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Fungicide efficacy and molecular characterization of North Carolina Colletotrichum populations causing Glomerella leaf spot and fruit rot on apple

Kendall Johnson: North Carolina State University

<div>Glomerella leaf spot (GLS) and fruit rot (GFR) are caused by fungi in the <em>Colletotrichum gloeosporioides</em> species complex. Knowledge gaps in causal species, pathogen biology, and fungicide efficacy have made management of GLS and GFR extremely challenging for North Carolina (NC) apple growers. To more effectively manage GLS and GFR during the growing season and post-harvest, field experiments investigating fungicide efficacy were conducted in a ‘Tenroy Gala’ research orchard in 2017. Fungicides representing different modes of action were applied in non-rotational programs from petal fall through 9th cover. Merivon (pyraclostrobin + fluxapyroxad) applications resulted in lower incidence and severity of GLS and GFR, but were not significantly different than multi-site fungicide applications (<em>p ≤</em> 0.0001). Additionally, 433 isolates of <em>Colletotrichum </em>spp. were collected from diseased fruit and leaves in NC commercial apple orchards for species identification and sensitivity to the quinone outside inhibitor (QoI) fungicides pyraclostrobin and trifloxystrobin. Initial multigene sequence analysis of 18 fruit isolates and 14 leaf isolates revealed <em>C. fructicola</em> as the most prevalent species causing GLS and GFR in NC. Currently, <em>in vitro</em> mycelial and conidial germination assays are being conducted to evaluate QoI fungicide sensitivity of species within the <em>C. gloeosporioides</em> complex and between <em>Colletotrichum</em> spp. populations in NC.</div>

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