- 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.
- Author: Lauren Fordyce
Did you know that disinfectants and sterilizers are pesticides? Any substance that claims to kill, destroy, prevent, or repel a pest, including germs, is considered a pesticide. So cleaning products that claim to sterilize or kill germs on surfaces or be effective against bacteria like E. coli or others, must be registered with the U.S. Environmental Protection Agency (EPA).
The EPA ensures pesticide products are effective and do not pose unreasonable risks to consumers when used according to the label, among other things. Recently, the EPA settled a lawsuit against Grocery Outlet Inc. for selling unregistered cleaning products claiming to be disinfectants and sterilizers. To know whether a product is a registered pesticide, look for the EPA registration number on the label. As with any pesticide product, always read and follow the label so the product can be used as safely and effectively as possible.
UC IPM is committed to educating the public on pesticides and their alternatives. View some of UC IPM's resources about antimicrobial pesticides and pesticide safety below, as well as in-depth resources from the U.S. EPA.
- What You Need to Know About Disinfectant Wipes (blog post)
- Using Disinfectants and Sanitizers Safely (blog post)
- Disinfectants are pesticides–so use safely! (blog post)
- What to Wear When Using Pesticides (blog post)
- EPA Registered Disinfectants (webpage)
- About Pesticide Registration (webpage)
- Using Disinfectants and Wipes Safely (webinar)
- What is a Pesticide? (video)
- Why do you need to read the pesticide label? (video)
- Author: Saoimanu Sope
Living with pests, or “unwanted guests” as some put it, can take a physical, mental and economic toll. For people living in multi-family unit housing, like an apartment complex where everyone lives under one roof, a single infestation of insects or rodents can expose all residents.
Using integrated pest management, or IPM, residents and property managers can detect infestations early and control severe ones and protect people. IPM programs can also save money. IPM saved a 75-unit complex in Contra Costa County $11,121 annually. Similarly, in Santa Clara County, a 59-unit complex saved $1,321 on pest control annually after implementing a proactive IPM program.
This summer, regional directors, property managers, residential service coordinators, maintenance managers and groundskeepers of Mercy Housing – a nonprofit organization that provides affordable, low-income housing – gathered in Long Beach to learn about in-home IPM. The session was led by Siavash Taravati, University of California Cooperative Extension area IPM advisor for Los Angeles, Orange, Riverside and San Bernardino Counties, and
Josh Shoemaker, an entomologist and private consultant.
Taravati and Shoemaker collaborated with StopPests in Housing, a national program out of Cornell University's Northeastern IPM Center, which seeks to improve pest control in affordable housing and teach management practices for cockroaches, bed bugs and rodents within and around the home.
During their presentation, Taravati introduced participants to the IPM principles and emphasized the importance of monitoring pests.
“IPM is all about making informed decisions which requires knowing the latest status of an infestation,” explained Taravati. “That's where monitoring comes into play. It can help us to identify the exact species we are dealing with as well as telling us if an infestation is growing or shrinking.”
“Monitoring is foundational,” agreed Shoemaker. “If a program does not include monitoring, it's not an IPM program.”
According to Shoemaker, the benefit of partnering with UC IPM is their sharp focus on general IPM, which includes monitoring. “It's real IPM, that prioritizes the well-being of the public,” said Shoemaker, who's eager to continue working with Cooperative Extension and Taravati to ensure that children are growing up in safe environments.
Pest control treatments commonly take place following a serious infestation or several complaints, but IPM promotes constant monitoring to prevent heavy infestations from ever happening. It's a proactive approach rather than a reactive or emergency-response. For many attendees, the training revealed a need to engage with pest management operators more closely.
Training prompts changes that improve safety for residents
Pest management operators commonly use pesticide sprays to control pests. Besides inconveniencing residents, forcing them to do extensive preparations and evacuate their unit until it's safe to return, sprays increase exposure risk to pesticides since the aerosols can linger and land on surfaces.
Instead, Taravati and Shoemaker recommend using gel baits, which are much safer to apply and can target a specific area of a home, including crevices, instead of along all the walls.
“Now that I'm more informed, I'll be speaking to my contractor to discuss how we can switch their approach from a bug spray to a gel,” said Leonardo Pinuelas, a maintenance manager for Mercy Housing.
Pinuelas is not the only one wanting to modify their program, however. According to feedback from staff members at the Housing Authority of the City of Los Angeles who experienced the same training earlier this year, they prompted their team to amend their pest extermination to include dusting, or applying insecticidal dusts, against roaches, and to review and update their existing IPM plan and practices where appropriate.
Cindy Wise, area director of operations for Mercy Housing, said that in her 35 years, this was one of the few trainings that engaged her staff so actively. “I couldn't help but text my regional vice president to say that our managers were actively participating and asking questions. That doesn't happen often, not even in our own meetings,” said Wise.
Many of the attendees, with their new understanding of how cockroaches move through a structure, shared that they are eager to return to work to meet with residents and support them.
“If you've got roaches in one unit, you've got them in the entire building,” Wise said.
Shoemaker recalls the words of Judy Black, senior technical entomologist for Orkin, and Dini Miller, entomologist at Virginia Tech, who urge the importance of inspections and documentation as IPM best practices.
