- Author: Andrew M Sutherland
Baits Eliminate and Prevent Subterranean Termite Colonies
Subterranean termites (Family Rhinotermitidae) are considered the most serious wood-destroying pests in the world, causing an estimated $32 billion in global economic impact each year. California is home to both native and introduced subterranean termite species (Figure 1). Infestations of wooden structures are widespread and common. Pest control operators (PCOs) have conventionally applied liquid termiticides to control these pests, usually as soil drenches or injections around structures. These treatments may not always be effective, however, especially if good underground coverage is not achieved, if local termite pressure is very high, or if dealing with the invasive Formosan subterranean termite in Southern California. Furthermore, the active ingredients in most liquid termiticides are increasingly monitored by the State as environmental contaminants and may be subject to legal restrictions in the future.
Bait systems for subterranean termites (Figure 2), which employ slow-acting insecticides that kill worker termites by preventing successful molting, may represent effective alternatives to liquid treatments. Baits, deployed within stations installed in the ground or in line with aboveground shelter tubes, have gained popularity during recent decades and are now considered the primary subterranean termite control tactics in many parts of the world. Adoption of bait systems in California has lagged most other regions, however. Reasons PCOs in California have reported being reluctant to use bait systems include 1) time required to achieve control is too long, 2) little efficacy data in California, and 3) the regular monitoring of bait systems is too labor intensive or otherwise does not fit established business models.
Recently, the third “adoption barrier” may have become less important: new product label guidelines allow PCOs to extend inspection intervals up to 12 months and allow for baiting without the previously required monitoring phase (provided the target pest is confirmed at the site). Considering the regular revenue streams created by “controlled service agreements”, where PCOs contract with property owners to prevent and control pests over a long term, these newer labels should drive more widespread use.
Some observations and case studies indicate that, indeed, bait system adoption is now slowly increasing in California. To address the other two reported barriers (speed of control and efficacy), we secured funds from the state's Structural Pest Control Board to evaluate and demonstrate three different in-ground bait systems in the San Francisco Bay Area and the greater Los Angeles area.
Bait Efficacy
Our first objective was to evaluate efficacy at single-family homes. To do this, we collaborated with five different PCO companies who expressed interest in the new business models made possible by the newer bait product labeling guidelines. Some of these companies had experience with baits, while some gained their first experiences through this project. Companies received research stipends to subsidize their participation. Fifteen single-family homes were eventually selected, based on several experimental criteria: 1) documented activity of subterranean termites within 1 meter of the structure, 2) no liquid termiticide application within the previous 5 years, and 3) no significant structural infestations detected during the initial inspection. Participating homes were in Alameda, Contra Costa, Los Angeles, Orange, and Santa Clara counties. Bait stations, baits, service equipment, and, in some cases, training, were provided by manufacturers.
The UC research team and the PCOs installed bait systems according to product labels, usually with one bait station for every 10–20 linear feet of the structural perimeter. Since all 15 sites had confirmed termite activity at the perimeter, all stations installed contained active bait, rather than monitors. The UC research team installed monitoring stations with wooden blocks immediately adjacent to each bait station. The UC team then visited each participating home every 3 months for 2 years, checking termite activity within monitoring stations and collecting termites whenever possible. The PCOs and the UC team visited each participating home every 6 months to check termite activity within bait stations, replenish baits (as per product label), and to collect termites. Collected termite specimens were sent to a collaborating lab for DNA analysis, where each sample was assigned a “Colony ID” based on its genetic signature, distinguishing it from all other colonies. At the end of the 2-year period, a final structural inspection was conducted at each home.
Findings
Most importantly, despite significant termite pressure, none of the 15 homes became infested during the study period. Foraging termites were observed and collected during initial inspections, from wood blocks during quarterly inspections, and from bait matrices during bi-annual inspections with PCOs. In some cases, termites were observed and collected from bait stations only 6 months after installation. 132 separate samples of western subterranean termites (Reticulitermes hesperus species complex) were collected. DNA analysis revealed that many of our research sites included between 3 and 5 unique colonies; 1 property included 15 unique colonies! Bait was consumed at all sites, to varying degrees. No termite colony recovered from bait stations was ever detected again.
