oklahomaThere is still no news about why mistletoe disappeared this last year in our area. No one really noticed it missing until late in summer. The absence of mistletoe became more apparent as deciduous trees that had been infested with it last year defoliated in autumn. What is even more strange is that the dead mistletoe plants deteriorated so quickly and efficiently that they are completely absent, as if something ate all the mistletoe, or took it away. The only evidence of former infestation in some trees are the swollen portions of stems where mistletoe had been attached. An article about this mysterious absence of mistletoe can be found here; https://tonytomeo.wordpress.com/2017/09/24/where-has-all-the-mistletoe-gone/ .

Someone who harvests mistletoe from local trees, both to eradicate it from a few trees, and also to sell it in local markets, made an interesting observation about the absence of mistletoe just within the past few day. He found that some mistletoe survives, but only in the upper extremities of tall trees. Most of the trees are locust trees, perhaps because they happen to be taller than most of the other trees that had been infested. One infested tree is a black walnut. The viable mistletoe plants are somewhat young and small. Larger plants or colonies that were as high as the smaller surviving plants are gone. Specie of mistletoe that infest coast live oak and some conifers have not been observed.

There are several variables that could account for the survival of relatively small mistletoe plants high in the canopies of host trees. Some pathogens that could affect mistletoe might proliferate in congested growth that limits air circulation, but not where air circulates efficiently through sparse and exposed growth higher up. Some pathogens that proliferate in cool and damp situations are inhibited by drier and sunnier situations. Some pathogens are more likely to infect hosts that are closer to the ground. If rodents are taking mistletoe vegetation, they prefer the shelter of more congested lower growth, and avoid the vulnerability of more exposed higher growth.

8 thoughts on “Mistletoe Un-Update

  1. Tony, are you referring to American Mistletoe (Phoradendron leucarpum)? If so, why do you call the presence of mistletoe an infestation? Technically mistletoe is a hemi-parasitic that produces its own chlorophyll. Because it photosynthesizes, it does not appear to harm trees, and it may provide some nutrients back to the host tree during winter when the tree has no leaves and no opportunity to produce chlorophyll. It is the host plant for caterpillars of the Great Purple Hairstreak butterfly and possibly others. Many birds rely on Mistletoe berries for food, while others use the round clumps for shelter and nests. Some mammals such as deer, elk, chipmunks and squirrel. An Australian study concluded that when Mistletoe was removed from a forest, bird diversity declined. I really don’t know much about mistletoe, and maybe trees do die earlier from the “infestation”, but these dead trees are useful to nesting birds and mammals. A forest with mistletoe may produce three times more cavity-nesting birds than a forest lacking mistletoe. I haven’t seen mistletoe here in years, and I actually miss it. I’m not sure what is lost when it is truly gone. I am not trying to be difficult or argumentative here; maybe I’m just ignorant of the negative effects. And then there’s the whole kissing thing . . .

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    1. It is termed as ‘infestation’ because it is unwanted in desirable trees. It might be compared to the native wood rats. They live here naturally, and contribute to the ecosystem, but when they come into our homes where we do not want them, they are an infestation. Two specie of mistletoe (and maybe a third specie that I have never seen) are native here, but I still do not want them in trees that I must maintain. They disfigure trees, and can kill locusts, alders, birches and a few others. Technically, many of the host trees could be classified as a different sort of infestations because they are not native, and the black locust really is an invasive exotic that infests the riparian areas of the San Lorenzo River. Yet, they are the trees that I work with and want to protect from mistletoe infestation, regardless of how mistletoe benefits the ecology of the forest beyond the landscape. It is funny that, now that you mention it, almost all of the trees that have serious problems with mistletoe happen to be exotic. Mistletoe is not as detrimental to the native valley oaks, bigleaf maples and so on. Mistletoe is mostly ignored out in the forests. There is nothing that anyone could do about it anyway.


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