Integrative Pest Management (IPM)
For the layperson thinking of using herbicide, key considerations are 1) avoid rain, avoid temps below 50 F or above 80F, 2) for annual weeds, apply herbicide when the weed is actively growing (not drought-dormant), 3) for woody perennials, fall is generally the best time to apply, 4) don't use selective "brush control" herbicides (like triclopyr or 2,4-D) to kill grass or bamboo - it only works on broadleaf plants, and 5) read the label for appropriate seasons, temperatures, PPE, risks, and dilution rates. Homeowners typically use far more herbicide than is needed which can reduce effectiveness. More is not better.
For the professional practitioner, the idea of avoiding pesticides when controlling pests and weeds is called, “Integrative Pest Management,” or “IPM.”
Before automatically resorting to chemicals, IPM considers other methods such as mechanical, biological, cultural, or physical tactics .
A mechanical method for weeding might be repeated mowing to reduce seeding of short-lived weeds and eventually starve unwanted plants. A cultural practice for rat infestations is not automatically rodenticides, rather, changing the conditions that attract rats, (removing clutter, blackberry and ivy that provide food and cover from raptor-predators). A combination of tactics can be effective, such as: mechanically string-trimming ivy, then smothering weakened resprouts with 8-12" of woodchip mulch. Another combination of tactics might be mulching with woodchips to reduce weed germination, then planting native plants, favoring evergreen groundcovers, shrubs, and trees to shade out weed re-invasions.
Best Management Practices (BMP)
Best Management Practice (BMP) means a "practice, or combination of practices, that is determined to be effective and practicable, including technological, economic, and institutional considerations," taking into account pesticide concerns, aiming for the best outcome for human and environmental health.
In a simple example of a weed-infested field, the practitioner community would consider IPM, but their accumulated experience would know that mowing kills ground pollinators yet doesn't kill the weeds' roots (Creeping thistle). Mowing spreads weed seeds (Herb robert, Shiny geranium) or spreads vegetative fragments that re-root (Knotweed, Yellow archangel). Practitioners also know that mowing Poison hemlock or Giant hogweed is extremely toxic to the operator, causing severe skin burns, permanent eye and lung damage. The best-management BMP might be spraying (outside of bloom-pollinator windows) a selective broad-leaf herbicide that doesn't affect grass, that is less toxic than the exhaust-pollution of mowing. Or, the BMP might be spraying a broad-spectrum herbicide (that kills both grasses and broadleaf weeds) to clear the way for replanting native species, including pollinator-friendly species. Spraying is considered a better practice than sodcutters, leaving topsoil intact, and far less toxic than the exhaust from the transport and operation of heavy-machinery. Any removal of topsoil reduces habitat for ground-nesting pollinators, and soil compaction reduces water infiltration and the success of replanting efforts. The loss of soil structure and organic matter in the ground suppresses fungal-water-transport networks that would otherwise support plants and make forests more resistant to disease and fires.
For carpeting weeds like English ivy, BMP's might deem that herbicide applications are necessary to avoid "non-point sources of pollution" (toxic stormwater runoff) caused by erosion of pollution-tainted soils, and is therefore preferred over manual-uprooting methods. This is particularly true on steep, erosion-prone sites where the cascading consequences of soil disturbance would likely prevent recovery of healthy soils and vegetation.
Practitioners who do the hard work of invasive plant removal have tried every "organic" trick in the books, repeatedly over decades. Hard-earned experience has concluded that eradicating certain invasive species requires herbicide, and that neglecting invasive monocultures is far more worrisome.
The best example is streamside knotweed with 10-ft deep roots that can’t be manually removed without eroding streambanks and smothering salmon nests with the resulting silt. Knotweed severely degrades native plant food sources that feed the bugs that feed salmon fingerlings. Covering knotweed with weed cloth has been tried over many years, but the manufacture, transport, and disposal of large rolls has its own environmental footprint, and it simply hasn't worked. Knotweed only regrows, spreads downstream at high rates, and continues to erode streambanks and impoverish food webs for salmon. To save salmon, the reluctant conclusion is that chemical treatment of knotweed with the safest effective herbicide is a necessity, followed up with native plant revegetation that shades and cools salmon streams while contributing detritus (leaves, twigs, and decaying organic matter) that feed the base of the food chain.
Restoration practitioners operate with oversight from the Department of Fish and Wildlife, Dept. of Ecology, and the State Dept. of Agriculture. Experienced practitioners are trained to use PPE to avoid repeated exposure to themselves, while carefully avoiding off-target herbicide damage to native plants and pollinators.
Do-it-yourself considerations
Many homeowner-stewards become discouraged with manual methods that may not work or make infestations worse. Unless they can find or afford experienced practitioners, they give up on control efforts. Homeowners who are considering herbicide applications must first assume responsibility for applications on their property only, including unintended effects to neighboring properties. Homeowners must also consider and accept the health-risks and environmental-cost trade-offs of chemical vs. manual removal methods. Do-it-yourself stewards should be confident with identifying both native and non-native invasive plants, while taking measures to preserve valuable native plants.
DIY-stewards must properly use PPE (gloves, eye pro, long pants and sleeves, or other recommendations per the label) before applying over-the-counter herbicide products. Avoid rain, and follow seasonal effectiveness listed in the Invasive Weed Calendar Guidelines. It is legally required for all pesticide users to read and follow the pesticide label.
Professional help
For professional help or advice, licensed herbicide professionals may be found at: https://agr.wa.gov/services/licenses-permits-and-certificates/pesticide-license-and-recertification/pesticide-and-spi-licensing/license-lists. Many restoration practitioners have licenses with Ornamental/Agricultural Weed, Right-of-Way, and/or Aquatic endorsements. Licensed practitioners have weighed the risks of herbicide vs. the risks of invasive neglect, and choose to judiciously apply herbicide in the appropriate season for the reasons below.