These observations strongly suggest that all three studied bait systems were effective at eliminating termite colonies and at preventing structural infestations over a 2-year period. Furthermore, post-project surveys conducted with property owners and PCOs indicated that all parties were satisfied with the services provided and control achieved; several companies new to baiting have now embraced the program we demonstrated as a new service offering for their customers.
Reducing “time-to-attack”
Our second objective in this research project was to investigate factors influencing bait interception time (also called “time-to-attack”). One explanation for lengthy bait interception times in California may be the interaction of climate (hot summers with little to no rain) and soil texture (high proportions of clay). Termite foraging at or near the soil surface may be limited or even nonexistent during summer months, especially when areas are not irrigated. Some research supports this idea: western subterranean termites have been observed to forage near the surface mostly during winter months in Southern California. This suggests that baits installed in summer may sit uninvestigated for 6 months or more. To test this hypothesis, we established five research plots at the UC Berkeley Richmond Field Station directly on top of areas where naturally occurring Reticulitermes termites had been observed or collected. Around these areas, we established 3 concentric rings of bait stations at 3 distances from the center, installing 1 station from each of 3 registered systems (Table 1) along each of the 3 distance rings at the beginning of each season over 1 year, for a total of 36 bait stations per plot. We didn't want to kill the termites in these plots because that would significantly confound our data, so we used cellulose bait matrices from manufacturers that did not contain the active ingredients. We also installed monitoring stations containing wood blocks at the center of each plot and along each of the three distance rings. We then checked each station every 2 months for 2 years, recording bait consumption and termite incidence.
Of the 180 bait stations and 20 monitoring stations installed, 78 bait stations and 9 monitoring stations had been hit by the end of the 2-year project period, representing an overall hit rate of 44%. Three stations were attacked within 60 days after installation, and 10 stations were attacked within 120 days. Overall, however, the average bait interception time was 367 days, supporting the general claims of California's pest control operators that baiting may take too long for most remedial termite control jobs. There were no significant differences between the three bait systems or the three distance rings.
Bait System, Manufacturer |
Bait Information |
Installation Specifications (for in-ground use) |
Service Specifications |
---|---|---|---|
Sentricon Always Active, Corteva Agriscience |
Recruit HD Termite Bait (EPA# 62719-608): cellulose tube, 0.5% noviflumuron |
≤ 20 feet intervals; buildings, fences, decking, utility poles, trees |
Inspections at least once annually; replace bait if damaged or ≥ 1/3 consumed |
Advance Termite Bait System (ATBS), BASF |
Trelona Compressed Termite Bait (EPA# 499-557): cellulose wafers in plastic housing, 0.5% novaluron |
≤ 20 feet intervals; buildings, trees, wood piles, landscape elements, railroads |
Inspections at least once annually; replace bait if damaged or ≥ ½ consumed |
Exterra Termite Baiting System, Ensystex |
Isopthor Termite Bait (EPA# 68850-2): cellulose wafers within burlap sachet, 0.25% diflubenzuron |
≤ 20 feet intervals; buildings and other structures |
Inspections every 45 – 120 d, up to six months allowed; replace bait “after sufficient consumption” |
Our study's main question was whether installation season significantly impacts “time-to-attack” due to seasonal differences in termite foraging in California. To answer this, we pooled data from all five sites and all three bait systems and then considered just the first year of observations. The result was clear: baits installed at the beginning of winter (December 16) were intercepted ~100 days faster than baits installed at the beginning of summer (June 24)!
