Viburnum-What’s a Nice Plant Like You Doing In a Place Like This?

You remember your first car, your first kiss with the girl down the street, and your favorite plant, but not necessarily in this order. I still remember my first viburnum—yes, she was a beauty.
    

My first viburnum was a gift from a nurseryman back in 1988.  It was an Alleghany viburnum, actually 6 of them.  I moved my Alleghany viburnums to my farm in upper Carroll County to a hill where it is always windy from December through April.  The plants were subjected to a winter when the temperature went below 0 for several days with cold, drying winds and they dropped a lot of their semi-evergreen foliage.  New foliage emerged in spring and they flowered heavily as they always do.  This summer they rode through more than 10 weeks of drought without a drop of rain.  The foliage drooped but there never was any branch dieback or leaf scorch on the plant.  After 19 years of observing these plants I must comment that they are one tough plant and I have yet to see any major insect or disease problems with the plant, at least in Maryland.
    

In the fall, the really spectacular feature of many viburnums is the berries.  Some are red or orange but a few exceptional ones are blue to purple. One that caught my eye on a visit to Waverly Farm in Frederick is a blue-berried beauty called ‘Perle Blue’.  The berry set on this eye-appealing plant was excellent in 2007.  Another nice blue-berried viburnum is ‘Blue Muffin.’  Cut flower growers in Maryland are using ‘Blue Muffin’ as a woody cut stem for sales to florists. I think ‘Blue Perle’ could sell in this same market.

What About Pests?
    
Up north, in New York State, Vermont, Maine and Pennsylvania, viburnums have problems, but really just one:  the viburnum leaf beetle.  One of my fellow entomologists, Paul Weston  at Cornell University, has published extensive papers on this nasty leaf-eating pest of the North and is one of the leading experts on this bug.  Native to Europe, it managed to wander over to North America.  Besides being found throughout New York State, this pest is now found in Vermont, Maine, Ontario, parts of Ohio and the northern part of Pennsylvania.  At every entomology meeting he tells me it is just a matter of time until they show up in Maryland.  Help me keep Paul wrong on this prediction.  Let’s keep this pest in New York and keep it out of Maryland for as long as we can.
    

Fortunately, viburnum leaf beetles infest only viburnum but they are doing a number on the ones they find.  They complete just one life cycle each year.  Adult females lay up to 500 eggs on viburnum twigs in summer and early fall.  The eggs overwinter and hatch in spring.  Larvae feed on foliage until early summer, then crawl down the shrub and pupate in the soil.  Adults emerge from the soil in midsummer, feed again on viburnum foliage, and mate.  From egg hatch to adult takes just 8 to 10 weeks.
    

Here is some of the information that Paul Weston and the Cornell University Department of Entomology has put out for the public in New York State:
    

Life cycle details: Adult females begin laying eggs in late June to mid-July and continue laying eggs as late as October, until the first killing frost.  They prepare laying sites by chewing small holes (about 1 mm in diameter, or about the size of a pinhead) into a small branch or twig. The laying sites are usually (though not always) on the current season’s growth.
    

Females typically deposit about eight eggs (though the number may vary) into the hole and seal the hole with a lid or “cap” made of a special cement of chewed bark and excrement. The caps actually sponge up and store water to help keep the egg cavity humid.
    

A female will continue up the twig excavating cavities and laying eggs, leaving a distinctive row of caps, usually along the underside of the branch or twig.  Egg laying occurs mostly at night.
    

The eggs overwinter in these snug little holes, and the larvae emerge from the eggs in late April or early May in response to warming temperatures. We are still learning about the relationship between spring weather conditions and when the eggs hatch.  You can help us to better understand this by observing viburnum with egg-laying sites often around the time larvae emerge. The young larvae feed together (often several to a leaf) beginning on the underside of tender, young, expanding viburnum leaves.  They often start with lower leaves, “skeletonizing” them, leaving only the midrib and major veins intact.  If the infestation is heavy enough, the larvae will completely defoliate the shrub.
    

Larvae go through three instars (stages) shedding their cuticle (“skin”) between each.  In early to mid-June, when they reach about 10 to 11 mm long, the larvae crawl down the shrub, enter the soil, and pupate. (This is the non-feeding stage between larvae and adult where the pupae develop within a cocoon, similar to the life cycle of butterflies.)  Pupae are very hard to find.  They need moist soil. If it’s too wet or too dry, the pupae don’t seem to survive as well.
    