The rationale for herbicide
The main reason for using herbicide is that it reduces soil erosion. Worldwide, one-third of topsoil has been lost since the agricultural revolution, mainly from tilling and over-grazing steep slopes. This trend must be reversed in farming, forestry, and restoration practices.
In restoration, herbicide applications on invasive plants retain treated roots in the ground to slowly decay, temporarily holding soil and building soil structure for the benefit of establishing native plants. Using herbicide is not a weeding strategy, rather, it's a restoration strategy necessary prior to re-planting with native species. These limited herbicide applications and "restoration" prevent the "weed vacuum" from getting re-infested.
Some herbicides may affect soil microbes, but for safer herbicides, it's generally considered short-term and minor compared to manual methods that remove food in the ground, effectively starving soil microbes. "Organic" manual removal methods can disturb and erode topsoil that takes many centuries to build, especially on slopes. Erosion reduces the soil's sponge and filter, a hedge against toxic stormwater, drought stress, floods, and wildfire risk.
In polluted settings, loss of rotting roots in the ground particularly reduces fungal filtration of toxic stormwater runoff. Stormwater is rain runoff from roads, roofs, and lawns tainted with oil, air pollution, animal feces, and unnecessary fertilizers and pesticides. Stormwater is considered the "number one polluter of Puget Sound" that can overwhelm combined-sewer systems (CSO's), dumping raw sewage into public waters. Considerable air pollution is deposited, sequestered, and partially neutralized in healthy soil, so judicious herbicide can mitigate soil disturbance that carries worse toxins into water bodies where "bio-accumulation" concentrates toxins up the food chain, in salmon, orcas, and people who eat salmon.
"Slow, insidious soil erosion threatens human health," and is considered one of "the biggest environmental problems the world faces" (https://news.cornell.edu/stories/2006/03/slow-insidious-soil-erosion-threatens-human-health-and-welfare). Our country has also "lost a third of its topsoil after two centuries of independence" (DIRT - The Erosion of Civilizations). Long before the chemical revolution, the Dust Bowl is a notorious example of erosion caused by tilling amplified by drought, resulting in ecological collapse.
Even "organic agriculture can prove as unsustainable as conventional (chemical) farming when tillage is a regular practice" (David R. Montgomery, Growing a Revolution, 2017). Many American farmers, having lost topsoil and fertility, are now leading soil conservation efforts with cover cropping, "no-till," disking, and chisel-plow farming methods to preserve soil health. Organic farmers are realizing greater yields per acre with diverse interplanting, mulching, and manuring from thoughtfully-managed farm animals.
For restoration professionals, herbicide is a key tool on erosion-prone slopes and for many species for which manual methods simply don't work: root fragments only grow back, creating thickets all the more difficult to control. Repeated pruning over many years may eventually starve invasive plants on small private lots, but public land managers dealing with exponentially spreading invasives on large acreages cannot rationalize transporting crews or volunteers with polluting vehicles to "organically" and ineffectively control invasive plants using methods that erode soil and are more harmful to the environment. Vehicle fuel is acutely more toxic and used in far greater quantities than herbicide. Given limited budgets, the magnitude of the invasive problem and compounding re-invasion rates, the efficacy of best practices is imperative.
No one wants unnecessary toxins, but minimizing the quantity of pesticides in our environment requires nipping invasive plants in the bud before they become monocultures region-wide. To put herbicides in perspective, agriculture consumes 19 percent of the total U.S. consumption of 134 billion gallons of gasoline per year. With each gallon of gasoline weighing 6.3 pounds, that's 780 billion pounds of gasoline per year. Quantities of annual glyphosate amount to 280 million pounds, or 4/100ths of one percent (.0004) the quantity of more toxic fossil fuels.
Lawn culture, tree farming, and industrial agriculture have repeatedly proven that monocultural crops attract pests as a result of losing biodiversity with its natural checks and balances (https://phys.org/news/2020-11-diversity-pesticide.html). Due to the rate of invasive spread and the fact aggressive introduced species have no natural checks, herbicides are necessary to preserve biodiversity needed to sustain wildlife, including pollinators. Unchecked spread of invasive plants would require greater quantities of herbicide applications in the future, and possibly worse rodenticides and insecticides. Skilled applicators apply herbicide in the right season, minimizing the quantities of products used. It's very important to read product labels carefully and/or hire qualified professionals guided by this application calendar.
Restoration professionals mostly use products with the active ingredients glyphosate, triclopyr, and imazapyr as directed by government agencies who have analyzed the health and environmental effects of various herbicides. Imazapyr is the herbicide most often used for holly and hawthorn injections, and for knotweed sprays. Professional products often are "aquatic" restricted-use formulations that are only available to licensed professionals, that are usually 50% active ingredient - the concentration used for cut&dab treatments. Aquatic herbicides are formulated without surfactants, and are deemed safe for fish and amphibians, necessary near wetlands or riparian zones. Concentrated herbicides are considered more risky to human health (although less than many risks we overlook daily - see below), and are therefore only available to licensed applicators trained for safe use and handling. Licensed applicators have a short list of aquatic surfactants vetted by the Dept. of Ecology (see calendar link in above paragraph) to assist the absorption of herbicide into the leaf when spraying. Professionals carefully dilute concentrated herbicides and surfactants to approximately 2% active ingredient (a.i.) for foliar sprays. Ready-to-spray consumer formulations are usually pre-mixed at 2% a.i. with surfactants that are not necessarily fish-safe, and therefore are not permitted for use around streams or wetlands. It's particularly important to avoid spraying consumer products unless you have one dry day followed by two forecasted dry days during the summer/fall growing season (but not when plants are drought-dormant).
Pesticide-pollinator concerns
The INTERNATIONAL PROGRAMME ON CHEMICAL SAFETY concluded that“glyphosate has low toxicity for bees and earthworms."
Whether or not the cited science is accurate or dated, the loss of biodiversity from invasive neglect is a greater risk, so skilled restoration practitioners selectively target invasives and avoid spraying pollinators. Granted, this does not prevent chemical exposure through uptake of systemic herbicides in farming practices, where nectar may contain trace amounts of herbicide that pollinators ingest.
