Chemicals can be good for healthy holiday tree Growers turn to pesticides, organic practices, biological controls to get healthy harvest

A Douglas Fir lot in Half Moon Bay. A Douglas Fir lot in Half Moon Bay. Photo: Eric Luse, The Chronicle 2007 Photo: Eric Luse, The Chronicle 2007 Image 1 of / 3 Caption Close Chemicals can be good for healthy holiday tree 1 / 3 Back to Gallery

Those of us who decorate yule trees must decide first: real tree or fake?

It's no surprise that the National Christmas Tree Association makes a strong case against artificial trees. Typically manufactured from PVC, they're not biodegradable nor recyclable. They're also a source of carcinogenic and otherwise nasty dioxins. And the industry group claims that 85 percent of artificial Christmas trees are imported from China.

Live trees can carry their own environmental baggage; so can favorite decorative plants like poinsettia and cyclamen.

Real trees perform valuable ecosystem services like carbon sequestration while they're alive and return nutrients to the soil as they decay. Christmas trees are as much of a farmed crop as soybeans; no one is harvesting them in significant numbers from the wildlands. It's a bit of a stretch to claim, as the association does, that "tree farms support complex eco-systems." Still, Christmas tree production doesn't approach the American corn complex in its potential for ecological damage.

The big variable in Christmas tree farming is pesticide use. Precise figures on its magnitude are hard to find. Oregon, a leading producer and the source of many trees sold in California, released its first statewide report on pesticides this year. But since Christmas tree farming was lumped with nursery operations, it's impossible to tell which of the reported chemicals - including the soil fumigants methyl bromide and chloropicrin and the herbicide glyphosate - were used in tree farming.

The California Department of Pesticide Regulation offers a more detailed breakdown. In 2006, the latest year for which data are available, the state's Christmas tree growers reported using 23 insecticides, miticides, herbicides, fungicides and rodenticides. Although some are relatively benign, others are capable of killing nontarget species and compromising the health of tree-farm workers.

Some examples: The heavily used glyphosate, the active ingredient in Roundup, is less problematic than polyethoxylated tallowamine (POEA), the surfactant that allows the solution to coat plants.

University of Pittsburgh biologist Rick Relyea reports that POEA is highly toxic to frogs; Monsanto, Roundup's manufacturer, disputes his findings. Pyrethroid insecticides like bifenthrin and esfenvalerate kill aquatic invertebrates and most insects. Carbaryl and imidacloprid poison honeybees. Dimethoate, an organophosphate used on insects and mites, also affects birds and fish and can cause headaches, nausea and breathing difficulty in humans.

Some tree growers have adopted organic practices, even though they may not be certified by the California Certified Organic Farmers organization. "It's way too expensive for us to be certified," said a representative of Skyline Tree Farm in La Honda. But the farm manages without pesticides: "We choose to plant the tree varieties that have less susceptibility to pests than others. For weed control, we mow. Certain kinds of brush we'll dig up or cut out."

Robert Criswell, who runs Black Road Christmas Tree Farm in Los Gatos, said he uses minimal concentrations of Roundup in spot applications but avoids insecticides. Last year, he handled an outbreak of Douglas-fir twig weevils by cutting and burning 50 truckloads of trees. Both farms practice stump culture, asking cut-it-yourself customers to leave a ring of branches on the stump. Criswell said new growth can be harvested in 2 1/2 to five years, with the cycle repeated up to six times.

For some problems, there's no chemical fix. Phytophtora ramorum, the fungus-like organism that causes sudden oak death, has been detected in some Christmas tree farms. Although the disease is not fatal to conifers like Douglas-fir and grand fir, infections can mar their foliage. There's concern that farmed trees may be carriers; California restricts movement of susceptible evergreens from Curry County, Ore., the northernmost outpost of sudden oak death. Fortunately, said Criswell, the holiday sales season is out of sync with the release of phytophtora spores in spring and early summer.

Trees aside, consider the poinsettia. The plant is not so poisonous as it's often accused of being, although its latex sap can be a mild irritant. But growers battle two insect pests, the greenhouse whitefly and silverleaf whitefly, that feed on the leaves and leave a sticky residue behind. Although imidacloprid has proved effective against whiteflies, the pests can evolve resistance. Growers respond by using it in rotation with pyrethroids and other chemicals. Biological controls - fungi and parasitic wasps - are available, but integrated pest management hasn't yet supplanted chemical pesticides in poinsettia greenhouses.

Another environmental cost to consider: transportation. Buying holiday flowers grown in Ecuador or Colombia is about as sustainable as using Chilean-grown avocados in your Christmas salad - a net loss of resources plus local jobs.