Although reporting pests in the home can make one feel embarrassed, Wise said she is more interested in making residents feel empowered to not only report signs of infestation to the staff, but to their neighbors.
Training residents is certainly beneficial, but as experts such as Black and Miller have pointed out, housing managers must do their part, instead of scapegoating tenants for their cleaning habits.
StopPests provides free IPM training and technical assistance to Housing and Urban Development assisted properties. If you are interested in the training provided by Taravati and Shoemaker, in collaboration with StopPests, visit StopPests.org for more information.
- Author: Mackenzie Patton
Eucalypt trees have become abundant in the California landscape, but so have the many invasive eucalypt pests that have arrived in California in the last couple decades.
In the fall of 2022, yet another invasive pest was added to the hoard of beetles, psyllids, and gall wasps that attack eucalypt trees. The dotted paropsine leaf beetle (Paraopsis atomaria) was found on a lemon scented gum tree (Corymbia citriodora) in Los Angeles County. It was the first report of the dotted paropsine leaf beetle in North America, and it has since become more problematic throughout Southern California. Currently the extent of the spread is unknown.
Like eucalypt trees, the dotted paropsine leaf beetle is native to Australia, where it is known as an abundant pest of at least twenty Eucalyptus and Corymbia species. Some of these tree species are commonly found in California, including the red gum (E. camaldulensis), rose gum (E. grandis), sugar gum (E. cladocalyx), and the silver-dollar gum (E. polyanthemos).
What does it look like?
Adult beetles are about 3/8 of an inch with oval bodies and little beady black eyes (Figure 1). They are tan in color and covered in orangish dots. There are darker spots along the top and edges of the wings. The antennae are straight and become slightly darker toward the tip.
Eggs are laid in a circular cluster around young stems and leaves. They are tan, cylindrical, and are laid in clusters of 20 – 100 eggs. The larvae of the dotted paropsine leaf beetle are yellowish in color with black heads and black ends (Figure 2). As they age, they develop black stripes along the top and sides. When larvae are threatened, they will raise their black back end. They will drop to the ground to pupate.
Damage and Solutions
Although small, the dotted paropsine leaf beetle and its larvae can cause significant damage to the leaves of a host tree. If they do not eat the whole leaf, they will leave behind distinct notches in the leaves like other eucalyptus leaf beetles. Severe infestations can cause defoliation and eventual death in stressed or young trees.
You can protect Eucalyptus or Corymbia species against insect infestations by providing proper horticultural care. Reducing any water or other environmental stressors will allow the tree to successfully fight off insect infestations.
If you are removing a eucalypt tree or dealing with a severe infestation, consider replanting with a California native or other tree that will not be susceptible to the dotted paropsine leaf beetle and other eucalypt pest.
Contact your local agricultural commissioner if you suspect you've found this beetle. For more information, please visit the LA County fact sheet regarding the dotted paropsine leaf beetle.
- Author: Belinda Messenger-Sikes
Have you been seeing a lot of defoliated sycamore trees recently? Sparse foliage and early leaf drop on sycamore trees might be due to anthracnose. The cool, wet spring in many parts of California provided the perfect conditions for this disease. Anthracnose is a common fungal disease sometimes called leaf, shoot, or twig blight. It can cause twisted, distorted branches in American sycamore, some varieties of London plane trees, and California sycamore trees. Sycamore anthracnose is primarily an aesthetic concern since it usually doesn't kill established trees.
Symptoms
Take a close look at the fallen leaves for the characteristic irregular blotches caused by this disease. Anthracnose can cause leaf spots, cankers, and wilting of young leaves in the spring (Figure 1). Emerging leaves turn brown and die. On older leaves, irregular spots or brown blotches begin on either side of the main leaf vein. The lesions spread, covering much of the leaf surface. Extensive twig or shoot blight occurs when young, growing shoots are killed. New shoots grow back from lower on the branch, eventually causing the branch to look gnarled with a “shepherd's hook” appearance (Figure 2).
Springtime disease
The fungus overwinters on infected sycamore twigs and dead leaves., The disease is most severe during wet years when temperatures during the leafing-out period are below 55°F. The disease is not a problem in hot, dry weather. While the first flush of leaves might be lost to the disease, the canopy will regrow as the second flush of growth matures.
Management
Sycamore anthracnose is best managed by cleaning up fallen infected leaves to prevent the spread of the spores to the following year's new growth. Rake and dispose of fallen leaves and twigs during the growing season and in the fall. Prune and dispose of infected twigs and branches in the fall or winter. Avoid sprinkler irrigation that keeps trees wet. When planting sycamore trees in gardens and landscapes, choose resistant cultivars.
Fungicides do not reliably control sycamore anthracnose in California. By the time you see symptoms, it's too late to treat since fungicides effective against the disease are preventive (before the symptoms appear), not eradicative (after the disease symptoms appear). In landscape and residential settings, chemical spray applications are usually not practical due to the size of the trees and the high potential for pesticide drift.
Most sycamore trees will fully recover from defoliation caused by anthracnose, so the best option could be to just rake up the fallen leaves to reduce disease inoculum for the following year.
For more information about anthracnose, see the UC IPM Pest Notes: Anthracnose.
[Originally published in the Summer 2023 Issue of the UC IPM Green Bulletin Newsletter]
