Regulations (pertaining to the Great Lakes region) Prohibited in Wisconsin under is. Admin. Code § NR 40. In New York, P. parvum is prohibited and cannot be knowingly possessed, sold, imported, purchased, introduced, or propagated under 6 NYCRR Part 575. Explicit regulations are not defined for P. parvum in Michigan, Minnesota, Illinois, Indiana, Ohio, Pennsylvania, or Ontario.
Note: Check federal, state/provincial, and local regulations for the most up-to-date information.
Control
Biological
Nonindigenous Arundo donax (giant reed) contains growth-suppressing and algicidal compounds that reduced the exponential growth rate of P. parvum (Patino et al. 2018). P. parvum blooms are suppressed by cyanobacteria presence (Roelke et al. 2010a, 2012) and the cyanotoxins microcystin and nodularin inhibit P. parvum growth (Pflugmacher 2002; Legrand et al. 2003; James et al. 2011)
Physical
Aquaculture facilities that experience P. parvum blooms have used flocculation with various mediums, including soil, sand, and clay mixtures to directly settle P. parvum cells (Sengco and Anderson 2004; Padilla et al. 2010), bind phosphate ions to reduce nutrient loads and P. parvum bloom potential (Chen and Pan 2012; Seger et al. 2015), and to remove algal toxins from the water (Prochazka et al. 2010; Seger et al. 2015). Most clays could efficiently remove >80% of P. parvum cells, however, only bentonite clays and a lanthanum based bentonite clay reduced toxin availability and ichthyotoxicity (Seger et al. 2015). A commerical oil absorbant sponge, typically used to remove petroleum hydrocarbons from stormwater, successfully removed 87-100% of P. parvum cells. However, algal toxins were released during filtration with the lanthanum based clay but were mediated by the addition of a charcoal filter (Armstead et al. 2017). Physical control via flocculation is successful in aquaculture but may have limited effects in natural environments depending on treatment and bloom specific conditions (Sengco et al. 2005).
Allelopathic chemicals produced by P. parvum were degraded in a few hours with light as low as 100 μE m2 s1 (Granéli and Salomon 2010) and two hours of exposure to UV light was shown to deteriorate toxins enough to prevent acute ichthyotoxicity (James et al. 2011). While effective, light treatment may be a useful control strategy in site-specific conditions but is costly on a large scale.
High flow events and intentional dilutions of bloom-containing waters can cause unfavorable bloom conditions for P. parvum by reducing salinity and ambient toxin concentrations, altering nutrient concentrations, and hydraulic displacement (Roelke et al. 2007, 2016; Errera et al. 2008; Hambright et al. 2010). Flooding infested waters with a hydraulic dilution reduced toxin production and increased zooplankton biomass by 225 times whose grazing reduced P. parvum’s reproduction and density by 52% (Schwierzke-Wade et al. 2011). Further, a large inflow event in Lake Granbury, Texas reduced P. parvum densities by 89% and completely negated any ichthyotoxicity (Roelke et al. 2010b). While hydraulic dilutions and flood events can effectively control harmful blooms after they’ve started, they are difficult to manipulate on a whole-lake scale.
Chemical
In aquaculture, ammonium sulfate and copper-based algaecides lysed P. parvum cells and potassium permanganate lowered toxicity (Barkoh et al. 2003, 2010, Rodgers et al. 2010; Umphres IV et. al 2012; Grover et al. 2013). However, these chemicals are broad-spectrum, and can harm or kill non-target organisms and can have unintended side-effects (e.g. ammonium additions may raise ammonia concentrations to harmful levels for fish) (Barkoh et al. 2003; Rodgers et al. 2010). A commercial peroxidizing aquatic herbicide suppressed P. parvum bloom formation but did not negatively impact Lepomis macrochirus (bluegill sunfish), making it a potentially safe and effective chemical control alternative (Umphres IV et al. 2012, 2013). Alternatively, P. parvum has demonstrated resistance to commercial peroxidzing agricultural herbicides and their use may give it a competitive advantage over other phytoplankton (Yates and Rogers 2011, Flood and Burkholder 2018). Glyphosate-based herbicides can also stimulate P. parvum growth in environmentally relevant concentrations, giving it a potential competitive advantage in water bodies surrounded by agriculture (Dabney and Patino 2018).
Nutrient additions (phosphorus and nitrogen) can also suppress P. parvum toxin production and growth and promote the dominance of native phytoplankton (Kurten et al. 2011). Both nitrogen (ammonia or nitrate) and phosphorus need to be added to achieve P. parvum suppression, as fertilization with only one has no effect and adding phosphorus alone can even increase P. parvum growth and toxicity (Kurten et al. 2010). However, excess nutrients can cause pH and dissolved oxygen problems and nitrogen additions using ammonia can lead to harmful concentrations and unhealthy pH levels (Barkoh et al. 2003; Kurten et al. 2007, 2011). Recommended fertilization rates for systems where high pH is a concern is 117 μg NO3-N ⁄l plus 16 μg PO4-P ⁄l applied three times weekly (Kurten et al. 2010).
Note: Check state/provincial and local regulations for the most up-to-date information regarding permits for control methods. Follow all label instructions.