Box tree moth (BTM) [Cydalima perspectalis (Walker, 1859); Lepidoptera: Crambidae] is a new, invasive species for Ohio that threatens the plant health of boxwoods (Buxus spp.) and the economic health of the green industry in our state (APHIS, 2022). A number of effective tools are in the BTM pest management toolbox (Boggs, 2024). The following information provides tips on how and when to apply these tools.
What Should You Do?
1. Do not make preventative insecticide applications to boxwoods
Insecticide applications should only be made to boxwoods with an identified BTM infestation, or to those boxwoods in close proximity to a confirmed BTM caterpillar infestation. Preventative insecticide applications outside the locations where BTM has been found are not recommended.
Making unwarranted insecticide applications is a waste of money and product and can also have unintended consequences including producing secondary pest outbreaks. Research has shown that applications of synthetic pyrethroids (e.g., caterpillar insecticides) can kill predaceous mites that help keep plant-feeding mites in check. This can then lead to plant-feeding mite outbreaks (Penman & Chapman, 1988; Gerson & Cohen, 1989).
Systemic applications of the neonicotinoid insecticide, imidacloprid, which is a common insecticide targeting boxwood leafminer [Monarthropalpus flavus (Schank)] and boxwood psyllid (Psylla buxi L.) stimulates increased egg production (fecundity) of the boxwood spider mite, Eurytetranychus buxi Garman (Szczepaniec & Raupp, 2013). This mite has been on the rise over the past several years.
2. Monitor boxwoods
Thus far, BTM in Southwest Ohio is far removed from the other known BTM infestations in North America (Boggs & Stone, 2024). This means BTM can appear anywhere. Be aware of what to look for with BTM and remain vigilant.
3. If you see it, report it!
It is essential to identify the geographical distribution of BTM in Ohio. This knowledge will guide the development of BTM management plans.
The Ohio Department of Agriculture (ODA) has developed an online reporting tool that allows reporting of BTM in three easy steps. One step involves sending a clear, in-focus picture(s) of BTM caterpillars. If BTM caterpillars are seen but conditions such as lighting makes it difficult to take a good picture, collect the caterpillars and preserve them in a freezer until they can be photographed. BTM caterpillars do not bite or sting, so they are safe to handle.
Photos of BTM ca be sent using the ODA reporting tool (go.osu.edu/odareportingtool).
4. Management
Currently, tools that support a robust BTM integrated pest management (IPM) program must be fully developed (Coyle et al., 2022). For example, field observations and preliminary host preference trials provide evidence that some boxwoods are less susceptible to BTM damage (Sisk et al., 2022). Figure 4 shows a heavily damaged boxwood surrounded by boxwoods that show no damage in a landscape with a high BTM population density. However, the selection and production of BTM-resistant boxwoods are in the early stages.
BTM caterpillars may draw the attention of various predators. Yellowjackets (family Vespidae) have been observed grinding-up BTM caterpillars to feed to their young (Figure 5). Assassin bugs (family Reduviidae) such as the wheel bug (Arilus cristatus L.) shown in Figure 6 have been found crawling within boxwoods heavily infested with BTM (Boggs & Perry, 2024).
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The impact of naturally occurring enemies of BTM including parasitoids, pathogens, and predators has not been measured in North America (Coyle et. al., 2022). Also, the use of bio-allies in a BTM IPM program has not yet been researched.
A so called “cut-and-spray” (or “trim-and-treat”) program may support the recovery of heavily damaged, established boxwoods by removing unsightly BTM defoliation along with damaged stems. Boxwoods are well-known for successfully responding to “rejuvenation pruning” to restore overgrown or mishappen plants (Rakow & Weir, 1996). The pruning should be done on dormant boxwoods in late fall, during the winter, or in early spring. Stems can be cut back to within six to 24 inches of the ground.
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The spray portion of a cut-and-spray boxwood recovery program involves closely monitoring the new stems and foliage for BTM caterpillars and spraying to kill the caterpillars. Although heavily pruned boxwoods will rapidly produce new stems and foliage in the spring, the production of a new canopy is supported by stored carbohydrates (food). Leaves are needed to support the replacement of the carbohydrates by photosynthesis.
Insecticides are currently the most reliable tool for suppressing BTM populations. BTM caterpillars can be killed using a wide range of insecticides (Eshenaur & Leeser, 2024). The following graphics (Figures 9, 10, 11, and 12) show BTM insecticides for home gardeners and horticulture professionals. Of course, it is the responsibility of the applicator to read and follow label directions.
Home Gardener Over-the-Counter BTM Caterpillar Insecticides
The following insecticides (Figure 9 and 10) are labeled for use on outdoor woody ornaments, ornamental trees and shrubs, herbaceous or woody plants by home gardeners. The lists were drawn from the New York State Integrated Pest Management Program (Eshenaur & Leeser, 2024) with additional insecticides included that can be used in Ohio.