This systemic uptake may play a role in pollinator decline given the repeat agricultural applications of glyphosate, and it could very well be a serious concern and a reason to support organic farming. Restoration practitioners avoid systemic uptake by cutting and treating only the stem/roots, or by brushcutting blackberry, for example, and spraying regrowth that is not in flower (spraying may actually use less active ingredient, but risks off-target damage to beneficial plants).
In contrast, forestry applications use 1 - 2% of herbicides used in agriculture, mostly for "conifer release" or "free-to-grow" aerial sprays that kill competing vegetation, "releasing" conifers from sun and water competition. In this author's opinion, conifer-release practices are old-school experiments that have reduced overall forest productivity due to erosion, loss of hydraulic redistribution (available water) through diminished fungal networks, loss of nitrogen fixing and anti-pathogen properties that are provided by symbiotic benefits of biological diversity in healthy soil. In contrast to conventional forestry practices, restoration (of soil and plant diversity) uses far less herbicide than tree farming, the minimal amount necessary to assist ecosystem recovery. Again, in restoration, herbicides help reduce erosion and are a tool to control invasive monocultures to preserve native plant diversity necessary to sustain insects, wildlife and pollinators.
Based on recent news reports, there is significant cause for concern for "neonic" insecticides (neonicotinoids) used in farming and the ornamental flower industry.
Insecticides are known to kill beneficial insects far beyond the target pests. But, insecticides often get confused with herbicides in misleading news reports that conflate what are both technically "pesticides."
"Pesticide is a broad term that includes insecticides, herbicides (weed or plant killers), fungicides, rodenticides, miticides (mite control), molluscicides (for snails and slugs), and other materials like growth regulators or antimicrobial products such as bleach and sanitary wipes that kill bacteria." (http://ipm.ucanr.edu/PMG/PESTNOTES/warning.html)
Some chemical-herbicide alternatives (concentrated vinegar) may change soil pH, risk irreversible eye damage, and just "burn down" tops of weeds guaranteeing the need for repeat applications. Vinegar herbicides are acutely toxic to bees and pollinators and can burn, even permanently blind the applicator. For homeowners wanting familiarity, vinegar may be a preferred method for weeds in sidewalk cracks around the home. For safety, wear proper PPE (gloves and eye protection ! ) and other precautions on the label of natural pesticides. Some people recommend mowing invasives as an alternative to herbicide, but again, gas-powered mowing emits air pollution more carcinogenic than glyphosate (see studies cited below) and routinely kills pollinators (70% of native bee species are ground nesting). Mowing may spread weed seeds and not kill invasive roots. In contrast, herbicide applications are usually limited to the target plants, where any "drift" can be tracked by yellowing leaves on affected plants (visible effects can be delayed). Whereas, air pollution from mowing is actually ingested by all people downwind, causing immediate and long-term health effects. Plus, CO2 remains in the atmosphere for centuries.
Again, insecticides are very different than herbicides, and it's important to analyze the properties of all chemicals, natural or otherwise. Efforts to ban certain pesticides might be misguided, causing more harm than good. A more pragmatic and effective approach might be to tax pesticide products according to downstream soil testing and water-quality monitoring so we can apply science-based fees commensurate with environmental and human health risks. Consumers notoriously use five times the amount necessary as recommended on the legal label, something that is rarely read. A price tag that reflects actual risks is more likely to be read and heeded, effectively reducing unnecessary pesticide applications. Regulations do little to proactively motivate more judicious applications.
The restoration profession's limited use of herbicide is intended to control invasive species, the second leading cause of species extinctions behind the number one cause, habitat destruction (such as paving and clearing for development, infilling wetlands, and high-intensity wildfires). Invasive plants degrade habitat and "are listed as a driver for more than half of the extinctions in each of the vertebrate taxa analysed" (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4780541/). Invasive infestations reduce resilience to disturbance (disease, insect pests, fire) and alter vital functions such as tree regeneration, forest structure and hydrology.
Risk Assessments for Human Health
Certain herbicides like imazapyr are considered "practically non-toxic (the EPA’s lowest toxicity category) to fish, invertebrates, birds and mammals." But for the sake of discussion, let's consider glyphosate, the most studied and most vilified "pesticide" on social media.
The International Agency for Research on Cancer (IARC), an arm of the World Health Organization (WHO), recently published an often-cited analysis of over 1,000 independent studies on glyphosate, the active ingredient in Roundup, the most heavily use herbicide in the world. An academic review of the WHO report can be found at: http://blogs.oregonstate.edu/mgcoordinators/2018/10/15/glyphosphate-questions-answers/
In short, the review explains that the IARC listed glyphosate as "a probable human carcinogen." This surprised many governmental agencies tasked with protecting public and environmental health. The IARC responded and clarified their listing as identification of "potential hazards," quite different than actual risk assessments (think "cliff" - a potential hazard but not a risk if you're not close). The classifications of carcinogenic categories can be found in the IARC's Preamble.
The IARC placed glyphosate in the Group 2 A list of probable carcinogens, a category that includes: 1) Red meat, 2) Indoor emissions from burning wood, 3) Emissions from high-temperature frying, 4) Late-night work shifts.
Group 2A is less risk than the Group 1 category of "known carcinogens" which include, but are not limited to: 1) Processed meats, 2) All alcoholic beverages, 3) Sunlight, 4) Engine exhaust (diesel), 5) Benzene (in gasoline), 6) Outdoor air pollution.
For many compounds, the "dose makes the poison" (aspirin, some vitamins, many natural remedies), and pesticide studies employ high concentration doses. While many governments are banning glyphosate due to public fear, their scientific agencies find over-the-counter dilutions of glyphosate or food residues “unlikely to cause cancer in humans." These scientific reports from governments with robust research resources include:
For ecologists who understand the health risks of losing bird populations and native pollinator habitat region-wide (from loss of plant diversity due to aggressive introduced plants), the risks of glyphosate exposures are far less worrisome. The probability of Non-Hodkins lymphoma (NHL) to ag workers is 2.8% compared to 2% for the general public, not a statistically significant difference, but boosting glyphosate to the "probable" 2A category.
