What are the plant diseases you as a grower might encounter during the month of December? Oregon State University Plant Clinic tells you what to watch out for this month and every month, whether the disease is bacterial, fungal, viral, abiotic, or parasitic in nature. This month’s guide outlines several molds and fungi that thrive on current conditions inside and outside the greenhouse, and explains something you may not have known: mistletoe can be a parasite.