Pucker up. Standing beneath the mistletoe over the holidays is a customary way to steal a kiss. Well, the holidays are long-gone, yet the mistletoe remains behind, slowly killing off the oaks.
Traveling Mountain Area roads, it’s hard to miss oak after oak riddled with this parasite. Some of the trees stand tall, slowly having their life sapped away, while others are nothing more than an empty shell. Generally, it’s only after the tree has died that the mistletoe dies, having nothing to feed from.
Mistletoe is a fungus that suffocates oaks, absorbing most of the tree’s nutrients, and with California heading into another year of lower-than-average rainfall, the problem has become exacerbated because the trees are stressed and in a weakened state.
“Multiple clumps of mistletoe cause the tree to lose the ability to photosynthesize, and no longer be able to support itself,” Hudson Fisk of Fisk’s Tree & Excavating Service said. “Once a tree loses 30-35% of its canopy, it goes into crisis state.”
It’s common for the initial infestation to occur on the older or larger trees because birds prefer to perch near the tops. It is mainly because of birds that mistletoe can spread from an unhealthy, mistletoe-infested oak to a healthy oak; it also seems that chances for infestation is far greater for those trees in close proximity to infected oaks.
The older mature plants can cause large swollen areas to develop on infected branches, and even if the visible portion of the plant is removed, new growth can grow from the haustoria. (Haustoria is the appendage of the mistletoe that penetrates the oak’s bark, drawing nutrients). While healthy oaks are able to withstand a few mistletoe branch infections, individual branches can become weak or die. Should the mistletoe be left in the tree long enough, it roots itself below the bark, where the circulatory tissue of the tree lies, making the oak more susceptible to disease and borers.
John Pape, co-owner of Kuhtz-Pape Consulting, LLC, has been a certified arborist for 45 years.
“The trees try to heal themselves, and native oak trees can live hand-in-hand with mistletoe for a certain period of time, having adapted at some level,” Pape explained, “but when a tree has a fair amount of mistletoe, it’s a good idea to prune it out. Mistletoe will take advantage of a weaker tree. It’s an opportunistic parasite that attaches to the heart of the tree, sucking out the raw materials the oak is bringing to its leaves - water, nitrogen, iron. As the tree becomes weaker and weaker, it becomes more vulnerable to insects and diseases. It’s like a person with a bad immune system unable to fight disease or illness off ... it’s usually a combination of things that kill the oak off.”
When a cluster of mistletoe has grown to about 18 inches in diameter, which can sometimes take years, it begins to flower and fruit. The berries are small, sticky, white, and very attractive to birds, who feed on them, excreting the living seeds that stick tightly to tree branches.
Removing the mistletoe is critical to saving the tree. Even though the best time to remove the parasite is as soon as possible, it’s best when the tree is dormant or going dormant.
Simply cutting the mistletoe out of an infested tree each winter is better than doing nothing. Even though the mistletoe will grow back, the spread is reduced. Sometimes this is the best avenue, especially when removing an infested tree limb is not a feasible option, or when mistletoe grows out of a tree’s trunk. However, to be effective a continuous check on the tree is necessary to ensure the plant never matures enough to flower and produce seeds.
For disposal, it’s best to burn mistletoe in a brush pile, which will kill both the living tissue and seeds. Once the oak dies, it is imperative to remove the dead tree as soon as possible.
At January’s Town Hall meeting, Madera County Cal Fire Battalion Chief Troy Cheek warned that this fire season will be one for the record books, with California experiencing its fourth consecutive winter drought. And dead trees are akin to “roman candles,” just waiting to go up in flames.
“The time it takes to kill the oak depends on the size and health of the tree,” Jason Neville, owner of Central Sierra Tree Company in North Fork, said. (He has been in the vegetation management business since 1999). “We’re seeing more death in oaks now because the drought, on top of the mistletoe, is stressing out the trees. It’s only a matter of time before the tree dies. Some trees can go a long time with problems, and some can’t ... just like people.”
“The mistletoe needs to be trimmed back to the next y (large lateral branch) in the tree,” Fisk, who has been in the business since 1989, said.
“That is the key ... you don’t want to cut branches off and leave stops that leave the tree looking like a coat rack. You want the tree to look natural. And generally, once a property is trimmed and the mistletoe is eradicated, it can take as long as 10 years to see any recurrence.”