- Author: Karey Windbiel-Rojas
- Posted by: Gale Perez
Weed management in landscaped areas can be challenging. Weeds may need to be controlled for public safety, fire reduction, aesthetics, and elimination of harborage for other pests. While many non-chemical options for controlling weeds exist—such as physical removal with tools, steam, flame or steam devices, grazing animals, and others—there are some situations that may require the application of herbicides.
For decades, glyphosate has been a common active ingredient used to control weeds in both agricultural and nonagricultural settings. However, there has been significant public concern about the use of glyphosate and other herbicides due to their potential effect on water quality, public health, and non-target species. Because of this ongoing issue, many practitioners have been considering organically-acceptable herbicides as alternative solutions. While some information exists on how organic herbicides work, there is little research on their efficacy in urban landscapes.
Glyphosate vs. organic herbicides
Concerns about the potential risks of glyphosate have led to increased use restrictions, including outright professional or municipal use bans in some California cities, counties, school districts, and other sites. Professional landscape managers and other pest management practitioners who aim to reduce or eliminate glyphosate from their IPM programs are therefore seeking alternative products to control weeds.
Organic and alternative herbicides seem like simple substitutes since treatments may not require new application equipment or knowledge. However, knowing the differences in modes of action among glyphosate, organic herbicides, and other alternatives is important to ensure weed management goals are reached.
Organic herbicides may not have the same qualities and performance practitioners have become accustomed to seeing with glyphosate and other conventional herbicide products. For instance, organic herbicides work on contact as opposed to glyphosate, which moves through the entire plant. These organic contact herbicides are most effective at higher temperatures (80°F and higher) and in full sun. Since they work on contact, they are applied after emergence and work best on small annual weeds. For larger or perennial weeds, organic herbicides generally will only damage or burn the top growth of the weed and, after a couple of weeks, the weeds regrow. From the data presented below, regular repeated applications of these products may still be useful tools within an overall IPM program.
The research presented here was designed to address the need for glyphosate alternatives by providing information about organic herbicide efficacy. These trials build on previous work by other researchers examining organic and alternative herbicides in non-agricultural settings (see references).
Trials included mostly organically acceptable materials as well as selected non-organic but naturally-derived products. Experiments were performed on the campus of the California State University, Sacramento (CSUS) in summer months of 2019 and 2021. The research site received little foot traffic, was regularly irrigated, mowed, and largely shaded underneath trees for most of the day. Weeds present at the site were a mixture of broadleaves, grasses, and sedge with predominant species being broadleaf plantain (Plantago major), dandelion (Taraxacum officinale), wild strawberry (Fragaria vesca), bermudagrass (Cynodon dactylon), and clovers (Trifolium spp.)
Slightly different products were used between the 2 research years. There were 10 or 11 herbicide treatments along with an untreated control (Table 1). All organic products in the experiment are post-emergent, nonselective, contact herbicides except for the iron HEDTA product (Fiesta), which is selective for broadleaves only. Weed damage was rated by visual inspection using an index (scale) from 0 (no observable plant injury) to 10 (complete plant injury above ground). This damage is referred to as burndown (Figure 1).
Preliminary results
Many products showed rapid plant damage on both grasses and broadleaves on the first day after treatment (DAT). Figure 2 shows results from the 2021 trial, which included results similar to those observed in 2019 and other trials. It was observed that by 3 DAT, ammoniated soap of fatty acids, pelargonic acid + fatty acids, ammonium nonanoate, and caprylic acid + capric acid showed the best control of both grasses (A) and broadleaf (B) weeds in the plots. Products containing citric acid + clove oil, d-limonene, and clove oil + cinnamon oil did not perform well in this trial even after a second treatment.
The iron HEDTA product targets broadleaf weeds only, so it is not included in the chart illustrating grass weed control. Acetic acid (Danger signal word) was not included in the 2021 experiments due to the risk of application to bystanders at CSUS. One product containing acetic acid is included in Table 1 for cost comparison of various alternative herbicide products.
In general, most weeds began to regrow or recover about 2 weeks after treatment. Multiple successive treatments were made after regrowth was observed (around 3 weeks). Efficacy of most products had declined and weeds once again showed regrowth 17 days after the second treatment (Figure 2).
Some of the organic herbicides tested exhibited quick results, with immediate burndown of contacted weeds observed within an hour or two. the majority of plant damage was observed between 1 DAT and 7 DAT. However, most weeds also completely regrew from the base or roots 2 to 3 weeks after each application.