Conclusions
Bait stations systems may be very useful pest control tactics for use against subterranean termites in California, especially when dealing with very large colonies of native western subterranean termites, multiple colonies, sensitive sites, or sites where liquid treatments have failed. According to the labels of the three products evaluated, systems can be installed with active ingredients present on Day 1, provided a licensed Field Representative has detected and identified the target species at the site. Licensed Applicators may, according to label language and California's Structural Pest Control Act, then service bait stations, replenishing bait that has been consumed or damaged. Two of the systems evaluated allow for annual inspections, while one allows for bi-annual (every 6 months) inspections. Operators in California may decrease the bait interception time, and therefore the perceived early efficacy, by targeting initial installations for the beginning of the wet season.
[Originally featured in the Fall 2023 edition of the Green Bulletin Newsletter for structural and landscape pest professionals.]
- Author: Andrew M Sutherland
- Author: Brandon Kitagawa
Multi-unit housing (MUH), such as apartment complexes and single-room occupancy (SRO) buildings, can harbor significant infestations of cockroaches, bed bugs, rodents, and other pests. Structural continuity (shared walls of adjacent units), budgetary constraints, poor maintenance and infrastructure, and cultural and social factors allow pests to infest and thrive in these environments.
Many of these pests threaten public health and wellbeing of the residents. For instance, German cockroaches (Blattella germanica) produce proteins that can be found in their feces and exoskeletons that, when dispersed into the air, can be inhaled, causing asthma in children.
Pest management is often conducted in response to complaints or after discovery of serious problems rather than proactively, especially in low-income communities. Proactive integrated pest management (IPM) programs that include regular monitoring of pests within every residential unit improve building-wide pest control and prevent significant infestations. These programs are labor-intensive, however, especially at the onset, and so may be considered too expensive by property owners and managers.
To show the effectiveness of proactive IPM and to investigate the relationship between cost and pest control, we partnered with affordable housing providers to provide one-year “IPM interventions” at two MUH sites in the San Francisco Bay Area: a 75-unit SRO building in Contra Costa County and a 59-unit low-income apartment complex in Santa Clara County. This work was led by Regional Asthma Management and Prevention, a program of the Public Health Institute, and sponsored by the California Department of Pesticide Regulation.
IPM Intervention Methodology
We worked with the pest control operators already in contract with the housing providers at the two sites and revised existing contracts to include unit-by-unit monitoring. The project included funds used to offset the increased costs associated with these revisions. Operators were asked to design programs that included monitoring for cockroaches and bed bugs in every unit at least once annually. When pests were detected, management tactics would be selected according to the pest densities observed, with the overall goals of eliminating pest populations and reducing pesticide exposure. Typically, baits were used against cockroaches and desiccants, spot treatments, vacuums, and whole-room heat treatments were used against bed bugs.
Independently, our team of researchers assessed pest incidence and density at three points during the one-year interventions: before IPM protocols were in place (baseline), roughly six months afterward (midpoint), and about one year afterward (final). At each monitoring period, we placed one glue trap behind the refrigerator and one pitfall trap in contact with the bed or sleeping surface for periods of one to two weeks. We also trained management, staff, and tenants on pest awareness, prevention, and reporting. Monthly costs associated with the pest control programs were calculated, including contract values, supplemental or add-on service values, and on-site staff effort hours. These costs were compared to monthly costs before the proactive IPM interventions began. Finally, surveys and interviews were conducted with residents and staff at the study sites to measure their relative satisfaction with the proactive IPM programs. Access to residential units required written notices delivered 24 hours before intended entry and accompaniment by on-site staff.
Study Results
Bed bugs (Figure 1) were the primary pests at the Contra Costa County site while German cockroaches (Figure 2) were the primary pests at the Santa Clara County site. Other pests present at these sites included small flies (of the families Psychodidae, Phoridae, and Drosophilidae), rodents, and stored-product pests like meal moths and grain beetles. Baseline assessments revealed that more than 20% of the units inspected in Santa Clara County were infested with German cockroaches and that about 10% of the units in Contra Costa County were infested with bed bugs.
High-density infestations were addressed first, with heat treatments for bed bugs and high-volume gel bait applications for cockroaches. Several of these high-density infestations were only discovered due to the unit-by-unit proactive monitoring process.