Perhaps the risks to farmers, ag workers, and restoration practitioners who handle concentrated formulations is greater than the risks to the general population, so professionals are highly advised to wear PPE and aim for zero exposure.
Still, farmers generally live longer than the average citizen, despite their above-average exposure to diesel exhaust and sunlight, both carcinogens in higher risk categories than glyphosate (https://www.ncbi.nlm.nih.gov/pubmed/29136183 and https://www.epa.gov/sites/production/files/2016-09/documents/glyphosate_issue_paper_evaluation_of_carcincogenic_potential.pdf). There is evidence that risks to ag workers may be due to fertilizer exposures, not necessarily glyphosate (https://cancercommun.biomedcentral.com/articles/10.1186/s40880-017-0225-4). One science-writer describes glyphosate risks as "negligible," comparable to "the risk of just being alive" (https://sciencebasedmedicine.org/update-on-glyphosate/). Still, practitioners are open to evolving science and want to know the properties of products we are tasked to use.
There appears to be growing research about glyphosate potentially affecting gut microbiomes, a possible factor in many western diseases in humans, and possibly affecting pollinators in similar ways. In addition, glyphosate is known to have mineral-binding capacity that chemically adheres to soil particles (a reason farmers often choose glyphosate - due to its negligible risk to groundwater). But it's unknown to this author whether glyphosate residues on food could bind up minerals in the body (such as calcium in bones), or how much glyphosate "demineralizes" soil and therefore the nutrient content of food (compared to the demineralization from tilling erosion or changes in soil pH from vinegar applications). Concerned consumers might be advised to buy organic food, or better, build your own soil health and grow your own organic food (be sure to conduct soil tests) to minimize dependency on carbon-based transport of industrially-produced farm products.
However, our food system and farming practices are not the focus of this website. We are explaining the tradeoffs of herbicide used for invasive plant control in order to preserve topsoil and biodiversity. We are not defending or opposing farming practices - farmers face their own economic and labor constraints and tradeoffs. We do encourage farmers to consider expanding their native plant diversity in hedgerows - even if establishing quality pollinator habitat requires initial herbicide applications.
What if...
The opinions shared in this practitioner perspective come from environmentalists who actually do the work, and we also want to know the risks or "relative worry" of products that government agencies direct us to use. For these vetted herbicides, the risks are considered low by a vast majority of scientists. Still, we would like to apply the "precautionary principle" to our environment and our own health. It begs the question: “What if someone downstream or one of our fellow practitioners gets cancer?”
Tragically, many people get cancer from many different causes, sometimes genetic or from impossible-to-pinpoint exposures to hundreds of toxins, many natural and many man-made, that may or may not be listed in the IARC report. When cancer strikes, blame is often directed toward a conditioned prejudice or "lightning rod."
Close to home, the web designer of this very website lost his battle with cancer. He was an employee, a beloved precious individual, and a restoration practitioner who didn’t for a moment think his herbicide work was to blame, because he contracted cancer well before starting his career. Plus, he did his research, earning a Masters of Science degree from the UW School of Environment and Forestry Sciences. He was proud of this website legacy, helping to explain the eco-logic behind herbicide, necessary to preserve native plant diversity required by the birds he loved. And he was comforted that all the trees he planted made a lasting contribution to the world. Co-workers continue to plant and spread the seeds of his favorite Pacific madrone.
Ironically, the tragedy of cancer helps explain the predicament of invasive species, because certain introduced species are themselves an ecological cancer. With many introduced species spreading region-wide, it's more accurate to describe it as a cancerous epidemic, one that is spreading by seed rain. We have to apply the "precautionary principle" to invasive species, because ecological cancers can shut down vital functions not limited to: 1) natural regeneration of native trees, 2) pollinator habitat needed for our food supply, 3) resilience to forest fires, 4) resistance to pest and disease outbreaks illustrated by rat infestation in ivy monocultures. In essence, when invasive species are the second leading cause of species extinctions, when cancer threatens human life, survival sometimes requires chemical treatment.
For some species like ivy, its uncontrolled growth is relentless, spreading in slow-motion. For others like holly, its spread is epidemic, at a near-exponential rates. Cancerous epidemics of invasive plants illustrate how epidemics operate: one property gets infested and then infests neighboring properties, and the only immunity is to restore healthy native vegetation that competes with perpetual reinfestations until everyone controls invasive seed rain sources at the same time.
"Sepsis" might be more a more accurate analogy, and this unfortunate reality forces our appeal. We ask that the public consider tolerating the necessity of chemical applications, and consider the proposals on the Stewardship Incentives page of this website.
"Fear sells" the same way that "illegal aliens" or "poisons" resonate with deep primal instincts, and I apologize for my use of "invasive" language that reinforces xenophobia. Glyphosate has become a ‘wedge issue’ that divides rural, environmental, and progressive concerns, and it is my hope that passionate, caring people can temper their emotional view of threats in the world and work together to limit unnecessary and reckless use of all toxic products, commensurate with science-assessed risks, rather than letting slanted media divide and blind us to greater risks. Notwithstanding valid concerns about toxins, misinformed fear can divert attention and resources away from more pressing issues, and fear itself can be a factor in disease.
Lastly, the longer we wait, the more expensive invasive control will be. Neglect is not an option - we are approaching a tipping point when invasive plant infestations will soon be entrenched and ungettable.