Considerations when using organic herbicides
Urban landscape professionals need to consider the differences among conventional herbicides, organic herbicides, and other alternative herbicides (Table 2). Switching from glyphosate-containing products to organic herbicides will require a reallocation of resources to accommodate for more frequent applications, lower dilutions, and higher application volumes.
Resource shifts may include increased labor costs due to more frequent applications, possible increased supplies costs due to additional personal protective equipment (PPE) required, increased training required for handling of more acutely toxic products (those with Signal Words other than Caution), and higher herbicide product acquisition costs (Table 2).
What's next?
We know from pesticide use reports gathered from the California Department of Pesticide Regulation that herbicides are applied year-round under various temperatures and conditions. Therefore, practitioners need information about how well these products work in different conditions; such as across a range of temperatures, with varied weed species, in the presence of clouds or a canopy cover, and other factors. UC Cooperative Extension will continue to investigate these variables and will share findings via articles, workshops, seminars, and other extension methods.
References
Reiter, M and K Windbiel-Rojas. 2020. Organic herbicides and glyphosate for weed control: results of coordinated experiments in urban landscapes. CAPCA Advisor Magazine. February 2020. Pp 24-30 https://capca.com/wp-content/uploads/2020/01/202002-CAPCA_ADV_Feb2020_UCIPM_M-Reiter.pdf
Wilen CA. 2018. UC IPM Pest Notes: Weed Management in Landscapes. UC ANR Publication 7441. Oakland, CA. http://ipm.ucanr.edu/PMG/PESTNOTES/pn7441.html
Neal J, Senesac A. 2018. Are there alternatives to glyphosate for weed control in landscapes? North Carolina State University Publications. https://content.ces.ncsu.edu/are-there-alternatives-to-glyphosate-for-weed-control-in-landscapes
Acknowledgments
The author would like to thank the California State University, Sacramento for the use of their property for these trials.
Karey Windbiel-Rojas is an Associate Director for the UC Statewide IPM Program and Urban Area IPM Advisor for UC Cooperative Extension serving Sacramento, Yolo and Solano counties.
Spring is finally here, but unfortunately so are the pests!
While doing your spring cleaning or staying indoors due to our recent rain, you may have noticed some insects and spiders have moved in with you. Many pests are emerging from their winter rest, and taking cover from the cool, wet weather.
If you've found tiny brown, white, and black patterned beetles on windowsills, curtains, or walls near entryways, they may be carpet beetles. Adult beetles are about 1/10 inch and feed on pollen and nectar from flowers like crape myrtle and spirea. They can be brought indoors on cut flowers or they may fly in from nearby plants outside. A few adult beetles inside your home are typically not a problem. However, be on the lookout for their larvae or signs of their damage. Carpet beetle larvae feed on natural fibers such as wool, silk, leather, fur, and pet hair. They can damage rugs and carpets, yarn, clothing, and leather book bindings. Larvae will not feed on synthetic fibers like polyester. You can reduce sources of food for larvae by cleaning up lint, hair, dead insects, or debris. Adults can be relocated to the outdoors, but larvae are more difficult to control. See Pest Notes: Carpet Beetles for management strategies.
Spiders often end up inside while looking for food and if the right conditions are present–dark, dusty, hidden areas–they may stay a while. Some people may not mind the occasional spider, as they feed on other pests like flies, moths, and beetles. It is uncommon for most California spiders to bite you, contrary to what many people think. This includes the brown recluse spider, which does not exist in California. To identify the various spiders you might come across, see the Pest Notes: Spiders.
There are many other household pests you might encounter now and throughout the year. Fortunately, UC IPM has tons of great information on what they are and how to control them! See Pests of homes, structures, people, and pets for more information, or watch UC IPM's webinar recording on Springtime Household Pests.
Spring into the following free webinars from the UC IPM Urban & Community Program! Held every third Thursday from 12:00-1:00pm PDT, these informative webinars will help you identify, prevent, and control pests in and around the home, garden, and landscape!
April 20, 2023: Aphids, Scales, and Mealybugs, Oh My!
Insects such as aphids, certain scales, mealybugs, and others can produce a sticky substance called honeydew that can create a big mess around gardens and landscapes. Learn how to identify, prevent, and control these honeydew-producing insects and their damage to plants. This presentation will be given by Karey Windbiel-Rojas, UC IPM Associate Director for Urban & Community IPM/Area IPM Advisor. Register for this webinar.
May 18, 2023: Birds: Friends or Foes?