Many residents refused our team's entry, especially during the baseline assessment in Contra Costa County. Participation and compliance improved markedly after an on-site education program for residents.
By the intervention's midpoint, pest density at both sites began to decrease (Figure 3), though pest incidence was largely unchanged. Incidence apparently increased since access to several infested units was only achieved several months after the intervention's onset. In these cases, distrusting residents gradually learned about the project's goals and about IPM through the resident education programs and eventually granted the team access to their units. The final pest assessment at the end of the one-year intervention showed continued decreases in pest density but relatively unchanged pest incidence at both sites (Figure 3). This means that the severe infestations (dozens to hundreds of cockroaches or bed bugs per unit) had been significantly decreased or eliminated but that a similar proportion of units were infested as had been at the beginning of the project. This may be very important for building-wide IPM since pests can disperse from high-density units to new units, usually those units next to or otherwise structurally continuous with the severe infestations. Overall, the pest control under the proactive IPM program was considered significantly more effective than the reactive programs previously in place.
Contract base values for the proactive IPM services increased significantly at both sites when compared to the reactive pest control services previously in place (Table 1). However, when considering the supplemental costs associated with add-on services, usually bed bug heat treatments not covered by the base contracts, monthly pest control costs decreased at both sites under the IPM programs (Table 1). In fact, monthly costs decreased by almost $1,000 at the Contra Costa County site, where a severe bed bug problem had been ongoing for many years prior to this project.
Site |
Santa Clara County (59 units) |
Contra Costa County (75 units) |
monthly service costs under reactive program |
$ 350 ($ 5.93 per unit) |
$ 240 ($ 3.20 per unit) |
annual supplementary costs under reactive program |
$ 18,565 ($ 315 per unit) |
$ 39,485 ($ 526 per unit) |
total annual costs under reactive program |
$ 22,765 ($ 385 per unit) |
$ 42,365 ($ 565 per unit) |
monthly service costs under IPM program |
$ 450 ($ 7.63 per unit) |
$ 360 ($ 4.80 per unit) |
annual supplementary costs under IPM program |
$ 16,044 ($ 272 per unit) |
$ 26,924 ($ 359 per unit) |
total annual costs under IPM program |
$ 21,444($ 363 per unit) |
$ 31,244 ($ 417 per unit) |
Annual Savings from IPM Program |
$ 1,321 |
$ 11,121 |
The majority of surveyed or interviewed residents (96% at the Contra Costa County site and 82% at the Santa Clara County site) reported being either “very satisfied” or “somewhat satisfied” with the pest management services being received, as compared with those in place before the intervention. About 87% of responding residents reported that they had received some educational materials about pests and IPM, and 93% of responding residents said that they would be likely to report pest sightings to management in the future. All staff interviewed reported that the IPM program was more effective, in their opinion, and that the unit-by-unit inspections allowed for more resident engagement surrounding pest control.
Overall, this project showed that proactive IPM programs that use regular unit-by-unit monitoring events can help detect unknown infestations, control severe infestations, reduce monthly costs, and satisfy on-site stakeholders. This result was somewhat unexpected, since IPM programs usually take more than one year to realize savings for MUH environments. In cases where expensive supplementary services, such as bed bug heat treatments, are common, however, savings under IPM programs may be realized very quickly.
[Originally featured in the Spring 2023 edition of the Green Bulletin Newsletter for structural and landscape pest professionals.]
/h2>/h2>- Author: Niamh M Quinn
Where is rodenticide exposure in wildlife coming from? Is it from use by residents or farmers? Applications by marijuana growers? Or from applications by qualified and trained structural pest control professionals? These questions are being asked by state legislators and regulators, special interest groups, and state pest associations across the country.
However, even though we don't fully know where all the exposure is coming from, action is already being taken to restrict the use of rodenticides in urban areas. In 2020, California legislators placed a moratorium on almost all uses of second-generation anticoagulant rodenticide. And local jurisdictions have also added restrictions to rodenticide use. For example, in southern California, the California Coastal Commission granted special approval to the city of Malibu to ban all uses of rodenticides.
