- 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: Karey Windbiel-Rojas
- Author: Elaine Lander
The CDC health advisory states “Veterinary formulations intended for use in large animals such as horses, sheep, and cattle (e.g., “sheep drench,” injection formulations, and “pour-on” products for cattle) can be highly concentrated and result in overdoses when used by humans. Animal products may also contain inactive ingredients that have not been evaluated for use in humans. People who take inappropriately high doses of ivermectin above FDA-recommended dosing may experience toxic effects.”
Incorrect use of any pesticide can lead to injury, negative health impacts, or severe illness. Be sure to always read and understand the label when using pesticides and only use them where specified on the label. As a reminder, disinfectants are pesticides too, and should be used properly to minimize health risks.
Visit our website for more information on pesticides in homes and landscapes. If you suspect that you or someone you know is experiencing serious illness due to pesticide exposure, contact the Poison Control hotline at 800-222-1222.
- Author: Karey Windbiel-Rojas
- Author: Belinda J. Messenger-Sikes
Instructions for making homemade mixtures to control pests are easy to find online and in social media, and it's tempting to make your own home remedy when pests invade. Doing so may seem like a natural, organic, and non-chemical solution, but did you know that what you are mixing is considered a pesticide? A pesticide is any mixture used to kill, destroy, repel, or mitigate a pest.
Pesticide mixtures of household ingredients like dish soap, garlic, and vinegar (Figure 1) may seem harmless and safer than storebought formulated pesticides, but they can actually pose unrealized risks.
What is the concern with homemade pesticides?
For example, some online sources describe making a homemade insecticide from the tobacco leaves found in cigarettes and tout it as “natural” or “organic.” While cigarettes are readily available for purchase, the resulting concoction (a pesticide) made from tobacco is extremely concentrated and highly poisonous to humans and pets. There are many additives used in producing products such as cigarettes, soaps, or detergents and these ingredients are not always known to the consumer.
Another concern is the potential hazard created during the mixing and making of home remedies. Even while natural, some ingredients become more toxic during the process of cooking the mixture, which may concentrate the ingredients and increase risks of harmful health side effects due to inhalation of fumes or contact with skin.
No instructions for use
Commercially available pesticides are required by law to have a label with instructions on use, mixing, storage, and first aid. Home remedies don't have instructions for specific dilution or use rates, nor do they identify how often mixtures should be applied. Home remedies also contain no guidance about wearing protective equipment like gloves or how to properly store the mixture.
Homemade mixtures are stored in containers that are either not labelled with what's inside or lack the required label information registered pesticides contain. Each year, poison control centers report poisonings of children and adults from drinking pesticides that have been stored in food or drink containers. Without a label and knowledge of how a mixture can affect people when exposed, first aid information isn't available. To prevent accidental poisoning, pesticides should never be mixed or stored in food or drink containers even if the container is marked.
Are home remedies effective?
Because homemade pesticides vary greatly in their makeup and are not tested through rigorous research studies, there is no data to support whether they consistently control targeted pests. Unlike commercial pesticides that must show their efficacy data before being registered, homemade remedies lack scientific studies to show that they are effective.
Applying ineffective homemade pesticides can make pest problems worse, may not control the pest, could be harmful to the plant, or contaminate waterways. In addition, a homemade pesticide sprayed in the garden may kill the “good bugs” as well as the targeted pest insects. Many commercial pesticides are formulated to work only on specific pests or groups of pests.
Many home remedies specify using dish soap mixed with other ingredients to kill insects, plant diseases, or weeds. Dish soap, which is a powerful detergent, can injure desirable plants by stripping the waxy layer off the leaves. Commercially available insecticidal, fungicidal, and herbicidal soaps, which are registered pesticides, are highly effective against the targeted pest and will not damage plants when used correctly. These products cannot be made at home with common household ingredients.
Are home remedies legal?
