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Pest SolutionsPESTS + WEEDSUSING PESTICIDES OR HERBICIDES?
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Purple loosestrife
Lythrum salicaria
Updated Oct 27, 2024
Make a Positive Identification
- Purple loosestrife grows in wet areas. It has showy pink to purple flowers.
- It is a perennial plant that lives more than two years. It dies back in the winter. Stems sprout in spring and can grow up to 10 feet tall.
- Purple loosestrife spreads by seed. Each plant produces many thousands of seeds. Seeds are carried by the water, wind, and animals to new areas. It can quickly dominate wet areas. It reduces habitat quality and clogs waterways.
Species: Purple loosestrife
"Purple Loosestrife Lythrum salicaria" by gailhampshire is licensed under CC BY 2.0
Purple loosestrife has square sided woody stems. It grows up to 10 feet tall. Mature plants may have many dozens of stems. The stems grow from a robust taproot.
Showy, abundant pink to purple flowers grow in spikes throughout summer.
Species: Purple loosestrife
"Lythrum salicaria - stem, leaves" by The NYSIPM Image Gallery is licensed under CC BY 2.0
Mature leaves are lance-shaped and rounded or heart-shaped at the base. Leaves are whorled and arranged opposite each other along the stem.
Species: Purple loosestrife
Gary L. Piper, Washington State University, Bugwood.org
Plants produce ¼ inch long fruits with many small, flat seeds. Each plant makes many thousands of seeds. They are dispersed in water and wind or on animals and people.
Species:
"Purple loosestrife infestation" by Oregon Department of Agriculture is licensed under CC BY-NC-ND 2.0
Purple loosestrife spreads quickly by seed. It transforms wet areas and reduces habitat value for wildlife. It has a harmful effect on recreational areas and can clog waterways and irrigation systems.
LOOK-ALIKE: DOUGLAS SPIREA and FIREWEED
Species: Douglas' Spirea
"J20170608-0025—Spiraea douglasii—RPBG—DxO" by John Rusk is licensed under CC BY 2.0
Douglas' spirea (Spiraea douglasii) is a native woody shrub. It often grows to 6 ft tall and occurs in wet areas. Its showy pink flowers form in spikes at the end of branches throughout summer. The leaves alternate along the stem. In comparison, purple loosestrife has an opposite and whorled leaf arrangement.
Helpful
Douglas' spirea is a native woody shrub. Tolerate it if possible.
Species: Fireweed
Dave Powell, USDA Forest Service (retired), Bugwood.org
Native fireweed (Chamerion angustifolium) has spires of pink flowers like purple loosestrife. The leaves alternate along the stem. In comparison, purple loosestrife has an opposite and whorled leaf arrangement. Purple Loosestrife stems are square, while those of fireweed are round.
Purple loosestrife Benefits
- Purple loosestrife flowers attract pollinators
Purple loosestrife Risks
- Purple loosestrife spreads quickly. It is difficult to control.
- It displaces desirable vegetation. It degrades wildlife habitat and reduces recreational opportunities.
- Purple loosestrife will dominate an area if not controlled.
Risk Card
Does it cause harm?
Adults & Children
Low
Abundant plant stems limit access to areas
Property
High
Dominates an area when left unmanaged
Pets
None
Annoyance
High
Difficult to control
Environment
High
Rapidly spreading to new areas
Action Highly Recommended
Take action to report and control this invasive weed
Take Action
If you have purple loosestrife on your property, take action to control it right away.
Do I need to take action?
Yes. Remove individual plants and small patches of purple loosestrife. Both small and large patches require several years of attention to control.
What if I do nothing?
Purple loosestrife spreads quickly and will dominate an area if not controlled.
Prevent Purple Loosestrife
Ohio State Weed Lab, The Ohio State University, Bugwood.org
Look for New Stem Growth Following Control Activity
- Look for and kill seedlings such as the one shown in the photo.
- Single purple loosestrife plants grow dozens of stems from their strong root system. Cut stems in early spring before flowering.
- Focus on stem reduction and flower removal in summer.
