ISU Extension horticulture experts are reminding iowans that holiday plants and trees can bring uninvited guests into your home. Aphids and spiders are the two most commonly found pests on fresh cut Christmas trees, while white flies and scale insects settle on poinsettias and Christmas cactus. Extension experts say you shouldn't spray insecticides on fresh-cut Christmas trees. They also advise checking the Extension website for tips on caring for seasonal indoor plants.