Thank you to the professionals and academics who have contributed their experience and knowledge to improve this educational website. And thank you (!) citizen-volunteers who steward their land, or any permitted land. There is SO much work to be done. Steve Richmond, October 2023
For the layperson thinking of using herbicide, key considerations are 1) avoid rain, avoid temps below 50 F or above 80F, 2) for annual weeds, apply herbicide when the weed is actively growing (not drought-dormant), 3) for woody perennials, fall is generally the best time to apply, 4) don't use selective "brush control" herbicides (like triclopyr or 2,4-D) to kill grass or bamboo - it only works on broadleaf plants, and 5) read the label for appropriate seasons, temperatures, PPE, risks, and dilution rates. Homeowners typically use far more herbicide than is needed which can reduce effectiveness. More is not better.
For the professional practitioner, the idea of avoiding pesticides when controlling pests and weeds is called, “Integrative Pest Management,” or “IPM.”
Before automatically resorting to chemicals, IPM considers other methods such as mechanical, biological, cultural, or physical tactics .
A mechanical method for weeding might be repeated mowing to reduce seeding of short-lived weeds and eventually starve unwanted plants. A cultural practice for rat infestations is not automatically rodenticides, rather, changing the conditions that attract rats, (removing clutter, blackberry and ivy that provide food and cover from raptor-predators). A combination of tactics can be effective, such as: mechanically string-trimming ivy, then smothering weakened resprouts with 8-12" of woodchip mulch. Another combination of tactics might be mulching with woodchips to reduce weed germination, then planting native plants, favoring evergreen groundcovers, shrubs, and trees to shade out weed re-invasions.
Best Management Practices (BMP)
Best Management Practice (BMP) means a "practice, or combination of practices, that is determined to be effective and practicable, including technological, economic, and institutional considerations," taking into account pesticide concerns, aiming for the best outcome for human and environmental health.
In a simple example of a weed-infested field, the practitioner community would consider IPM, but their accumulated experience would know that mowing kills ground pollinators yet doesn't kill the weeds' roots (Creeping thistle). Mowing spreads weed seeds (Herb robert, Shiny geranium) or spreads vegetative fragments that re-root (Knotweed, Yellow archangel). Practitioners also know that mowing Poison hemlock or Giant hogweed is extremely toxic to the operator, causing severe skin burns, permanent eye and lung damage. The best-management BMP might be spraying (outside of bloom-pollinator windows) a selective broad-leaf herbicide that doesn't affect grass, that is less toxic than the exhaust-pollution of mowing. Or, the BMP might be spraying a broad-spectrum herbicide (that kills both grasses and broadleaf weeds) to clear the way for replanting native species, including pollinator-friendly species. Spraying is considered a better practice than sodcutters, leaving topsoil intact, and far less toxic than the exhaust from the transport and operation of heavy-machinery. Any removal of topsoil reduces habitat for ground-nesting pollinators, and soil compaction reduces water infiltration and the success of replanting efforts. The loss of soil structure and organic matter in the ground suppresses fungal-water-transport networks that would otherwise support plants and make forests more resistant to disease and fires.
For carpeting weeds like English ivy, BMP's might deem that herbicide applications are necessary to avoid "non-point sources of pollution" (toxic stormwater runoff) caused by erosion of pollution-tainted soils, and is therefore preferred over manual-uprooting methods. This is particularly true on steep, erosion-prone sites where the cascading consequences of soil disturbance would likely prevent recovery of healthy soils and vegetation.
Practitioners who do the hard work of invasive plant removal have tried every "organic" trick in the books, repeatedly over decades. Hard-earned experience has concluded that eradicating certain invasive species requires herbicide, and that neglecting invasive monocultures is far more worrisome.
The best example is streamside knotweed with 10-ft deep roots that can’t be manually removed without eroding streambanks and smothering salmon nests with the resulting silt. Knotweed severely degrades native plant food sources that feed the bugs that feed salmon fingerlings. Covering knotweed with weed cloth has been tried over many years, but the manufacture, transport, and disposal of large rolls has its own environmental footprint, and it simply hasn't worked. Knotweed only regrows, spreads downstream at high rates, and continues to erode streambanks and impoverish food webs for salmon. To save salmon, the reluctant conclusion is that chemical treatment of knotweed with the safest effective herbicide is a necessity, followed up with native plant revegetation that shades and cools salmon streams while contributing detritus (leaves, twigs, and decaying organic matter) that feed the base of the food chain.
Restoration practitioners operate with oversight from the Department of Fish and Wildlife, Dept. of Ecology, and the State Dept. of Agriculture. Experienced practitioners are trained to use PPE to avoid repeated exposure to themselves, while carefully avoiding off-target herbicide damage to native plants and pollinators.
Do-it-yourself considerations
Many homeowner-stewards become discouraged with manual methods that may not work or make infestations worse. Unless they can find or afford experienced practitioners, they give up on control efforts. Homeowners who are considering herbicide applications must first assume responsibility for applications on their property only, including unintended effects to neighboring properties. Homeowners must also consider and accept the health-risks and environmental-cost trade-offs of chemical vs. manual removal methods. Do-it-yourself stewards should be confident with identifying both native and non-native invasive plants, while taking measures to preserve valuable native plants.
DIY-stewards must properly use PPE (gloves, eye pro, long pants and sleeves, or other recommendations per the label) before applying over-the-counter herbicide products. Avoid rain, and follow seasonal effectiveness listed in the Invasive Weed Calendar Guidelines. It is legally required for all pesticide users to read and follow the pesticide label.
Professional help
For professional help or advice, licensed herbicide professionals may be found at: https://agr.wa.gov/services/licenses-permits-and-certificates/pesticide-license-and-recertification/pesticide-and-spi-licensing/license-lists. Many restoration practitioners have licenses with Ornamental/Agricultural Weed, Right-of-Way, and/or Aquatic endorsements. Licensed practitioners have weighed the risks of herbicide vs. the risks of invasive neglect, and choose to judiciously apply herbicide in the appropriate season for the reasons below.
The rationale for herbicide
The main reason for using herbicide is that it reduces soil erosion. Worldwide, one-third of topsoil has been lost since the agricultural revolution, mainly from tilling and over-grazing steep slopes. This trend must be reversed in farming, forestry, and restoration practices.
