Viburnum Leaf Beetle

ANR-39
Date: 
08/03/2016
Curtis E. Young, PhD, Assistant Professor, Extension Educator, Agriculture and Natural Resources, Van Wert County

The viburnum leaf beetle (VLB) (Pyrrhalta viburni) [order Coleoptera: family Chrysomelidae] damages a variety of viburnum species and hybrids by feeding and egg-laying activities. Both adults and larvae feed on the foliage of the host plant; larvae feed on the foliage from mid-spring to early summer and adults feed on the foliage from mid-summer into the fall. Highly susceptible viburnum shrubs are usually completely defoliated by the beetle. Mated female viburnum leaf beetles chew pits into the bark of twigs and stems of the host shrubs into which eggs are laid. These pits create weak points along the twigs and stems which are break points and cause twig and stem tips to die. Heavy infestations by VLB can defoliate shrubs, cause dieback, and eventually kill plants. Valued plantings of the European cranberrybush viburnum can be severely damaged by larval and adult feeding. Shrubs repeatedly defoliated over a period of two to three years are likely to die. 

Host Plants for Viburnum Leaf Beetle (VLB)

VLB is restricted to feeding on viburnum plants in the genus Viburnum. VLB activity is observed in both native populations and ornamental plantings of viburnums. 

VLB Identification

VLB has a complete life cycle with four distinct stages: egg, larva (3 larval instars), pupa and adult. Pictures and descriptions of the life cycle stages are below.

Eggs are ball-shaped, yellow-brown to brown in color with a sculptured surface and about 1/16" in diameter. Eggs are not laid in plain view. They are laid in rows of pits (3 to 8 eggs/pit) chewed into the new shoots (current year and sometimes the one-year old shoots, as well) during late summer. Once the pits are filled with eggs, the pits and eggs are covered with a “cap” of feces and chewed bark and wood mixed with saliva. See figures below of the capped egg pits as shown in Figures 1a and 1b. These rows of capped pits can be observed from July through the following spring.

Newly hatched larvae are tiny and dark in color, but lighten as they grow and elongate as shown in Figure 2. Mature larvae are thick-bodied with the thorax having six obvious legs, grow to a length of about 1/2", and are yellow-green in color with a pattern of black spots, and black head and legs as shown in Figure 3.

Pupae are approximately 1/4" to 5/16" in length and start out bright yellow in color, but are not often seen because they are hidden in the soil. See the pupae in Figure 4 below. Adult beetles have a typical leaf beetle appearance as shown in Figure 5, are between 1/4" and 3/8" in length (females tend to be larger than males), and mostly golden-brown in color. Beetles may have a metallic sheen appearance when observed in the direct sunlight. The sheen is produced by short, golden-grey hairs. The head, thorax and elytra (wing covers) are generally golden-brownish, but the shoulders of the elytra and front edge of the front wings are darker brown.

Figure 1a: Viburnum “capped” egg pits. Photo by Curtis E. Young, Ohio State University Extension. Figure 1b: Viburnum “capped” egg pits. Photo by Curtis E. Young, Ohio State University Extension.

Figure 2: Newly hatched, first instar viburnum leaf beetle larvae and damage. Photo by Paul Weston, Cornell University, Bugwood.org. Figure 3: Viburnum leaf beetle third instar larva. Photo by Curtis E. Young, Ohio State University Extension.

Figure 4: Viburnum leaf beetle pupae recovered from soil beneath host plant. Photo by Curtis E. Young, Ohio State University Extension. Figure 5. A pair of adult viburnum leaf beetles. Photo by Curtis E. Young, Ohio State University Extension.

VLB Life Cycle and Plant Injury

VLB overwinters in the egg stage in the pits in which they were laid. By early to mid-May, the eggs hatch and the larvae (grubs) disperse to the newly expanding viburnum foliage. Newly hatched larvae tend to feed side-by-side on the underside of the leaves between the veins of the leaf. Frequently the young larvae lay parallel to the leaf veins. Feeding initially appears as a skeletonization (lower leaf surface and middle layer of leaf is consumed and upper leaf surface is left intact). This damage becomes more exaggerated as the leaf continues to mature and expand resulting in the skeletonized areas ripping out from between the veins, leaving only midribs and major veins intact. As the larvae grow, their feeding becomes more aggressive and holes are produced through the entire leaf. Heavy feeding by the larvae can result in leaf drop to total defoliation. 

After leaves are no longer providing enough sustenance, larvae will move to the new, green-stem growth and chew the bark off of the young stems causing stem dieback. Larval feeding continues through late spring to early summer. Once larval feeding is complete, larvae abandon the host plant, transverse down the plant to the soil, enter the soil and pupate. The pupal stage lasts 10 to 14 days. No damage occurs during the pupal stage.

Adults appear in mid-summer (late June to early July) and may be found on host plant foliage and stems until the first heavy (killing) frost. Adults also feed on the leaves of host plants as seen in Figure 6 below. Adult feeding damage consists of irregular circular holes. Heavy feeding by adults can also result in defoliation, shown in Figure 7. Thus, host plants have the potential to be defoliated twice each growing season. Multiple defoliations can weaken and/or kill host plants. 

Figure 6: Adult viburnum leaf beetle injury from feeding. Photo by Curtis E. Young, Ohio State University Extension. Figure 7. Defoliation by viburnum leaf beetle. Photo by E. Richard Hoebeke, Cornell University, Bugwood.org.

