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Ulverstone, Australia

Jones S.J.,University of Tasmania | Gent D.H.,Oregon State University | Pethybridge S.J.,Agricultural Services Pty Ltd. | Hay F.S.,University of Tasmania
Plant Pathology

To improve sampling efficiency and precision in the assessment of white mould (caused by Sclerotinia sclerotiorum) disease incidence on bean (Phaseolus vulgaris), the spatial characteristics of epidemics were characterized in 54 linear transects in 18 bean fields during 2008-2010 in northern Tasmania, Australia. The incidence of diseased pods and plants was assessed prior to harvest. Distributional and correlation-based analyses indicated the incidence of diseased pods was characterized by a largely random pattern at the individual plant scale, with some patches of similar disease levels on pods occurring at a scale of 1·5m or greater. Collectively, these results suggested epidemics may be dominated by localized sources of inoculum. Sequential sampling approaches were developed to estimate or classify disease incidence above or below provisional thresholds of 3, 5 and 15% incidence on pods near harvest. Achieving prespecified levels of precision by sequential estimation was possible only when disease incidence on pods was greater than approximately 4% and sampling was relatively intense (i.e. 10 pods evaluated on each of at least 64 plants). Using sequential classification, correct decisions on disease status were made in at least 95% of independent validation datasets after assessment of only 10·1-15 plants, depending on classification threshold and error rates. Outcomes of this research provide the basis for implementing more efficient sampling and management strategies for this disease in Australian fields. © 2011 The Authors. Plant Pathology © 2011 BSPP. Source

Jonesa S.J.,University of Tasmania | Gent D.H.,U.S. Department of Agriculture | Gent D.H.,Oregon State University | Pethybridge S.J.,Agricultural Services Pty Ltd. | Hay F.S.,University of Tasmania
New Zealand Journal of Crop and Horticultural Science

In Tasmania, Australia, if more than 5% of bean pods are affected by white mould (Sclerotinia sclerotiorum) shipments may be rejected by the processor. This standard dictates prophylactic fungicide application over flowering, although in some instances treatment may not be warranted because oflow disease risk. Surveys were conducted to identify relationships among edaphic factors, weather variables, and production practices associated with white mould. Correlations were found between disease incidence and the number of apothecia, fungicide timing, and mean minimum air temperature in the 10- and 30-day periods preceding harvest. Significant differences in disease incidence also were detected among cultivars and bean canopy densities. A nonparametric discriminant analysis model based on the predictor variables ofmean minimum air temperature in the 10- and 30-day periods before harvest, cultivar, bean canopy density, and fungicide application correctly predicted presence of white mould on pods in 77% of bean fields. Several factors that can be manipulated to reduce disease risks were identified. © 2012 The Royal Society ofNew Zealand. Source

Lang M.D.,University of Tasmania | Evans K.J.,University of Tasmania | Pethybridge S.J.,Agricultural Services Pty Ltd.
Acta Horticulturae

Walnut blight, caused by Xanthomonas arboricola pv. juglandis, has been responsible for significant losses in early-leafing walnut crops in Tasmania, Australia. Research over three growing years was undertaken to study disease epidemiology and refine the copper spray programme. The progression of disease incidence was best described by the monomolecular growth model in 2004-2005 and 2006-2007, implying a monocyclic epidemic. In contrast, the logistic growth model described a polycyclic epidemic in 2005-2006. For monocyclic epidemics, two sprays of copper formulated with mancozeb applied one week apart from 5% terminal bud-burst provided commercially acceptable control. For the polycyclic epidemic, four copper-mancozeb applications from bud-burst significantly reduced blight incidence in comparison to three or fewer applications; however, disease control was inadequate. Reducing active copper from 1.5 kg to 0.75 kg per hectare in monocyclic epidemics maintained control of blight. For polycyclic epidemics, half rates of copper resulted in similar levels of blight infection compared to the full rate; however, full rates significantly increased nut yield in comparison to nontreated plots. This study indicated that strategic application of copper-based bactericides, timed according to pathogen activity, may adequately control walnut blight and limit unnecessary applications of copper. Source

Javid M.,University of Melbourne | Zhang P.,University of Melbourne | Taylor P.W.J.,University of Melbourne | Pethybridge S.J.,Agricultural Services Pty Ltd. | And 2 more authors.
Crop and Pasture Science

The effects of waterlogging, alone and combined with ray blight disease (caused by Stagonosporopsis tanaceti), on pyrethrum (Tanacetum cinerariifolium) plant growth were quantified in glasshouse trials. Six pyrethrum cultivars were initially studied for their response to 6 days of waterlogging and their recovery from waterlogging during 26 days post-waterlogging. Waterlogging caused substantial root death and leaf wilting and accelerated senescence in all cultivars. Root growth was 80% more reduced than shoot growth. Cultivar 'F' showed significantly higher root porosity and growth following waterlogging than other cultivars. In contrast, cv. 'C' had the greatest growth reduction from waterlogging and poor root-system recovery after waterlogging. Plants of cvv. C and F inoculated with S. tanaceti and then waterlogged were more significantly affected than were those exposed to waterlogging only. For both cultivars, shoot growth under the combined treatment, relative to initial growth, recovered up to 25%, but root growth suffered irreversible damage. The combined treatment decreased the number of stems by 39% compared with waterlogging alone after the post-waterlogging period. In conclusion, pyrethrum cultivars showed differential reactions to waterlogging; but growth in all cultivars was seriously affected by a combination of waterlogging and infection by ray blight. © 2013 CSIRO. Source

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