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* Biorational (Figure 9) is generally defined as insecticides with relatively low mammalian toxicity and few environmental side effects. However, it does not mean they will not kill non-target organisms. Also, biorational does not mean the products are compatible with organic practices as approved by the Organic Materials Review Institute (OMRI). Products that are approved by the OMRI can be found on the OMRI website (omri.org/about-products-list).
Horticulture Professional Insecticides to Control BTM Caterpillars
The following insecticides (Figure 11 and 12) are labeled for use by horticulture professionals on outdoor woody ornaments, ornamental trees and shrubs, and herbaceous or woody plants to control BTM caterpillars. The lists are drawn from a multi-state IR-4 project fact sheet (Frank et al., 2022) and from the New York. State Integrated Pest Management Program (Eshenaur & Leeser, 2024).
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** Biorational (Figure 11) is generally defined as insecticides with relatively low mammalian toxicity and few environmental side effects. However, it does not mean they will not kill non-target organisms. Also, biorational does not mean the products are compatible with organic practices as approved by the Organic Materials Review Institute (OMRI). Products that are approved by the OMRI can be found on the OMRI website (omri.org/about-products-list).
Disclaimer: The information provided in the tables above is presented with the understanding that no product discrimination is intended, and no endorsement of any product mentioned, or criticism of unnamed products is implied. Labeling, registrations, and uses can change. The label is the law: Applicators are responsible for reading and following all label directions.
References
Animal and Plant Health Inspection Service (APHIS). (2022). Pest Alert: Box Tree Moth (Cydalima perspectalis). United States Department of Agriculture.
aphis.usda.gov/sites/default/files/alert-box-tree-moth.pdf
Boggs, J. (2023, July 17). Re-visiting Volutella and Browned boxwoods. Buckeye Yard and Garden OnLine (BGYL).
bygl.osu.edu/node/2198
Boggs, J. (2023, September 27). Box tree (boxwood) moth: New detection what to look for, and management. Buckeye Yard and Garden OnLine (BGYL).
bygl.osu.edu/node/2262
Boggs, J. (2024). Box tree moth (BTM) damage is ramping up: Insecticide options. Buckeye Yard and Garden OnLine (BGYL).
bygl.osu.edu/node/2409
Boggs, J. (2024). Box tree moth (BTM) damage is ramping up: Insecticide options. Buckeye Yard and Garden OnLine (BGYL).
bygl.osu.edu/node/2335
Boggs, J., & Perry, K.I. (2024). Wheel bugs are on the hunt: Look but don’t touch! Buckeye Yard and Garden OnLine (BGYL).
bygl.osu.edu/node/2413
Coyle, D.R., Adams, J., Bullas-Appleton, J., Llewellyn E.J., A. Rimmer, A., Skvarla, M.J., Smith, S.M, & Chong, J.H. (2022). Identification and Management of Cydalima perspectalis (Lepidoptera: Crambidae) in North America. Journal of Integrated Pest Management, 13(1), 1–8.
doi.org/10.1093/jipm/pmac020
Eshenaur, B., & Leeser, J. (2024). Box tree moth (Cydalima perspectalis) [Fact sheet], Cornell College of Agriculture and Life Sciences (CALS), New York State Integrated Pest Management.
cals.cornell.edu/new-york-state-integrated-pest-management/outreach-education/fact-sheets/box-tree-moth
Frank, S., Gilrein, D., Havers, M., & Palmer, C. (2022). Box tree moth: Fact sheet, management & visual guide [Fact sheet], NC State/Cornell/Rutgers/IR-4 Fact Sheet.
ir4.cals.ncsu.edu/EHC/InvasiveSpecies/BTM_FactSheet_VisualGuide.pdf
Gerson, U., & Cohen, E. (1989). Resurgences of spider mites (Acari: Tetranychidae) induced by synthetic pyrethroids. Experimental & Applied Acarology, 6(1), 29–46.
doi.org/10.1007/BF01193231
Penman, D. R., & Chapman, R. B. (1988). Pesticide-induced mite outbreaks: pyrethroids and spider mites. Experimental & applied acarology, 4(3), 265–276.
doi.org/10.1007/BF01196190
Rakow, D. A., & Weir, R. (1996). Pruning: An illustrated guide to pruning ornamental trees and shrubs (information bulletin 23). Cornell University, Cornell Cooperative Extension.
hdl.handle.net/1813/3573
Sisk, E., Brindley, J., & Del-Pozo, A. (2022). Box tree moth in the United States (ENTO-525NP) [Fact sheet]. Virginia Cooperative Extension.
pubs.ext.vt.edu/content/pubs_ext_vt_edu/en/ENTO/ento-525/ento-525.html
Szczepaniec, A., & Raupp, M. J. (2013). Direct and indirect effects of imidacloprid on fecundity and abundance of Eurytetranychus buxi (Acari: Tetranychidae) on boxwoods. Experimental and applied acarology, 59, 307–318.
doi:10.1007/s10493-012-9614-1