Threats to Monarchs from Pesticides
There are three types of pesticides. Within each category there are some that are natural and other that are synthetic (chemical).
Insecticides kill insects by attacking their nervous systems, hormones, or protective coatings. Among the most harmful synthetic insecticides are the neonicotinoids such as imidacloprid (e.g., Merit). Some natural insecticides, such as neem oil, can be harmful to monarchs whereas others, like kaolin clay and insecticidal soap, are unlikely to cause harm.
Herbicides kill unwanted plants like weeds. They can also be very dangerous to insects and other animals (including humans). Examples of particularly dangerous chemical herbicides are DDT, 2,4-D (e.g., Weed-B-Gon) and glyphosate (e.g., Roundup). Some natural herbicides generally considered safe for pollinators are clove and citrus oil.
Fungicides prevent or treat disease caused by fungi like powdery mildew or rust. Examples of natural fungicides include sulphur and potassium carbonate. Examples of synthetic ones are myclobutanil (e.g., Immunox) and clorothalonil (e.g., Daconil).
A Very Brief History of Pest Management
For thousands of years, human used natural substances such as sulphur to kill insects attacking their crops. Then in the 1940s chemical pesticides -- also called synthetic pesticides – were developed and became widely used on agricultural crops.
Harmful to a wide array of plants and animals other than the target species, synthetic pesticides are also known for their persistence, often lingering in soil, water, and living organisms for decades.
Concerns about the harmful effects of synthetic pesticides arose shortly after their development. These concerns were articulated in a landmark publication in October 1959 issue of the agricultural science journal Hilgardia, published by the UC Division of Agriculture and Natural Resources. The 20-page paper clearly and concisely described the consequences of pesticide overuse and detailed their vision of a sustainable pest control system. Based on ideas presented in this paper, scientists developed an approach called “supervised insect control.” This approach advocated supporting natural-enemy populations in an area and using synthetic pesticides only as a last resort.
Throughout the 1960s, this approach was further refined, resulting in Integrated Pest Management (IPM), an approach that is still widely used in many agricultural and open spaces as well as in urban areas.
One excellent source of information about pesticides is the Beyond Pesticides website. Highly recommended!
Two individuals, Ray Smith and Perry Addison are generally credited as leaders in the development of the Integrated Pest Management approach. A co-author of the Hilgardia article mentioned above, Smith joined the faculty at UC Berkeley in 1941. In 1972 he became associate project director of the Huffaker Project which coordinated IPM research projects across 18 universities in the US. Perry L. Adkisson, a professor at Texas A&M University, was his close associate on the Huffaker Project.
Smith and Adkisson were awarded the World Food Prize in 1997 for their achievements in implementing IPM in the US and in developing countries.
Rachel Carson’s work was hugely influential in bringing concerns about synthetic pesticides to the general public. A marine biologist and writer, she was able to communicate scientific information in clear and compelling articles and books read by the general public as well as specialists. Her most influential book was Silent Spring, published in 1962. Her work was highly praised by the scientific community, but she nevertheless sustained strong attacks by the chemical industry, whose representatives challenged her research and mocked her as a “bird and bunny lover.” However, her position found favor in the US government, and in 1963 John F. Kennedy’s Science Advisory Committee issued a report backing Carson’s scientific claims. Carson is widely credited as one of the chief inspirations behind the environmental movement in the US.
Just What is Integrated Pest Management?
Step one: Prevent pests and their damage by managing the ecosystem. For example, grow a healthy crop that can resist pest attacks or using disease-resistant plants. This involves looking at the environmental conditions that affect the pest’s ability to thrive and then creating conditions that are unfavorable for it.
Step two: Monitor the site to identify the pests and note the damage they have caused. This information is key to knowing how much of a problem the pest poses.
Step three: Figure out a combination of management approaches — including biological control (e.g., beneficial insects and natural enemies), cultural control (e.g., crop rotation), physical control (e.g., traps), and as a last resort, chemical control (targeted pesticide use).
Is IPM used in Marin Open Spaces?
Areas in Marin that are managed by the federal government adhere to the IPM approach. IPM is cited as a governing principle within the Golden Gate National Recreation Area and Point Reyes National Seashore, for example. Herbicides are used as little as possible, mostly for removing invasive non-native plants. Similarly, insecticides are rarely used and typically involve only targeted approaches such as wasp sprays in public access areas.
Marin County has also endorsed the IPM approach. Marin is a strong advocate of IPM. The IPM Commission is charged with overseeing implementation of the Marin County IPM policy as well as planning, advising and making recommendations to the IPM Coordinator and Board of Supervisors. Read more about the IPM Commission, and learn about the Marin Monarch Working Group’s selection as the County’s 2024 IPM Award winner. This website by Our Water Our World also offers helpful ideas for controlling pests using natural methods.
What about IPM in Marin’s Cities and Towns?
Within Marin, each city or town controls its own pest-management policies in its buildings, parks, and roadside spaces. The city with the strongest anti-pesticide policies is Fairfax, which prohibits the use of all synthetic pesticides in parks, open space parcels, public rights-or-way, and town owned and maintained buildings.
Fairfax is an IPM pioneer. In 2001, the town council approved an ordinance — authored by council member Frank Egger — that required property owners to notify their neighbors prior to using herbicides and pesticides. This ordinance, the first of its kind in California, was intended to protect residents from chemical sprays that can drift downwind, linger in the soil and migrate via surface-water runoff.
Other towns that have banned some lethal pesticides such as glyphosate include Novato, San Rafael, Larkspur, and Mill Valley.
IPM is supported in national and county open space areas.
Fairfax council member Frank Egger in 2001.
