Cabomba caroliniana (Fanwort) in The Netherlands

3rd International Symposium on Weeds and Invasive

Johan van Valkenburg, Rudi Roijackers & Rosalie Léonard The species involved

• A common component of your selection

2 | October 2011 Cabomba caroliniana or ?

• In trade Cabomba aquatica is often misapplied to C. caroliniana plants

C. aquatica C. caroliniana

Flowers Yellow White

Submerse 3-dimensional Mostly 2- leaves dimensional

Emerse Round Elliptic leaves

3 Cabomba caroliniana | October 2011 Cabomba caroliniana distribution

2010

Published sources

4 Cabomba caroliniana | October 2011 A brief history for The Netherlands

• First record 1989 Maasbracht (Meuse River) NOT invasive • Since 2005 at Loosdrecht INVASIVE • Spring 2006 first attempt at eradication • Summer 2007 Oranje channel near Orvelte expanding • Summer 2008 suburban area at Hoogeveen & fish pond Groningen • Summer 2010 suburban area Hardinxveld, Ridderkerk, Barendrecht • Summer 2011 suburban area Heerenveen

5 Cabomba caroliniana | October 2011 What to do ?

• Identification tools & training of field staff • Research on habitat requirements • Research on genetic diversity • Research on management options

6 Cabomba caroliniana | October 2011 Identification tools

• Field guide • Info sheet

7 Cabomba caroliniana | October 2011 Habitat requirements Survey March, July, October 2008 Visit at the 3-4 known localities

Results: • Wide tolerance for nutrient levels • Large range in conductivity level • Floating plants limit growth • Competition with Myriophyllum heterophyllum

Conclusions: • Site conditions do not explain difference in invasive behaviour • Can grow in any eutrophic stagnant to slow flowing water with a sediment poor to very rich in organic matter

8 Cabomba caroliniana | October 2011 Genetic diversity • In collaboration with Plant Research International and CSIRO • Sampling of all known localities in NL • Additional samples invasive populations in France, Germany and Australia • Samples from import shipments SE Asia

9 Cabomba caroliniana | October 2011 Management options EUPHRESCO DeCLAIM project

Funding: UK Defra and NL LNV

Partners: • Plant Protection Service NL • Wageningen University & Research • CEH - Wallingford

Target species: • Cabomba caroliniana • Hydrocotyle ranunculoides • Ludwigia grandiflora • Myriophyllum aquaticum

10 Cabomba caroliniana | October 2011 EUPHRESCO Cabomba trials at Loosdrecht

11 Cabomba caroliniana | October 2011 Cabomba management

Field testing 4 methods at Loosdrecht • Standard practice • Washing out • Covering surface • Covering bottom

CHARISMA model to assist DSS • Detailed measurements in time • Predicting competition • Timing of management actions

12 Cabomba caroliniana | October 2011 Trial lay out • Standard 3 X 100 m & enclosures • Washing 3 X 100 m & enclosures • Surface coverage 2 X 100 m • Bottom coverage 10 X 10 m

• Scheduled for early April performed by May 20th (standard) and July 14th (washing)

13 Cabomba caroliniana | October 2011 Location map trials Loosdrecht

14 Cabomba caroliniana | October 2011 Standard practice J M u a n y e

D e c J e u m l b e y r

15 Cabomba caroliniana | October 2011 Result of standard practice • After 1 year dominance Cabomba just like it was before management (June 75-90%; August 80-90%)

Enclosures (1 x 1 m) • On average 9(3-30) stems of Cabomba present • Elodea nuttallii July 15-40 % coverage August 40-100% coverage

Dominance Cabomba resulting from regrowth, inflow of fragments and competitive advantage grazing

16 Cabomba caroliniana | October 2011 Washing out with hydro-venturi system

17 Cabomba caroliniana | October 2011 Result of washing out • After 1 year dominance Cabomba still reduced (June 5-10%; August 25-50%)

Enclosures (1 x 1 m) • Just 1 cage with a few stems of Cabomba entering from the side • Elodea nuttallii coverage August 25-100% coverage

Recovery of Cabomba resulting most likely from inflow of fragments and competitive advantage grazing

18 Cabomba caroliniana | October 2011 June 2010 enclosure with Cabomba

19 Cabomba caroliniana | October 2011 June 2010 outside enclosure

20 Cabomba caroliniana | October 2011 August 2010 Elodea nuttallii (other enclosure)

21 Cabomba caroliniana | October 2011 Coverage with black woven geotextile Coverage of sediment Coverage of surface • Recolonisation of Cabomba on new • No plant growth in July sedimentation on top of fabric • No plant growth after 1 month partial removal of fabric Does not work in a situation with siltation and large quantities of August 2011 propagules in the vicinity • 1st ‘removed’ stretch 2 Cabomba stems & 5 plants M. verticillatum 50% cover • 2nd ‘removed’ stretch No Cabomba & 7 plants M. verticillatum 50% cover M. verticillatum and U. vulgaris on top of fabric

Non discriminant effective method

22 Cabomba caroliniana | October 2011 Surface coverage experiment August 2010

23 Cabomba caroliniana | October 2011 Surface coverage experiment August 2011

24 Cabomba caroliniana | October 2011 CHARISMA model • Determine growth parameters • Life-cycle knowledge • Vulnerable stages in development • Energy allocation • First findings

25 Cabomba caroliniana | October 2011 Charisma ‘conclusions’

Predictions on growth and competition do not match field observations

• Growth potential underestimated • Critical role of root system • Photosynthesis parameters to be evaluated

April 2011

26 Cabomba caroliniana | October 2011 Conclusions

• Standard practice will not eradicate Fanwort in eutrophic waters • Yearly cleaning in autumn has resulted in 100% dominance of Fanwort in ditches • Washing out is a quite effective method to remove macrophytes rooting in the sediment (e.g. Cabomba & M. heterophyllum) • There is no ‘best management ‘ option • Solution has to be adapted to the actual site conditions: Dimensions of the waterway Conditions of the bank Function of the waterway

27 Cabomba caroliniana | October 2011