UC Nursery and Floriculture Alliance
University of California
UC Nursery and Floriculture Alliance

Fall 2011: Mitigating Pesticide Runoff While Managing Invasive Pests

Regional Report Ventura and Santa Barbara Counties by Julie Newman

In the past decade, invasive pests such as light brown apple moth (LBAM), Asian citrus psyllid (ACP) and glassy-winged sharpshooter (GWSS) have caused considerable economic hardship for certain flower and nursery growers in Ventura and Santa Barbara counties due to restrictions on the movement of potentially infested nursery plants. Moreover, some of the pesticide treatments that are mandated in quarantine protocols are known to impair water quality and have been detected in ag waiver and TMDL monitoring programs. The continued degradation of surface waters and documented exceedance of pesticide and toxicity benchmarks set by the Central Coast and Los Angeles regional water boards have led to increasing regulations. Meanwhile, there is a threat of new invasive species from neighboring counties (e.g., red palm weevil, red imported fire ant) that could potentially lead to more mandated pesticide treatments in the future. It is therefore critical that flower and nursery growers in Ventura and Santa Barbara counties implement BMPs to prevent pesticides, including those required in quarantine protocols, from moving off production sites in irrigation and storm runoff.

Reducing Pesticide Loads

An important strategy for reducing chemical inputs is to establish an IPM program that includes a regularly scheduled monitoring program. Scouting to detect pests is especially critical when there is risk of establishment of invasive pest species. In fact, quarantine compliance agreements for pests such as LBAM require monitoring and written documentation of in-house inspections and results. All nursery personnel should be trained to recognize pests found in the nursery, especially any invasive pests.

Implement preventative control techniques to prevent spread of pests and diseases and reduce the size of areas requiring treatment. Landscapes, native plants and weeds in nonproduction areas can serve as a source of infestations and should be repeatedly inspected, in addition to the crop. Good sanitation practices are critical and include starting with clean plants and maintaining a clean growing environment (e.g., heat steaming or chemically treating growing media before establishing a new crop). In addition to good sanitation, practices that help to reduce pesticide loads include using resistant plant varieties and providing a growing environment that promotes plant health to improve host resistance to pests and diseases.

Nonchemical control methods (cultural, mechanical, environmental and biological control) should be incorporated as appropriate in the overall IPM program to reduce chemical inputs. For example, one mechanical control method is pest exclusion: in areas where there are quarantine restrictions for invasive pests such as LBAM or glassy-winged sharpshooter, pest access to outdoor nursery stock can be restricted by using hoop covers or greenhouses to protect preferred host species.

When selecting pesticides, chemical inputs can be minimized by rotating pesticides from different modes of action (although choices may be limited by quarantine protocols) and using other management strategies to avoid pesticide resistance. Choosing pesticides that are the most selective for the target pest species may also reduce chemical inputs by minimizing disruption of control by natural beneficial populations.

When applying pesticides, the use of adjuvants such as spreader-stickers may reduce the amount of pesticides applied. Generally, pesticides should be applied only when justified by pest population size and crop damage-threshold levels. This will result in fewer pesticide applications and reduce pesticide drift and runoff.  However, when invasive pests are detected in quarantine areas, quarantine protocols for destruction/treatment of infested plants must be followed.

Spot-spray applications should be made only to infested plants to limit the negative impact on other organisms, including beneficials. Re-inspect treated plants after the label re-entry period expires to confirm treatment efficacy. When spot treatment fails, infestation is widespread, or recurrence of infestation is demonstrated, entire blocks of plants known or suspected to be infested may need to be treated, especially for eradication of an invasive pest.

Reducing Pesticide Movement in Water

When pesticides are selected, it is important to know the site conditions of the area to be treated and potential hazard of spray drift or subsequent pesticide movement to surrounding areas. Check the label and online resources, such as the “Water Quality Compare Treatments” provided in the University of California IPM Pest Management Guidelines (http://www.ipm.ucdavis.edu/PMG/crops-agriculture.html), to select products with reduced runoff potential and toxicity. When quarantine protocols specify the use of pesticides that could potentially impair water quality (e.g., certain organophosphates, carbamate insecticides, synthetic pyrethroids), it is especially important to implement practices to prevent pesticide movement off site.

Irrigation efficiency, irrigation uniformity, methods of irrigation, and timing of irrigation events all affect pesticide runoff. Irrigation systems should be designed to ensure uniform irrigation distribution. Regular irrigation system maintenance is critical to maintain irrigation uniformity and prevent runoff due to leaks and clogged lines. Irrigation should be based on environmental conditions and plant water requirements, applying the required amount of water only to plants, and not to walkways or roads. To reduce runoff when using overhead irrigation, place containers as closely as possible without reducing plant quality. With drip systems, ensure that each emitter is located in a pot.  When containers are moved, plants should be reconsolidated and the irrigation turned off in unused portions.  Hand watering should be performed carefully to avoid creating runoff between pots and on walkways. Do not apply pesticides before an irrigation or storm event, unless label instructions specify otherwise.

