © 2015 British Society for Plant Pathology.

Nadel R.L.,Institute for Commercial Forestry Research ICFR | Noack A.E.,University of New South Wales
International Journal of Pest Management | Year: 2012

Thaumastocoris peregrinus is a serious insect pest of Southern African and South American Eucalyptus plantations. Native to Australia, T. peregrinus was initially discovered infesting street, garden and amenity eucalypts in Sydney. With a host range of over 30 Eucalyptus species and hybrids this pest became established concurrently in both South Africa and Argentina, and has since spread at an extraordinary rate to neighbouring countries. In its native range T. peregrinus is distributed across several climatic regions in Australia. Basic biological data have been obtained on T. peregrinus although progress has been limited by culturing difficulties in the laboratory. Monitoring of T. peregrinus populations has been conducted at the individual tree, tree stand and regional levels to understand the population dynamics of the pest. Chemical control is effective in controlling T. peregrinus in an urban setting, however, biological control using Cleruchoides noackae is presently the main focus of control efforts at the international level. Three new species of Thaumastocoris have been identified as potential pests, based on their geographical distribution and host range. Research into further understanding the biology of T. peregrinus and identifying other potential biological control agents is crucial for the management of present and future Thaumastocoris infestations. © 2012 Copyright Taylor and Francis Group, LLC.

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