There 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.