What's being done?
Researchers at the University of California Division of Agriculture and Natural Resources (UC ANR) South Coast Research and Extension Center in Irvine have been examining some of these questions over the past seven years. UC ANR's Human-Wildlife Interactions Advisor Dr. Niamh Quinn and colleagues have looked at urban coyotes' exposure to anticoagulant rodenticides (ARs), which active ingredients they were exposed to, and the amounts of AR exposure.
Almost all coyotes examined had been exposed to at least one anticoagulant rodenticide and usually, multiple active ingredients (Table 1). Some were exposed to low amounts of ARs and some were exposed to very high levels. However, less than 1% of the coyotes examined had died from AR exposure. Recent studies on the sublethal effects of exposure have not shown any clear links between AR exposure and sublethal impacts (such as reduced body condition or parasite load). There is also no link between AR exposure and mange in coyotes in urban southern California.
Do coyotes eat rats?
The diet of the urban coyote in southern California was questioned, specifically “Do they eat roof rats?” and “If they don't eat roof rats, how else could they be getting exposed to anticoagulant rodenticides?” It turns out that coyotes do eat rats (Figure 1). They eat a variety of other things too, but rats are among their preferred mammalian prey items, along with rabbits and domestic cats (Table 2).
In one of the first studies of its kind, we examined which animals were actually visiting rodenticide bait stations. We were surprised to find that in southern California, it is mostly roof rats, rather than nontarget animals. This was confirmed in another study sponsored by BASF. In southern California, less than 1% of mammals entering bait stations in urban area were nontarget wildlife. This is good news!
However, if pest management professionals are using anticoagulant rodenticide and are exposing just roof rats, and coyotes are eating said rats, does this mean that legal applications are responsible for the urban coyote AR exposure?
Another interesting finding from these studies concerned how rats use bait stations. With non-toxic baits used during this study, we photographed rats entering only 59–70% of the bait stations, suggesting that roof rats may be reluctant to enter bait stations, even when no rodenticide was present. Even in yards where rats eventually entered stations, it took 7 to 8 days for them to first encounter the bait directly.
What does this mean?
Because the first mortalities from anticoagulant rodenticide might not occur for several more days, pest management professionals should be prepared to communicate these possible delays to their customers. This will prevent customers from becoming impatient and taking more drastic (and potentially illegal) measures when results are not immediate.
Tracing applications of anticoagulant rodenticides
The ability to trace the applications of anticoagulant rodenticides has been lacking, but we may have developed a method to trace AR movement. We have created a bait that can be traced up multiple levels of the food chain. Therefore, we will be able to finally trace the rodenticide bait from its point of application to see if a legal application of anticoagulant rodenticide ends up in multiple levels of the urban and suburban food chain.
Two separate studies were conducted to see where animals exposed to anticoagulant rodenticides die and what scavenges them. One was conducted by Dr. Roger Baldwin in an agricultural setting and one by Dr. Paul Stapp from Cal State Fullerton in the suburban environment. Dr. Baldwin discovered that ground squirrels exposed to first generation anticoagulant rodenticides were mostly dying below ground (Figure 2). Dr. Stapp discovered that rats left in backyards are scavenged on by all sorts of animals including crows, skunks, opossums, and domestic cats. After 7 days, almost all (65%) of the carcasses had been either partially removed or removed completely.
Do coyotes and other large predators also scavenge rats? In research conducted in Europe, 92% of dead rats were inaccessible to large predators and scavengers. It is thought that rats killed by brodifacoum in and around farm buildings don't seem to present a major secondary exposure risk to large vertebrates.
What is next for rodenticide research?
We are developing methods to monitor rodenticide exposure in wildlife in a more meaningful way. The Quinn Lab and other institutions are working on methods to sample for rodenticides in live mammals and birds of prey with the aim of being able to detect any population -level impacts of rodenticide exposure. These methods will provide a mechanism by which rodenticide exposure can be monitored in live populations.
