- Author: Lauren Fordyce
Plentiful rainfall in California this spring created an ideal environment for many plants to thrive, including wildflowers, trees, and shrubs that desperately needed the water. However, other potentially harmful species also benefited from the unusually wet weather. Of particular concern are poisonous plants which are growing abundantly in parks and wildlands this year. These plants pose health risks to people, especially children, and pets. Being able to identify poisonous plants and understand available control options is critical for the safety of people who encounter them. While several poisonous plants grow in California, a few of the more common are detailed below along with information on how best to remove or manage them.
Poison Hemlock
Poison hemlock (Conium maculatum) is an invasive weed that thrives in disturbed areas but it can also invade native plant communities. It is commonly found in meadows, pastures, and fields, and may spread quickly after the rainy season. All parts of the plant are toxic to humans and animals when ingested. Touching poison hemlock may cause contact dermatitis for some people.
Poison hemlock can easily be mistaken for its relatives in the family Apiaceae, like carrot, parsley, parsnip, or celery, especially when plants are young. Leaves are triangular shaped, deeply lobed, and have opposite branching (Figure 1). Unlike invasive wild carrot (Daucus carota), poison hemlock lacks hairs on its leaves and stems. Poison hemlock has white, umbrella-shaped flowers, similar to those of native cow parsnip (Heracleum maximum). However, cow parsnip has much wider leaves that are arranged in threes and can measure up to 16 inches wide. You can also distinguish poison hemlock from similar plants by checking for purple streaks or spots along its hollow stems. Mature plants can reach almost 10 feet tall.
Poison hemlock is best controlled when young, before it sets seed. It releases seeds over several months, and copious amounts of seed can build up in the soil. Small infestations of poison hemlock can be managed by hand removal while wearing gloves or hoeing the area. The taproot must also be removed to prevent regrowth. Repeatedly mowing poison hemlock can deplete its energy and prevent seed production. Be sure to clean mower blades to avoid moving seeds to new areas. Herbicides containing 2,4-D, triclopyr, or imazapyr work best on seedlings. Glyphosate, chlorsulfuron, and metsulfuron are effective on larger, rapidly growing plants. Repeated herbicide applications may be required for several years until the seedbank has been depleted. Never burn poison hemlock as this can release its toxins into the air.
Poison Oak
Poison oak (Toxicodendron diversilobum) is a deciduous native plant that is widespread through California's coastlands, woodlands, rangelands, riparian areas, and urban parks and gardens. Poison oak, like its eastern relative poison ivy, contains an oil called urushiol that can cause contact dermatitis and itchy, weeping rashes on the skin of people who are sensitive to urushiol. The allergy-causing oils can persist on tools, clothing, and other objects for months or even years.
The old adage “leaves of three, let it be” often holds true for poison oak, but not always. Plants normally consist of 3 leaflets, but may sometimes contain 5, 7, or 9. Leaves are slightly lobed and occur alternately along the stem (Figure 2). They can vary in color and texture from glossy to dull, and thin to leathery. In open, sunny areas poison oak can grow to be a dense shrub. In more shaded areas it grows as a climbing vine. It can easily spread to cover large areas via seeds and rhizomes.
Poison oak can be removed through hand pulling and digging (including roots) with a shovel; wear protective clothing and gloves, and promptly wash or discard them afterwards. Removed plants should be carefully disposed of since the oils remain hazardous even after the plants have dried. Never burn or mow poison oak as it will release its oils into the air, posing an inhalation risk. Herbicides that contain at least 41% glyphosate or 61% triclopyr ester have been shown to provide effective control. Dicamba and imazapyr can also be used. Foliar applications should be made in the late spring or late summer, depending on the chemical used. Cut-stump treatments can be performed in the spring or fall.
Burning and Stinging Nettles
Unlike poison oak and poison hemlock which may only affect some people, burning and stinging nettles (Table 1) cause burning rashes to anyone who touches them. The rashes are caused by a toxin in the prickly hairs on the leaves and stems. Contact with burning and stinging nettles can cause blisters and red patches. Itching, burning, and tingling sensations may persist on the affected skin for several hours.
