The Ohio Department of Agriculture (ODA) announced this past week that Box Tree Moth (BTM) (Cydalima perspectalis, family Crambidae) had been confirmed in Hamilton and Clermont counties in southwest Ohio. The location is near where the two counties meet Warren and Butler counties. It’s the first time this non-native boxwood (Buxus spp.) defoliator has been found in Ohio.
You can read our June 26, 2023, BYGL Alert reporting the BTM confirmation announcement by clicking on this hotlink: https://bygl.osu.edu/node/2183
Heavy leaf and stem damage by BTM over multiple generations can kill boxwoods. Quoting from the USDA APHIS, 2022 New Pest Response Guidelines (see “Selected References” below): “In introduced areas where box tree moth has 2 generations per year, boxwood stands have declined over 95% in 8 years or less.”
Boxwoods were some of the oldest plants used in U.S. landscapes with planting records dating back to the late 1700s. They are currently some of the most common plants found in Ohio landscapes and remain a mainstay of our nursery industry. According to the ODA, the current inventory of boxwoods in Ohio nurseries is valued at over $200 million.
Why This Follow-Up Alert?
The location of BTM in southwest Ohio is far removed from where the moth has been previously discovered in North America. This means BTM can appear anywhere. Thus, it’s important to know the symptoms that point toward BTM or something else.
The detection and confirmation of BTM in Ohio were based on male moths caught in pheromone traps. Before last Wednesday, we had no caterpillar sites. That changed thanks to John Day, ODA Nursery Inspector, who discovered boxwoods damaged by BTM caterpillars within the area where adult moths have been trapped.
The discovery provides an opportunity to assess BTM development in Ohio. This is important to our educational outreach efforts. For example, the image below of a mature BTM caterpillar was used in our first BYGL Alert to show what the caterpillars look like. However, the second image shows our caterpillars in Ohio are currently in an early instar stage.
Equally important, images of the BTM caterpillar damage can be compared and contrasted with symptoms produced by winter injury and other boxwood problems. Boxwoods throughout Ohio were damaged by the deep-diving temperatures experienced the week of Christmas.
We have been concerned that the winter damage as well as other boxwood problems may mask BTM infestations. However, as shown in the following image, the two types of damage are significantly different.
Diagnostics: Current BTM Caterpillar Symptoms and Damage in Ohio
BTM’s lifestyle is unique among boxwood pests. There are no native pests that specifically defoliate boxwoods in Ohio and only a small number of caterpillars that may occasionally nip boxwood leaves. Defoliation by a caterpillar would point towards BTM.
The most obvious symptom of a BTM infestation is bedraggled “stick shrubs” that are totally or mostly defoliated producing see-through plants. This symptom may be seen at a distance. There are few leaves on the ground, only debris. Heavy BTM damage may kill boxwood plants as shown below.
Early instar BTM caterpillars commonly feed on the upper or lower leaf surfaces as skeletonizers. They may also feed along the edges of leaves to produce notches. This symptom may be difficult to detect in the early stages of an infestation.
The leaf damage produced by larger, later instar caterpillars is very obvious with entire leaves being consumed. It’s the “signature” symptom of BTM. The caterpillars are also sloppy feeders with pieces of leaves left behind that remain attached to plants.
A close examination will also reveal evidence of caterpillars feeding on the tips and bark of small twigs. It’s commonly reported that the caterpillar will strip bark from larger branches if they run out of foliar food.
As shown below, BTM caterpillars produce silk. They are not heavy silk producers like fall webworms (Hyphantria cunea); however, early instar caterpillars may produce small silk nests. Later instars produce wispy collections of silk entangling feeding debris.
Prior to pupation, the last instar caterpillars use silk to wrap themselves in boxwood leaves that are still on the plant. They then spin a silk cocoon and pupate. These pupation structures remain evident for some time and may consist of live or dead leaves as well as leaves the caterpillars have fed upon.
BTM spends the winter as caterpillars in the 3rd – 4th instar stage. The overwintered caterpillars resume feeding and development in the spring.
The literature notes that BTM may have as many as 5 generations per season depending on climatic conditions. In Canada, 2 overlapping generations have been consistently observed. However, a PennState fact sheet notes if BTM were to be found in Pennsylvania, the moths may have as many as 3 generations.
