6.1.1 Floating pennywort Hydrocotyle ranunculoides

Beneficial

Chemical control using herbicides

1A controlled, replicated field study in the UK found that the herbicide 2,4-D amine achieved almost 100% mortality of floating pennywort, compared with the herbicide glyphosate (applied without an adjuvant) which achieved negligible mortality. Assessment: beneficial (effectiveness 80%; certainty 70%).
http://www.conservationevidence.com/actions/1127

Likely to be beneficial

Flame treatment

2A controlled, replicated study in the Netherlands found that floating pennywort plants were killed by a three second flame treatment with a three second repeat treatment 11 days later. Assessment: likely to be beneficial (effectiveness 60%; certainty 50%).
http://www.conservationevidence.com/actions/1131

Physical removal

3Two studies, one in Western Australia and one in the UK, found physical removal did not completely eradicate floating pennywort. Assessment: likely to be beneficial (effectiveness 40%; certainty 40%).
http://www.conservationevidence.com/actions/1126

Unknown effectiveness (limited evidence)

Combination treatment using herbicides and physical removal

4A before-and-after study in Western Australia found that a combination of cutting followed by a glyphosate chemical treatment, removed floating pennywort. Assessment: unknown effectiveness (effectiveness 70%; certainty 35%).
http://www.conservationevidence.com/actions/1128

Unlikely to be beneficial

Biological control using co-evolved, host-specific herbivores

5A replicated laboratory and field study in South America found that the South American weevil fed on water pennywort but did not reduce the biomass. Assessment: unlikely to be beneficial (effectiveness 20%; certainty 50%).
http://www.conservationevidence.com/actions/1123

Use of hydrogen peroxide

6A controlled, replicated study in the Netherlands found that hydrogen peroxide sprayed on potted floating pennywort plants at 30% concentration resulted in curling and transparency of the leaves but did not kill the plants. Assessment: unlikely to be beneficial (effectiveness 10%; certainty 60%).
http://www.conservationevidence.com/actions/1129

No evidence found (no assessment)

7We have captured no evidence for the following interventions: • Biological control using fungal-based herbicides

• Biological control using native herbivores

• Environmental control (e.g. shading, reduced flow, reduction of rooting depth, or dredging)

• Excavation of banks

• Public education

• Use of liquid nitrogen

6.1.2 Water primrose Ludwigia spp

Likely to be beneficial

Biological control using co-evolved, host specific herbivores

8A controlled, replicated study in China, found a flea beetle caused heavy feeding destruction to the prostrate water primrose. A before-and-after study in the USA found that the introduction of flea beetles to a pond significantly reduced the abundance of large-flower primrose-willow. Assessment: likely to be beneficial (effectiveness 60%; certainty 50%).
http://www.conservationevidence.com/actions/1135

Chemical control using herbicides

9A controlled, replicated laboratory study in the USA found that the herbicide triclopyr TEA applied at concentrations of 0.25% killed 100% of young cultivated water primrose within two months. A before-and-after field study in the UK found that the herbicide glyphosate caused 97% mortality when mixed with a non-oil based sticking agent and 100% mortality when combined with TopFilm. A controlled, replicated, randomized study in Venezuela, found that use of the herbicide halosulfuron-methyl (Sempra) resulted in a significant reduction in water primrose coverage without apparent toxicity to rice plants. Assessment: likely to be beneficial (effectiveness 80%; certainty 60%).
http://www.conservationevidence.com/actions/1139

Combination treatment using herbicides and physical removal

10A study in the USA found that application of glyphosate and a surface active agent called Cygnet-Plus followed by removal by mechanical means killed 75% of a long-standing population of water primrose. A study in Australia found that a combination of herbicide application, physical removal, and other actions such as promotion of native plants and mulching reduced the cover of Peruvian primrose-willow by 85–90%. Assessment: likely to be beneficial (effectiveness 70%; certainty 55%).
http://www.conservationevidence.com/actions/1140

Unlikely to be beneficial

Physical removal

11A study in the USA found that hand pulling and raking water primrose failed to reduce its abundance at one site, whereas hand-pulling from the margins of a pond eradicated a smaller population of water primrose at a second site. Assessment: unlikely to be beneficial (effectiveness 30%; certainty 50%).
http://www.conservationevidence.com/actions/1138

No evidence found (no assessment)

12We have captured no evidence for the following interventions:

• Biological control using fungal-based herbicides

• Biological control using native herbivores

• Environmental control (e. g. shading, reduced flow, reduction of rooting depth, or dredging)

• Excavation of banks

• Public education

• Use of a tarpaulin

• Use of flame treatment

• Use of hydrogen peroxide

• Use of liquid nitrogen

• Use of mats placed on the bottom of the waterbody

6.1.3 Skunk cabbage Lysichiton americanus

Likely to be beneficial

Chemical control using herbicides

13Two studies in the UK found that application of the chemical 2,4-D amine appeared to be successful in eradicating skunk cabbage stands. One of these studies also found glyphosate eradicated skunk cabbage. However, a study in the UK found that glyphosate did not eradicate skunk cabbage, but resulted in only limited reduced growth of plants. Assessment: likely to be beneficial (effectiveness 60%; certainty 50%).
http://www.conservationevidence.com/actions/1102