Birds are sometimes considered pests around homes, buildings, and in gardens, but they can also help to control other pests. This webinar will cover pest bird biology, identification, monitoring, and common types of damage; in addition to predatory birds and ways to enhance their control of pests. This presentation will be given by Breanna Martinico, Human-Wildlife Interactions Advisor, Napa, Lake, and Solano counties. Register for this webinar.
June 15, 2023: Summertime Household Pests
This webinar will cover identification, prevention, and management of common household pests that can be a problem in the summer months. Dr. Andrew Sutherland, Area Urban IPM Advisor for the San Francisco Bay Area, will present the webinar. Register for this webinar.
July 20, 2023: Natural Enemies & Beneficial Bugs: What are they?
While some insects can be damaging pests, many others are actually useful and keep pest species in check by parasitizing them or preying on them. These beneficial bugs are known as natural enemies and are vital to help keep pests from getting out of control. In this webinar, learn about natural enemies, how to identify them, and how they can help you out in your home and garden. This presentation will be given by Eric Middleton, Area IPM Advisor for San Diego county. Register for this webinar.
Can't make a webinar? Don't worry, all presentations are recorded and posted on the UC IPM YouTube channel! More webinars will be announced in the late summer. Follow us on social media @ucipmurban for the latest IPM content and news.
Webinars from the IPM Institute of North America
From April 10-14, Midwest Grows Green and Green Shield Certified will host Green Shield Week, a series of webinars discussing sustainable landscaping and pest management practices, strategies and policies. The webinars include:
- Monday, April 10th – Barry Draycott from Tech Terra Environmental discusses how to protect our water resources while maintaining a healthy and resilient lawn. Register for free at bit.ly/GreenLawns23.
- Tuesday, April 11th – Bradley Herrick from the University of Wisconsin Madison Arboretum focuses on best management practices, control methods and latest research of jumping worms. Register for $10 at bit.ly/InvasiveJumpingWormsWebinar.
- Thursday, April 13th– Dr. Doug Richmond from Purdue University's Soil Insect Ecology Laboratory presents a systems approach for integrating cultural, biological and low impact chemical tools to reduce the ecological footprint of managing turf pests. Register for $10 at bit.ly/SustainablePest23.
Termite Awareness Week is a campaign created by the National Pest Management Association to call attention to the damage termites can cause to structures and to make sure residents and professional pest managers understand how to prevent and deal with termite infestations.
Did you know?
- Of the 23 species of termites in California, only 3 are considered pests. The three pest species are dampwood, drywood, and subterranean termites.
- Subterranean termites are the most common in California. They live in underground nests and can be found infesting wood that is in contact with the soil, including structural lumber in homes and landscapes, as well as fallen trees, tree stumps, or other dead wood.
- If you come across groups of insects on the ground that appear to be winged termites, they may actually be winged ants. For help distinguishing ants from termites, see the UC IPM Ant Key.
- Dampwood termites are larger than subterranean and drywood termites. They are most common in cool, humid areas along the coast and are attracted to lights at dark.
- Termites play a very important role in California forests, woodlands and deserts by helping to break down woody organic matter which helps return nutrients to the soil. And contrary to popular belief, termites rarely injure or kill healthy trees.
If you suspect you might have a termite infestation in your home, contact a professional. Do-it-yourself insecticide treatments are not recommended and are often not effective. To learn more about termites and available management strategies for professionals, read the Pest Notes: Subterranean and Other Termites and the Pest Notes: Drywood Termites.
As you may know, Groundhog Day is observed on February 2nd to predict if there will be an early spring or if six more weeks of winter are in order. Groundhogs are large, ground-dwelling rodents found mainly on the East Coast that can cause severe damage to landscapes, gardens, and structures.
While California doesn't have these future-predicting rodents, the West Coast is home to groundhog relatives and look-alikes that are often considered pests in our landscapes and homes. These include other destructive, burrowing rodents like pocket gophers, ground squirrels, voles, Norway rats, and the invasive aquatic rodent, nutria.Though not rodents, moles are another burrowing animal that you may encounter in gardens and landscapes.
Burrowing animals and vertebrate pests in general are difficult to manage, especially in and around our homes and landscapes. The safest and most effective way to control these pests is by trapping, exclusion, and habitat modification.
To learn more about vertebrate pests in and around the home and garden, see UC IPM's vertebrate Pest Notes publications or visit the Wildlife Pest Identification Tool for help identifying vertebrate pests and finding management solutions.