In early July, the adult beetles emerge from the soil and start feeding on viburnum foliage. They continue to feed, mate and lay eggs until the first killing frost.  This is the stage where they may migrate to other plants that haven’t yet been infested.

Can This Pest Move South?

Sure it can.  Fortunately most plant material from nurseries moves from the South to the North.  If plant materials, especially viburnums, from New York State, are imported for your plant jobs keep a close eye out for adults, larvae or eggs.  You can get sample to us at CMREC or to Plant Protection at MDA in Annapolis.

Resistance?

Part of your IPM approach should be to select plant material that has some natural resistance.  We don’t have this bug yet but if you are a forward thinking, and not a “sea-of sameness” type nursery manager or grower you should be planting viburnum tolerant of this pest.
    

Paul Weston has posted the following list of viburnums with a rating system for damage susceptibility to viburnum leaf beetle.  Just because a species is listed as most resistant doesn’t mean that it won’t be infested.
     

Highly susceptible species are the first to be attacked, and are generally destroyed in the first 2-3 years following infestation.  These include:

•    V. dentatum complex, arrowwood viburnums
•    V. nudum, possum-haw, smooth witherod viburnum
•    V. opulus, European cranberrybush viburnum
•    V. opulus var. americana (formerly V. trilobum), American cranberrybush viburnum
•    V. propinquum*, Chinese viburnum, Taiwanese viburnum
•    V. rafinesquianum, Rafinesque viburnum

Susceptible species are eventually destroyed, but usually are not heavily fed upon until the most susceptible species are eliminated.  Some examples are:

•    V. acerifolium, mapleleaf viburnum
•    V. lantana, wayfaringtree viburnum
•    V. rufidulum, rusty blackhaw, southern black-haw
•    V. sargentii, Sargent viburnum
•    V. wrightii, Wright viburnum
  

 Moderately susceptible species show varying degrees of susceptibility, but usually are not destroyed by the beetle.  These may be:

•    V. alnifolium (syn. V. lantanoides), hobblebush
•    V. burkwoodii Burkwood viburnum
•    V. x carlcephalum, Carlcephalum viburnum
•    V. cassinoides, witherod viburnum
•    V. dilatatum linden viburnum
•    V. farreri , fragrant viburnum (except ‘Nanum’, which is highly susceptible)
•    V. lantanoides (syn. V. alnifolium), hobblebush
•    V. lentago, nannyberry viburnum
•    V. macrocephalum, Chinese Snowball Viburnum
•    V. x pragense pragense viburnum
•    V. prunifolium, blackhaw viburnum
•    V. x rhytidophylloides, lantanaphyllum viburnum
•    V. tinus*, laurustinus viburnum

Resistant species show little or no feeding damage, and survive infestations rather well.  Most species in all susceptibility groups exhibit more feeding damage when grown in the shade, including:

•    V. bodnantense, dawn viburnum
•    V. carlesii, Koreanspice viburnum
•    V. davidii*, David viburnum
•    V. x juddii, Judd viburnum
•    V. plicatum, doublefile viburnum
•    V. plicatum var. tomentosum, doublefile viburnum
•    V. rhytidophyllum, leatherleaf viburnum
•    V. setigerum, tea viburnum
•    V. sieboldii, Siebold viburnum

*Based on observations at the Van Dusen Botanical Garden, Vancouver, B.C. by Carolyn Jones

Final Words

Viburnums are tough plants, tolerant of a wide range of growing conditions, with nice flower displays and great berries on some species.  The viburnums are great for cut stems when berries color up.  We don’t have the nasty viburnum leaf beetle in Maryland yet so my feeling is to keep using this terrific plant, but be sure to select species and cultivars that are resistant to damage—just in case Paul Weston wins his bet with me.

Stanton Gill

Extension Specialist

Stanton Gill is an extension specialist (professor-ranked principal agent) in IPM and entomology with the University of Maryland Extension, based at the Central Maryland Research and Education Center in Ellicott City. He is also a professor in the Landscape Technology Program at the Germantown Campus of Montgomery College. Contact him at [email protected]