Pesticide spraying equipment should be calibrated to ensure the best coverage and accurate application rates. Pesticide mixing and loading operations should be conducted on an impermeable surface such as a concrete floor to avoid groundwater infiltration. To eliminate disposal problems associated with excess spray solutions, only mix up the volume of spray that is actually needed. If there are leftover pesticide materials, consult the pesticide label for proper disposal instructions.

Practices should be implemented to avoid leaks or spills during pesticide transportation, usage and storage. Any pesticide spills should be cleaned immediately according to a predetermined protocol based on the product MSDS. Any runoff from areas where pesticides are used should be contained or directed to a treatment area for mitigation.


Some pesticides like pyrethroids and chlorpyrifos that are used to control invasive pests such as glassy-winged sharpshooter (left) and light brown apple moth (right) are known to impair water quality. Photos by Jack Kelly Clark.

Reducing Pesticide Movement on Soil and Potting Media

Pesticides like synthetic pyrethroids that are strongly adsorbed to soil particles run off with loose soil particles, including potting soil mix. Spills of potting media during production and transportation have been identified as a main source for pesticides. Furthermore, historical pesticides such as DDT compounds still persist in farm soil and are consistently detected in agricultural monitoring programs. Therefore, growers must implement practices to keep soil, sediment and potting soil on site.

If pesticides are mixed into container media before transplanting, concrete curbs or sand bags should be used to isolate these areas so that media is not washed away.  Any spilled potting media that contains pesticide residues should be collected to avoid off-site movement by wind or water.  Storing container media in a location sheltered from wind and away from drainage channels reduces the risk of media blowing into water bodies.

Bare soil and hillsides in nonproduction areas must be protected from concentrated flows of water that cause erosion by establishing plant covers or ground covers (e.g., mulch, gravel) or sediment barriers (e.g., sand bags, straw wattle, synthetic hay bales).  Areas susceptible to erosion can also be treated with polyacrylamides (PAM) to improve stabilization.

Treating and Capturing Runoff and Sediment

If irrigation or storm water is discharged from the nursery, pollution can be mitigated by first conveying runoff water through treatment areas such as vegetative buffers (e.g., filter strips, bioswales, constructed wetlands, landscape plantings) and sand filtration systems. Furthermore, water bodies and drainage channels located on the nursery property should be protected by vegetated filter strips. Growers should be aware that vegetative buffers may harbor pests such as active LBAM or glassy-winged sharpshooter infestations. These plants should therefore be included in scouting and pest management programs.

Many types of impoundments are used in nurseries for capturing runoff water and sediment (e.g., sediment basins, detention basins, retention basins, ponds, recycling systems, tailwater recovery systems, reservoirs). Water dissipates by evaporation and by infiltration into the ground from unlined impoundments.  Seepage into the ground could be problematic and should be considered in the design of the impoundment. Impoundments may not have the capacity to store all rainfall from precipitation events. Discharges and overflow from impoundments should be treated to prevent polluted runoff from off-site movement. Overflow may be alleviated by using the collected water to irrigate landscapes and other non-crop areas, or by recycling it for irrigating crops.


Growers should contact their local ag commissioner concerning specific county requirements for quarantined pests. In addition, regulatory requirements, including some monitoring and treatment information, is available at the California Department of Food and Agriculture (CDFA) website (e.g., GWSS http://www.cdfa.ca.gov/pdcp/Regulations.html,  LBAM http://www.cdfa.ca.gov/phpps/regs_lbam.html, ACP http://www.cdfa.ca.gov/phpps/regs_acp.html). The Light Brown Apple Moth Nursery Industry Best Management Practices: Integrated Pest Management Practices Manual (www.cdfa.ca.gov/phpps/PDEP/lbam/rpts/LBAM_BMP-Rev_3.pdf) is an excellent resource guide for reducing risk caused by LBAM. It includes practices that result in reduction of pesticide loads.

There is a wealth of information available from the University of California on invasive pests of interest to flower and nursery growers in Ventura and Santa Barbara counties. For example, for general pest management information and pest biology of invasive pests, a good source of information is the Center for Invasive Species Research at http://cisr.ucr.edu/invasive_species.html. ANR Publications provides free downloadable information on ACP monitoring and treatment (http://anrcatalog.ucdavis.edu/Citrus/8205.aspx). For GWSS, there is a DVD on pest identification and monitoring (http://anrcatalog.ucdavis.edu/GrapesGrapeProducts/6584D.aspx) and free downloadable information on pest management guidelines (http://www.ipm.ucdavis.edu/PMG/r280301711.html).

There are numerous resources on BMPs for reducing pesticide runoff. For example, Greenhouse and Nursery Management Practices to Protect Water Quality (available at http://anrcatalog.ucdavis.edu/Items/3508.aspx) includes a chapter on pesticide use and water quality management, as well as a list of BMPs to mitigate pesticide runoff. A more in-depth list of BMPs can be found in the Checklist for Assessing and Mitigating Runoff in Greenhouses and Nurseries, available on my website at http://ceventura.ucdavis.edu/Com_Ag/Ag_Water/.

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