- Herbicide treatments are most effective in late summer and fall before plants begin to lose their leaves. They are also effective throughout the growing season.
- Continue to monitor the area each year. Control it as needed.
Weston Miller, Oregon State University
Remove Dirt from Shoes and Equipment
- After working or traveling in an area with purple loosestrife, clean your boots and tools.
- Use a wire brush to remove soil that may contain seeds or root fragments.
- If you drive into a purple loosestrife stand, use a pressure washer to clean your vehicle before traveling into new areas.
Weston Miller, Oregon State University
Replant the Affected Area
- After purple loosestrife is removed, desirable plants that were buried under it often regrow.
- Removal of purple loosestrife may significantly damage the site. If this happens and few or no desirable plants remain, replanting is needed.
- Replanting stabilizes the soil surface and shades out purple loosestrife seedlings.
- Plant with a variety of native species.
- Check plantings yearly for new purple loosestrife plants.
Replant Larger Areas with Technical Support
- Purple loosestrife is hard to remove from an infested area. Replanting a previously infested area requires planning and effort.
- Create a multi-year re-vegetation plan. Plans include site preparation and planting details, plant care, and follow-up control. Plan for at least 2-3 years of monitoring and maintenance.
- Your local Extension specialist in Oregon and in other states, or a professional revegetation specialist, can suggest strategies for your area.
Look for purple loosestrife shoots and seedlings in early spring.
Managing established plants requires several years of followup monitoring and treatment.
Solutions for Purple Loosestrife
Early Detection and Rapid Response
- The best purple loosestrife management strategy is to remove small patches before they become a bigger problem.
Physical Removal of Plants and Non-Chemical Methods
- Established patches are difficult to control. Several years of effort are required to get rid of it.
- Stem cutting reduces seed production but does not kill plants.
- Several insects feed on purple loosestrife. Some of them are established in Oregon.
Herbicides (Weed Killers)
- Herbicides effectively control purple loosestrife when used according to the label directions.
Monitoring and Follow-Up
- Look in patches for regrowth in the early spring. Look in nearby areas for seedlings.
NEED HELP?
Consider a licensed pest control company. Learn How to Hire a Pest Control Company.
Your local Extension Specialist in Oregon and other states can suggest other methods.
Jump to
| Method | Does it work? | Is it safe? | Recommendation |
|---|---|---|---|
A Physically Remove Plants |
Effective |
Low risk |
Recommended |
B Biological Control |
Effective |
Low risk |
Recommended |
C Control with Herbicides |
Effective |
Moderate risk |
Use if Necessary |
|
D If Using Herbicides, Protect Yourself & Minimize Risks
|
A
Physically Remove Plants
Non-Chemical Method
Leslie J. Mehrhoff, University of Connecticut, Bugwood.org
Physically Remove Plants
Recommended
- For small patches, cut stems with loppers and saws. Following stem cutting you must return to the site to remove new shoots.
- Remove entire plants by digging out the roots.
- Kill seedlings.
- Remove flowers before seeds form.
- Dispose of the plant parts in the trash or take them to a landfill. Do not compost this invasive plant.
| Does it work? | Effective Stem cutting reduces seed production and depletes root energy reserves. |
| How much effort? | High effort Do not leave the cut stems or root material on the ground. Root and stem fragments can root and form new plants when left on wet soil. Following stem cutting you must return to the site to remove new shoots. |
| What's the risk? | Low risk |
| Possible risk of exposure or harm from chemicals | NONE |
Signe Danler, Oregon State University
B
Biological Control
Non-Chemical Method
Mark Schwarzlander, University of Idaho, Bugwood.org
Biological Control
Recommended
Several introduced insects feed on purple loosestrife and suppress its growth. They play a role in large scale, long term control strategies.
