Assessing new methods of integrated pest management for apple orchards in the Midwest and phenology of sooty blotch and flyspeck fungi on apples in Iowa

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Sisson, Adam
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Mark L. Gleason Matthew Liebman
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Plant Pathology and Microbiology

Four apple management strategies were compared in an Iowa orchard for codling moth, sooty blotch and flyspeck (SBFS), apple scab, and weeds. An orchard block with three apple scab-resistant cultivars (Redfree, Liberty, and Goldrush) was used to compare two new integrated pest management (IPM) systems that incorporated weather-based disease-warning systems and alternative pesticides (Treatments 3 and 4) with an existing IPM regime (Treatment 2) and a conventional system with calendar-based timing of fungicide and insecticide sprays (Treatment 1). Mean incidence (%) of fruit with disease or insect injury was recorded at harvest and marketable and cull fruit were counted and weighed. The new IPM strategies were as effective as calendar-based and existing-IPM treatments for most apple pests, and yields were equivalent. An economic analysis indicated that Treatment 4 was the least expensive for larger orchards and Treatment 3 was the most expensive for all orchard sizes in 2008. Treatment 4 also had the least pesticide applications during the 2008 growing season. Active ingredients, spray rates, and applications of pesticides were used to develop an environmental risk rating for each treatment. New IPM treatments lowered ecological risks compared to calendar-based spraying and existing IPM. Composted hardwood mulch was also compared with bare soil for weed control efficacy; mulch suppressed weed coverage and biomass compared to bare soil and required fewer herbicide applications.

Sooty blotch and flyspeck (SBFS) is a complex of >60 fungal species that blemish the surface of apple fruit in humid regions worldwide. Blemishes become visible in mid-to late summer, reducing the value of fresh fruit. To test the hypothesis that SBFS species appear on apples at characteristic times during the growing season, 30 apples were monitored weekly for appearance of SBFS colonies at each of three Iowa orchards in 2006 and seven orchards in 2007. Colonies were marked with colored pens to denote the date of appearance. After harvest and storage of apples, SBFS colonies on each fruit were counted and classified by morphology, and a representative subset of colonies were removed. Fungal DNA, extracted from colonies scraped from the surface of the peel, was amplified with primer pair ITS1-F/ Myc1-R. Polymerase chain reaction products were digested with HaeIII, and fragment patterns were observed with gel electrophoresis and compared to a library of previously identified SBFS species. Sterile mycelia spp. RS1 and RS2 were the first to appear in all but one of the Iowa orchards surveyed where SBFS signs were observed. Dissoconium aciculare consistently appeared on fruit during the week prior to harvest, and additional colonies of this species appeared during storage. The species that were most prevalent in Iowa orchards were also the most abundant. Knowledge of species prevalence and chronology of appearance on apple fruit could lead to improved SBFS management strategies.

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Thu Jan 01 00:00:00 UTC 2009