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Science
Volume 40 Issue 4 • May 27-June 2, 2010
now in our 40th season

Honeysuckle

by Dr. Sarah D. Oktay
Managing Director UMass Boston Nantucket Field Station

We were fortunate to be setting on the deck of a beautiful and charming place on Lincoln Avenue on a recent May evening with our friend, the poet Richard Cambridge, who serves as the caretaker.  We were enjoying the expansive view of the homes, backyards, beaches, and Nantucket Harbor that stretched beyond a sea of white and yellow fragrant flowers (cue dramatic ominous music) that belonged to the dreaded Japanese Honeysuckle!  Adored by children for decades for their tiny drops of nectar and found on almost every plot of land on the island including the Field Station, the Japanese Honeysuckle is one of several local and state listed exotic invasive plants.  Japanese Honeysuckle, Lonicera japonica Thunb., was introduced into the United States as an ornamental vine approximately 200 years ago.  It is listed as an invasive plant on the U.S. Department of Agriculture’s web site (www.invasivespeciesinfo.gov/plants/honeysuckle.shtml) in addition to being on the undesirable list of many biodiversity groups including the Nantucket and Massachusetts lists.

Honeysuckle

Exotic invasive plants are non-native or non-indigenous plants that may be introduced to an area deliberately in order to provide color, because they are aesthetically pleasing, or as an erosion control method, or as fodder for animals, food for humans, and sometimes (in the case of some native species of England) simply as a cure for homesickness.   Many of the elegant estate gardens created in the Northeast housed an amazing variety of imported plants that escaped the confines of their vine-covered walls.  Invasive exotic plants are frequently introduced accidently through bilge water transport across the ocean or on the hulls of boats or through the transport of fill or other plants as weeds or seeds.  Birds, insects, and mammals and simply the wind or storms can carry the seeds or plant fragments.  Without the control measures that may exist in their native ecosystems, these plants can out-compete native species for space and resources.  These invasions can cause aesthetic, biological, chemical, and economic damage to natural areas and in your backyard.

Back to our seemingly benevolent friend of childhood walks:  Japanese honeysuckle is a perennial woody vine of the honeysuckle family that spreads by seeds, underground rhizomes, and above-ground runners (pretty much everything short of taking the subway).  It has opposite oval leaves, 4-8 cm long, that are semi-evergreen in northern states and evergreen (leaves stay attached to the stems) in southern states.  Older stems are hollow with brownish bark that peels in long strips.  The vines can grow to thirty feet in length and easily encircle most large shrubs and small trees.  When disturbances occur causing the canopy to open, Japanese honeysuckle responds with dense growth.

The flowers are fragrant, two-lipped, and typically in pairs.  Flowers are tubular, with five fused petals, white to pink, turning yellow with age, very fragrant, and occur in pairs along the stem at leaf junctures.  Stems and leaves are sometimes covered with fine, soft hairs.  Japanese honeysuckle blooms from late April through July and sometimes into October.  Small black fruits are produced in autumn, each containing 2-3 oval to oblong, dark brown seeds about 1/4 inch across.  The honeysuckle creates dense tangled thickets by a combination of stem branching, nodal rooting, and vegetative spread from rhizomes (www.in.gov/dnr/files/Japanese_Honeysuckle.pdf and www.nps.gov/plants/alien/fact/loja1.htm).  L. japonica is mainly dispersed by birds that eat its fruits.  The plant also spreads locally via runners.  Japanese honeysuckle is distinct from two other trailing honeysuckles, the trumpet honeysuckle (L. sempervirens) and wild honeysuckle (L. dioica), both of which are found in Massachusetts.  The fruits of the other honeysuckles are red to orange-red berries, and their uppermost leaf pair is joined together.  Lonicera japonica is often an early successional species in disturbed sites.  It is found along the edges of forests, in floodplains, and can be a dominant understory plant in early successional forests. This plant grows best when it has full sun and rich soil, but is shade tolerant and can survive in poor soils.

The Japanese Honeysuckle is also known by the name “Hall’s Honeysuckle” and in Shakespeare's time, the plant was called “woodbine.”  The etymology of the word honeysuckle starts from the Middle English honysoukel, alteration of honisouke, from Old English hunīsūce : hunig, honey + sūcan, to suck. The genus name Lonicera, includes many climbing, erect or prostrate shrubs, of the natural order Caprifoliaceae, named after the 16th-century German botanist Adam Lonicer (1528-1586, town physician in Frankfurt-am-Main and noted author of herbal texts). 

Japanese Honeysuckle’s long standing in Japanese culture and literature leads to its various names and anglicized derivatives including: Chin Yin Hua, Chin Yin T'Eng, Jen Tung, Jen Tung Chiu, Jen Tung Kao, Sui-Kazura, Yin Hua, White honeysuckle, Chinese honeysuckle, and Halliana.  In its native Japan, this species is a valuable medicinal plant, used for the treatment of dozens of ailments from dysentery to skin diseases to rheumatoid arthritis to the mumps.  It has recently been studied for its capacity as an inhibitor of human immunodeficiency virus-1 reverse transcriptase activity (HIV-1 RT) relative to acquired immunodeficiency syndrome (AIDS) treatments.  The web site www.druidry.org/obod/trees/honeysuckle.html is an exhaustive and fun source of “all things honeysuckle.”