It’s reasonable to assume we will see at least 2 generations in Ohio with the possibility of a 3rd generation developing. However, the bottom line is that we are not certain of the number of generations that will be observed given that ours is the southernmost BTM infestation found thus far in North America. This is an important point because the overall damage from a BTM infestation can increase dramatically with each new generation.
More lightly infested boxwoods in our Ohio infestation have thus far retained some healthy stems and foliage as indicated by green foliage developing near the base of boxwood plants or interspersed among heavily damaged branches. However, subsequent generations of caterpillars will no doubt target this foliage and the additional defoliation coupled with stem damage may kill these plants.
Diagnostics: Symptoms of Winter Damage in Ohio
It’s common throughout Ohio, including within the area where BTM has been found, to see boxwoods with brown sections or plants that are almost entirely brown. The sectional dieback may appear randomly throughout the plants, or it may be concentrated on one side.
The leaves on winter-damaged boxwoods may range in color from slightly chlorotic to deep, reddish-brown. However, the affected leaves are entirely intact and remain attached to boxwoods with winter injury. Thus far, leaves are not being shed in large numbers from the affected plants. So, the boxwoods are not see-through shrubs. This is the most obvious difference between symptoms produced by winter injury and damage produced by BTM caterpillars.
Although winter injury to boxwoods, and other plants, appeared early in the season, symptoms are continuing to develop. We are seeing boxwoods that had only a few stems affected earlier this season now having large areas affected, sometimes entire plants.
On the other hand, some boxwoods that suffered winter injury are showing signs of recovery as long as entire stems were not killed. Parting the damage may reveal new foliage growing beneath damaged leaves. Selective pruning to remove dead stems will help plants recover more quickly.
Diagnostics: Boxwood Fungal Diseases
There are two fungal diseases found in southwest Ohio that may produce symptoms that could be mistaken for BTM. Volutella Blight, which is sometimes called Volutella Canker, or Pseudonectria Canker, is caused by the fungus, Pseudonectria buxi (formerly Volutella buxi). Boxwood Blight is produced by the fungus, Calonectria pseudonaviculata (formerly Cylindrocladium pseudonaviculatum or Cylindrocladium buxicola)
Volutella blight is not normally a boxwood killer. The disease usually causes sectional dieback with browned leaves clinging to the affected stems for weeks or months after the stems are killed by cankers. Affected plants are recoverable by selectively pruning out the affected stems as long as cuts are made below the cankers.
Boxwood blight is a boxwood killer. However, research has shown a wide range of susceptibility among boxwood species, varieties, and cultivars with some being resistant. Symptoms include blackened leaves that are eventually shed. This is the only disease problem that may produce dramatic see-through boxwoods, but the shed leaves are intact and can be seen littering the ground beneath affected plants.
A “field diagnosis” should not be the final word on boxwood blight or Volutella blight/canker. Samples should be sent to our OSU C. Wayne Ellett Plant and Pest Diagnostic Clinic (PPDC) for confirmation before taking action. You can learn how to take and send samples to the PPDC by clicking on this hotlink: https://ppdc.osu.edu/
Although we can now report first-hand the signs and symptoms of BTM caterpillars in Ohio, it’s important to remain aware of what adult moths look like. Obviously, male moths are found in pheromone traps deployed by the ODA. The traps continue to serve as an important tool for learning more about our BTM infestation.
However, homeowners should be aware that BTM adults may fly to porch lights at night. The moths have two different color forms with both forms having two distinctive white dots as shown in the picture below. Moths with light-colored wings are much more common than those with dark-colored wings.
A Possible Look-A-Like Moth
The native Melonworm Moth (Diaphania hyalinata, family Crambidae) is a possible look-a-like to BTM. The caterpillars feed on members of the Cucurbitaceae family, particularly squash. However, aside from the distinct differences shown in the image below, the literature indicates this moth fails to survive Ohio winters. Still, the moths may occasionally be blown northward, so it’s important to be aware of their similar appearance to BTM.
If You See It; Report It
The ODA has developed an online reporting tool that includes many helpful features including an interactive map so you can pin the exact location of your observation. The reporting tool requires a picture, so make certain you take clear, in-focus pictures to upload with your report.
Here is the hot like to the ODA reporting tool:
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Skvarla, M.J., 2023. Box Tree Moth. PennState Extension Fact Sheet, Available at: https://extension.psu.edu/box-tree-moth
2022 Pest Alert: Box Tree Moth (Cydalima perspectalis), March, USDA PPQ. Available at: