Lindera benzoin, commonly known as northern spicebush, common spicebush, wild allspice, Benjamin bush, and fever bush, is a woody shrub in the Laurel family that is native to eastern North America. It is widespread throughout much of the eastern region of the United States from Texas, Oklahoma, Kansas, Iowa, and Wisconsin, and to the north, into the parts of Ontario, Canada.

Approximately 100 species of Lindera have been reported worldwide, with three species native to eastern North America. The genus name Lindera honors the Swedish botanist Johann Linder, while the species name benzoin often refers to the aromatic oil found in the leaves, which is characteristic of the Lauraceae family. Other members of this family include sassafras (Sassafras spp), cinnamon (Cinnamomum verum), camphora tree (Camphora officinarum), and avocado (Persea americana).

Two other species of Lindera occur in the southeastern United States. Lindera melissifolia (pondberry) and Lindera subcoriacea (bog spicebush) are considered rare within their range.

In this article, the name ‘spicebush’ refers to Lindera benzoin.

In May 2024, Forest Entomologist Kayla Perry from the OSU Entomology Department visited A. B. Williams Memorial Woods in the Cleveland Metroparks North Chagrin Reservation in Mayfield, Ohio. During the field visit, Kayla and Josh Philipps, Natural Resources Area Manager for Cleveland Metroparks, observed red thrips and dieback symptoms on spicebush in the reserve. She collected a few samples and brought them to the OSU Entomology Department for further analyses. The red thrips were identified as nymphs belonging to the suborder Tubilifera or tube-tailed thrips. Tube-tailed thrips are characterized by a tubular 10th abdominal segment. At this time, there is no evidence of a connection between the dieback symptoms and the presence of the thrips.

During a field visit to Holden Arboretum in late May 2024 and a follow up visit to A. B. Williams Memorial Woods, a higher severity and incidence of the dieback symptoms and thrips infestation was observed. Concerned about the extent of damage across Cleveland Metroparks, Josh requested the OSU Entomology Lab further investigate the affected plants to identify the causal agents.

While some of the plants show twig dieback (see the images), others suffer from wilting of the entire plant.

Some of the leaves collected at A. B. Williams Memorial Woods showed chlorotic leaves with a mottled pattern. These symptoms are often indicative of a viral infection.

Similar dieback and viral symptoms to those observed at Holden Arboretum and A. B. Williams Memorial Woods have also been observed in spicebush at Secrest Arboretum in Wooster, Ohio. However, no thrips were observed on those plants.

There are some reports of these symptoms on spicebush at other parks within the region. The occurrence of these issues in multiple locations may indicate a more widespread problem.

Spicebush dieback and vascular streak dieback (VSD)

We submitted symptomatic twigs for pathogen analysis at the C. Wayne Ellett Plant Pest Diagnostic Clinic (CWE PPDC) from spicebush sampled in A. B. Williams Memorial Woods. By following up on the guidance from Erik Draper, the Commercial Horticulture Educator in Geauga County, Dawn Gerlica, Senior Horticulturist, Myrtle S. Holden Wildflower Garden, Holden Forests & Gardens link also submitted symptomatic twigs to the CWE PPDC for pathogen analysis.

Dr. Francesca Rotondo, Program Director and Plant diagnostician of the CWE PPDC, did not observe the characteristic vascular streaking associated with vascular streak dieback (VSD) from the submitted samples. VSD is a fungal disease caused by Ceratobasidium theobromae, which can result in severe losses in many woody ornamentals, including spicebush. Medley (1996) documented dieback in spicebush during 1993–1994 at two locations in southwestern Ohio, but did not mention whether the dieback was caused by any pest, disease, or other abiotic condition.

Due to the destructive nature of VSD, the samples were tested for the fungus using a PCR assay specific to VSD despite the absence of characteristic streak symptoms. However, the assay did not detect the pathogen in any of the samples. Other symptoms observed on the samples included black necrosis of the petioles, some vein spotting, and leaf chlorosis. Culture plates showed the growth of Colletotrichum sp., a well-known pathogen capable of infecting a wide range of host plants and causing various host-specific symptoms such as dieback, leaf spots, fruit lesions. Diseases caused by Colletotrichum spp. are often referred as anthracnose.

Laurel wilt is another destructive fungal disease that can affect spicebush. The fungus, Harringtonia (formerly Raffaelea) lauricola, is transmitted by the redbay ambrosia beetle (Xyleborus glabratus). Symptoms of laurel wilt in spicebush include wilting of leaves and dieback of branches that ultimately result in mortality. The leaves may exhibit a dark green or brown color, and premature leaf drop is often observed.

Monitoring efforts are crucial as the spread of laurel wilt can have significant ecological consequences. The disease has been reported in several southeastern states, prompting concern about its introduction into northern regions, including Ohio. Research on the dynamics of laurel wilt is ongoing, including its spread and impact on native ecosystems, as well as potential management strategies to mitigate its effects (Olatinwo et. Al., 2021).

Josh Philipps mentioned thrips and spicebush dieback have been observed in several other Cleveland Metroparks properties. These reservations are located across three Ohio counties, Cuyahoga, Lake, and Medina.