In restoration, herbicide applications on invasive plants retain treated roots in the ground to slowly decay, temporarily holding soil and building soil structure for the benefit of establishing native plants. Using herbicide is not a weeding strategy, rather, it's a restoration strategy necessary prior to re-planting with native species. These limited herbicide applications and "restoration" prevent the "weed vacuum" from getting re-infested.
Some herbicides may affect soil microbes, but for safer herbicides, it's generally considered short-term and minor compared to manual methods that remove food in the ground, effectively starving soil microbes. "Organic" manual removal methods can disturb and erode topsoil that takes many centuries to build, especially on slopes. Erosion reduces the soil's sponge and filter, a hedge against toxic stormwater, drought stress, floods, and wildfire risk.
In polluted settings, loss of rotting roots in the ground particularly reduces fungal filtration of toxic stormwater runoff. Stormwater is rain runoff from roads, roofs, and lawns tainted with oil, air pollution, animal feces, and unnecessary fertilizers and pesticides. Stormwater is considered the "number one polluter of Puget Sound" that can overwhelm combined-sewer systems (CSO's), dumping raw sewage into public waters. Considerable air pollution is deposited, sequestered, and partially neutralized in healthy soil, so judicious herbicide can mitigate soil disturbance that carries worse toxins into water bodies where "bio-accumulation" concentrates toxins up the food chain, in salmon, orcas, and people who eat salmon.
"Slow, insidious soil erosion threatens human health," and is considered one of "the biggest environmental problems the world faces" (https://news.cornell.edu/stories/2006/03/slow-insidious-soil-erosion-threatens-human-health-and-welfare). Our country has also "lost a third of its topsoil after two centuries of independence" (DIRT - The Erosion of Civilizations). Long before the chemical revolution, the Dust Bowl is a notorious example of erosion caused by tilling amplified by drought, resulting in ecological collapse.
Even "organic agriculture can prove as unsustainable as conventional (chemical) farming when tillage is a regular practice" (David R. Montgomery, Growing a Revolution, 2017). Many American farmers, having lost topsoil and fertility, are now leading soil conservation efforts with cover cropping, "no-till," disking, and chisel-plow farming methods to preserve soil health. Organic farmers are realizing greater yields per acre with diverse interplanting, mulching, and manuring from thoughtfully-managed farm animals.
For restoration professionals, herbicide is a key tool on erosion-prone slopes and for many species for which manual methods simply don't work: root fragments only grow back, creating thickets all the more difficult to control. Repeated pruning over many years may eventually starve invasive plants on small private lots, but public land managers dealing with exponentially spreading invasives on large acreages cannot rationalize transporting crews or volunteers with polluting vehicles to "organically" and ineffectively control invasive plants using methods that erode soil and are more harmful to the environment. Vehicle fuel is acutely more toxic and used in far greater quantities than herbicide. Given limited budgets, the magnitude of the invasive problem and compounding re-invasion rates, the efficacy of best practices is imperative.
No one wants unnecessary toxins, but minimizing the quantity of pesticides in our environment requires nipping invasive plants in the bud before they become monocultures region-wide. To put herbicides in perspective, agriculture consumes 19 percent of the total U.S. consumption of 134 billion gallons of gasoline per year. With each gallon of gasoline weighing 6.3 pounds, that's 780 billion pounds of gasoline per year. Quantities of annual glyphosate amount to 280 million pounds, or 4/100ths of one percent (.0004) the quantity of more toxic fossil fuels.
Lawn culture, tree farming, and industrial agriculture have repeatedly proven that monocultural crops attract pests as a result of losing biodiversity with its natural checks and balances (https://phys.org/news/2020-11-diversity-pesticide.html). Due to the rate of invasive spread and the fact aggressive introduced species have no natural checks, herbicides are necessary to preserve biodiversity needed to sustain wildlife, including pollinators. Unchecked spread of invasive plants would require greater quantities of herbicide applications in the future, and possibly worse rodenticides and insecticides. Skilled applicators apply herbicide in the right season, minimizing the quantities of products used. It's very important to read product labels carefully and/or hire qualified professionals guided by this application calendar.
Restoration professionals mostly use products with the active ingredients glyphosate, triclopyr, and imazapyr as directed by government agencies who have analyzed the health and environmental effects of various herbicides. Imazapyr is the herbicide most often used for holly and hawthorn injections, and for knotweed sprays. Professional products often are "aquatic" restricted-use formulations that are only available to licensed professionals, that are usually 50% active ingredient - the concentration used for cut&dab treatments. Aquatic herbicides are formulated without surfactants, and are deemed safe for fish and amphibians, necessary near wetlands or riparian zones. Concentrated herbicides are considered more risky to human health (although less than many risks we overlook daily - see below), and are therefore only available to licensed applicators trained for safe use and handling. Licensed applicators have a short list of aquatic surfactants vetted by the Dept. of Ecology (see calendar link in above paragraph) to assist the absorption of herbicide into the leaf when spraying. Professionals carefully dilute concentrated herbicides and surfactants to approximately 2% active ingredient (a.i.) for foliar sprays. Ready-to-spray consumer formulations are usually pre-mixed at 2% a.i. with surfactants that are not necessarily fish-safe, and therefore are not permitted for use around streams or wetlands. It's particularly important to avoid spraying consumer products unless you have one dry day followed by two forecasted dry days during the summer/fall growing season (but not when plants are drought-dormant).
Pesticide-pollinator concerns
The INTERNATIONAL PROGRAMME ON CHEMICAL SAFETY concluded that“glyphosate has low toxicity for bees and earthworms."
Whether or not the cited science is accurate or dated, the loss of biodiversity from invasive neglect is a greater risk, so skilled restoration practitioners selectively target invasives and avoid spraying pollinators. Granted, this does not prevent chemical exposure through uptake of systemic herbicides in farming practices, where nectar may contain trace amounts of herbicide that pollinators ingest.
