- Author: Karey Windbiel-Rojas
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 nonchemical 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.
Herbicide trials
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).
Consideration |
Conventional glyphosate products1 |
Organic nonselective herbicide |
Mode of action |
Systemic |
Contact |
Signal word |
Caution |
Variable depending on product: Caution, Warning, or Danger |
Personal Protective Equipment (PPE) |
California minimum PPE (long-sleeved shirt, long pants, shoes plus socks, protective eyewear, and chemical-resistant gloves) |
Variable depending on product, may include: California minimum PPE, chemical-resistant footwear, coveralls, or respirator |
Rate of observable weed injury |
Visible injury in 4 to 10 days |
Visible injury in hours to days |
Reapplication frequency for broadcast spray |
Lower reapplication frequency |
Higher reapplication frequency |
Active ingredient volume |
Lower volume of active ingredient |
Higher volume of active ingredient |
Cost per application area |
Lower cost per application area |
Higher cost per application area |
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.
[Originally featured in the Winter 2023 edition of the Green Bulletin Newsletter for structural and landscape pest professionals.]
Acknowledgments: The author would like to thank the California State University, Sacramento for the use of their property for these trials.
All pesticide products mentioned have been reviewed by the UC Office of Pesticide Information and Coordination and are current at the time of publication. Always read and carefully follow all precautions and safety instructions provided on the pesticide container label, as well as any other regulations regarding the use of pesticides. Not following label directions, even if they conflict with information provided herein, is a violation of state and federal law. No endorsements of named products are intended, nor is criticism implied of products not mentioned.
/h2>/h2>/h2>/h2>/h2>- Author: Hanif Houston
Researchers seek insight on emerging controlled environment agriculture trends
Greenhouse operators are encouraged to participate in the 2023 State of Controlled Environment Agriculture survey. IUNU, a technology company that specializes in AI and computer vision solutions for the agriculture industry, and the University of California Agriculture and Natural Resources are conducting the survey to gain insights on emerging trends and challenges to share with the controlled environment agriculture industry.
The survey takes approximately 25 minutes to complete. All growers using CEA – greenhouse, high tunnel or indoor – are invited to participate. All data collected is confidential and shared only as anonymous trends. No identifying information is ever shared. Growers who participate will get early access to the survey results report and will get access to an exclusive webinar to discuss the results with the authors of the report.
The fourth State of CEA Survey can be completed at https://www.surveymonkey.com/r/FVXJSY9.
The report, first released in 2016, was formerly titled “State of Indoor Farming” and managed by Artemis, which was acquired by IUNU in 2021.
This year, IUNU has expanded the survey to include the different leading segments of the controlled environment agriculture industry: greenhouse fruit and vegetable, and greenhouse ornamental production.
UC ANR's VINE agrifood technology innovation program, Global Controlled Environment Agriculture Consortium (GCEAC), and UC Davis-led AI Institute for Next Generation Food Systems (AIFS) are collaborating on the report.
“An industry-led, market-driven approach to guiding innovation priorities and investments is critical as we consider the future of indoor farming,” said Gabe Youtsey, UC ANR chief innovation officer and co-founder of The VINE. “I'm thrilled to partner with IUNU on the development of this State of CEA report with our UC innovation teams from The VINE, GCEAC and AIFS to create a robust state of CEA report that will guide our CEA open innovation priorities this year.”
Since the survey launched in 2016, more than 500 growers have participated in the survey and more than 2 million people have downloaded the report. The industry reports have become one of the most widely circulated and respected sources of industry data.
"This report is a trusted resource for the industry and we're thrilled to bring it back in an expanded capacity,” Allison Kopf, IUNU chief growth officer, said. “Over the past year, we've seen a swell of news around our industry. This report will go deeper into those stories and share data on how companies are performing, big market opportunities, and the real challenges growers are facing.”
Past CEA reports are available for download at https://artemisag.com/guides_reports.
About IUNU
Founded in 2013 and headquartered in Seattle, IUNU aims to close the loop in greenhouse autonomy and is focused on being the world's leading controlled environment specialist. IUNU's flagship platform LUNA combines software with a variety of high-definition cameras – both fixed and mobile – and environmental sensors to keep track of the minutiae of plant growth and health in indoor ag settings. LUNA's goal is to turn commercial greenhouses into precise, predictable, demand-based manufacturers that optimize yield, labor and product quality. www.IUNU.com
About The VINE by UC ANR
The VINE is California's agriculture, food and biotech innovation network powered by the University of California Agriculture and Natural Resources. We believe that the state's continued prosperity rests on creation of more productive, sustainable and equitable food systems. Every day, we harness the power of open innovation to connect entrepreneurs to a broad network of public and private sector resources to enable them to grow and scale globally, build collaborations that catalyze the development of climate-smart technology-based solutions to solve industry challenges, and grow regional capacity to support global innovation as an economic opportunity – because our future, and the nation's, depends on it.
The Global Controlled Environment Agriculture Consortium – an initiative of The VINE – seeks to build a worldwide ecosystem to bring technology to market that addresses global challenges in food, health and sustainability. GCEAC is an open innovation partnership between industry, university and government sectors in the United States and The Netherlands, led from California.
/h3>- Posted by: Lauren Fordyce
- Author: Belinda J. Messenger-Sikes
Common causes of abiotic disorders include too much or not enough water, compacted soil, nutrient deficiency (often caused by imbalanced soil pH), excess soil salinity, too much heat or sunlight, herbicides, air pollution, and mechanical injuries.
