Locust and alder trees in my region are commonly infested with mistletoe. Some were severely infested. A few of the locust trees downtown were actually unsightly because they are so stressed and sparse from mistletoe infestation, and also because they were so full of big shaggy mistletoe bushes that obviously do not belong there. Now, viable mistletoe can not be found. Even the carcases of the big dead mistletoe bushes are hard to find. They seem to have died and deteriorated before anyone noticed. The formerly infested trees are noticeably healthier, and producing more healthy foliage than they normally do, partly hiding any remnants of dead mistletoe.
No one here seems to know what happened. Is this part of their natural life cycle? Is there something that sets them off to die all in the same season like some specie of bamboo do? Is there a disease or insect that we should know about? Is this isolated to our region, or is it happening elsewhere as well?
I know I should be pleased that the mistletoe is gone, even if it is only temporary. It is such a destructive parasitic weed! The concern is that we just do not know what happened.
Years ago, Phytophthora ramorum started killing tan oaks. At first, not many of us minded. After all, tan oaks are considered to be trashy trees that clutter otherwise pure redwood stands, or compete with more desirable oaks. Dead tan oaks were better than live ones, and only needed to be cut and split to be sold as seasoned firewood.
The following year, the same disease started to kill coast live oaks. Then we had a problem. Coast live oak is one of the two most majestic oaks in our region (and the most majestic in the Santa Cruz Mountains where the valley oak is uncommon). It took a long time to identify the disease because the ambrosia beetle, which is a secondary pathogen, was initially blamed for the widespread death, which became known as Sudden Oak Death Syndrome, or SODS. It took a few years for the worst of the SODS epidemic to subside, and it continues to kill oaks sporadically.
That is why it is hard to ignore what is happening with the mistletoe, even though we really should be pleased to see it go.