Additional damage to host plants is produced by the egg-laying process. When a female lays eggs, she will typically chew pit after pit in the young stems. The stems are weakened by the pit-chewing process. The pits are easy break points on the stem and points where moisture loss occurs. Death of the young stems may occur through the winter. Complete development from egg hatch to adult emergence generally takes 8 to 10 weeks.

From late June or early July until October, females chew holes (1/8" x 1/8") in small branches or twigs of viburnum (generally the current year’s growth, but occasionally in the previous year’s growth) for laying eggs. The egg-laying sites are often arranged in a straight row on the undersurface of the terminal twig. A female can lay up to 500 eggs.

From summer through fall, adults will continue to be active, mating, laying eggs on terminal twigs, and feeding upon foliage until the first killing frosts. There is one generation annually.

VLB Management Strategies

Mechanical Control

The most effective means of mechanical control of VLB on small plants and small-scale plantings is to prune and destroy infested twigs after egg laying has ceased in the fall, anytime from October to April. The capped egg pits are easy to see on the stems after leaf-drop. Pruned twigs should be removed from the area and buried, burned, or placed into an active composting pile.

Cultural Control

Planting species or cultivars of Viburnum that are resistant or less susceptible to VLB may reduce the severity of an infestation preventing defoliation. Weston (2003) classified a number of common viburnum species into categories of most susceptible, moderately susceptible, and least susceptible species based on a multitude of field observations. A summary of those mostly found in Ohio:

Most susceptible viburnums:
  • Arrowwood viburnum (V. dentatum)
  • European cranberrybush viburnum (V. opulus)
  • American cranberrybush viburnum (V. opulus var. americanum = V. trilobum)
  • Rafinesque viburnum (V. rafinesquianum)
Moderately susceptible viburnums:
  • Sargent viburnum (V. sargentii)
  • Wayfaringtree viburnum (V. lantana)
  • Nannyberry viburnum (V. lentago)
  • Blackhaw viburnum (V. prunifolium)
Least susceptible viburnums:
  • Koreanspice viburnum (V. carlesii)
  • Burkwood viburnum (V. burkwoodii)
  • Doublefile viburnum (V. plicatum var. tomentosum)
  • Judd viburnum (V. x juddii)
  • Lantanaphyllum viburnum (V. x rhytidiphylloides)
  • Leatherleaf viburnum (V. rhytidiphyllum)
Chemical Control—Standard Insecticides

Several insecticides include VLB on their labels. These products may be sprayed when the larvae first appear in May. However, repeat sprays may be needed for adults in July if adults migrate back into plantings. Spraying against adults alone is not an effective control strategy. 

Pyrethroid and other contact insecticides are useful for control of the larvae once they are actively feeding. These same insecticides may also have to be used later in the season in order to eliminate any adult beetles that have flown in from untreated plants. Watch the plants carefully as the adults can move into an area from July through September.

Neonicotinoid insecticides and other systemics can be used for adult or larval control, but these treatments should be avoided if you are treating species of viburnum that are within 4 to 6 weeks of flowering. There is concern that the residues of these insecticides will end up in the nectar or pollen and harm pollinators. In this case, use a contact insecticide in the pre-bloom period for control of the larvae and then use a systemic after flowering to control the adult beetles.

Chemical Control—Low Impact Insecticides

Horticultural oils (generally 2 to 3 percent) and/or insecticidal soaps are useful for control of VLB larvae. Thorough coverage of plant foliage is needed as these pesticides only kill by contacting the insects. There is some evidence that oils and soaps can also kill the adults, but since there is no residual activity of these products, numerous reapplications will be needed in order to prevent adults from laying eggs.

Contact your county OSU Extension office for more information. A listing of offices is available at extension.osu.edu.

Spread of VLB

The viburnum leaf beetle (VLB), Pyrrhalta viburni (Paykull), which is native to most of Europe, consumes the foliage of plants in the Genus Viburnum to support its growth and development. VLB was first discovered and identified in North America in 1947 in the Niagara Peninsula of Ontario, Canada, and has spread from there (Ventresca and Kessel 2012). 

In 1994, VLB was detected in the United States in Maine and Cayuga County of the state of New York in 1996 (Weston 2005). In 2002, VLB was found in Ashtabula County, Ohio, where it appeared to have been established for at least two years based on egg pit scars from two different growing seasons. 

As of 2015, VLB has spread into British Columbia, Canada, and portions of Connecticut, Illinois, Maine, Massachusetts, Michigan, New Hampshire, New Jersey, New York, Ohio, Pennsylvania, Vermont, Washington and Wisconsin (Liesch 2015, Murray 2004, Tiddens 2015, Weston et al. 2012, Weston and Nuzzo 2008, Wilson 2011). VLB is likely to establish throughout Ohio. 

References

Disclaimer—This publication may contain pesticide recommendations that are subject to change at any time. These recommendations are provided only as a guide. It is always the pesticide applicator’s responsibility, by law, to read and follow all current label directions for the specific pesticide being used. Due to constantly changing labels and product registrations, some of the recommendations given in this writing may no longer be legal by the time you read them. If any information in these recommendations disagrees with the label, the recommendation must be disregarded. No endorsement is intended for products mentioned, nor is criticism meant for products not mentioned. The author and Ohio State University Extension assume no liability resulting from the use of these recommendations. 

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