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Mountain Pine Beetle: To Spray or Not to Spray? Alternatives?

Introduction -
This is a commentary on the carbaryl pesticide by RMEHA member Christine Weeber. It was written as a letter to the editor for local newspapers for personal and community edification and not as an article for RMEHA. The views are those of the author and do not necessarily represent the Rocky Mountain Enviromnental Health Association. Kindly address any questions to the author.


In responding to the Mountain Pine Beetle (MPB) infestation, let's not repeat past mistakes. Pesticides often have larger impacts than we intend. Carbaryl, the active ingredient in the most common sprays used to protect trees against MPB, is no different. It is a neurotoxin that is dangerous to humans and pets through skin contact, inhalation, and ingestion from food or water. And it is highly toxic to bees, stoneflies, and some fish. In 2005, twelve groups representing farmworkers, beekeepers, and environmentalists called on the Environmental Protection Agency (EPA) to cancel carbaryl due to the unreasonable risks associated with it. In 2007, the EPA restricted many pet and home uses of carbaryl.

Past mistake: The pesticide used in the 1980s against MPB, ethylene dibromide (EDB), was eventually banned by the EPA for being 'extremely toxic to humans' and a 'probable human carcinogen.' In 2007, EDB was found in a new well drilled on the Frisco peninsula in Summit County--the levels exceeded the EPA's limits. Blame has been placed on the 1980's spraying for MPB.

Let's not make a similar mistake. Carbaryl (trade names: Sevin®, Tercyl®, Adios®, and Carbamec®) has been declared a likely carcinogen by both the US EPA and the UK Government Committee on Carcinogenicity. As a result, in Britain, it is no longer approved for use by nonprofessionals.

Symptoms from exposure include shortness of breath, respiratory irritation, eye inflammation, nausea, stomach cramps, diarrhea, restlessness, twitching, and/or convulsions.

Carbaryl can also cause lower pregnancy rates, pregnancy loss, infertility in both pesticide applicators as well as those exposed in daily life , according to researchers from the Institute of Toxicology in Nanjing, China, and the UCLA School of Public Health (2004).

Cats and dogs can both be affected by carbaryl, showing behavioral changes, excessive tearing and salivation, muscle tremors, twitching, vomiting, and diarrhea. Severe intoxications can result in paralysis and death. Birth defects have been seen in studies on Beagles.

Carbaryl has been found in water supplies. Yet, both the U. S. Forest Service (USFS) and Rocky Mountain National Park (RMNP) are spraying thousands of trees here in Colorado. What risk does this pose to downstream water users? Who will monitor streams, ditches, and wells for carbaryl? Forty percent of Boulder's water is from Barker Reservoir, so it is of great concern that the Silverthorne/Dillon Joint Sewer Authority declared they found carbaryl in the Silverthorne plant effluent (i.e., treated water) in 2007.

If ethylene dibromide could show up 20 years later in a new well in Frisco, how do we know carbaryl won't show up in our own wells? And who will be monitoring such a potential problem? Carbaryl is one of the three most frequently detected insecticides in surface water, according to U. S. Geological Survey (USGS) reports from 1991-2001. Carbaryl degrades quickly in neutral and alkaline waters (2.5 - 10.5 days), but it can last up to 1,500 days at pH 5 and 27 degrees C, (75 degrees Fahrenheit) according to Health Canada's report on carbaryl.

ALTERNATIVE: Pheromone packets, called Beetle Block, are a recently approved eco-friendly alternative. These contain verbenone, a synthetic pheromone, and are hung on trees to repel MPB by sending a message that a tree has reached maximum beetle saturation. The EPA says there is no risk expected to humans or the environment from verbenone.

The packets need to be placed on trees before the beetles fly in early summer. Beetle Block has been most successful when used as part of an overall plan to thin forests and remove infested trees, and when used in forests that are less than 20 percent infested. Though relatively less successful than carbaryl, Beetle Block is not toxic. Packets can be purchased from AgBio in Westminster (303-469-9221) and Pherotech International in B.C. (1-800-665-0076). I have no fiduciary or other interest in either company.

Verbenone has been used by Banff National Park (Canada), USFS, state agencies, recreation areas, HOAs, and homeowners for MPB. In 3-year tests in Montana, the packets successfully protected trees from MPB. In another study, mass attack was reduced to an average of 3.6 percent; in untreated areas, 48.3 percent of trees were mass attacked. In 2005, the Bark Beetle Technical Working Group, which consists of U.S. and Canadian entomologists, many of whom work for the U.S. Forest Service, state agencies, and various universities, stated that verbenone was effective in protecting trees in many instances from MPB.

Some homeowners have also placed mulch around the base of the tree and used drip irrigation systems to water 3-4 times a month during warmer months.

If you do decide to spray, please alert your neighbors so they can close their windows and keep their children and pets inside. Please also post a sign so people know what trees have been sprayed. RMNP posts signs for 60 days after spraying trees in the park (and people are kept 200 feet away from sprayed trees for at least 12 hours).


