As the chilly nights and falling leaves set the stage for All Hallows’ Eve, the scene inside many of our Michigan greenhouses is a strong signal that the December holiday season is just around the corner. In what were seemingly endless drifts of lovely green foliage only a few weeks ago, we now find hints of white, red and pink in clearly delineated masses of rapidly developing holiday cheer. Poinsettias are probably the most famous floral symbol of the Christmas season, but their beauty doesn't manifest overnight. It takes time, patience and a little bit of luck. In some seasons, we're very lucky: the weather is favorable, disease incidence is negligible and pest pressure is low. The 2018 season isn't one of those seasons.
This season, the struggle is real.
For decades, whiteflies have been one of the most—if not the most—troublesome pest for poinsettia growers throughout the United State and Canada. Before the 1980s, the whitefly species that gave growers the most trouble was the greenhouse whitefly (Trialeurodes vaporariorum). It flourishes on a wide range of plant species and can, at the right temperature, produce offspring at staggering rates. Around 1985, the sweet potato whitefly (Bemisia tabaci) began showing up in greenhouses and quickly displaced the greenhouse whitefly as the predominant whitefly species on many crops, including poinsettia.
This is where things get confusing.