This systemic uptake may play a role in pollinator decline given the repeat agricultural applications of glyphosate, and it could very well be a serious concern and a reason to support organic farming. Restoration practitioners avoid systemic uptake by cutting and treating only the stem/roots, or by brushcutting blackberry, for example, and spraying regrowth that is not in flower (spraying may actually use less active ingredient, but risks off-target damage to beneficial plants).
In contrast, forestry applications use 1 - 2% of herbicides used in agriculture, mostly for "conifer release" or "free-to-grow" aerial sprays that kill competing vegetation, "releasing" conifers from sun and water competition. In this author's opinion, conifer-release practices are old-school experiments that have reduced overall forest productivity due to erosion, loss of hydraulic redistribution (available water) through diminished fungal networks, loss of nitrogen fixing and anti-pathogen properties that are provided by symbiotic benefits of biological diversity in healthy soil. In contrast to conventional forestry practices, restoration (of soil and plant diversity) uses far less herbicide than tree farming, the minimal amount necessary to assist ecosystem recovery. Again, in restoration, herbicides help reduce erosion and are a tool to control invasive monocultures to preserve native plant diversity necessary to sustain insects, wildlife and pollinators.
Based on recent news reports, there is significant cause for concern for "neonic" insecticides (neonicotinoids) used in farming and the ornamental flower industry.
Insecticides are known to kill beneficial insects far beyond the target pests. But, insecticides often get confused with herbicides in misleading news reports that conflate what are both technically "pesticides."
"Pesticide is a broad term that includes insecticides, herbicides (weed or plant killers), fungicides, rodenticides, miticides (mite control), molluscicides (for snails and slugs), and other materials like growth regulators or antimicrobial products such as bleach and sanitary wipes that kill bacteria." (http://ipm.ucanr.edu/PMG/PESTNOTES/warning.html)
Some chemical-herbicide alternatives (concentrated vinegar) may change soil pH, risk irreversible eye damage, and just "burn down" tops of weeds guaranteeing the need for repeat applications. Vinegar herbicides are acutely toxic to bees and pollinators and can burn, even permanently blind the applicator. For homeowners wanting familiarity, vinegar may be a preferred method for weeds in sidewalk cracks around the home. For safety, wear proper PPE (gloves and eye protection ! ) and other precautions on the label of natural pesticides. Some people recommend mowing invasives as an alternative to herbicide, but again, gas-powered mowing emits air pollution more carcinogenic than glyphosate (see studies cited below) and routinely kills pollinators (70% of native bee species are ground nesting). Mowing may spread weed seeds and not kill invasive roots. In contrast, herbicide applications are usually limited to the target plants, where any "drift" can be tracked by yellowing leaves on affected plants (visible effects can be delayed). Whereas, air pollution from mowing is actually ingested by all people downwind, causing immediate and long-term health effects. Plus, CO2 remains in the atmosphere for centuries.
Again, insecticides are very different than herbicides, and it's important to analyze the properties of all chemicals, natural or otherwise. Efforts to ban certain pesticides might be misguided, causing more harm than good. A more pragmatic and effective approach might be to tax pesticide products according to downstream soil testing and water-quality monitoring so we can apply science-based fees commensurate with environmental and human health risks. Consumers notoriously use five times the amount necessary as recommended on the legal label, something that is rarely read. A price tag that reflects actual risks is more likely to be read and heeded, effectively reducing unnecessary pesticide applications. Regulations do little to proactively motivate more judicious applications.
The restoration profession's limited use of herbicide is intended to control invasive species, the second leading cause of species extinctions behind the number one cause, habitat destruction (such as paving and clearing for development, infilling wetlands, and high-intensity wildfires). Invasive plants degrade habitat and "are listed as a driver for more than half of the extinctions in each of the vertebrate taxa analysed" (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4780541/). Invasive infestations reduce resilience to disturbance (disease, insect pests, fire) and alter vital functions such as tree regeneration, forest structure and hydrology.
Risk Assessments for Human Health
Certain herbicides like imazapyr are considered "practically non-toxic (the EPA’s lowest toxicity category) to fish, invertebrates, birds and mammals." But for the sake of discussion, let's consider glyphosate, the most studied and most vilified "pesticide" on social media.
The International Agency for Research on Cancer (IARC), an arm of the World Health Organization (WHO), recently published an often-cited analysis of over 1,000 independent studies on glyphosate, the active ingredient in Roundup, the most heavily use herbicide in the world. An academic review of the WHO report can be found at: http://blogs.oregonstate.edu/mgcoordinators/2018/10/15/glyphosphate-questions-answers/
In short, the review explains that the IARC listed glyphosate as "a probable human carcinogen." This surprised many governmental agencies tasked with protecting public and environmental health. The IARC responded and clarified their listing as identification of "potential hazards," quite different than actual risk assessments (think "cliff" - a potential hazard but not a risk if you're not close). The classifications of carcinogenic categories can be found in the IARC's Preamble.
The IARC placed glyphosate in the Group 2 A list of probable carcinogens, a category that includes: 1) Red meat, 2) Indoor emissions from burning wood, 3) Emissions from high-temperature frying, 4) Late-night work shifts.
Group 2A is less risk than the Group 1 category of "known carcinogens" which include, but are not limited to: 1) Processed meats, 2) All alcoholic beverages, 3) Sunlight, 4) Engine exhaust (diesel), 5) Benzene (in gasoline), 6) Outdoor air pollution.
For many compounds, the "dose makes the poison" (aspirin, some vitamins, many natural remedies), and pesticide studies employ high concentration doses. While many governments are banning glyphosate due to public fear, their scientific agencies find over-the-counter dilutions of glyphosate or food residues “unlikely to cause cancer in humans." These scientific reports from governments with robust research resources include:
- US Environmental Protection Agency, December 18, 2018
- European Food Safety Authority, November 12, 2015
- Australian Pesticides and Veterinary Medicine Authority, March 15, 2017
- New Zealand Environmental Protection Authority, August 2016
- Health Canada, April 2015
For ecologists who understand the health risks of losing bird populations and native pollinator habitat region-wide (from loss of plant diversity due to aggressive introduced plants), the risks of glyphosate exposures are far less worrisome. The probability of Non-Hodkins lymphoma (NHL) to ag workers is 2.8% compared to 2% for the general public, not a statistically significant difference, but boosting glyphosate to the "probable" 2A category.
