Organic Insect Management in Arboriculture: Theory, Practices and Pesticides

The notion of “organic” with respect to plant culture dates back to 1940, when Lord Northbourne (Walter Ernest Christopher James), a visionary agriculturalist, coined the term “organic farming” in his book Look to the Land. His concept of organic farming centered on an approach to farming that was ecologically balanced and sustainable.

The operative principles of organic pest management in general, and organic food production in particular, stem from landmark legislation passed in 1990 called the “Organic Foods Production Act” (OFPA). This bill created what is known as the National Organic Program (NOP). This program is charged with defining organic farming practices and developing a list of products to be used in the production of organic crops and livestock. Growers adhering to the laws and regulations of the OFPA would enjoy the marketing advantage of products certified as “organic.”

While wading through the legalistic jargon of the regulations in the NOP, I was struck by the definition for “organic production,” which was defined as “a production system that is managed … to respond to site-specific conditions by integrating cultural, biological and mechanical practices that foster cycling of resources, promote ecological balance and conserve biodiversity.”

Fast forward to 2016 and the ANSI 300 Part 10 Integrated Pest Management (IPM) standards for arborists. This standard defines IPM as “a sustainable approach to managing pests by combining biological, cultural, physical and chemical tools in a way that minimizes health, environmental and economic risks. Choice of tactics is based on effectiveness, environmental impact, site characteristics, safety, economics and client expectations and preferences.”

While not mentioning organic pest management specifically, surely the focus on sustainability, environmental impacts, prevention and alternatives to pesticides is inherent to the philosophy and practice of both the NOP and the IPM standard for arboriculture. Beyond philosophical parallels between the NOP and the ANSI 300 standard, are practices used for organic food production viable in arboriculture? A strategy to manage pests such as insects, weeds and diseases in organic crop production goes by the acronym PAMS, short for prevention, avoidance, monitoring and suppression. How does this jive with ANSI standards for IPM?

Prevention and avoidance are the first line of defense against insects, weeds and diseases. Preventing and avoiding pest outbreaks by selecting resistant plants well adapted to urban landscapes, using sound practices of installation, culture and maintenance to reduce the likelihood of pest attack and reducing abiotic stress are hallmarks of IPM and PHC programs in arboriculture (Lloyd 1997, Herms 2002, Dreistadt et al. 2004, Davidson and Raupp 2014).

A second cornerstone of both arboricultural IPM and organic food production is monitoring for biotic agents such as insects and pathogens and abiotic factors such as nutrient and water deficiencies and excesses that harm plants. Monitoring plants and pests provides the information by which sound decisions are made (Raupp 1995, Lloyd 1997, Davidson and Raupp 2014).

However, one question that lies at the heart of pest management for organic crop producers and arborists attempting to manage pests organically is, what tactics and products are available to suppress pest populations once they are established and the decision has been made to intervene? In its “Introduction to Organic Practices,” (2015), the USDA lists mechanical and biological practices such as mulch to control weeds or the release of predatory insects as primary pest-intervention tactics in organic production. These tactics are well known in arboriculture, where practices such as sanitation pruning to arrest diseases such as Dutch elm disease, the physical destruction of egg masses or tents of caterpillars and the use of barrier bands to prevent invasions of cankerworms in street trees are employed to suppress insect pests and reduce their damage (Lloyd 1997, Dreistadt et al. 2004, Davidson and Raupp 2014).

Many highly successful biological-control programs involving the release of predators, parasites or pathogens have helped suppress major urban-forest pests, including spongy (formerly gypsy) moth, ash whitefly and eucalyptus long-horned borer. The use of predatory and parasitic insects, entomopathogenic nematodes and other biological-control agents in arboriculture has been reviewed by Dreistadt et al. 2004 and Davidson and Raupp 2014. Much recent interest in nonchemical approaches to manage pests of trees and shrubs has centered on designing landscapes to attract, support and conserve biological control agents through the addition of flowering insectary plants (Smitley et al. 2019). When nonchemical approaches have been exhausted, are there pesticides that are considered organic that can be used by arborists to control insects and mites on trees and shrubs in landscapes?

