Debbie Croft: Mistletoe can be the kiss of death

December 27, 2013 

Mistletoe is often associated with ancient folklore and holiday traditions.

Sometimes during December, small bouquets of mistletoe can be purchased from young entrepreneurs and in local gift shops. Tied with a red ribbon and hung over a doorway, the greenery provides an excuse for stealing a kiss.

This time of year in the foothills, when most leaves have fallen from oak branches, clumps of greenery are visible. The green clumps are broadleaf mistletoe, which typically clings to limbs of native blue oak and interior live oak trees.

According to University of California’s Division of Agriculture and Natural Resources, a few species of mistletoe grow on several types of trees in the Central Valley and Sierra foothill regions.

A parasitic plant, mistletoe has earned a nasty reputation as a tree killer. But the Sierra Foothill Conservancy states that the parasite does have some redeeming qualities that are beneficial to the natural ecological system.

This evergreen plant produces berries, appearing October through December.

As the natural wildlife food supply becomes depleted toward late fall, two birds in the Sierra foothills especially rely on mistletoe. The small, sticky and pale berries are a source of nutrition for western bluebirds and the Phainopeplas.

Cattle, deer, elk, squirrels and chipmunks also eat the berries, as well as the leaves. Mistletoe is high in protein, but is poisonous to humans and dogs.

Mistletoe nectar provides food for butterflies, and bees benefit from the nectar and pollen in the spring. Birds and flying insects also use the plant as a nesting site.

Perched high in the treetops, birds devour the berries, letting seeds fall. Some land on branches below. Once a seed germinates, the plant grows through the bark and into the water-conducting tissues of the tree, where it forms roots. Mistletoe then has the means to obtain nutrition from its host.

Kristine Randal, master gardener coordinator for Merced and Mariposa counties, said that “mistletoe kills the ash tree in the Central Valley, and kills gray pines (also known as foothill pines) in the mountains.”

Residents of Tuolumne and Mariposa counties are noticing a decline in the gray pine population. The U.S. Forest Service believes mistletoe may be a contributing factor. Dwarf mistletoe is the species known to attack conifers.

Under normal conditions, oak trees can survive for decades with mistletoe attached. But the negative impact of drought and-or disease can cause a tree’s health to be compromised. The parasite will rob the tree of what little water and mineral nutrients it has available.

Human activities such as building new roads or driveways, or planting vegetation can also have a negative impact on trees. When root systems are disturbed, it can lead to the tree’s demise.

For anyone planning new landscaping, it’s best to plant trees known to be resistant to mistletoe. Redwoods and cedars appear to be resistant, along with crape myrtle, eucalyptus, gingko, sycamore, liquidambar, golden rain tree, Chinese pistache and Bradford flowering pear trees.

When mistletoe spreads on established trees, infected branches should be pruned. To remove a limb, make the cut at least 12 to 18 inches away (toward the trunk) from where the plant is growing.

Mistletoe has a spreading root system, and oaks are sensitive to pruning. The following link provides helpful information on controlling the parasite: www.ipm.ucdavis.edu/pmg/pestnotes/pn7437.html.

Debbie Croft writes about life in the foothill communities. She can be reached at composed@tds.net.

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