Published online by Cambridge University Press: 12 June 2017
The effects of temperature and dew period on infectivity of Puccinia chondrillina Bubak and Syd. and the effect of light intensity on uredospore germination were studied under controlled environmental conditions. When rush skeletonweed (Chondrilla juncea L.) plants were inoculated with uredospores at 8, 16, and 24 C, larger pustules developed faster at 24 C than at the cooler temperatures. The greatest amount of infection occurred at 8 and 16 C (75% of the leaf area infected compared to 25% at 24 C). The greater number of infection sites at cooler temperatures was coincident with an increase in uredospore germination at 8 and 16 C compared to 24 C. Increasing the dew period from 0 to 6 h increased the amount of infection by the rust. Light intensities as low as 0.5 klux significantly reduced uredospore germination on water agar. Germ tube growth was restricted significantly by light intensities of 2.5 to 4.5 klux. Applications of uredospores to aid in biological control of this serious weed would be most successful if made at dusk under cool temperatures when an extended dew period is expected.