Organic Materials Review Institute – guide to organic pesticides

Where does one shop for products approved for use in organic crop production that overlap with pests found on woody and herbaceous plants? Enter the Organic Materials Review Institute (OMRI). OMRI is a nonprofit organization founded in 1997 with the expressed purpose of providing organic growers, manufacturers and suppliers with an independent review of products intended for use in certified organic production, product handling and processing.

After review by OMRI, acceptable products are OMRI listed for use in the U.S. and Canada. After visiting the OMRI website, I was astonished to learn that scores of insecticides and miticides regularly recommended for use in arboriculture (Davidson and Raupp 2014) were OMRI listed. Products in this collection include naturally occurring microorganisms and their products, insecticides naturally derived from plants and a limited number of approved synthetic substances (USDA 2015).

The list that follows was gleaned primarily from the website of Forestry Distributing, Inc., a provider of forestry products and services. All products and brand names could not be listed due to space limitations. The following synopsis is organized categorically by types of pesticides and active ingredients. It provides information on modes of action and target pests, and has comments regarding use. To learn more about specific products and brands, visit www.forestrydistributing.com/omri-listed-organic-insecticides.

Botanically based active ingredients

Azadirachtin – This insect growth regulator is derived from the seeds of the neem tree. In addition to being a growth regulator, this biopesticide has antifeedant (naturally occurring or synthetic compounds that prevent insect feeding or cause cessation or slowing of further feeding) and repellent properties. It is effective against immature stages of insects. It works slowly, and repeat applications may be necessary. It is broadly labeled for sucking insects (adelgids, aphids, psyllids, leafhoppers, mealybugs, scales, whiteflies), caterpillars, beetles, leafminers, thrips and other pests. It has systemic activity and can be applied as a foliar spray, injected into plants or used as a soil drench. It has low toxicity to humans and beneficial insects. (Photo 1)

Photo 1: Azadirachtin products can be injected into ash trees to disrupt development of emerald ash borer larvae.

Pyrethrins – These naturally occurring organic compounds, derived from chrysanthemums, affect the nervous system of insects. Products with pyrethrins are broadly labeled for many chewing and sucking insects (aphids, plant bugs, psyllids, cicadas, lace bugs, leafhoppers, mealybugs, whiteflies), caterpillars, thrips and beetles. They provide quick knockdown and are often used in combination with other insecticides, such as insecticidal soap or neem oil, to increase toxicity. They are highly toxic to bees and fish. (Photo 2)

Photo 2: Pyrethrins are often used in combination with soaps or oils to control aphids and many other insect pests.

Botanical oils (neem oil, garlic oil, cinnamon oil, rosemary oil, geraniol, peppermint oil, thyme oil and others)Derived from a variety of plants, these oils have repellent activity, disrupt gas exchange, disrupt cell membranes and affect nerve transmission. Broadly labeled for mites and soft-bodied insects, including sucking insects (aphids, psyllids, leafhoppers, mealybugs. scales, whiteflies), thrips, beetles and caterpillars. Some kill eggs as well as feeding stages. Don’t apply when pollinators are present. (Photo 3)

Photo 3: Eggs and feeding stages of spider mites, such as these two spotted spider mites, can be killed by plant derived oils. Photo courtesy of John Davidson.

Mineral- and fatty-acid-based active ingredients

Mineral oils – These compounds are unsulfonated, thereby greatly reducing the likelihood of phytotoxicity. They have complex modes of action disrupting gas exchange, cell membranes and cuticular waxes and reducing moisture retention. They are effective against many soft-bodied insects and mites and their eggs. They are labeled for use against sucking insects (aphids, adelgids, mealybugs, psyllids, plant bugs, lace bugs, scales, whiteflies), beetles, caterpillars, sawfly larvae, thrips, eriophyid mites and spider mites. Residual activity of oil is short, and contact with the target is essential for control. Thorough coverage is a key to control. Due to their short residual, oils have minimal impact on beneficial insects.