Burning nettle | Stinging nettle |
Found in disturbed sites, roadsides, orchards, and gardens; common along the coast | Found in unmanaged areas, riverbanks, moist wildlands, and roadsides |
Summer annual; blooms January to April | Perennial; blooms March to September |
Spreads by seed | Spreads by seed and rhizomes |
5 inches to 2 feet tall when mature | 3½ to 10 feet tall when mature |
Opposite leaves with toothed margins; ½ inch to 2 inches long (Figure 3) | Opposite leaves with toothed margins; 2½ to 5 inches long |
Burning and stinging nettles can be nuisance plants as well as health hazards. However, they are not considered invasive or noxious weeds. In fact, stinging nettle is native to California so control should only be performed if plants are causing economic or health concerns. Hand pulling while wearing gloves can be effective, but the underground stems (rhizomes) of stinging nettle must also be removed. Mowing close to the ground can prevent seed development and spread, but if done too early in the season the nettles will regrow rapidly from the rhizomes. The active ingredients 2,4-D, aminopyralid, dicamba, glyphosate, and triclopyr provide excellent control for both stinging and burning nettles.
To learn more about controlling these toxic weeds in landscapes and natural areas, see the Weeds page on the UC IPM website at ipm.ucanr.edu/PMG/menu.weeds.html or the Weed Research Information Center wric.ucdavis.edu. These and other weeds are described in the book Weed Control in Natural Areas in the Western United States, available from the UC ANR catalog anrcatalog.ucanr.edu.
/h2>/h2>/h2>- Posted by: Gale Perez
Speaker: Doug Johnson from the California Invasive Plant Council (Cal-IPC)
Topic: Managing Invasive Plants in Wildlands Requires an IPM Approach on Several Fronts
One is prevention, which can be aided by evaluating which species pose a high risk of becoming harmful in the future. Another is selecting the best control techniques for a given management situation. Cal-IPC has projects addressing both of these needs: one project teams with other Western states to evaluate the risk of potential invasive plants using the online PRE tool, and the other project teams with UC IPM to build the online WeedCUT decision-support system for selecting control techniques.
The IPM Hour is a monthly online seminar covering a variety of IPM-related topics and research. It's held the second Wednesday of each month at 12 noon Pacific Time and features two 20-minute presentations followed by 10 minutes of discussion each. You can tune in live or check out the recordings on the Western IPM Center YouTube channel.
Other weed science-related IPM Hour recordings:
Episode 18 - WATCH RECORDING
Managing Herbicide-Resistant Italian Ryegrass with Electric Current in Hazelnut Orchards
Presenter: Marcelo Moretti, Assistant Professor and Extension Weed-Management Specialist, Oregon State University
Episode 16 - WATCH RECORDING
Use of Precision Applied Steam to Control Soilborne Pathogens and Weeds in Lettuce
Presenter: Mark Siemens, Department of Biosystems Engineering, University of Arizona
Description: Lettuce drop (Sclerotinia spp.) and in-row weed control are major concerns of California and Arizona lettuce growers. Soil disinfection using steam is a highly effective technique for controlling plant pathogens and weeds, but is cost prohibitive since conventionally steam is applied to the entire soil profile. To address this, a prototype band-steam was developed where only narrow strips of soil centered on the seed line are treated. The device is principally comprised of a 35 BHP steam generator mounted on a bed shaper. The system's design and operation, as well as field trials results will be presented and discussed.
Episode 16 - WATCH RECORDING [Begins at 26:00]
Developing Non-chemical Harvest Weed Seed Control Strategies in Dryland Crops
Presenter: Eric Westra, Department of Agricultural Biology, Colorado State University
Description: The presentation will cover updates on field trials evaluating how chaff lining fits into dryland cropping systems in the Central Great Plains as an integrated weed management tool. Evaluation of chaff lining weed control efficacy in wheat, corn, and grain sorghum will provide information on how this integrated weed management tactic will fit in new geographic regions.
Episode 15 - WATCH RECORDING [Begins at 30:25]
Medusahead Impacts on Livestock Production and Low-Cost Management Options
Presenter: Jeremy James, Dept. of Natural Resources Management and Environmental Sciences, Cal Poly
Description: Medusahead is a widely dispersed invasive annual grass across the West with limited low-cost options for management. Here we first examine the potential economic impacts of medusahead on livestock production and then discuss the potential to use very low rates of aminopyralid applied in spring as a means to sterilize medusahead seed and increase abundance of desired plants. We show the potential for aminopyralid to reduce medusahead seed viability at management scale and pasture wide reduction in medusahead abundance. We also show how economic impacts of medusahead can change depending on grazing management decisions.
