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Injection of Herbicides into Rhizomes of Knotweeds and Other Invasive Species

John LampeGreen Shoots, LLC

Saint Paul, Minnesota

Upper Midwest Invasive Species ConferenceOctober 29-31

La Crosse, Wisconsin

Knotweed – Why Control?

• It is listed by the World Conservation Union as one of the world's 100 worst invasive species.

• This is not precise ranking but does show recognition of how problematic species is.

Outline of Talk

• Background on Knotweed

• Current Chemical Control Methods

• How Can Our Methods be Improved to:– Reduce quantity of herbicide used– Reduce off-target harm

Common Species of Knotweed

• Japanese knotweed (Polygonum cuspidatum)

• Giant knotweed (Polygonum sachalinense)

• Bohemian knotweed (Polygonum x bohemicum) – hybrid

Identification

Good source: Prather TS, Miller TW, Robins SS, Knotweed shrubs: identification, biology, and management, Pacific Northwest Extension Publication 2009

Knotweed Colony

Knotweed Leaves

Photo Credit: Steve Manning, Invasive Plant Control, Bugwood.com

• Dark green leaves• Un-toothed• alternate

Knotweed Stems - Young

Knotweed Stem - Dry

Photo Credit: James H. Miller, USDA Forest Service, Bugwood.com

• Hollow internodes• Septum separating• Up to 2 in. dia.

Knotweed Rhizome

Rhizome

Knotweed Spreads by

• Rhizome extension – up to 6 to 8 feet a year

• Distribution of plant parts– Rhizome pieces – as small as 0.7 g (Brock 1992)– Node pieces

• Seeds – not major source in WA. (Miller 2005)

Knotweed Badness

• Riparian areas especially vulnerable

• Out-compete other plants => monoculture– Loss of trees– Changes in soil fertility– Erosion along streambeds and stream banks

Knotweed Monoculture

Photo Credit: Justin Knabe, Minnesota DOT

Knotweed Rhizome Extension

Photo Credit: Popplewell Associates, York, UK

Knotweed Rhizome Extension

Knotweed Rhizome Extension

Non-Chemical Control

• Not practical except with small infestations

• Danger of vegetative spread

• See King County, Best Management Practices (2008)

Chemical Control Methods

• Foliar

• Stem injection

• Cut stem

Key Herbicides

• Glyphosate – aquatic label

• Triclopyr – aquatic label; only foliar

• Imazapyr – aquatic label; only foliar

Knotweed Rhizome Tough to Kill!

Key Problem: older parts of rhizome and dormantbuds are weak sinks. (Bashtanova et al. 2009.)

Knotweed Rhizome – Tough to Kill!

Foliar

• Advantages– Fastest application method– Decent control: 81%. (Miller 2005)

• Disadvantages– Off-target harm: Avg. injury: 68%. (Miller 2005)– Hard to treat tall plants

Stem Injection

Stem Injection

• Use hypodermic or special injector• Inject up to 5 ml into stem• Between 1st and 2nd node above ground

Stem Injection

• Advantages– Precision– No stem disposal– Efficacy; Avg control: 88% (Miller 2005)

• Disadvantages– Time-consuming– Id of treated stems– Non-target injury: 26% (Miller 2005)

Biggest Disadvantage of Stem Injection

• Requires 5 ml of herbicide per aerial shoot– Equivalent to frill application on 10 to 15 inch

woody stem. AquaMaster Label.• Aerial shoot density averages about 9

stems/m2. Brock 2007.• 45 ml of 54% a.i. glyphosate per square

meter.• May explain 26% non-target injury found by

Miller.

Cut Stem

• Cut stem 5 to 10 inches off ground• Immediately pour up to 3 ml into hollow of

stem

Pouring Herbicide into Cut Stem

Cut Stem

• Advantages– Low cost equipment– Control? (Miller did not test)

• Disadvantages– Time-consuming– Disposal of green aerial shoots– Amount of herbicide used

Stem Wipe

• Inconsistent Results (Miller 2005)

Follow-Up Applications

• Washington State Dept Agriculture:

– Data show “significant decrease in knotweed following six years of annual treatments.

– However, knotweed is still present at each monitoring site.” (Statewide Knotweed Control Program; 2010 Progress Report)

How Can Methods Be Improved?

• Reduce repeat applications

• Reduce quantity of herbicide used

• Reduce off-target harm

We Have Been Trying Several Methods

Rhizome Injection

Rhizome and Roots

Rhizome Injection

Needle reaches to below-ground Internode

Herbicide Used

• AquaMaster – glyphosate; 54% a.i.

• Dose at 2ml

• Well below AquaMaster label rate for hollow stem injections: 5 ml

Inserting Needle into Cut, Dead Stem

Injecting into Rhizome through Cut Stem

Inserting Needle into Bent Live Stem

Results?

Ongoing Rhizome Injections

• Winter and early spring injections did not produce results

• Late spring injections show promise

• Currently doing tests – late summer and Fall

Other New Methods Being Explored

Cut, Bend, and . . .

Treat with Foam Herbicide

Munch, Bend, and . . .

Treat with Foam

Tromp, Wait, and . .

Treat Regrowth with Foliar Applied

Low Volume Foam Herbicide

Bend and Immediately Treat . . .

Stems and . . .

Foliage

Potential Advantages of Foliar Methods

• Not treating tall plants – reduces off-target harm

• Treating with Foam Herbicide– Improves adhesion– Reduces drift

• Late season – should improve treatment success

Rhizome Injection Methods

• Less time consuming

• Less herbicide

• Injecting into rhizome – will this improve treatment success?

Bent Stem Wiping Methods

• Exposing vascular tissue

• Foam herbicide sticks to stem

• Uses a lot less herbicide

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Green Shoots

John Lampe – contact:• john@greenshootsonline.com • 651-245-4682 (cell)Website: www.greenshootsonline.com • Email or call for copy of

presentation