Do not apply in conjunction with pesticides containing sulfur within 30 days. Plants under drought stress may exhibit injury, and several species and cultivars are known to be sensitive and should not be treated. Oil will remove the waxy bloom from some blue varieties of plants. Avoid spraying during periods of high relative humidity and heat. Do not tank-mix with fungicides and herbicides and certain other materials (see labels). Do not exceed label rates or apply more often than recommended. Keep spray agitated frequently during application. Oils are labeled for both summer (growing season) and dormant uses. Oils are toxic to fish. Oils also have activity against some foliar pathogens. (Photo 4)

Photo 4: Horticultural mineral oils can be applied in summer to kill crawlers of scale insects, including those of elongate hemlock scale. Timing is critical.

Kaolin clay – A mineral product that coats leaves and acts as an irritant to deter feeding by insects. It leaves a white film on plants. It is labeled for suppressing feeding activity of weevils, leaf beetles, leafhoppers, Japanese beetles and thrips on landscape plants. (Photo 5)

Photo 5: Repellent activity of kaolin clay can reduce feeding damage by adult Japanese beetles.

Insecticidal soaps – These are potassium salts of fatty acids that kill active stages and eggs of many soft-bodied insects and mites. The mode of action is not fully understood, but soaps likely work in four ways: by dissolving the waxy covering of the skin, causing dehydration and death; affecting insect growth and development; blocking breathing ports; and interfering with energy production.

They are labeled for use against many sucking insects (adelgids, aphids, lace bugs, leafhoppers, mealybugs, psyllids, scales, whiteflies), caterpillars, beetles (leaf beetles, scarab beetles), sawfly larvae, thrips and spider mites. Contact must be made with the target pest for control. Excellent coverage is the key to success using soaps.

The short residual activity reduces unwanted impacts on beneficial insects and other non-targets. The list of plants sensitive to soaps is long, so read and follow label directions. Users have expressed concern regarding use on recently installed plants and those under drought stress. Insecticidal soaps also have activity against some foliar pathogens. (Photo 6)

Photo 6: Insecticidal soaps can reduce scale populations, including reddish crawlers of pine needle scale, when applied just after egg hatch.

Formulated microbials and microbial products

Bacteria – Bacterial products disrupt physiological processes and kill pests. Several are labeled for use in landscapes and are OMRI listed. Specificity of bacterial insecticides results in low impact on predatory beneficial insects.

Bacillus thuringiensis kurstaki and B.t. azawai kill caterpillars, and Bacillus thuringiensis galleriae is labeled for use against Japanese beetle adults and grubs. When ingested, a toxic protein produced by the bacterium kills cells in the insect’s gut, causing cessation in feeding and death. Bts for caterpillars works best on early instars. (Photo 7) Its specificity for herbivorous target pests reduces risk to predatory non-target insects and pollinating bees and wasps.

Photo 7: Early instar spongy (formerly gypsy) moth caterpillars are more susceptible to Bacillus thuringiensis than later instars. Unless otherwise
noted, photos courtesy of Michael Raupp.

Chromobacterium subtsugae is a naturally occurring microbe. A fermentation product of this microbe is a stomach poison and will control or suppress activity of many leaf-feeding insects, including caterpillars and sucking insects (aphids, psyllids, whiteflies, plant bugs, mealybugs), thrips and mites. It is applied as a foliar spray. It may repel honeybees from plants for several days. (Photo 8)

Photo 8: Mealybugs are among many different kinds of chewing and sucking insects labeled for control by Chromobacterium subtsugae.

Saccharopolyspora spinosa is the source of spinosad, a fermentation product derived from this soil bacterium. Spinosad disrupts the normal function of the nervous system in insects. It kills caterpillars and larvae of sawflies, leaf beetles, leaf-mining flies and gall-making flies. In addition to these, it is labeled against thrips, spider mites, emerald ash borer and Nantucket pine tip moth. It has contact activity and is systemic when absorbed through the leaf’s surface. Do not use when bees are present on flowers. (Photo 9)

Photo 9: Spinosad provides excellent control of many species of caterpillars, including bagworms.

