Field Evaluation of a New Sequential Sampling Technique for Determining Apple Scab “Risk”

Abstract

Most fungicide sprays applied to apple orchards in the New England states are targeted at the management of apple scab. Researchers have developed action thresholds that aid in decision-making on whether early spring fungicide applications could be eliminated without a significant increase in the incidence of fruit scab at harvest. To facilitate grower adoption of these thresholds, a simplified, sequential sampling technique in autumn to determine the “scab risk” of an orchard for the following spring was proposed in the scientific literature. However, this technique had not been evaluated in the field. In autumn 1999, 2000, and 2001, orchards were evaluated using the new sequential sampling technique to determine scab risk. Risk ratings were compared with those obtained by the original, nonsequential procedure in each orchard. Data also were examined using a simulation sequential sampling computer program to determine whether or not risk ratings would change if different trees or shoots were used. In two of the assessed orchards, “delayed-spray” experiments involving two treatments (a delayed-spray and full-spray treatment) were conducted in 2000 and 2001. Delayed-spray replicates were to receive no fungicide sprays until after the third primary infection period (but before the fourth) or until the pink stage of bud development, whichever came first; full-spray replicates received fungicide sprays starting at the green-tip stage of bud development. The sequential sampling technique provided scab-risk ratings consistent with the original, nonsequential procedure, at potentially significant time savings. Also, following the delayed-spray strategy in low-risk orchards did not result in significant differences in fruit scab at harvest compared with initiating spraying at the green-tip phenological bud stage.

Resistência parcial de cultivares antigas de macieira a Venturia inaequalis

“…O controle químico da sarna da macieira, a tática mais utilizada pelos produtores, inicia-se imediatamente após a brotação e pode chegar a um total de 9 a 15 aplicações de fungicidas durante o ciclo da cultura (Reardon et al, 2005). Entretanto, a demanda crescente dos consumidores por produtos com níveis adequados de resíduos, a cobrança social por sistemas de cultivo de menor impacto ambiental e a redução na eficiência dos fungicidas pela seleção de isolados de V. inaequalis resistentes geram a necessidade de buscar táticas alternativas e complementares para o manejo da doença (Jobin & Carisse, 2007).…”

Disease Decision Support Systems: Their Impact on Disease Management and Durability of Fungicide Effectiveness

“…As a result, a sequential sampling procedure was developed based on the analysis of 66 fall assessments of leaf scab (MacHardy et al, 1999;Reardon et al, 2005). This sampling procedure is use to classify orchards as "low risk" or "high risk" (Reardon et al, 2005). Fig.…”

“…Nevertheless, despite the large amount of research that has been done on apple scab, the disease is still one of the most destructive and economically important disease in several apple production areas. Scab management may require 6 to 16 sprays annually depending on disease pressure, cultivar susceptibility, weather conditions, and marketing objectives (Reardon et al, 2005, Van der Sheer, 1992, Holb et al, 2005. Intensive use of fungicide in apple production has led to unstable control as fungicide resistance arose.…”

Spatial heterogeneity, incidence-incidence and incidence-lesion density relationship of apple scab (Venturia inaequalis) in managed orchards

“…In eastern North America, most current strategies for managing apple scab are based on controlling primary infections in order to avoid epidemic build-up caused by secondary infections and, thus, reduce or eliminate the need for subsequent fungicide applications during the summer months. To achieve this goal, fungicide applications generally begin in the spring at the green tip phenological stage and continue throughout spring in to early summer, resulting in approximately 8-10 fungicide applications (Reardon et al 2005). If this approach fails to control scab adequately, then fungicides must be applied during the summer and the annual number of fungicide sprays could rise to 14-16, depending on the prevailing weather conditions during the summer months (MacHardy 1996; Reardon et al 2005).…”

“…To achieve this goal, fungicide applications generally begin in the spring at the green tip phenological stage and continue throughout spring in to early summer, resulting in approximately 8-10 fungicide applications (Reardon et al 2005). If this approach fails to control scab adequately, then fungicides must be applied during the summer and the annual number of fungicide sprays could rise to 14-16, depending on the prevailing weather conditions during the summer months (MacHardy 1996; Reardon et al 2005). It is therefore important to develop tools to precisely estimate the level of control of primary infections.…”