Parrot’s feather: Use of herbicides - diquat

Overall effectiveness category Likely to be beneficial
Number of studies: 3
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How is the evidence assessed?

Effectiveness

60%
Certainty

40%
Harms

0%

Calculating overall effectiveness category

Background information and definitions

Chemical herbicides have been used for the localized control of parrot’s feather (e.g. Morreira et al. 1999). Herbicides licensed for use around the world use a wide diversity of different active ingredients (e.g. 2,4-D, imazapyr, carfentrazone-ethyl, diquat). However, herbicide control of aquatic vegetation is prohibited in numerous countries (e.g. no herbicides are approved for submerged species in Europe) (De Winton et al. 2013; Hussner et al. 2017). Therefore it is important to consider local regulations before using herbicide control. Legislative restrictions may be lifted for herbicides under particular conditions (Hussner et al. 2017). Impacts on non-target species should be considered prior to herbicide use.

Emerged and submerged vegetation may require different herbicides, and adjuvants may increase the efficacy of the treatment. More than one application of the herbicide is often required. The use of fungal-based herbicides to control parrot’s feather is discussed under the intervention ‘Biological control using fungal-based herbicides’.

De Winton M., Jones H., Edwards T., Özkundakci D., Wells R., McBride C., Rowe D., Hamilton D., Clayton J., Champion P. & Hofstra D. (2013) Review of Best Management Practices for Aquatic Vegetation Control in Stormwater Ponds, Wetlands, and Lakes. Auckland Council technical report, TR2013/026.

Hussner A., Stiers I., Verhofstad M.J.J.M., Bakker E.S., Grutters B.M.C., Haury J., van Valkenburg J.L.C.H., Brundu G., Newman J., Clayton J.S. & Anderson L.W.J. (2017) Management and control methods of invasive alien freshwater aquatic plants: A review. Aquatic Botany, 136, 112-137.

Moreira I., Ferreira T., Monteiro A., Catarino L. & Vasconcelos T. (1999) Aquatic weeds and their management in Portugal: insights and the international context. Hydrobiologia 415, 229–234.

Study locations

Key messages

Two laboratory studies (including a replicated, randomized, controlled study) in the USA found that diquat reduced the growth of parrot’s feather.
One replicated, randomized, controlled field study in Portugal found that growth was not reduced after the application of diquat.

About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

Supporting evidence from individual studies

A replicated, randomized, controlled, field study conducted in summer 1986 in Portugal (Moreira et al. 1999) found that the application of the herbicide diquat did not reduce the biomass of parrot’s feather Myriophyllum aquaticum. For three out of three comparisons, the fresh weight of parrot’s feather plants treated with diquat did not differ from untreated plants (15–25 vs 22–26 kg/m²). Additionally, the biomass of parrot’s feather plants treated with diquat (15–25 kg/m²) was higher than that of plants treated with 2,4-D amine (2–9 kg/m²) for three out of three comparisons, was higher than that of plants treated with gluphosinate-ammonium (9–22 kg/m²) for five out of nine comparisons, and was higher than of plants treated with glyphosate (9–14 kg/m²) for two out of three comparisons. Parrot’s feather biomass was assessed in 20 x 7 m plots and each herbicide rate was tested in four replicates. Herbicide rates were 2 kg/ha for diquat, 6.5 kg/ha for 2,4-D amine, 1–2.4 kg/ha for gluphosinate-ammonium and 3.6 kg/ha for glyphosate.
Study and other actions tested
Referenced paper
Moreira I., Monteira A. & Ferreira T. (1999) Biology and control of parrotfeather (Myriophyllum aquaticum) in Portugal. Ecology Environment and Conservation, 5, 171-179.
A small, replicated, randomized, controlled, laboratory study conducted in 2006 in the USA (Wersal et al. 2010), found that the application of the herbicide diquat reduced growth of parrot’s feather Myriophyllum aquaticum. After four weeks, the dry weight of parrot’s feather plants treated with diquat was lower than untreated plants (1–3 vs 6 g/pot). Daytime and night-time application of the herbicide resulted in similar results. Parrot’s feather shoots were propagated in 3.78 l pots and placed inside 246 l containers filled with water. Each herbicide rate (0.19 and 0.37 mg/l) was applied to three plants.
Study and other actions tested
Referenced paper
Wersal R.M., Madsen J., Massey J., Robles W. & Cheshier J. (2010) Comparison of daytime and night-time applications of diquat and carfentrazone-ethyl for control of parrotfeather and Eurasian watermilfoil. Journal of Aquatic Management, 48, 56-58.
A small, replicated, controlled, laboratory study conducted between 2007 and 2008 in the USA (Wersal & Madsen 2010), found that the application of the herbicide diquat reduced growth in parrot’s feather Myriophyllum aquaticum. After six weeks, the dry weight of parrot’s feather plants treated with diquat was reduced compared to untreated plants (2–6 vs 18 g/pot). Six weeks after application, diquat had controlled parrot’s feather plants by 50–70% (visual assessment, with 0% corresponding to no control and 100% to complete control). Parrot’s feather shoots were propagated in 3.78 l pots and placed inside 246 l containers filled with water. Each herbicide rate (subsurface: 0.19 and 0.37 mg/l; foliar: 4.5 kg/ha) was applied to four 246 l containers, each holding four plants. Number of plants used as control is not presented and control in the context of the visual assessments was not clearly defined.
Study and other actions tested
Referenced paper
Wersal R.M. & Madsen J.D. (2010) Comparison of subsurface and foliar herbicide applications for control of parrotfeather (Myriophyllum aquaticum). Invasive Plant Science and Management, 3, 262-267.

Please cite as:

Aldridge, D., Ockendon, N., Rocha, R., Smith, R.K. & Sutherland, W.J. (2020) Some Aspects of Control of Freshwater Invasive Species. Pages 555-87 in: W.J. Sutherland, L.V. Dicks, S.O. Petrovan & R.K. Smith (eds) What Works in Conservation 2020. Open Book Publishers, Cambridge, UK.

Where has this evidence come from?

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This Action forms part of the Action Synopsis:

Control of Freshwater Invasive Species

Related Actions

Actions	Effectiveness	Studies	Category
Parrot’s feather: Biological control using plant pathogens Action Link	Unknown effectiveness (limited evidence)	1	Synopsis Link
Parrot’s feather: Multiple integrated measures Action Link	No evidence found (no assessment)	0	Synopsis Link
Parrot’s feather: Use of herbicides - diquat Action Link	Likely to be beneficial	3	Synopsis Link