Physical removal

14Two studies in Switzerland and the Netherlands, reported effective removal of recently established skunk cabbage plants using physical removal, one reporting removal of the entire stock within five years. A third study in Germany reported that after four years of a twice yearly full removal programme, a large number of plants still needed to be removed each year. Assessment: likely to be beneficial (effectiveness 65%; certainty 55%).
http://www.conservationevidence.com/actions/1101

No evidence found (no assessment)

15We have captured no evidence for the following interventions:

• Biological control using co-evolved, host-specific herbivores

• Biological control using fungal-based herbicides

• Biological control using native herbivores

• Combination treatment using herbicides and physical removal

• Environmental control (e.g. shading, or promotion of native plants)

• Public education

• Use of a tarpaulin

• Use of flame treatment

• Use of hydrogen peroxide

• Use of liquid nitrogen

6.1.4 New Zealand pigmyweed Crassula helmsii

Beneficial

Chemical control using herbicides

16Seven studies in the UK, including one replicated, controlled study, found that applying glyphosate reduced Crassula helmsii. Three out of four studies in the UK, including one controlled study, found that applying diquat or diquat alginate reduced or eradicated C. helmsii. One small trial found no effect of diquat on C. helmsii cover. One replicated, controlled study in the UK found dichlobenil reduced biomass of submerged C. helmsii but one small before-and-after study found no effect of dichlobenil on C. helmsii. A replicated, controlled study found that treatment with terbutryne partially reduced biomass of submerged C. helmsii and that asulam, 2,4-D amine and dalapon reduced emergent C. helmsii. Assessment: beneficial (effectiveness 78%; certainty 75%).
http://www.conservationevidence.com/actions/1279

Decontamination to prevent further spread

17One controlled, replicated container trial in the UK found that submerging Crassula helmsii fragments in hot water led to higher mortality than drying out plants or a control. Assessment: beneficial (effectiveness 80%; certainty 70%).
http://www.conservationevidence.com/actions/1308

Likely to be beneficial

Use lightproof barriers to control plants

18Five before-and-after studies in the UK found that covering with black sheeting or carpet eradicated or severely reduced cover of Crassula helmsii. Assessment: likely to be beneficial (effectiveness 65%; certainty 50%).
http://www.conservationevidence.com/actions/1294

Use salt water to kill plants

19Two replicated, controlled container trials and two before-and-after field trials in the UK found that seawater eradicated Crassula helmsii. Assessment: likely to be beneficial (effectiveness 80%; certainty 45%).
http://www.conservationevidence.com/actions/1288

Unknown effectiveness (limited evidence)

Use a combination of control methods

20One before-and-after study in the UK found that covering Crassula helmsii with carpet followed by treatment with glyphosate killed 80% of the plant. Assessment: unknown effectiveness (effectiveness 75%; certainty 30%).
http://www.conservationevidence.com/actions/1313

Unlikely to be beneficial

Use dyes to reduce light levels

21One replicated, controlled study in the UK found that applying aquatic dye, along with other treatments, did not reduce cover of Crassula helmsii. Assessment: unlikely to be beneficial (effectiveness 0%; certainty 53%).
http://www.conservationevidence.com/actions/1293

Use grazing to control plants

22One of two replicated, controlled studies in the UK found that excluding grazing reduce abundance and coverage of Crassula helmsii. The other study found that ungrazed areas had higher coverage of C. helmsii than grazed plots. Assessment: unlikely to be beneficial (effectiveness 23%; certainty 43%).
http://www.conservationevidence.com/actions/1301

Use hot foam to control plants

23One replicated, controlled study in the UK found that treatment with hot foam, along with other treatments, did not control Crassula helmsii. A before-and-after study in the UK found that treatment with hot foam partially destroyed C. helmsii. Assessment: unlikely to be beneficial (effectiveness 20%; certainty 50%).
http://www.conservationevidence.com/actions/1286

Use hydrogen peroxide to control plants

24One controlled tank trial in the UK found that hydrogen peroxide did not control Crassula helmsii. Assessment: unlikely to be beneficial (effectiveness 0%; certainty 50%).
http://www.conservationevidence.com/actions/1281

No evidence found (no assessment)

25We have captured no evidence for the following interventions:

• Alter environmental conditions to control plants (e.g. shading by succession, increasing turbidity, re-profiling or dredging)

• Biological control using fungal-based herbicides

• Biological control using herbivores

• Bury plants

• Dry out waterbodies

• Physical control using manual/mechanical control or dredging

• Plant other species to suppress growth

• Public education

• Surround with wire mesh

• Use flame throwers

• Use hot water

• Use of liquid nitrogen