Fungi – Two species of fungi labeled for use by arborists are Beauveria bassiana and Isaria fumosorosea. Beauveria and Isaria are naturally occurring fungi with activity against a wide range of insects, including sucking insects (whiteflies, psyllids, plant bugs, mealybugs, aphids) caterpillars, thrips, spider mites, leafminers and beetles, particularly root-feeding weevils like black vine weevil, where it can be used as a soil drench or injection for larvae. Both of these fungi have shown promise against the new invasive spotted lanternfly. Fungi perform best when relative humidity is high. (Photo 10)

Photo 10: Beauveria and Isaria have proven lethal to spotted lanternfly in the field and laboratory. Photo courtesy of Paula Shrewsbury.

Conclusion

Is it time for organic approaches to managing insects and mites for trees and shrubs?

In January of 2016, Raemelton Farms in Adamstown, Maryland, became the first wholesale nursery in the U.S. to offer USDA Certified Organic trees. Insects, mites and pathogens on more than two dozen species and cultivars of trees were managed using practices and materials described in this article. Raemelton has enjoyed a significant marketing advantage by virtue of organic production.

Catch words and phrases such as sustainability, environmental responsibility and organic practices are in vogue and on the minds of consumers and arborists alike. Interest and demand for products and services defined as organic are at all-time highs. Expanding portfolios of training materials and web-based information sources provided by our professional organizations, universities and government agencies have created opportunities to bring organic pest management in arboriculture from the realm of possibility to the point of reality.

Acknowledgments

Grants from the TREE Fund and USDA National Institute of Food and Agriculture (NIFA) and McIntire Stennis programs support my research and outreach. Thanks to TCIA for inviting me to share information and thoughts on organic approaches to managing insects and mites, and to Dr. Paula Shrewsbury for editing a draft of this manuscript and providing the image of spotted lanternflies.

References and literature cited

Organic Foods Production Act of 1990
http://uscode.house.gov/view.xhtml?path=/prelim@title7/chapter94&edition=prelim

National Organic Program
http://www.ecfr.gov/cgi-bin/retrieve
ECFR?gp=&SID=358ee98f730c3e72d7f
687191134d707&mc=true&n=pt7.3.205&r=PART&ty=HTML#se7.3.205_12

Organic Materials Review Institute
https://www.omri.org/

USDA National Organic Program Agricultural Marketing Service 2015 Introduction of Organic Practices.
http://www.ams.usda.gov/sites/default/files/media/Organic%20Practices%20Factsheet.pdf

ANSI A300 (Part 10)-2016: IPM
https://www.tcia.org/TCIA/Build_Your_Business/A300_Standards/Part_10.aspx

Davidson, J. A., and M. J. Raupp. 2014. Managing Insect and Mite Pests on Woody Plants: An IPM Approach. 2014. Third Edition. Tree Care Industry Association. Londonderry, NH. 174 pp.

Dreistadt, S.H., J. C. Clark and M. L. Flint. 2004. Pests of landscape trees and shrubs: an integrated pest management guide. University of California System. Division of Agriculture and Natural Resources. 327 pp.

Herms, D.A. 2002. Strategies for Deployment of Insect Resistant Ornamental Plants: Substantial Hurdles, Vast Potential. In Mechanisms and Deployment of Resistance in Trees to Insects by Michael R. Wagner, Karen M. Clancy, François Lieutier and Timothy D. Paine. Springer Science+Business Media Dordrecht. 332 pp.

Lloyd, J. 1997. Plant health care for woody ornamentals: A professional’s guide to preventing and managing environmental stresses and pests. International Society of Arboriculture. Champaign, Il. 223 pp. 

Raupp, M. J. 1985. Monitoring: An essential factor to managing pests of landscape trees and shrubs. J. Arboric. 11:349 – 355.

Smitley, D., D. Brown, R. Finneran, E. Elsner, J. Landis, P. Shrewsbury and D. Herms. 2019. Protecting pollinators in urban landscapes. Michigan State Extension Bulletin E3314. 30 pp.

Michael Raupp, Ph.D., is a professor emeritus of entomology in the Department of Entomology at the University of Maryland in College Park, Maryland. He works closely with arborists to develop and implement sustainable management approaches for insect and mite pests in urban forests. His most recent book, Managing Insects and Mites of Woody Plants: An IPM Approach, is in its third printing and is available through TCIA, as is his children’s book, 26 Things That Bug Me. Visit his blogs at www.bugoftheweek.com and www.youtube.com/user/BugOfTheWeek.

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