Buckthorn: Identification, Impacts, and Control

Buckthorn:Identification, Impacts, and ControlSusan BurksInvasive Species Program CoordinatorMNDNR, ForestrySpecial Thanks to Laura Van Riper, MNDNR EWR

Common and Glossy Buckthorn• 2 species in MN• Native to Europe• Invasive in MN• Widely planted forhedgerows, starting inmid-1800s• Both species (and theircultivars) are nowrestricted noxious weedsin MN (can’t sell ortransport)Common buckthorn(Rhamnus cathartica)Glossy buckthorn(Frangula alnus)(Heneghan et al. 2002; Schmidt and Whelan 1999)

Economic Impacts• Forms dense thickets– Shades out hardwoodregeneration– Excludes herbaceousplants– Hinders trail & woods use• Overwintering host for soybeanaphids – a pest of soybeancrops• Host for a crown rust fungusthat impacts oat crops

Ecosystem Impacts• Changes soil nitrogen, increase soil pH• Reduces leaf litter layer• Possible facilitation of earthworm invasions– All earthworms are non-native to MN• Possible effects on native plants through allelopathy orcompetition• Shades out other plants– contributes to erosion• Degrades wildlife habitat

How do I recognize buckthorn?There are native look-alikesCommon buckthornRed Twig DogwoodGrey Dogwood & Buckthorn

Common BuckthornCommon Buckthorn• Leaves alternate or subopposite,bluntly toothed• Twigs tipped with sharp thorn• Buds pressed to stem• Leaves with 3-5 curvedparallel veins• Berries black with severalseedsCherries & Plums• Leaves alternate• Buds often clustered neartips• Berries red or black withsingle hard seed• Some species have thornsBuckthornCherry

Glossy BuckthornSmooth leaf edge, Alternate leaves,7-9 pair of leaf veins

Time of year• Fall: Both buckthorn species hold theirleaves later than native trees• Spring (May): flowers are small, yellowgreen,not very showyCommon buckthorn flowerGlossy buckthorn flower

Make sure its buckthorn!!There are native look-alikesGrey DogwoodCommon BuckthornBlack CherryRed Twig Dogwood

Chemical Control• The chemical and the application method used depends on the targetspecies and site conditions.• Do you homework - know which product works best in your situationand how to use it.• Always follow label directions – it’s the law• Always wear safety equipment prescribed on the label• Plan ahead for accidental spills• Track conditions at time ofapplication so can assesstreatment success (or failure)• Store product in safe (child-proof)location

Herbicides• For cut stump or frill treatments– Triclopyr (Ortho Brush-B-Gon, Garlon 3A or 4)– Glyphosate (Roundup, Rodeo, etc.)• For basal stem– Triclopyr ester, oil dilutent (Garlon 4)• Foliar applications– Glyphosate (Roundup, Rodeo, etc.)– Triclopyr amine (Garlon 3A)• Glyphosate will kill all actively growing/green tissue onwhich it is sprayed (cambium or leaves)• Triclopyr will kill broadleaf plants and will not harmgrasses when applied properly.

Roundup Brush KillerSome BrushKillers containTriclopyr (amine)Garlon 3ACrossbow-Triclopyrand 2-4, DGarlon 4 & Remedy-Triclopyr (ester)Diluent Blue-solvent

Timelines• Mark trees in fall after natives drop their leaves• Cut-stump, frill & basal bark treatments can beapplied anytime temperature >32° and snow coverisn’t too deep• Foliar applications are best in early spring beforenative plants bud out or in fall after native plantshave gone dormant• Do not treat during April, May or June

Tools• Brush cutters• Saws• Pruners• Sprayers• Dob and wickapplicators• Weed wrenches

Cut Stump Treatment• Cut plant near ground &treat cut surface with alabeled herbicide• Use dye to see whereyou’ve treated• Treat outer growth ring

Cut Stump Continued• Cut stump treatment can create large volumes of brush.• Pile on site, chip, burn, or haul brush to a brush dump.• Consider use as biofuel• Be sure to get permitMDA before transportingmaterialfrom

Hack (Frill) & Squirt Applications• Cuts are made aroundthe stem at a downwardangle through thecambium and into thesapwood.• Herbicide is applied tothe cut surface.

Low Volume Basal Bark Spray• Wet basal part of treefrom 18 inches to groundlevel• Do not wet to point ofrunoff• Tree can be left standing• Need an oil-basedherbicide

Foliar Application• Works well on seedlings and smallplants.• Can be used as a spot spray orbroadcast applications (monoculture)• Do not spray nativeplants. Herbicides willkill native herbaceousnatives.• Buckthorn seeds remainviable for 5 years – needto follow-up

Mechanical Control• Hand pulling effective on shallowrooted seedlings• Weed wrench works well onsmall to medium saplings• Pull major roots & place wherewon’t reroot• Soil disturbance may harmnative species or createseed bed for invasive species• Tamp soil & native plants backinto place

Follow-up Mgmt• Seedlings & sprouts growquickly & can crowd outdesirable species• Follow-up control a mustOak seedlingBuckthorn seedlings• Larger trees were killed, butnot under-story seedlingswhich again took over the site

Biological Control• Several potential species for common buckthorn• Testing host-specificity• Evaluating high levels of seed and seedling mortality inEurope to determine cause• Challenges– Obtaining and rearing hosts and insects under lab conditions– Limited choice of insects that are both host specific ANDcapable of causing high damage levels on buckthorn

Restoration• Past glossy buckthorn sites(typically higher site index) mayregenerate naturally if buckthorncontrolled• Common buckthorn sites willlikely need to be seeded aftercontrol, or underplanted prior toharvestSeeded w/ red fescueFollow-up spot treatments canalso help release desirable plants

Any Questions?• Susan Burks• Susan.burks@state.mn.us• 651-259-5251