There is a huge need for data-driven mitigation measures for rodenticide exposure in California. We have been testing the efficacy of different management practices. We are testing trapping only, second-generation anticoagulant only, and a mix of both trapping and anticoagulant rodenticide. Using a combination of tracking rodents by collaring them and measuring how long it takes them to die, and by using tracking tunnels, we are measuring how quickly and how effectively these management options manage roof rat populations in southern California.
A mutation associated with second-generation anticoagulant rodenticide resistance, the Y25F mutation, has been found in roof rats in California. We don't know what this discovery means for rats in California. We need to explore more and find out to what extent they are resistant. Resistance management is essential for prolonging the life of all pesticide active ingredients.
Rodent management is complex, time consuming and we are tackling the unknown. We know more about polar bears than we do about commensal rodents. We need to know more to address inadequacies in rodent management. To reduce the amount of secondary AR exposure in the environment, it is necessary to ensure that rodent populations do not rebound and that they are not continually being exposed to active ingredients that can bioaccumulate in the food chain. If predators continue to eat commensal rodents, it is important to figure out ways to reduce the number of them that are exposed to rodenticides.
What does the future of rodent management look like?
It is important to continue work with municipal managers, schools, and customers to ensure that they do their parts. Exclusion and sanitation must be important components of a rodent management plan, especially as there continue to be restrictions on rodent management tools. In some countries, the sale and use of glue boards to catch rodents are prohibited. Certain snap traps have failed rigorous testing in some countries and are considered to cause unacceptable pain and suffering so are prohibited for use. It is important that pest management professionals use tools according to labels and trapping specifications. PMPs must rely on safe and effective methods.
Managing rodent populations such as roof rats is increasingly difficult since there are expanding restrictions on management tools and a dearth of applied research on commensal rodents. To solve these issues, we must find more sustainable and effective management practices.
Our funders and collaborators for these research projects were Cal State Fullerton, the Pest Management Foundation, the California Structural Pest Control Board, the National Wildlife Research Center, California Department of Pesticide Regulation, California Department of Food and Agriculture, and the Anticoagulant Taskforce.
[Originally featured in the Summer 2022 edition of the Green Bulletin Newsletter for structural and landscape pest professionals.]
/h2>/h2>/h2>/h2>/h2>/h2>- Author: Siavash Taravati
Licensing for perimeter spraying under California's pest control laws is dependent on the situation and site (Table 1). Structural Pest Control Board (SPCB) licensees, Department of Pesticide Regulation (DPR) Qualified Applicator License (QAL) holders, and DPR Qualified Applicator Certificate (QAC) holders are all legally allowed to make perimeter spray applications to control ants and other pests immediately around structures. However, the intent of these applications determines the specific license needed.
SPCB licenses
If the perimeter spraying is performed to prevent the entry of ants or other insects into the structure, then a structural license is required. If the pests are coming from the lawn, then the lawn is considered as a “pest reservoir” and can be treated by the Branch 2 licensee.
DPR licenses
It is important to know what DPR license type allows the applicator to perform perimeter sprays.
- QAL holders with Category A (Residential, Industrial, and Institutional) can do perimeter treatments for ants or other pests that occur indoors and near the structure. QAL Category A licensees, however, cannot provide commercial service to customers (for hire). This license category is most common for governmental employees or institutional employees who perform in-house pest control services as part of their job.
- QAL holders with Category B (Landscape Maintenance) can do perimeter sprays as part of their landscape management efforts. For instance, if landscape shrubs get infested by aphids and tended by ants, then treatment of those plants and perimeter spraying, which incidentally prevents an ant invasion to the structure, is permitted.
- QAC, subcategory Q (Maintenance Gardeners) are also permitted to do perimeter sprays when the application is made as an incidental part of their maintenance gardening work.
It is wise for any pesticide applicator to make sure they are applying pesticides in the right place, at the right time, and for the right reason. Such forethought helps reduce environmental contamination and helps applicators avoid regulatory violations and their consequences.
