Lythrum stands can deleteriously impact wildlife habitat used by birds and furbearers. L. salicaria forms dense homogeneous stands that restrict native wetland plant species, including some endangered plants. L. salicaria can overrun wetlands and almost entirely eliminate open water habitat if left untreated. The recreational and aesthetic value of wetlands and waterways is diminished as dense stands of L. salicaria choke waterways and decrease biodiversity. A review of literature by Lavoie (2010) found that out of fourteen animal species or groups studied only six were negatively affected, while others were either not affected or positively affected by purple loosestrife. The strongest negative effects were on tadpoles and the marsh wren (Cistothorus palustris). The American toad (Bufo americanus is also negatively affected by compounds leached from L. salicaria. There have been no studies published on the impacts on fish, mammals or waterfowl (Lavoie, 2010). \r\n

In North American freshwater wetlands, L. salicaria alters decomposition rates and nutrient cycling, water chemistry, leads to reductions in wetland plant diversity, reduces pollination and seed output of the native Lythrum alatum, and reduces habitat suitability for specialized wetland bird species such as black terns, least bitterns, pied-billed grebes, and marsh wrens (Blossey et al., 2001; Fickbohm & Zhu, 2006). L. salicaria effects on wetlands, incurring from lost forage and control costs have been estimated to cost US $28 million per year (Barbier & Knowler, 2006). However, according to Lavoie (2010) “their analysis was apparently based on a previous estimation of the damages calculated by Thompson et al. (1987), damages that were only conjecture.”

Physical: Small infestations (< 100 plants) of L. salicaria can be controlled but cutting and pulling. Cutting should be done just before the plants begin flowering to avoid spreading seed. Pulling should be done by carefully removing all root fragments and disposing of all uprooted plants. Plant materials should be dried and burnt where possible. These fragments and uprooted plants could grow into new plants, possibly making the problem worse. Mowing and burning is ineffective and sometimes makes the problem worse.

Chemical: Herbicides are most commonly used for quick, effective control of L. salicaria. Spot treating with a glyphosate type herbicide (e.g., Rodeo for wetlands, Roundup for uplands) is effective on older plants. These herbicides may be most effective when applied, as plants are preparing for dormancy, however, mid-summer and late season treatments may be needed to reduce the amount of seed produced. In Canada, only Roundup is registered for the control of Lythrum in terrestrial areas only. Multiple chemical treatments are usually required as new seedlings annually emerge from the seed bank. Chemical treatments may not be desired in sensitive wetland habitats.

Biological control: Conventional methods such as physical, mechanical or chemical, have continuously failed to curb the spread of Lythrum salicaria or to provide satisfactory control. State and federal agencies as well as private citizens and schools now participate in rearing, release and monitoring of Galerucella beetle species which have been released in 33 states and >1500 wetlands nationwide. Large populations of G. calmariensis have developed in many of the monitored release sites and have caused up to 100% defoliation of L. salicaria. Stem height was reduced 73–85%, percent plant cover was reduced 61–95%, and richness of nontarget plant species increased significantly at four out of five sites. By 2001, L. salicaria stem height and percent cover were reduced 38–81% and 32–74%, respectively, and nontarget plant species richness increased significantly at all five sites. Of the 19 additional sites monitored for 3–5 years post release, 50% (4/8) of the 1997 releases have developed into large G. calmariensis populations and produced severe damage to L. salicari (Blossey et al, 2001; Landis et al, 2003).

A long-term assessment of biological control impacts after 10 years in central New York State concluded that Galerucella species had significant impacts on plants at the individual level, i.e. shorter plants and reduced flowering rates. However there was no change at the population level: there was no change in overall plant density or in size of stands. Surveys of beetle movement from release site showed only limited spread of beetles to new areas (Grevstad, 2006).

Integrated management: Results from a study conducted in Manitoba, Canada indicated that an integrated strategy using herbicides (glyphosate and triclopyr amine), combined with biological control G calmariensis outperformed herbicide alone treatments and Galerucella calmariensis alone (Henne et al, 2005).