Episode 10 - WATCH RECORDING
Spot It! Report It! Remove It! Mobilizing Residents in the Fight Against Invasive Weeds
Presenter: Qiting Chen, IPM Coordinator, City of Edmonton, Alberta
Description: Public education and awareness of invasive plant species are essential to support integrated pest management efforts in municipalities. The public plays an important role in detection, data collection and early intervention of invasive plant species. In Edmonton, efforts to engage the public in IPM activities have been ongoing and in 2019 the city launched a social marketing campaign called Spot it, Report it, Remove it. Tactics used include public outreach events, community weed pulls, door-to-door outreach campaigns, and the weed identification feature in the Edmonton 311 app. We will discuss the results and lessons learnt from the campaign.
Episode 06 - WATCH RECORDING
Revegetating Weed-Infested Rangeland
Presenter: Jane Mangold, Professor and Extension Invasive Plant Specialist, Montana State University
Description: Seeding desired vegetation to compete with weeds is sometimes necessary when weeds have dominated rangeland for many years and remnant vegetation is scarce. This presentation will share research results from a variety of Montana studies where seeding was integrated with other weed-control strategies.”
Episode 05 - WATCH RECORDING
Ecological Management of Kochia in Irrigated Western Cropping Systems
Presenter: Prashant Jha, Associate Professor and Extension Weed Specialist, Iowa State University
Description: This presentation will highlight on how to best implement sustainable integrated weed management programs to reduce herbicide reliance and manage weed resistance to herbicides in sugar beet-based crop rotations of the Western United States.
Episode 04 - WATCH RECORDING [Begins at 29:12]
A Developing and Developed Countries Perspective on Implementation of Integrated Weed Management
Presenter: Anil Shrestha, Weed Science Professor, California State University, Fresno
Description: Concepts of integrated weed management with examples from South Asia and the United States, including social and economic issues.
Original source: The Western IPM Center
/span>- Author: Marie Jasieniuk
- Posted by: Gale Perez
The global horticultural trade in ornamental plants is well known to be a primary source of non-native invasive plant introductions worldwide. In the United States, non-native species make up as much as 80% of the ornamental nursery stock and account for most nursery revenue. Although only a small percentage of these species escape cultivation and become invasive, the large number and diversity cultivated, especially in California, results in ornamental plants contributing to more than half of the invasive weeds currently damaging California's wildlands and remnant natural areas in urban landscapes.
The majority of ornamental plants are purchased and grown by the public. Thus, educating consumers to make informed choices towards purchasing non-invasive ornamentals has been an effective mechanism championed by local groups and organizations, such as PlantRight (https://plantright.org/) and Cal-IPC (https://www.cal-ipc.org/), to reduce ornamental plant invasions across the state. Both organizations also work with California's ornamental nursery industry to remove potentially invasive plants from sale and promote non-invasive alternatives (https://plantright.org/about-invasive-plants/plant-list/).
Expansion of residential and urban areas into wildlands has substantially increased the risk for ornamental plant invasions of natural areas. However, perhaps even more concerning today are the impacts of urbanization and ornamental vegetation on wildfires in the Wildland-Urban Interface (WUI), i.e. the zone of transition between wildland and human development. Each year, wildfires consume hundreds of homes and cause too many wildfire-related deaths in the WUI in California. Fire is, and always has been, an integral component of California's natural ecosystems due to the Mediterranean climate. However, in recent years, the frequency and intensity of fire events have increased dramatically such that the 2018 wildfire season was the deadliest and most destructive wildfire season ever recorded in the state. Increases in human-caused fire ignitions, due to the rise in numbers of people living near wildlands, combined with climatic changes characterized by very high summer temperatures, increased drought periods, and strong winds, have markedly increased the risk of devastating wildfires in WUI areas.
