Submitted to: Society for Invertebrate Pathology Annual Meeting Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: April 18, 2005
Publication Date: August 7, 2005
Citation: Wraight, S.P., Ramos, M. 2005. Effects of day versus evening application times on efficacy of beauveria bassiana foliar sprays against colorado potato beetle. Society for Invertebrate Pathology Annual Meeting Proceedings. 38:100.
Fungal pathogens are often applied during late afternoon or early evening under the assumption that favorable nighttime conditions of high humidity and moderate temperatures will support greater efficacy. Few studies, however, have actually tested this assumption. In a study conducted over four field seasons between 2000 and 2004, we compared efficacy of Beauveria bassiana strain GHA treatments applied early to mid-day with treatments applied at sunset. Three or four sprays of wettable powder formulation, each at the rate of 2.5 E13 viable conidia per ha in a volume of 467 L, were applied at 3–4 day intervals using a tractor-mounted hydraulic sprayer. Each test employed a randomized complete block design, with 5 replicate plots per treatment. Control treatments included untreated and spray-carrier-treated plots. Control of actively feeding larvae was poor (usually < 30%); however, populations of second-generation adults (summer adults) were reduced 65–90%, depending on seasonal weather conditions. The day versus evening spray applications produced means (±SE) of 68.5 ± 3.2 and 76.2 ± 7.0 percents control, respectively, and the difference was not statistically significant. The results indicate that the initial night following inoculation of the host with this slow acting fungal pathogen may not be as important in determining efficacy as is commonly believed. Inoculation of infectious propagules onto areas of the host cuticle protected from the harsh conditions of the ensuing day and exploitation of multiple nights of favorable conditions or extended periods of wet conditions resulting from rainy weather may be more important factors.