Constance Hausman, Senior Conservation Science Manager with Cleveland Metroparks, mentioned that she has seen the same characteristic caused dieback on spicebush outside of Cleveland Metroparks properties (on partner park districts or other protected lands) in Lake, Ashtabula, and Geauga Counties, suggesting the problem is likely more widespread.

Michael Munster, Plant Disease Diagnostician at North Carolina State University, mentioned that black twig borer (Xylosandrus compactus) and its associated fungus (Fusarium sp) can also cause dieback in spicebush. However, he noted that it is unclear whether the dieback is caused by the direct damage from the beetles or the impact of the associated fungus.

We split open a few twigs of the affected spicebush but did not see any signs or symptoms of black twig borer.

Spicebush virus

In 2017 and 2018, spicebush samples were tested for virus by USDA-ARS NGRL (National Germplasm Resources Laboratory) in Beltsville, Maryland and by Plant Pest Diagnostic Laboratory (PPDL) link at Purdue University in West Lafayette, Indiana. Spicebush samples from Virginia and Kentucky were tested by Dimitre Mollov at USDA-ARS and the samples sent from Ohio and Missouri were tested by PPDL and published the results. The authors mentioned that all the symptomatic samples were tested positive for the newly discovered Emaravirus.

Characteristic symptoms of Emaravirus infections are chlorotic mottling and shrinking of the leaves (Fan, 2021).

We observed similar symptoms on spicebush in A. B. Williams Memorial Woods and in Secrest Arboretum. Samples from symptomatic spicebush were sent to John Hammond at USDA-ARS Floral and Nursery Plant Research Unit (FNPRU) in Beltsville, Maryland for molecular identification of the virus. We are currently waiting for the results.

Thrips on spicebush

We were able to collect a large number of adult thrips in June 2024, a few weeks after we first observed the thrips on spicebush.

Not every spicebush had thrips. Large populations of thrips were found on a few plants where they were congregating on the underside of the leaves.

I used Mound & Kibby 2005 to morphologically identify the adult thrips to the genus Liothrips in the family Phlaeothripidae.

However, the order Thysanoptera was revised in 2013 using advanced molecular phylogenetic analyses, and this revision placed several species of Liothrips into other closely related genera (Buckman et al. 2013). Therefore, we sent the specimens to the National Identification Services (NIS) for species identification through Pest Survey Specialist Mark Hitchcox at USDA APHIS in Reynoldsburg, Ohio.

A few weeks later, the NIS confirmed the identification of the thrips as Pseudophilothrips in the family Phlaeothripidae. However, a species determination could not be made due to the limited genetic database of Thysanoptera in GenBank or BOLD.

According to Mound et al. (2010), 13 described Neotropical thrips species in the genus Liothrips were transferred to Pseudophilothrips following molecular phylogenetic analysis.

Pseudophilothrips species reported in the United States

The classification of Liothrips and Pseudophilothrips can be complex, especially with the discovery of new species and the re-evaluation of existing ones. Stannard (1968) listed 32 described Liothrips speciesin North America in 1957, before the revision of the Order, Thysanoptera in 2013. However, this group is understudied, and more work is needed to reevaluate the genus for the United States.

So far, two species of Pseudophilothrips are reported from the United States. Pseudophilothrips ichini was introduced as a biocontrol agent in Florida in 2019 (Wheeler et. al. 2022) to control the invasive weed Brazilian peppertree, Schinus terebinthifolia (Anacardiaceae).

Pseudophilothrips varicornis is commonly known as hollyhock thrips. This species has been reported from California on Althea, Hibiscus, Sida, and Sphaeralcea (Malvaceae), but no crop damage has been observed so far.

Importance of spicebush and What we can do to protect them?

The health of spicebush populations in Ohio is threatened by various environmental and biological factors, including insects, disease, and viruses. By understanding how to diagnose the signs and symptoms of these issues and options for management, landowners and gardeners can take proactive measures to support spicebush in the landscape. Monitoring, proper cultural practices, and timely interventions are essential for maintaining healthy spicebush populations.

All three spicebush species in the United States are native plants with cultural significance. Native Americans protected these plants and greatly benefited from their use as a cold, cough, dermatological, and respiratory analgesic. Some use the leaves of spicebush and berries as a spice when cooking, including as a replacement for cinnamon.

Spicebush is a useful plant for the butterfly garden since it serves as the host for several native swallowtail butterfly species and other pollinators, including spicebush swallowtail (Papilio troilus) and promethea silkmoth (Callosamia promethea).

Spicebush is a must-have shrub in your backyard. They are special for many reasons such as the fragrant bright yellow flowers that cover the branches in early spring and the warm yellow leaves in the fall. Spicebush is easy to grow. The plant prefers partial to full shade and thrives in moist, well-drained soil rich in organic matter.

The plants can be pruned in the second year after planting. Prune lightly after flowering to maintain shape and to remove any dead or damaged branches. While spicebush does not need to be fertilized, a balanced slow-release fertilizer applied in early spring will promote healthy growth. Proper spacing and air circulation can help prevent common issues such as leaf spots or powdery mildew. Spicebush can be propagated from seeds or cuttings. Plant the seeds in the fall for best results.

With its beautiful flowers, vibrant fall foliage, and important role in supporting local native butterflies, spicebush is a fantastic addition to any garden.

Ron Wilson