Perhaps the risks to farmers, ag workers, and restoration practitioners who handle concentrated formulations is greater than the risks to the general population, so professionals are highly advised to wear PPE and aim for zero exposure.
Still, farmers generally live longer than the average citizen, despite their above-average exposure to diesel exhaust and sunlight, both carcinogens in higher risk categories than glyphosate (https://www.ncbi.nlm.nih.gov/pubmed/29136183 and https://www.epa.gov/sites/production/files/2016-09/documents/glyphosate_issue_paper_evaluation_of_carcincogenic_potential.pdf). There is evidence that risks to ag workers may be due to fertilizer exposures, not necessarily glyphosate (https://cancercommun.biomedcentral.com/articles/10.1186/s40880-017-0225-4). One science-writer describes glyphosate risks as "negligible," comparable to "the risk of just being alive" (https://sciencebasedmedicine.org/update-on-glyphosate/). Still, practitioners are open to evolving science and want to know the properties of products we are tasked to use.
There appears to be growing research about glyphosate potentially affecting gut microbiomes, a possible factor in many western diseases in humans, and possibly affecting pollinators in similar ways. In addition, glyphosate is known to have mineral-binding capacity that chemically adheres to soil particles (a reason farmers often choose glyphosate - due to its negligible risk to groundwater). But it's unknown to this author whether glyphosate residues on food could bind up minerals in the body (such as calcium in bones), or how much glyphosate "demineralizes" soil and therefore the nutrient content of food (compared to the demineralization from tilling erosion or changes in soil pH from vinegar applications). Concerned consumers might be advised to buy organic food, or better, build your own soil health and grow your own organic food (be sure to conduct soil tests) to minimize dependency on carbon-based transport of industrially-produced farm products.
However, our food system and farming practices are not the focus of this website. We are explaining the tradeoffs of herbicide used for invasive plant control in order to preserve topsoil and biodiversity. We are not defending or opposing farming practices - farmers face their own economic and labor constraints and tradeoffs. We do encourage farmers to consider expanding their native plant diversity in hedgerows - even if establishing quality pollinator habitat requires initial herbicide applications.
What if...
The opinions shared in this practitioner perspective come from environmentalists who actually do the work, and we also want to know the risks or "relative worry" of products that government agencies direct us to use. For these vetted herbicides, the risks are considered low by a vast majority of scientists. Still, we would like to apply the "precautionary principle" to our environment and our own health. It begs the question: “What if someone downstream or one of our fellow practitioners gets cancer?”
Tragically, many people get cancer from many different causes, sometimes genetic or from impossible-to-pinpoint exposures to hundreds of toxins, many natural and many man-made, that may or may not be listed in the IARC report. When cancer strikes, blame is often directed toward a conditioned prejudice or "lightning rod."
Close to home, the web designer of this very website lost his battle with cancer. He was an employee, a beloved precious individual, and a restoration practitioner who didn’t for a moment think his herbicide work was to blame, because he contracted cancer well before starting his career. Plus, he did his research, earning a Masters of Science degree from the UW School of Environment and Forestry Sciences. He was proud of this website legacy, helping to explain the eco-logic behind herbicide, necessary to preserve native plant diversity required by the birds he loved. And he was comforted that all the trees he planted made a lasting contribution to the world. Co-workers continue to plant and spread the seeds of his favorite Pacific madrone.
Ironically, the tragedy of cancer helps explain the predicament of invasive species, because certain introduced species are themselves an ecological cancer. With many introduced species spreading region-wide, it's more accurate to describe it as a cancerous epidemic, one that is spreading by seed rain. We have to apply the "precautionary principle" to invasive species, because ecological cancers can shut down vital functions not limited to: 1) natural regeneration of native trees, 2) pollinator habitat needed for our food supply, 3) resilience to forest fires, 4) resistance to pest and disease outbreaks illustrated by rat infestation in ivy monocultures. In essence, when invasive species are the second leading cause of species extinctions, when cancer threatens human life, survival sometimes requires chemical treatment.
For some species like ivy, its uncontrolled growth is relentless, spreading in slow-motion. For others like holly, its spread is epidemic, at a near-exponential rates. Cancerous epidemics of invasive plants illustrate how epidemics operate: one property gets infested and then infests neighboring properties, and the only immunity is to restore healthy native vegetation that competes with perpetual reinfestations until everyone controls invasive seed rain sources at the same time.
"Sepsis" might be more a more accurate analogy, and this unfortunate reality forces our appeal. We ask that the public consider tolerating the necessity of chemical applications, and consider the proposals on the Stewardship Incentives page of this website.
"Fear sells" the same way that "illegal aliens" or "poisons" resonate with deep primal instincts, and I apologize for my use of "invasive" language that reinforces xenophobia. Glyphosate has become a ‘wedge issue’ that divides rural, environmental, and progressive concerns, and it is my hope that passionate, caring people can temper their emotional view of threats in the world and work together to limit unnecessary and reckless use of all toxic products, commensurate with science-assessed risks, rather than letting slanted media divide and blind us to greater risks. Notwithstanding valid concerns about toxins, misinformed fear can divert attention and resources away from more pressing issues, and fear itself can be a factor in disease.
Lastly, the longer we wait, the more expensive invasive control will be. Neglect is not an option - we are approaching a tipping point when invasive plant infestations will soon be entrenched and ungettable.
Thank you to the professionals and academics who have contributed their experience and knowledge to improve this educational website. And thank you (!) citizen-volunteers who steward their land, or any permitted land. There is SO much work to be done. Steve Richmond, October 2023