Dispersal of Conidia of Zygophiala jamaicensis in Apple Orchards

Abstract

Sutton, T. B. 1990. Dispersal of conidia of Zygophiala jamaicensis in apple orchards. Plant Dis. 74: 643-646. Conidia of Zygophiala jamaicensis, the causal agent of flyspeck, were trapped in apple (Malus domestica) orchards or near reservoir inoculum sources from late May or early June through harvest (mid-September). Hourly spore concentrations were positively correlated with temperature and windspeed and negatively correlated with relative humidity and leaf wetness. Conidia concentration in the air was characterized by a distinct diurnal periodicity; most conidia were trapped between 0700 and 1300 hours. Fruit infections were usually observed about 1 mo after the first conidia were trapped. Management practices for flyspeck in apple orchards need to account for the presence and abundance of reservoir hosts, environmental conditions, orchard management strategies, and fungicide choice and timing. Flyspeck (caused by Zygophiala jamaicensis Mason; teleomorph, Schizothyrium pomi [Mont. & Fr.] Arx), is one of the most important diseases of apples (Malus domestica Borkh.) in the southeastern United States. Z. jamaicensis overwinters on apple twigs and on numerous reservoir hosts (2,9). Ascospores mature in late spring and initiate primary infections on apples and reservoir hosts. Conidia, produced from primary infections, initiate secondary cycles throughout the growing season. Numerous reservoir hosts are sources of inoculum. Rubus spp. are the most abundant reservoir hosts in North Carolina, however, at least 37 additional hosts have been identified (9). Control of flyspeck is based on the application of protectant fungicides applied at 10- to 14-day intervals. Not all fungicides registered for flyspeck control are equally effective against Z. jamaicensis. For instance, the ethylenebis[dithiocarbamate] (EBDC) fungicides are much more effective than captan (1); however, captan is often preferred because it provides better fruit finish early in the season and is more active against white rot (caused by Botryosphaeria dothidea [Moug. ex Fr.] Ces. & De Not.) and black rot (caused by Botryosphaeria obtusa [Schwein.] Shoemaker). Consequently, growers are often faced with the problem of knowing in