Site/ Situation |
License Required |
Section Cited |
Description of Pest Control Conducted |
Adjacent to structure, garden, or orchard pest |
QAL Cat A, Cat B or QAC Subcat Q |
FAC §§ 11701 or 11704 |
Control (for the purpose of eliminating ants, earwigs, garden or non-crop orchard pests, or to assist in the control of honeydew producing insects) even where treatment is applied adjacent to a structure and incidentally prevents invasion of the structure. |
Landscape plants & turf |
QAL Cat B or QAC Subcat Q |
FAC §§ 11701 or 11704 |
Any application of a pesticide to existing landscape plants & turf, irrespective of their location in respect to a structure, except for incidental contact of foliage or plants with a pesticide arising from structural pest control activities. Any pesticide application made directly to interiorscapes in business buildings, office complexes, malls, houseplants within households. |
Structures, interior or exterior |
Structural |
B&PC § 8550 |
Control of ants, earwigs, cockroaches, silverfish, termites, birds, or rodents invading structures is strictly structural pest control, whether carried on within or outside of the structure. |
Structures, in or around |
Structural Branch 2 |
B&PC § 8550 |
Control of pests to humans and their pets, (it would apply to pests other than fleas, for example, mosquitoes) in or around a structure, including treatment of outside areas to control nearby nest or pest reservoir. |
[Originally featured in the Fall 2021 edition of the Green Bulletin Newsletter for structural and landscape pest professionals.]
Disclaimer: Readers should get the most updated regulatory information from federal, state, county, and city resources. Remember, laws change all the time!
Reference: PUE Program Standards Compendium Volume 1: General Administration of the Pesticide Use Enforcement Program – Section 10: Quick Reference Charts. cdpr.ca.gov/docs/enforce/compend/vol_1/entirerep.pdf
/caption>/h2>/h2>If your company does residential landscape pest control, your employees should be trained to know what to do when they encounter a vegetable garden, or fruit or nut trees in a yard (Figure 1). Their training should include how to answer a customer's questions about the safety of their pesticides around vegetables or herbs. Talking to a customer about the edible plants in their garden so you don't accidentally spray their plants might save that account from subsequent cancellation.
Is it appropriate for a technician to recommend that a resident simply wash their vegetables after having their yard treated for say, mosquitoes, or should the vegetables be thrown away? What about a perimeter spray around the home? The answer to these questions depends on whether the plants were directly exposed to the sprayed pesticide and what the product label says about proximity to edible crops.
Insecticides used for perimeter sprays and mosquito control generally don't allow application to edible plants. For example, the Suspend Polyzone label states “do not apply this product to edible crops.” The Termidor SC label says, “DO NOT treat within a distance of one foot out from the drip line of edible plants. DO NOT treat fruit-bearing or nut-bearing trees.” Some product labels make no mention of vegetables or edible crops at all. If application on edible plants is not explicitly mentioned, it is not allowed.
Will pesticides make a plant toxic?
Many insecticides, including some common active ingredients familiar to urban pesticide applicators, are used legally on agricultural crops. This is allowed by the United States Environmental Protection Agency (US EPA) only if that pesticide has been granted a tolerance for a given crop, and certain days-to-harvest intervals are followed. These rules work to ensure that any pesticide residues left after a pesticide application are below levels of concern for human health. The 2019 Pesticide Data Program survey by USDA shows that this system works. Out of 10,000 market food samples analyzed in the study, nearly 99% had residues well below the EPA established tolerances. More than 42% had no detectable pesticide residue.
Insecticide residues on plants are not necessarily acutely toxic, especially when label directions are followed, and adequate time passes to allow the product to naturally degrade. The products used by professional pesticide applicators may contain the same active ingredients used by farmers; but they may differ in concentration and formulation. Most importantly, insecticides used for landscapes and homes do not carry food-treatment labels, so they cannot legally be used on edible crops.