Abiotic disorders can develop for several reasons:
- the site was not well prepared before landscaping,
- the plants were improperly planted,
- the plant species is not well adapted to conditions at that location,
- the plants did not receive the correct cultural care.
Avoid abiotic disorders by giving plants the right amount of water, sunlight, and nutrients. You must water plants properly, and the soil must drain well. The soil must contain the correct nutrient levels, pH, and salinity. Fix any extreme light or temperatures issues like too much sunlight. Protect plants from herbicide and fertilizer damage as well as from mechanical injuries.
When you suspect an abiotic disorder, find out both the species and variety of the plant so you know the plant's expected appearance and its specific cultural needs. Inspect the plant and surrounding plants for symptoms. Some abiotic disorders can be recognized by their characteristic damage symptoms (e.g., distorted, discolored, or dying foliage). However, diagnosing the cause of disorders can be difficult. Plants will react differently to abiotic issues depending on their age and specific variety. Different abiotic causes can produce the same symptoms, and more than one cause can affect plants at the same time.
To solve plant problems, it's important to distinguish abiotic disorders from similar-looking damage caused by pests such as insects, mites, nematodes, pathogens, and vertebrates. See Table 1 for details.
Characteristics | Abiotic disorder | Disease/pest |
Plants affected | Unrelated | One type or closely related |
Plant age | Various ages | Same age more likely |
Pattern of symptoms | Regular or uniform | Random or irregular |
Rate of development | Sudden onset | Slow, worsens over time |
Spread | Does not spread | Infectious, spreads on host over time |
Signs | No evidence of pest or pathogen | Presence of pest, mycelium, mushrooms, rust, pustules, bacterial ooze, honeydew, frass |
For more information about abiotic plant problems, see the UC ANR publications Abiotic Disorders of Landscape Plants and Pests of Landscape Trees and Shrubs. Content adapted from Abiotic Disorders of Landscape Plants and Pests of Landscape Trees and Shrubs.
We're looking for your feedback! Please consider taking a quick, anonymous survey to help us serve you better: https://bit.ly/2ZJJVEI
/span>/span>If you have eucalyptus trees, you might have noticed white, crusty growth on the leaves. Or maybe you saw a sticky, blackened mess of fallen leaves under a eucalyptus tree. These are signs of the redgum lerp psyllid, one of the most common psyllid pests that damages eucalyptus trees in California.
The adult psyllid is very small and as nymphs, they are concealed under a waxy cap, or lerp. As they feed, they excrete honeydew which can lead to the growth of black sooty mold, the source of those sticky leaves under the tree.
Although under biological control in coastal areas, this pest is still a problem under some growing conditions and on specific Eucalyptus species. Cultural practices to manage lerp psyllids, such as avoiding fertilization of eucalyptus trees and pruning only when and where needed, can help reduce lerp psyllid problems.
The newly revised and expanded Pest Notes: Eucalyptus Redgum Lerp Psyllid, authored by entomologists Timothy D. Paine, UC Riverside; Kent M. Daane, UC Berkeley and UC ANR Kearney Agricultural Research and Education Center; Steve H. Dreistadt, UC IPM Program; and Raymond J. Gill, California Department of Food and Agriculture, contains detailed information about the identification, biology, and management of this pest.
This revision has more information about the lerp psyllid's biology and damage they cause on eucalyptus, a list of eucalyptus trees resistant to this pest, and an expanded section on biocontrol, with detailed information about the imported parasitic wasp that only attacks redgum lerp psyllid.
We're looking for your feedback! Please consider taking a quick, anonymous survey to help us serve you better: https://bit.ly/2ZJJVEI
- Author: Belinda J. Messenger-Sikes
- Editor: Karey Windbiel-Rojas
Pampasgrass and jubatagrass facts
Pampasgrass (Cortaderia selloana) is a common ornamental landscape plant that readily naturalizes throughout California's coastal areas and some interior regions. Historically, pampasgrass was planted for erosion control, but it has since escaped cultivation and spread along sandy, moist ditch banks throughout coastal regions of southern California. Pampagrass can also grow in the hot, dry climate of inland areas of California.
A similar-looking invasive grass, jubatagrass (Cortaderia jubata) is more widespread and aggressive and is a major pest in coastal redwood forest areas. Jubatagrass thrives in cool, foggy environments and does not tolerate temperature extremes or drought.
Both pampasgrass and jubatagrass outcompete native plants; a single floral plume can make 100,000 seeds in a year. They create fire hazards with excessive build-up of dry leaves, leaf bases, and flowering stalks. The tough leaves have serrated edges that can easily cut skin.
What can you do?
Plant other ornamental grasses in your garden or landscape. Many species including native grasses can be planted that resemble pampasgrass but aren't problematic. This includes several species of Muhlenbergia: deer grass, white awn muhly, and Lindheimer's muhly. California native Pacific reedgrass grows well on the coast and is deer resistant. For a large, tough bunchgrass, try giant sacaton, a native of the Southwest. Giant wildrye, another California native, will grow into dense stands that attract birds.
For more information, see the University of California Weed Research and Information Center fact sheet at https://wric.ucdavis.edu/PDFs/pampasgrass%20and%20jubatagrass%20WRIC%20leaflet%2099-1.pdf