Click the image above for Trouble-shooting Tips. Inspect your houseplants for signs of insect pests or disease. As we turn on the heat indoors, the air dries out. Reduced humidity challenges plants' natural defenses, making them more susceptible to pest problems. Increase the humidity around plants by placing them on a tray of pebbles that you keep filled with water. The water evaporates around the plants and increases the local humidity.