The U.S. Federal Insecticide, Fungicide and Rodenticide Act (FIFRA) covers the use of homemade pesticides. According to FIFRA, in order to legally apply a material as a pesticide it must be either registered with the Environmental Protection Agency (EPA) or be exempt from registration. There is a list of active ingredients (the part of a pesticide that affects the pest) that can be used in pesticide products without requiring registration; these are called minimum risk or 25(b) products) The active ingredient list allows the use of single chemicals, like sodium lauryl sulfate (found in soap), as unregistered pesticides, but does not include commercial products like dish soap that may contain other ingredients, such as viscosity modifiers, preservatives, and pH adjusters.
Alternatives to pesticides
Many pests in the home and garden can be managed without pesticides. In a garden, grow plants suited to the environment and keep them healthy with proper irrigation and fertilization. Weeds can be controlled by hand-pulling, mulching, or weeding tools. For more information, see the UC IPM Home and Garden pages.
[Original article published in the Spring 2021 issue of the Retail Newsletter.]
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- Author: Elaine Lander
- Author: Karey Windbiel-Rojas
While we continue to spend more time than usual indoors, you may have noticed a few unexpected (and perhaps unwanted) co-occupants like ants, cockroaches, or mice. Luckily, UC IPM has a series of fact sheets called Pest Notes to help you identify and manage hundreds of different pests in and around the home, only a portion of which might come indoors.
Any room in the home can attract and harbor indoor pests including kitchens, pantries, bathrooms, closets, storage areas, or other living spaces. Prevent and reduce indoor pest problems by cleaning and decluttering indoor spaces. This removes access to food, water, and shelter for pests such as ants, carpet beetles, rodents, and pantry insects. Find out where the pests are entering your home and prevent them from getting in. Keep reading for tips that will help limit potential infestations.
Kitchen and Pantries
Living Spaces and Closets
Storage Areas
Garages, basements, attics, and other storage spaces can also attract unwanted pests. When possible, seal cracks and openings in foundations and around doors, windows, pipes, wires, and vents to reduce access to these areas by rats, mice, or raccoons. Use snap traps to control rats and mice indoors. Organize belongings in airtight containers such as plastic bins to keep out carpet beetles, mice, and silverfish. Store bins off the floor and away from walls to reduce clutter in storage areas.
Houseplants
Houseplants may be attacked by pests that are typically found outdoors including scale insects, mites, mealybugs, whiteflies, or fungus gnats. However, indoor management of these pests can differ from methods recommended for outdoor plants. Houseplant leaves and stems can be washed with water to remove soft bodied insects and mites. Use sticky traps to reduce fungus gnat populations by trapping adult gnats and adjust your watering. Pesticides such as insecticidal soap or horticultural oil may help control some of these pests but be sure products are labeled for indoor use on the houseplant species and against the pest you have identified. See the recently published Pest Notes: Houseplant Problems for more information.
Found a spider? Before you squish it, remember that spiders are predators which are beneficial and help control other pests around the home. If you are comfortable, let the spider be or capture and release it outside. See this video on how to do it.
Another visitor you might spot is a house centipede, but these invertebrates are also beneficial and do not damage plants or household items.
Wherever you may find pests in the home, use integrated pest management (IPM) to solve your specific pest problem. The combination of science-based methods suggested above will help exclude and manage pests so you can reduce any undesired co-occupants.
You can find much more information about all the pests mentioned in this article in the UC IPM Pest Notes publications located in the Household Pests section online.
[Original article published in the Winter 2020 issue of the Retail Newsletter.]
/h2>/h2>/h2>/h2>- Author: Belinda J. Messenger-Sikes
- Author: Karey Windbiel-Rojas
- Author: Elaine Lander
Sooty mold is a black fungal growth that looks like a layer of soot covering the leaves of a plant or a sidewalk. The aptly named disease is common in gardens and landscapes, appearing wherever a large infestation of plant-sucking insects are found. Sooty mold grows on honeydew, a sticky substance excreted by plant-sucking insects.
While sooty mold doesn't actually damage plants or other surfaces, a thick growth of the fungus can block light to plant leaves, reducing photosynthesis. This can lead to stunted growth and premature leaf drop.
The key to reducing sooty mold is management of honeydew-producing insects, and ants. For specific tips on how to do achieve this, see the newly revised Pest Notes: Sooty Mold updated by Karey Windbiel-Rojas and Belinda Messenger-Sikes of the UC Statewide IPM Program.