Title: Influence of plant culture conditions on efficacy of foliar applications of entomopathogenic fungi against western flower thrips Authors
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: June 15, 2012
Publication Date: August 12, 2012
Citation: Wraight, S.P., Ramos, M. 2012. Influence of plant culture conditions on efficacy of foliar applications of entomopathogenic fungi against western flower thrips. Meeting Abstract. 45:92. Technical Abstract: A series of greenhouse tests was conducted to assess the efficacy of foliar applications of two commercially available entomopathogenic fungi, Beauveria bassiana strain GHA and Metarhizium brunneum strain F52, against western flower thrips infesting potted impatiens grown with subirrigation. Unformulated conidia were applied at a high rate and volume of 2.15 x 10**14 viable conidia in 4,073 liters of water per hectare. The two pathogens produced similar levels of control. Under conditions of high humidity (relative humidity greater than 75 percent) maintained for 2 days after each application, thrips populations in pollen-bearing flowers were reduced by 50-65 percent relative to those in carrier-controls (0.01 percent Silwet L-77). Substantially greater reductions (75–90 percent) were recorded in foliage samples. Control was slow to develop, coinciding with plant growth to the point of canopy closure (2–3 weeks after initiation of spray programs). Efficacy was highly dependent upon ambient moisture conditions. Population reductions did not exceed around 30 percent in flowers or 50 percent in foliage when humidity was low or only intermittently high (e.g., when limited to overnight periods), and control was also significantly reduced, regardless of plant age or humidity conditions, when plots were exposed to ventilation sufficient to produce a constant perturbation (visible movement) of foliage in the crop canopy. These results are in accord with grower reports of inconsistent efficacy of fungal pathogens applied against thrips in greenhouse crops, and indicate that efficacy can be expected to vary markedly with many aspects of crop culture, including ambient humidity, duration and periodicity of high humidity conditions, plant age (size), and plant location relative to air circulation within a greenhouse.