The species was introduced into the United States in 1806 on Long Island, NY. It now occurs throughout the eastern half of the United States, an area encompassing 26 states.  Japanese honeysuckle’s range is limited to the north by severe winter temperatures and to the west by insufficient precipitation and prolonged droughts. In North America, Japanese honeysuckle has few natural enemies which allows it to spread widely and out-compete native plant species. Its evergreen to semi-evergreen nature gives it an added advantage over native species in many areas. Shrubs and young trees can be killed by girdling when vines twist tightly around stems and trunks, cutting off the flow of water and nutrients through the plant.  Dense growths of honeysuckle covering vegetation can gradually kill plants by blocking sunlight from  reaching their leaves. Vigorous root competition also helps Japanese honeysuckle spread and displace neighboring native vegetation. 

Japanese honeysuckle is very hard to remove and usually should be eliminated by hand-pulling when possible.  Although it has been known to be an aggressive invader for many years, this species is still sold by some American nurseries, often as the cultivar “Hall's Prolific.”  It is an effective groundcover, and does have pleasant, strong-smelling flowers, but the damage it does far outweighs any positive qualities.  The only invasive exotics that compete with this plant for total damage done in the eastern United States are Kudzu and Multiflora rose.  Virginia creeper (Parthenocissus quinquefolia) and trumpet creeper (also known as trumpet honeysuckle, Lonicera sempervirens) are recommended as native replacement plants. Another beautiful native plant that makes a nice substitute is Virgin’s bower (Clematis virginiana), but it is important not to accidentally plant sweet autumn clematis (Clematis terniflora or Clematis paniculata), which is another invasive.
Being semi-evergreen, Japanese honeysuckle is easier to detect during the fall when most native species have dropped their leaves.  Control methods for Japanese honeysuckle in areas of heavy and light infestations include mowing, grazing, prescribed burning, and the application of herbicides.  Mowing and grazing reduces the spread of vegetative stems but does not completely remove the vegetation; instead, vigorous re-sprouting sometimes increases stem density.  Small populations may be controlled by careful hand pulling, grubbing with a hoe or shovel, and removing trailing vines.  Some invasive plant web sites recommend a solution of Glyphosate herbicide (1.5-2% solution, applied during the fall before a hard freeze) to control Japanese honeysuckle. Care must be taken not to harm native species as glyphosate herbicide is non-selective and great care should be taken when handling any pesticide, with most applications best handled by a licensed and trained professional.

Other locally worrisome exotic invasives are autumn olive, oriental bittersweet, multiflora rose, Japanese black pine, Japanese knotweed, black swallowwort, giant reed, and spotted knapweed, and purple loosestrife.  Nantucket is very lucky to have a cadre of plant ecology experts who have formed a subcommittee to advise the Nantucket Biodiversity Initiative. Information for homeowners can be found on the Nantucket Invasive Plant Species Committee brochure “Weeds Gone Wild” (produced by the generous assistance of the Nantucket Garden Club), which is available online at www.nantucketbiodiversityinitiative.org click on the Invasive Plant Species Committee link and portions excerpted below:

“Almost all invasive plant introductions are accidental.  Non-native invasives are commonly introduced to gardens as landscape plants, or as hitchhikers in soil, compost and seed packets.  Be a responsible gardener, look for native landscape plants and know the contents of your imported soil and seeds.

The Nantucket Invasive Plant Species Committee (IPSC), a standing committee of the Nantucket Biodiversity Initiative, is an on-island collaborative of people and organizations interested in and actively pursuing non-native invasive plant species identification, management, research, education and eradication. The Mass. Department of Agricultural Resources has begun implementing a ban on the sale and importation of over 140 species known to be invasive in Massachusetts. This is a very important step in preventing the establishment of invasive plants. To review the complete list visit: www.mass.gov/agr/farmproducts/Prohibited_Plant_Index2.htm

Upcoming Invasive Plant Species Committee related public events (free!) include: Nantucket Family Adventure Plant Walk at Lily Pond: 5 pm, Thursday May 27th; Lily Pond Invasives and Natives nature walk: 5 pm, Thursday July 22nd; Smooth Hummocks Invasives Safari (How exotic!): 9 am, Saturday, August 21st: NBI Week ‘Sconset Invasives Walk: 9 am, Saturday September 18th. More information on these walks is available by calling the Nantucket Conservation Foundation at 508-228-2884 and speaking to the ISPC Chair, Kelly Omand, or by checking www.nantucketbiodiversityinitiative.org.
There are many excellent sources of information on locally important exotic non-native plant species such as the Invasive Plant Atlas of New England (IPANE) found at http://nbii-nin.ciesin.columbia.edu/ipane/ or at the links provided in the IPSC brochure. Next time you relive your childhood by grabbing a honeysuckle flower to sip at the nectar, remember, even the loveliest of plants can be an invader!

 

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