This species is Quarantined: Class B Noxious Weed  

Treatment Concerns: 

• A single purple loosestrife plant can produce over a million seeds, and those seeds have high germination rates and can remain viable in the seedbank for years. This impacts the overall effectiveness of any treatment.  
• Because of the high risk of spread by seeds, treatments are most effective before the plants go to seed.  
• This species is so widespread, and most populations are large or dense, making eradication unlikely. Preventing spread, containing existing infestations, and removing plants from new sites are the best strategies.  

General Guidance  

• Most methodologies alone will not suffice and should be part of an integrated pest management plan.  
• Which methods you choose also depend on the purpose of control: eradication (removal of all plants, plant parts, and seed bank), or containment (reducing seed production, reducing spread, reducing growth, removing individual plants near site of concern).  
• All action promotes disturbance - mechanical, chemical, and even just doing nothing. Our work is in figuring out how to minimize disturbance and maximize positive benefits. 
• The intent of mechanical or chemical treatment is to kill target plants. 
• Management options listed below are representative of research by institutions like The Nature Conservancy, Invasive Plant Councils, PennState Extension, and the US Forest Service. 
• Here are additional guidance documents on best management practices for purple loosestrife. 
• Ontario Invasive Plant Council Best Management Practices for Purple Loosestrife 
• PennState Extension Resource on Purple Loosestrife 
• Invasive Species Council of Metro Vancouver Factsheet on Purple Loosestrife 
• US Forest Service Fire Effects Information System Report on Purple Loosestrife  

Summary of Mechanical Treatment Options

• Mechanical treatment can sometimes cause greater disturbance than if the site was left alone or if another treatment option was utilized. 
• If pulling or digging, remember that soil disturbance can encourage growth from seed bank.

Summary of Chemical Treatment Options

• There are a limited number of pesticides found to effectively treat purple loosestrife. This is compounded by the fact that the location of most infestations necessitates an aquatic formulation. And the effective aquatic formulations for purple loosestrife are often chemicals that are non-specific, killing all vegetation that is treated. Broadcast applications, like foliar, of these aquatic formulations are more likely to result in non-target impacts.  
• Be careful not to damage or kill nearby native plants when conducting management work.
• Always read and follow pesticide label directions. Application of pesticides may require a certification from the Agency of Agriculture, Food and Markets. The Agency website provides information on what applicator certification is needed.
• If a treatment for a specific species isn’t listed on a given product, don’t use it. 
• Product labels may require you to check Endangered Species Protection Bulletins. Learn more about protection bulletins here.  
• Understand the risk of, and how to avoid, drift.  
• The timing of some chemical treatments may overlap with when certain plants are flowering, and, in order to protect pollinators, herbicides should not be applied when plants are flowering. To mitigate the risk, consider utilizing an integrated pest management plan, such as cutting the plants to set back flowering time, and then applying pesticides in the lowest effective volume. 
• Chemical treatments pose a risk to plants, animals, and humans, but can be used in ways that greatly reduce this risk, and provide a solution to otherwise hopeless scenarios. 
• For questions regarding the appropriate chemical to use for a particular situation, or general information on pesticide safety, ingredients, and more, contact the Vermont Agency of Agriculture, Food & Markets’ Pesticide Program.  
• For questions about certification and continuing education credit opportunities, contact the Vermont Agency of Agriculture, Food & Markets’ Pesticide Program.  
• For questions about additional training opportunities, contact the UVM Extension Pesticide Safety Education Program.  
• Special permits are required to apply herbicides in a wetland. Contact Vermont Department of Environmental Conservation’s Wetlands Section for more information.  
• Herbicides cannot be applied within 200 feet of a Public Water Source Protection Area unless the Water Supply Division is notified. Call 1-800-823-6500 for more information. Similar requirements may be in place for proximity to private water sources.  
• Forests that are certified organic or adjacent to organically certified agricultural lands may carry restrictions regarding chemical application. Check with the Northeast Organic Farming Agency of Vermont for more information.  
• The National Pesticide Information Center provides objective, science-based information about pesticides. Check out their website for more information or call 1-800-858-7378. 

Biocontrol

Although they will not eradicate purple loosestrife, biocontrol agents can reduce the severity of impacts from an infestation.

• Insects: There are four species of beetles from Europe, which are fairly host-specific on purple loosestrife, that are currently available for control efforts, though availability varies; insects can be collected from known wild populations, or potentially from a supplier, though this may be regulated.  
• Livestock: Intensive, rotational grazing by large herbivores (sheep, etc.) can potentially reduce flowering but this is not well studied, nor is it ideal for all areas and habitats. Grazing can help reduce cover, thus helping other desirable vegetation thrive. Appropriate precautions should be taken if utilizing this method and may require special permissions if occurring in or near a wetland.