Mistletoe

I'll never forget my first encounter with mistletoe. One crisp December morning in grade school I distinctly remember walking through a hallway that our teachers had painstakingly decorated for the holidays. There were poinsettias, wreaths and a profusion of color and twinkling lights hugging the corridor. But one thoughtful instructor had collected a plant from a tree in her front lawn and hung it where it would cause us boys a great deal of grief that day.  Hanging mistletoe over the threshold of a doorway is a holiday tradition that has its origins in Europe.

On that cool morning I saw a suspicious looking girl standing in the doorway of Mrs. Saxon's sixth grade math class. She was obviously waiting for something. I couldn't figure out what was wrong with her body language and I tried to shuffle past her without being noticed. That was a big mistake. Once my foot crossed the threshold, her arms shot up and blocked my way. Then she planted a kiss on my right cheek. I was in shock.

 Mistletoe is an ectophyte, meaning it's obligated to grow as a parasite drawing some part of its nutrition from a host organism. You're already familiar with other ectophytes such as ticks and lice and you've probably seen mistletoe growing in trees. The most commonly observed mistletoe species in Texas is the American mistletoe. Every part of this plant is known to be poisonous; therefore it should be kept away from children.

The tacky jelly-like mistletoe seeds are spread by birds that seem to be immune to the toxins. The seeds adhere to bark and sprout a root known as a haustorium. Haustoria penetrate tiny openings and grow in the vascular system of the tree. Although mistletoe leaves have chlorophyll and can manufacture their own food, they need to draw water and minerals from the tree to use as building blocks in their photosynthesis.

This pest is usually more of a nuisance than a serious health risk for trees. However, heavy infestations of mistletoe will kill branches and the loss of several branches can weaken a drought-stressed tree. Mistletoe is one more stressor in the urban decline of West Texas trees. Some long-term control can be achieved by pruning infected branches at least 18 inches below the parasite. Research hasn't yet provided an effective tool for conclusively removing mistletoe. Maintaining healthy trees seems to be the best option.