Full-season and post-harvest applications of sterol-inhibiting fungicides to reduce ascospore formation in Venturia inaequalis

Field and in vitro trials were conducted to establish the influence of the biological control agent Microsphaeropsis ochracea on the ejection pattern of ascospores by Venturia inaequalis and on apple scab development, and to establish the best timing of application. The ejection pattern of ascospores was similar on leaves sprayed with M. ochracea and on untreated leaves. Fall application of M. ochracea combined with a delayed-fungicide program was evaluated in orchards with intermediate and high scab risk. For both orchards, it was possible to delay the first three and two infection periods in 1998 and 1999, respectively, without causing significant increase or unacceptable leaf and fruit scab incidence. To evaluate the best timing of application, sterile leaf disks were inoculated with V. inaequalis and then with M. ochracea 0, 2, 4, 6, 8, 10, 12, 14, and 16 weeks later. After incubation under optimal conditions for pseudothecia development, the number of ascospores was counted. Similarly, M. ochracea was sprayed on scabbed leaves on seven occasions from August to November 1999 and 2000. Leaves were overwintered on the orchard floor and ascospore production was evaluated the following spring. Ascospore production was reduced by 97 to 100% on leaf disks inoculated with M. ochracea less than 6 weeks after inoculation with V. inaequalis, but ascospore production increased with increasing period of time when M. ochracea was applied 8 to 16 weeks after the inoculation with V. inaequalis. In the orchard, the greatest reduction in production of ascospores (94 to 96% in 2000 and 99% in 2001) occurred on leaves sprayed with M. ochracea in August. The production of ascospores was reduced by 61 to 84% in 2000 and 93% in 2001 on leaves sprayed with M. ochracea in September, reduced by 64 to 86% in 2000 and 74 to 89% in 2001 on leaves sprayed in October, and reduced by 54 and 67% in 2000 and 2001, respectively, on leaves sprayed in November. It was concluded that M. ochracea should be applied in August or September and that ascospore maturation models and delayed-fungicide program could be used in orchards treated with this biological control agent.

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A review of non-fungicidal approaches for the control of apple scab

Carisse¹,

Dewdney²

2005

phyto

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Apple scab is the single most important disease of apple in Canada and the most costly to control. Failure to control apple scab results in severe yield losses and a reduction in market value of harvested fruits. Currently, the strategy to control apple scab relies on multiple applications of fungicides. These sprays are a significant cost to growers and the indirect environmental impact may be substantial. Reliance on fungicides can be reduced by the integration of non-fungicidal control measures that include genetic, physical, and biological approaches. Recommendations for chemical control of apple scab are often based on the highly susceptible cultivar McIntosh. This was justified because up to 60 to 70% of orchards in northeastern North America were planted with this cultivar. Today, the situation is changing as more and more growers are planting new cultivars, some of which are less susceptible to apple scab. A change in the recommendations to account for cultivar susceptibility could result in a reduction in the number of fungicide applications required. In addition, there has been long-standing research on resistant cultivars, but none of the scab-resistant cultivars have been widely accepted. However, with new molecular techniques to identify and locate the resistance genes, there is potential for progress on this front. Furthermore, fungicide applications for primary infections can be delayed if the number of ascospores is reduced after fall treatments that include leaf shredding, the application of biological control agents, or urea. These methods are preventive and can be integrated into existing management programs. However, the integration of all or some of these methods is more complex than simply the use of fungicides. Nevertheless, integrated management of apple scab may prove more sustainable on a long-term basis, mainly because it does not depend on the use of a single method. Hence the risk of the development of fungicide resistance in the pathogen population is reduced.

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Full-season and post-harvest applications of sterol-inhibiting fungicides to reduce ascospore formation in Venturia inaequalis

Cited by 3 publications

References 10 publications

Apple leaf shredding as a non-chemical tool to manage apple scab and spotted tentiform leafminer

Apple leaf shredding as a non-chemical tool to manage apple scab and spotted tentiform leafminer

Effect of Timing of Application of the Biological Control Agent Microsphaeropsis ochracea on the Production and Ejection Pattern of Ascospores by Venturia inaequalis

A review of non-fungicidal approaches for the control of apple scab

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