The effect of fungicides on urediniospore germination and disease development of daylily rust

Abstract

In response to the recent introduction and rapid spread throughout the United States of daylily rust caused by Puccinia hemerocallidis, research was conducted on the relative efficacy of seven fungicides (myclobutanil, propiconazole, flutolanil, triadimefon, chlorothalonil, mancozeb, and azoxystrobin) for control of this disease. Fungicides were applied at varying rates 24 h before spray–inoculation of daylilies ( Hemerocallis sp. cv. Pardon Me) with urediniospore suspensions. Disease development was evaluated by counting rust pustules on six to eight leaves per plant after 15 days. Nearly all fungicides reduced the number of pustules cm −1 of leaf length compared to the untreated control in all greenhouse trials. The protectant fungicides chlorothalonil and mancozeb significantly reduced pustule development. Of three sterol-biosynthesis inhibiting compounds, triadimefon provided greatest reduction in pustule development. Myclobutanil and propiconazole did not affect in vitro urediniospore germination on fungicide-amended potato dextrose agar (PDA). All concentrations of azoxystrobin and chlorothalonil significantly reduced urediniospore germination. A 24 h exposure to PDA amended with azoxystrobin (1.0–100.0 μg a.i. ml −1), chlorothalonil (100 μg a.i. ml −1) or mancozeb (10.0 and 100.0 μg a.i. ml −1) eliminated subsequent urediniospore germination on non-amended PDA. The data indicate that daylily rust can be controlled under greenhouse conditions by applications of fungicides.