Christine Weeber chris AT christineweeber DOT net

Sources for the above letter about carbaryl and an alternative (Beetle Block)


1. EPA Interim Reregistration Eligibility Decision: states environmental impacts in detail, including effects on endangered species, bees, fish, amphibians, etc:

2. Letter to cancel carbaryl and revoke all tolerances for it, from the Natural Resource Defense Council (NRDC). See links to the right of the listing for the active ingredient carbaryl. Also available is a fact sheet on carbaryl (hasn't been updated):

3. EPA Reregistration Eligibility Decision (RED) for carbaryl (2007), which the EPA finally completed after having been sued by the NRDC (see www.nrdc.org/media/2007/070228.asp):

4. Fact sheet on carbaryl from the Northwest Coalition for Alternatives to Pesticides/NCAP:

5. Carbaryl has been declared a potential human carcinogen by the United Kingdom Government Committee of Carcinogenicity: carbaryl will no longer be approved for non-professional uses.

From 'Carbaryl Curbed':

6. Carbaryl can produce adverse effects in humans by skin contact, inhalation or ingestion. Its main mode of action involves the inhibition of the nerve enzyme cholinesterase and consequential disruption of the nervous system.


Studies indicate that carbaryl is slightly mutagenic(15,16). A World Health Organization (WHO) assessment concludes from available data that carbaryl does not pose a threat of inducing genetic changes in humans(17). However, carbaryl can react with nitrite under certain conditions to form N-nitrosocarbaryl. This chemical is highly mutagenic at low levels in laboratory test systems. This may be of concern because nitrite can be found in food additives and human saliva which can react with carbaryl in the stomach to form N-nitrosocarbaryl(18):

7. Genotoxic Effects on Spermatozoa of Carbaryl-Exposed Workers:

8. National Pesticide Information Center (NPIC) fact sheet on carbaryl:

NPIC fact sheets are designed to answer questions that are commonly asked by the general public about pesticides that are regulated by the U.S. EPA. This document is intended to be educational in nature and helpful to consumers for making decisions about pesticides.

9. The Problems with Sevin (carbaryl):

10. Poisoning our pets: how a bug killer almost killed my dog' by Sue Sturgis:


1. EPA Reregistration Eligibility Decision (RED) for carbaryl (2007), see page 14:

2. Health Canada's fact sheet on carbaryl (1991); which Health Canada says can last up to 1500 days:

3. Tree spraying in Summit (County) beetle battle could threaten water quality, by Harriet Hamilton, Summit County correspondent, Aspen, CO March 24, 2008.

SILVERTHORNE, Colo. The chemicals local towns and neighborhoods are spraying to prevent the spread of the pine beetle could be contaminating local water supplies, according to the Silverthorne/Dillon Joint Sewer Authority.

4. Toxic chemical, ethylene dibromide, found in new well in Frisco, Colorado:

a.) Frisco will consider water protection plan. Puzzling pollution at test well is no threat to drinking supplies.

FRISCO, Colo. Traces of pollution in a relatively new well on the Frisco peninsula could help spur the Town to study the idea of a source water protection plan:

b.) Blog: Toxic Chemical Found in Frisco Well Water:


1. Colorado State Forest Service re: preventive spraying for mountain pine beetle:

2. Information on the USFS spraying on the Boulder and Clear Creek Ranger Districts:

Boulder Ranger District Pesticide Spraying Hotline (303)-541-2539 (updated twice daily during spraying).

Also see page 4 in the /Forests to Grassland/ newsletter:



Banff National Park of Canada: They are ONLY burning, thinning, taking our infested trees, and using pheromones:


Spraying in the Park: Rocky Mountain National Park, Brian Verhulst (970) 586-1433. In late April until before Memorial Day weekend, the park will be applying Sevin Brand XLR (carbaryl) to as many as 5,000 high-value trees to protect them from bark beetle.

Includes the following campgrounds and visitor centers:

Beaver Meadows visitor center,
East and West Side park service housing areas,
Fall River entrance and Bighorn Ranger Station,
Fall River visitor center,
Glacier Basin,
Kawuneeche visitor center,
McGraw and Holzwarth ranches,
Moraine Park Museum and William Allen White Studio,
Moraine Park,
Timber Creek,
Wild Basin entrance and employee housing

The Longs Peak Campground will remain chemical free this year.

The Bark Beetle Management Plan:


1. AgBio's website. They sell Beetle Block packets:

The label for Beetle Block:

AgBio has more info on where these have been used, how successful these have been, etc.

2. EPA Fact Sheet on verbenone:

3. 2005 Bark Beetle Technical Working Group:


1. Use a drip irrigation system or soaker hose to avoid wasting water. Place drip emitters away from the trunk of the tree, to better reach roots. Plan to water three to four times a month during warmer months of spring and summer (water at least once a month during the winter).

Place a layer of mulch around the tree to cool the soil and conserve water, but keep mulch away from the trunk of the tree.

Remove weeds and other competitive vegetation around trees to ensure efficient water usage. Do not fertilize; fertilizer can increase tree stress levels. To further conserve water, only apply during evening or early morning hours to avoid the heat of the day.

2. Soap and essential oils. Other ideas taken from treating lawns for Chinch Bugs:

3. Ernie suggests hanging suet cakes on your favorite trees to encourage woodpeckers to help control the beetles.

Follow the links below to learn more about RMEHA and Environmental Illness.

Revised '10-Jul-2009,12:47:18'