Parasitic mistletoe

Asked April 25, 2016, 11:55 AM EDT

We purchased a home last fall that has mature walnut and maple trees in the yard. They appear to be infested with a parasitic mistletoe. Is there any way to get rid of it or, at least, to save the trees? Is this common in the area? We live in the southern part of Louisville.

Jefferson County Kentucky

1 Response

Mistletoe is very common in Kentucky and Jefferson County is no exception. It is a well known parasitic plant. Mistletoe makes much of its own food, but its parasitism causes atrophy of the branch distal to the infections, sometimes inducing galls, swellings or witches brooms at the point of attachment. Mistletoe seeds are spread by birds which feed on the berries. The seeds germinate on young smooth-barked tree branches where they germinate and penetrate the host. Mistletoe plants will tend to cluster where birds have been roosting. Mistletoe plants grow on twigs and branches of their host, extracting water, mineral elements, and some food from the tree by way of a parasite nutrient-uptake organ. The osmotic pressure of mistletoe is higher than the host tree (the ability to transfer water through absorption). Thus, the parasite gets the water first and continues to respire even if the host tree is stressed. Mistletoe plants are most harmful to the tree during times of stress, and although they may not be too damaging in the wild, they would harm trees growing in the already stressful urban environment.

They can be safely controlled now by pruning, if necessary. Prune below or completely remove branches with mistletoe clumps.

The plant growth regulator ethephon may be used to control mistletoe in dormant host trees. This is a restricted chemical and can be applied only by a certified, licensed pesticide applicator. This chemical can damage tree tissue if it is applied when the tree is actively growing as it is now.

Feel free to contact our office if you have other questions.

Let me know if I can help you further!

Carol Wilder
Horticulture Technician
Jefferson County Cooperative Extension Service
810 Barret Ave
Louisville KY 40204