Pesticide Free Zone is an active and effective local organization focused on reducing the use of pesticides throughout the county. Established in 1997, and then known as Marin Beyond Pesticides Coalition, the group included 44 Marin organizations and businesses working to change the way people view the use of pesticides. The group’s first objective was to work with the County to reduce the use of pesticides in public spaces and implement an integrated pest management (IPM) strategy. That goal was realized in December 1998 when the Marin County Board of Supervisors passed the IPM Ordinance, which was subsequently revised and adopted in 2010.
The group is currently focused on encouraging the use of IPM in home and school gardens.
IPM in Agricultural Spaces
NOTE: This Section is under construction!
Nation-wide, the overwhelming majority of pesticides are used in agriculture, which includes crop cultivation and livestock (beef and dairy) production. Non-agricultural uses of pesticides, including domestic and industrial applications, represent only 10-15 percent of the global market by value.
State and County roles regarding synthetic pesticides on ag lands
Marin County does not have a general ban prohibiting the use of synthetic pesticides on private agricultural lands as part of its county regulations.
The Marin County Dept of Agriculture, Weights & Measures enforces pesticide use to ensure that California-approved pesticides are used safely and that commercial applicators are trained, licensed, and compliant with state and federal laws.
Marin County’s role is enforcement and oversight, not outright prohibition. The County Ag Commissioner has authority to inspect storage and applications, ensure proper licensing, and investigate complaints.
What this Dept is enforcing are standards and allowable products specified by the California Department of Pesticide Regulation (CDPR)
The principles of IPM guide county departments but do not prohibit synthetic pesticides on private agricultural lands. For example, the county has reduced glyphosate use on county landscapes, but this applies to public property management, not a ban on agricultural pesticides by private farmers.
ORGANIC FARMING
According to the 2022 US Census of Agriculture county profile, 46 of the 255 farms (18%) in Marin reported farming organically. This includes 51,000 acres (2022), including pasture, rangeland, cropland, and other organic uses. But there aren’t stats on the breakdown. However, most of Marin’s ag land is dominated by pasture and grazing land, and Main ag is heavily weighted toward dairy and beef production much of which is organic. So likely that a lot of the organic acreage in the county is pasture/rangeland for grazing. In contrast, because of the coastal soils and hillsides, Marin’s land is less suited to cultivated row crops.
Organic means that the farm met the USDA’s definition of organic operation. This means no prohibited synthetic pesticides or fertilizers for at least 3 years, use of approved organic practices, detailed record keeping, and annual inspections. Organic practices include maintaining soil health, engaging in crop rotation, supporting biodiversity, following manure/compost rules, and managing pests without prohibited chemicals.
While this is a relatively small percentage, it is more than in many other counties.
The most common pesticides reported on Marin farm land include:
glyphosate — herbicide used to control weeds on crop land, pasture edges and around agricultural infrastructure; among the most widely used herbicides nationally, and in California agriculture generally.
Aminopyralid (broadleaf weed control) — used to control problematic weeds in pasture and grazing areas
Clopyralid — same as aminopyralid
What kind of involvement does MALT have in pesticide use?
MALT does not ban or specify pesticide policies, but their stewardship work supports sustainable land management that implicitly aligns with ecological health goals, which includes soil and water quality — issues that can be affected by pesticide practices.
MALT’s conservation easements remain privately owned and the landowners retain rights to farm the land, including decisions about production practices. So they don’t micromanage unless a specific easement has unique, negotiated restrictions.
Indirect effects of ag pesticides on non-ag spaces
Effects of pesticides used in agricultural settings are felt in wild and urban spaces as well. Pesticides can be absorbed into the soil where they may move below the surface into creeks, wetlands and riparian habitats. They can also run off the soil surfaces, ending up in storm drains connected to urban areas and waterways in wild areas. Some pesticides bind to soil particles and move downslope into wetlands. And they can drift as dust particles or tiny droplets into neighboring habitats. Look at the Marin Countywide Stormwater Pollution Prevention Program website for more information about pesticides in Marin’s waterways.
Effects of ag pesticides on monarchs
Even though Monarch butterflies do not typically congregate in agricultural spaces, they are nevertheless vulnerable to the poisonous effects of inappropriate use of pesticides in these areas. As noted pesticides applied in agricultural spaces can easily move into wild areas and home gardens. Recent research has demonstrated the presence of a variety of pesticides on milkweed in urban, wild, and agricultural spaces in Northern California.
For example, in a study conducted in the Central Valley of California researchers collected milkweed from 19 sites representing different land use types and tested for the presence of one or more pesticides on every plant. The sampling occurred during June, when monarch larvae were likely to be present on the milkweed. They found a variety of pesticides on every sample, even at sites with little or no direct pesticide use. Pesticides were detected on every land type, and at least some of the contaminants from the agricultural field had spread to the home gardens and wild areas. The authors conclude that their findings support the idea that pesticide exposure from agriculture could be a contributing factor to Western monarch declines, even though monarchs were rarely found on agricultural lands.
Which Marin Nurseries Practice IPM?
Adherence to IPM varies significantly from one nursery to another. The highest adherence can be found in local nurseries that are devoted exclusively to native plants and that have certifications or sustainability programs.
The following are some of the nurseries in Marin that focus on California native plants and neither use pesticides on their stock nor advocate its use for purchased plants.
Home Ground Habitats: 1875 Indian Valley Road, Novato
California Native Plant Nursery: 254 Shoreline Hwy, Mill Valley
O’Donnell’s Fairfax Nursery: 1700 Sir Francis Drake Blvd, Fairfax
Most other independent retail nurseries and conventional garden centers are likely to use parts of IPM but may not always have a firm policy of using chemical pesticides as a last resort.