Ornamental vegetation used in landscaping can increase the vulnerability of homes to wildfire as this vegetation can act as “ladder fuel” and ignite houses and other structures. Thus, in addition to providing consumers with lists of invasive ornamental plants and suggested non-invasive alternatives to protect California's environment (e.g., https://plantright.org/about-invasive-plants/plant-list/), plant lists of flammable ornamental plants and suggested low-flammability alternatives could reduce the risks of destructive wildfires in WUI areas. Obviously most, if not all, plants will burn in a high intensity fire but it is possible to suggest ornamentals that have lower flammability. For instance, FIRESafe Marin (https://www.firesafemarin.org/) has developed a list of common native and non-native fire-safe plant species suitable to the climate of Marin County (https://www.firesafemarin.org/plants/fire-resistant/table), based on reviews by fire, forestry, and botany experts. Scientific studies of plant flammability in terms of quantitative measurements of ignitability, heat release, and fire spread rate of ornamental, invasive, and native species are also being conducted in California and other regions of the world. Results of the plant flammability studies, paired with knowledge of the relative invasiveness of ornamental plant species, will provide useful guidelines to homeowners for reducing fire risk and preventing the spread of invasive plants in the wildland-urban interface.
- Author: Ben Faber
This is the most recent activity summary of a group of organizations working on the Invasive Shot Hole Borers and their associated fungal symbionts. This pest/disease complex affects avocado along with a large number of native and landscape plants in California, as well as in other parts of the world (http://ucanr.edu/sites/pshb/; http://ucanr.edu/sites/pshb/files/238251.pdf):
Invasive Shot Hole Borers
Quarterly Situation Report
January through March 2018
Executive Summary
Overview
Education, outreach, and monitoring activities were robust during the cool damp winter months of 2018. Infestations continued to dominate Orange, San Diego, and Los Angeles counties, with lesser activity in Ventura and Santa Barbara counties. The need for funding of research, education, outreach, and waste management associated with ISHB was brought to the attention of state governance. Preventative efforts to increase awareness of ISHB in unaffected counties continued. Collaborative efforts of numerous agencies, educational institutions, and non-profit groups resulted in the successful efforts listed below.
Statewide
The two-day Invasive Species Summit was held in the State Capitol for legislators and their staff to learn about environmental pressures and costs created by these species statewide. Three pieces of proposed legislation were written either specific to or with components addressing ISHB. They are: AB 2054 (Gonzlez Fletcher), AB 2166 – California Farm Bill, AB 2470 (Grayson) – Invasive Species Council.
The Statewide SHB Network convened telephonically to discuss ISHB, spread, threat, and help educate those in unaffected counties. An ISHB presentation was given at a statewide horticultural convention in northern California.
The triennial California Native Plant Society Conservation Conference was held near Los Angeles International Airport. ISHB was addressed at a pre-conference invasive species workshop, throughout the conference by tabling and poster session, and during the Invasive Species Session.
Regional
UCCE San Diego helmed a two-part GSOB/ISHB-FD webinar, along with other UCCE and CALFIRE collaborators. The first installment streamed in March.
UCCE San Diego began work on an online ISHB survey assessment tool that will be accessible when completed on PSHB.org. This feature will help the public determine if tree symptoms may be due to an ISHB infestation. An added component will allow UCCE to monitor reporting. The decision tree that is part of the assessment takes the reporter to part of the site whereby photos can be submitted if the tool determines a probability of ISHB infestation. This tool will be completed, tested, reviewed, and posted to the website by summer 2018.
