October 4, 2014
1 - Mistletoe management is difficult, but there are things you can do.
2 - A reader suggests a fun way to disrupt tent caterpillar and fall webworm webs in trees.
Yard and Garden 8October 4, 2014*
I was referred to you from the Grant County Extension Office in hopes that you could provide some assistance with the trees in and around our parking area. It seems that some trees are suffering from mistletoe and a few others are just looking downright sickly.
I was wondering if you might have some suggestions.
** -Timothy B.**
The mistletoe on your trees is a semi-parasite. It is green and can photosynthesize and make its own food, but causes a redirection of nutrients and water from the rest of the tree to itself. The result is that the tree declines in the manner that your photographs indicate. If there are other environmental stresses - drought, winter injury, or even lack of water when irrigated because of paved areas restricting water to the roots, the effects are even greater.
Mistletoe plants grow haustoria (root-like structures) into the wood of the tree to extract water and nutrients. It produces hormones that encourage the movement of extra water to the mistletoe, and thereby steals from the tree. If you want to completely remove the mistletoe from the tree, you must cut the infected branches of the tree well below the mistletoe to remove the haustoria. If you leave part of the haustoria of mistletoe in the tree, the mistletoe will regrow. In some cases such pruning so alters the appearance and beauty of the tree such that removal of the tree is the best option. If the mistletoe has invaded the trunk, there may be no possibility of removing the mistletoe.
In addition to pruning out the mistletoe infected portions of the tree, there is another option. You can delay the death of the tree and reduces the spread of the mistletoe by removing the mistletoe at the point where it emerges from the host tree branch. The mistletoe will return from that point, but if you are persistent, you can reduce the impact of the mistletoe on the tree, and more importantly, prevent the formation of the mistletoe fruit (white berries) to prevent the spread of the mistletoe to other trees. Birds often eat the mistletoe berries and in the process spread the seeds to previously uninfected trees. In this case, mistletoe may be removed frequently by mechanical pruning of the mistletoe from the tree, or by use of a chemical that contains ethephon. This chemical causes abscission (breaking off) of the mistletoe branches, but leaves the haustoria to regrow the mistletoe. If you choose to use chemical removal, be sure the product you purchase is labeled for this purpose and that you follow the directions on the label.
Last week the Yard and Garden column discussed fall webworm that is plaguing Santa Fe and other parts of New Mexico this year. I received an interesting response that I wanted to share:
Response: A teenage friend of mine showed me how to use a paint ball gun to destroy early season "tent caterpillars" We have used it with great success the two years we had an infestation in our aspens. Besides it was great fun doing it.
Be sure that you do not paint your neighbor's house or do unneighborly things while shooting paintballs up into a tree. I am sure most people would not need this caution, but in print, it is a necessary addition.
Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: firstname.lastname@example.org, office: 505-865-7340, ext. 113.
For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms.
Please copy your County Extension Agent and indicate your county of residence when you submit your question!