Management of Daylily Rust with Different Fungicide Combinations and Spray Intervals

Abstract

Daylily (Hemerocallis spp.) is a popular herbaceous perennial plant and was considered to be relatively disease free until 2000, when daylily rust, caused by Puccinia hemerocallidis, was first detected in the United States. Management of daylily rust in nurseries is dependent on the use of fungicides, which are typically applied to the foliage of large blocks of plants at 21- or 28-day intervals. The objectives of this study were to determine the most effective fungicides or fungicide combinations and application intervals for managing daylily rust in the field. Foliar sprays of azoxystrobin alone at 14-, 21-, or 28-day intervals, combinations of azoxystrobin + propiconazole, azoxystrobin + chlorothalonil, propiconazole + chlorothalonil, and chlorothalonil + thiophanate-methyl applied at intervals of 21or 28 days, and a nontreated control were evaluated under high disease pressure, at three locations in Griffin, GA in 2014. In all three fields, all treatments that included azoxystrobin were effective at reducing area under the disease progress curve (AUDPC) compared with the nontreated control. At two of the three locations, azoxystrobin applied at 14-day intervals had significantly lower AUDPC than when applied at 21- or 28-day intervals. The addition of propiconazole or chlorothalonil to azoxystrobin did not improve rust control. Disease ratings for propiconazole + chlorothalonil and thiophanate-methyl + chlorothalonil applied at 21- or 28-day intervals did not differ from the untreated control. The 21-day treatments resulted in significantly lower disease than 28-day treatments (all fungicides) in the middle and end of the season. Elimination of less efficacious active ingredients and unnecessary applications can help growers maximize profitability by reducing expenses as well as simplifying fungicide inventory and storage.