Effect of fungicide timing and environmental conditions on production and viability of urediniospores of puccinia hemerocallidis

Abstract

Daylilies infected with Puccinia hemerocallidis were placed under continuous light or alternating light-dark and dark-light treatments for 24 h. A separate experiment tested the effects on urediniospore germination and production of three temperatures (15, 20, and 30ºC) and low vs. high relative humidites. Light, temperature, and humidity did not significantly affect urediniospore germination, but urediniospore production per lesion was significantly higher with continuous light exposure, 30ºC and low relative humidity. Azoxystrobin, chlorothalonil, myclobutanil, propiconazole, and triadimefon were tested to determine fungicide efficacy on three post-inoculation stages of disease development. All fungicides reduced urediniospore germination at all stages of disease development to < 45% of control one day after treatment application. Only azoxystrobin and chlorothalonil were able to reduce urediniospore germination at all stages of disease development to < 5% seven days after treatment. Fungicides did not have a significant effect on urediniospore production per lesion.