Water Pineapple, Saw Tooth, Water Aloe

Nonindigenous Occurrences: The only wild populations of S. aloides in North America occur in five locations within the Trent River and Black River in Ontario, Canada: (1) In the Trent River approximately between the town of Trent River and the south end of Crowe Bay, but scattered plants have been found as far as the east end of Percy Reach, County of Northumberland; (2) in a watering pond for cattle in Trent Hills, County of Northumberland; (3) in a pond at Blackstock in the Township of Scugog, Regional municipality of Durham; (4) in an artificial pond near Bayfield, Huron County; and (5) in the Black River, near Sutton, Regional Municipality of York  (Snyder et al. 2016).

This species has vegetative reproduction. Vegetative propagules are formed as axillary buds. When the bottom leaves of the rosette decay, these buds are released. On average 4.7 (±0.28 SE) buds are formed per mature rosette (n = 83) (Sarneel 2013). Buds have high capacity to disperse over long distances via water (84% of propagules re-sprouted, and 92% were still floating after 187 days) (Sarneel 2013).

Potential pathway(s) of introduction: Dispersal, Hitchhiking/Fouling, and Stocking/Planting/Escape from Recreational Culture

Stratiotes aloides occurs in the Trent River, Ontario, with a population of over 22,000 plants (Campbell 2009). Aquatic macrophytes are commonly found on trailered boats, and the Trent-Severn waterway is a popular destination for boaters (http://thewaterway.ca/#sthash.L82cPc3u.dpbs). The infestation in the Trent River began as an accidental escape (Ontario Ministry of Natural Resources 2009, 2014).

Stratiotes aloides has a moderate probability of establishment if introduced to the Great Lakes (Confidence level: High).

Stratiotes aloides has been described by government agencies as likely to crowd out native vegetation (Ontario Ministry of Natural Resources 2009, 2014), though no primary literature exists to support this in introduced habitats. It does form "dense, almost monospecific stands" in native habitat (Strzalek and Koperski 2009). Most species in the genus produce vegetative fragments and reproduce easily. Stratiotes aloides can overwinter in the Great Lakes; the population in Finland overwinters fine in temperatures similar to those experienced in the Great Lakes.

Summary of species impacts derived from literature review. Click on an icon to find out more...

Environmental	Socioeconomic	Beneficial

Stratiotes aloides forms "dense, almost monospecific stands" in native habitat (Strzalek and Koperski 2009) and has the potential to crowd out native vegetation (Ontario Ministry of Natural Resources 2009).

Stratiotes aloides has the potential to alter surrounding water chemistry, which may harm phytoplankton and other aquatic organisms (Ontario Ministry of Natural Resources 2009).  The exact mechanism has not been elucidated, but the likely cause is allelopathy (Mulderij et al. 2006).

Stratiotes aloides has the potential for moderate socio-economic impact if introduced to the Great Lakes.

Stratiotes aloides’s sharp leaves can cut skin (CommunityPress.ca 2009). Dense floating mats of Water Soldier can hinder recreational activities, such as boating, angling, and swimming. This would likely result from a massive infestation, but has not been quantified.

There is little or no evidence to support that Stratiotes aloides has the potential for significant beneficial impacts if introduced to the Great Lakes.

It has not been indicated that Stratiotes aloides can be used for the control of other organisms or improving water quality. There is no evidence to suggest that this species is commercially, recreationally, or medically valuable. It does not have significant positive ecological impacts.

Regulations

It is illegal to import, possess, deposit, release, transport, breed/grow, buy, sell, lease or trade S. aloides in Ontario (Invasive Species Act 2015). Michigan prohibits the introduction, importation, movement, sale, or distribution of S. aloides (NREPA Part 413 as amended, MCL 324.41302(3)(a)). Illinois lists S. aloides as an injurious species as defined by 50 CFR 16.11-15. Therefore, S. aloides cannot be possessed, propagated, bought, sold, bartered or offered to be bought, sold, bartered, transported, traded, transferred or loaned to any other person or institution unless a permit is first obtained from the Department of Natural Resources. Illinois also prohibits the release of any injurious species, including S. aloides (17 ILL. ADM. CODE, Chapter 1, Sec. 805). Wisconsin prohibits the transport, possession, or introduction of S. aloides (Wisconsin Chapter NR 40). It is also prohibited for a person to possess, import, purchase, sell, propagate, transport, or introduce S. aloides in Minnesota (Minnesota Rule 6216.0250). There are no regulations on S. aloides in New York, Pennsylvania, Ohio, Michigan, or Indiana.

Note: Check federal, state, and local regulations for the most up-to-date information.

Control

Biological

Herbivorous birds and fish may be able to limit the establishment and growth of S. aloides in the Great Lakes basin. Veen et al. (2013) found that grazing by a variety of vertebrate aquatic herbivores reduced the biomass growth of S. aloides by 60% and resulted in decreased survival over 16 weeks. S. aloides is also vulnerable to fungi such as Fusarium roseum (Cook and Urmi-Konig 1983), but use of any pathogenic control should be cautiously employed in order to minimize non-target effects.

Physical

Despite being less efficient, removal by hand in the Trent River, Ontario was found to be initially as effective as chemical treatments. However, difficulty in detecting S. aloides in dense macrophyte communities and turbid water reduce the efficacy of hand removal (Anonymous 2014 in Snyder et al. 2016). Shade-cloth enclosures designed to prevent sunlight were utilized on three populations of S. aloides in Ontario. After two months, all water soldiers plants covered by the enclosures were deceased (Ontario’s Invading Species Awareness Program 2016). Other physical control methods, such as mechanical harvesting, have not been conclusively evaluated (Snyder et al. 2016).

Chemical

Several studies investigating the efficacy of diquat revealed that at least 16 hours of 370 ug L-1 was required to achieve a complete collapse of plants without any regeneration over the following six weeks. However, the effectiveness of diquat is limited in deep, fast-flowing, or turbid water (Snyder et al. 2016). In order to minimize non-target impacts, herbicide treatments should be conducted in Fall (September and October) when water soldiers remain actively growing and other native aquatic plants have gone dormant (MNRF 2016).

Intensified agricultural practices and anthropomorphic stressors over the last half century have contributed to the decline of S. aloides in parts of Europe (Smolders et al. 2003; Abeli et al. 2014). Smolders et al. (2003) determined that the decline of S. aloides is mainly due to increased sulphate reduction rates, which can lead to sulphide toxicity, iron deficiencies, and increased internal eutrophication due to mobilization of phosphate. Additionally, increased competition from free-floating plants and increased ammonium concentrations also have contributed to its decline. Sites in Italy where S. aloides had been extirpated were characterized by high inorganic nitrogen concentrations and low CO2 concentrations (Abeli et al. 2014). Therefore, eutrophication events that are seen in areas like Green Bay and the Western Basin of Lake Erie may affect S. aloides if it were to become established in these areas.

Note: Check state and local regulations for the most up-to-date information regarding permits for pesticide/herbicide/piscicide/insecticide use.