Talstar products, for example, consist of the active ingredient bifenthrin, the same active ingredient used by farmers and even home gardeners under a variety of trade names. The Talstar® P label however, says "do not use on edible crops." You must follow the label for the product you are using.
Spray contamination
If an insecticide is deliberately sprayed on an edible crop or plant, and the product is not labeled for such use, the plant would not be considered safe by EPA standards. The implication is that the whole plant, or at least the edible parts, should be thrown away. Your customer could replant unless that is prohibited by the label.
Backpack mistblowers are commonly used for applying residual insecticides in areas such as mosquito resting sites; but mists should be applied carefully to avoid drift onto fruit and nut trees and vegetable gardens.
Labels generally do not, however, prohibit use of these products in the vicinity of a vegetable garden. Take care to keep sprays directed away from vegetable gardens, so that any incidental drift from nearby spraying does not land on edible plants. Thermal foggers and ULV applications used nearby should leave insignificant residues if the application orifices are always directed away from edible plants.
Applicators should always be aware of weather conditions and the locations of edible plants. If wind is blowing toward a garden, upwind applications should be avoided.
What should you do if a fruit, nut, vegetable, or herb is accidentally sprayed? Notify the customer that an accidental spray contamination has occurred. Annual plants should be pulled. For both annual and perennial plants, the produce must be discarded by the customer and not eaten.
Systemic insecticides
Some insecticides are "systemic," meaning they have enough water solubility to be taken up by plant roots and translocated to other parts of the plant. Although the EPA allows some systemic insecticides on crops, in general systemics are not labeled for use on food crops because they can leave residues in edible plant tissues that do not quickly degrade.
Insecticides containing neonicotinoids and acephate are examples of professional grade insecticides that may be systemic in plants. These include products like Premise, Alpine, Tandem, Transport, Temprid, Orthene and others. Herbs and other root or leafy vegetables exposed to systemic insecticides should be considered contaminated for the season and should not be consumed.
Some termiticides can also be systemic in plants, leading to concerns about vegetable gardens and fruit trees planted next to homes treated for termites. Fipronil, for example, is slightly systemic in some plants; and the Termidor SC label says not to apply around edible plants. The label does not say explicitly how far away an edible plant must be, although the Premise Pro label (whose active ingredient, imidacloprid, is much more water soluble) is more specific. It says to "not treat within a distance of one foot out from the drip line of edible plants." The Premise instruction is probably a good, conservative guidelines for all termiticides. Keep the outermost leaves of garden plants at least a foot away from any soil-applied termiticide.
Washing Crops
A concerned customer whose nearby yard or house perimeter has been treated with an insecticide spray should consider washing their vegetables or other harvested edibles. Washing is a good idea whether p
esticides have been used or not. The best washing technique is to gently rub off any dirt while holding the produce under running water. This is a great way to remove dust, microorganisms, and any traces of pesticides from vegetable and fruit surfaces.
Would you recognize an edible plant?
Can you and your technicians and applicators tell basil from begonia, mint from marigold, or pear from poplar? Applicators following label directions around a home needs to be aware of what plants are present. You don't have to be a botanist or know all the local tree species; but you should recognize the most common fruit and nut trees, herbs, and vegetables (Figure 2).
When visiting a residence for the first time, ask your customer if they have any herbs, fruit trees, nut trees, or vegetables. Gardeners may plant edible plants within flower gardens, so they might have a basil plant or a tomato plant growing among the daisies. Assume your customers don't use pesticides in their vegetable garden and avoid these areas accordingly.
Your customers will appreciate any extra consideration you give to their edible garden plants. Treat them well and they might even greet you at the door with a big bag of zucchini!
Based on the article “Bugs and basil: Insecticides and veggies don't always mix” by Dr. Mike Merchant, Texas AgriLife Extension at https://insectsinthecity.blogspot.com/2018/08/pesticides-and-veggie-gardens.html
[Originally featured in the Fall 2021 edition of the Green Bulletin Newsletter for structural and landscape pest professionals.]
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