Effect of environmental factors on seventy of stemphylium leaf spot on asparagus

Abstract

Light intensity, photoperiod, relative humidity, and temperature during fern growth and fern age at time of inoculation, and wetness duration, light intensity, and temperature during infection period were examined to establish their effect on severity of Stemphylium leaf spot on asparagus. Plants were inoculated with a conidial suspension of two isolates of Stemphylium sp. from asparagus. Disease assessments based on percentage stem area necrosis, percentage dieback of stem, and percentage infection of cladode tissue were made 10–14 days after inoculation. Asparagus fern grown under conditions of low light (particularly a reduced photoperiod), high relative humidity, and temperature became severely infected. Disease severity decreased with increasing age of fern at time of inoculation. Two days of wetness following inoculation were sufficient for maximum disease development; plants held at low temperature (14°C) had higher levels of infection than those held at 20 or 26°C. Light intensity during the infection period had no effect on disease severity levels. Of the three methods of disease assessment, cladode infection provided the most reliable measure of disease severity levels. The method of assessing percentage of cladode infection on a group of seedlings in a pot was more reliable than the assessments made on individual seedlings. © Crown copyright 1991.