San Diego County
- Two ISHB public educational events were presented
- Buy It Where You Burn It campaign distributed literature countywide
Orange County
- Four ISHB public educational events were presented
- Numerous trap and monitoring sites are established throughout the county primarily in wildlands and parks
- Orange County Waste and Recycling learned 28% of all trees at Prima Deshecha Landfill in San Juan Capistrano are infested with ISHB/FD or Botryospaeria. Most of the vegetation at this site is comprised of native species
- A post-incident GSOB/ISHB reconnaissance was conducted in Weir Canyon, where the Canyon II Fire burned in autumn 2017
- Orange County Parks continued to track tree losses and costs associated with ISHB infestations on its properties. An economic report was publicly released
Los Angeles County
- Three ISHB public educational events were presented
- A funding request was submitted to County governance to continue the ISHB trapping program coordinated by the Resource Conservation District of the Santa Monica Mountains
- The Huntington continued monitoring and green waste processing at the 207-acre facility. An ISHB trapping trial by principal investigator at UC Riverside was initiated that utilizes castor wood as the attractant
Ventura County
- Twenty-six traps are established and monitored in the Santa Clara River watershed extending from the estuary to Piru
- Fifteen traps are established and monitored in the Ventura River watershed. This number is down by two after being lost during the Thomas Fire
- A new infestation was identified in the City of Santa Paula proximal to a known infestation in the Santa Clara River
- One ISHB educational event was presented to Master Gardeners
Santa Barbara County
- Seven traps are being monitored in Montecito and the City of Santa Barbara
- Three traps in Montecito were lost from the January debris flow disaster
- One ISHB educational event was presented to Master Gardeners
San Luis Obispo County
- One ISHB educational event was presented to Master Gardeners
Articles:
A. Raver. The tiny menace. Landscape Architecture Magazine. March 2018.
https://landscapearchitecturemagazine.org/2018/03/13/the-tiny-menace/
Images:
Shot Hole Borer galleries, cottonwood
Shot Hole Borer entry point, sycamore. Curtis Ewing, CAL FIRE
![shot hole borer galleries shot hole borer galleries](/blogs/blogcore/blogfiles/54881.jpg)
![shot hole borer sycamore shot hole borer sycamore](/blogs/blogcore/blogfiles/54882.jpg)
- Author: Travis M Bean
Invasive plants don't get much coverage in the news, especially at the state and national level. As I've argued previously, this lack of media attention is a problem when it comes to motivating the public and political players into proactively funding invasive plant management and mitigating impacts to human health, infrastructure, and natural resources. Admittedly, as a weed scientist, I'm biased on the issue.
However, sometimes there is a particular plant that is just so terrifying that it lends itself to coverage in a major news outlet, as was the case for this article about giant hogweed (Heracleum mantegazzianum) by Caitlin O'Kane on CBS news last month: "Giant hogweed, plant that causes blindness and third-degree burns, discovered in Virginia." As the headline suggests, this is a plant you should keep a safe distance from if you are unlucky enough to come across it. Just in case you're thinking that this is just sensationalism, there's a page on Snopes that confirms the assertions about giant hogweed's dangerous sap (and also confirms its place in popular culture). I won't provide a direct link here, but a simple Google search of "giant hogweed" turns up some images of what look like very painful giant hogweed injuries. The photograph below was taken by Gavin Edmondstone:
Giant hogweed is native to the Caucasus region and southwest Asia, and is presently found in Europe, Canada, the United States, Australia, and New Zealand, where it was likely introduced as an ornamental for its showy inflorescence. Apparently it was a well known nuisance in Britain, so much so that the band Genesis released the ominous song "Return of the Giant Hogweed" on their 1971 album Nursery Cryme:
"Turn and run
Nothing can stop them
Around every river and canal their power is growing..." (Google the song title for the complete lyrics- they are fantastic! And strangely factual...)
Here in the US, giant hogweed is mostly found in New England and the Pacific Northwest. As the article suggests, giant hogweed has expanded down the east coast and was recently discovered for the first time in Virginia. Over on the west coast, it has made it as far south as northwestern Oregon. Californians should be on the lookout however, as we do share some similar habitats with Oregon, particularly in the northern part of the state. California also has a native congener called "cowparsnip" (Heracleum maximum), suggesting that suitable habitats do exist across the state.
For those involved with management of this plant, a great resource with information on controlling giant hogweed can be found in DiTomaso et al. (2013) Weed Control in Natural Areas in the Western United States, as well as several state conservation webpages. Before embarking on control, be careful not to confuse with natives that may look similar- your local county Natural Resources Advisor can be of great help in correctly identifying invasive plants. And it should go without saying, but given the potential for painful injury, this is a plant you may want to enlist the help of professionals with if you have it on your property.
As the band Genesis proclaims:
We must destroy them
They infiltrate each city with their thick dark warning odor
They seem immune to all our herbicidal battering"
Now if we could just get some similar coverage in the press or popular culture for our less glamorous but equally terrifying invasive grasses...