Persistence of Beauveria bassiana, Nomuraea rileyi , and Nosema necatrix on Soyhean Foliage 1

Abstract

Bioassay techniques were employed to determine the persistence of Beauveria bassiana (Bals.) Vuill., Nomuraea rileyi (Farlow) Sampson, and Nosema necatrix (Kramer) on soybean foliage. One-half of the original activity of each pathogen was lost between 5 and 10 days postapplication. The average % mortality of Spodoptera frugiperda (J. E. Smith) larvae resulting from exposure to the foliage treated with B. bassiana ranged from 83.2% on the day of application to no deaths 10 days later. The average % mortality caused by N. rileyi decreased from 98.4% to 10.4% over the same period, while the average % infection of Heliothis zea (Boddie) larvae caused by N. necatrix ranged from 91.2% on the day of application to 14.4% on the 10th postapplication day. The effects of precipitation, relative humidity, and direct solar radiation are possible reasons for the observed decreases in pathogen activity.