Sclerotinia fructicola ascospore fluctuations in a peach orchard during blossom

Abstract

A Hirst spore trap was operated within a peach orchard during blossom at Levin, New Zealand, from 6 September to 3 October 1977 to monitor ascospore dissemination. ApotheciaJ emergence began in mid August, and ceased in late September, overlapping the blossom period at both ends, and peaking in early September during full bloom, at a density of 4.7/m² of ground surface. Ascospore dissemination followed a diurnal rhythm; ascospores Were generally absent in significant numbers during the night and until late morning, then peaking between noon and late afternoon before falling away again by evening. A peak maximum of 1213 ascospores/m³ /hour occurred on 16 September, and for 21 of the 27 days exceeded 100/m³ /hour for 2–6 hours each day. The daily rise in ascospores coincided always with increasing air temperature and falling relative humidity, with correlations significant at 1 % probability. In unsprayed trees 91 % blossom blight was recorded at late petal fall on 26 September, the first 58% of infection being caused by ascospores.