Black-margined loosestrife beetle (Galerucella calmariensis) and the golden loosestrife beetle (G. pusilla) attack purple loosestrife. Adults and larvae feed heavily on leaves, stems, and buds.
| Does it work? | Effective The Galerucella beetles have provided notable control in Oregon. |
| How much effort? | Low effort |
| What's the risk? | Low risk |
| Possible risk of exposure or harm from chemicals | NONE |
C
Control with Herbicides
Chemical Method: Use with caution
Chameleonseye, iStock
Control with Herbicides
Use if Necessary
| Does it work? | Effective
|
| How much effort? | Moderate effort Requires several years of effort and monitoring. |
| What's the risk? | Moderate risk
|
| Possible risk of exposure or harm from chemicals | El uso de herbicidas conlleva cierto grado de riesgo. El riesgo más bajo se presenta con el uso de métodos alternativos. You may be exposed to an herbicide if you:
Follow directions closely to reduce risk. |
Some herbicides are available for home use, and are listed below. These products used individually or in a mixture are effective chemical treatments for purple loosestrife. Look for these chemical names in the “Active Ingredients” section of product labels.
- Triclopyr
- Glyphosate
- Imazapyr
Suggested active ingredients are from the Pesticide Information Center Online (PICOL) Database. They are permitted for HOME use in Oregon. Read the label for application directions and effectiveness information.
ONLY professional pesticide applicators can use Restricted-Use Pesticides (RUP) that may be more effective. For larger stands of purple loosestrife contact a licensed pesticide applicator with experience controlling purple loosestrife.
Herbicide Application Requirements for Aquatic Areas
- Aquatic-use products may not be approved for Home Use in your area.
- Consult a licensed pesticide applicator or your local university extension agent before purchasing or using an aquatic herbicide product.
- Herbicides applied over or near a water body must be registered for aquatic use.
- Treating purple loosestrife near aquatic areas requires specialized skills. This ensures the herbicide is applied effectively. It also protects waterways.
Consider hiring a licensed pesticide applicator to manage purple loosestrife in aquatic areas. Contact your county Weed Control program for herbicide application information for riparian areas. Find contact information here: County Weed Control Programs
Minimize the impact of herbicides on bees and other pollinators. Treat purple loosestrife plants before they flower. Or apply herbicides in the morning or evening when bees are less active. Avoid spraying pollinators directly. For more information, see OSU’s How to Reduce Bee Poisoning from Pesticides.
If Using Herbicides, Protect Yourself & Minimize Risks
Chemical Method: Use with Caution
Brian Lasenby, iStock
Why is it important to read herbicide labels?
- They have detailed information on how to use the product correctly and legally.
- They contain information on potential hazards of the product.
- They provide instructions you should follow for poisonings and spills.
- Following label instructions helps you to minimize the risks and maximize the benefits.
Key Herbicide Safety Tips
- Read the entire label front to back.
- Follow the instructions.
- Review the instructions even for brands you know.
- Only apply the product where the label says it may be applied.
- Be precise in your application. More is not better.
The Label is the Law
ALWAYS read the label before using herbicide products. The label is a legal document that provides information on how to safely use the herbicide. This helps avoid harm to human health and the environment. Using an herbicide in off-label ways is illegal. It can result in legal enforcement actions.
READ THE LABEL & Follow Instructions
It has instructions to protect you and the environment.
- Labels are different for every product and they often change over time.
- Use a magnifying glass for small print.
- Pay attention to CAUTION, WARNING, and DANGER statements.
- Pay attention to the PRECAUTIONARY STATEMENTS.
- The law states you must read and follow herbicide instructions.
Protect Yourself
Eye, skin & lung irritants
- Wear the right protective gear. This often includes chemical-resistant gloves, safety glasses, a long-sleeve shirt, pants, socks, and shoes.
- Mix outdoors or in a well-ventilated area.
- Wash hands after mixing or applying, and before eating or smoking.
- Take a shower immediately after handling herbicides.
- Wash clothes worn while mixing or applying separately from other laundry.
Protect Children & Pets
Children and pets are at risk if they eat or touch the plants before it dries.
- Keep them away during and after applying herbicides (read label for how long).
- Remove toys and pet dishes from yard before applying.
- Don’t track herbicide products into your home on shoes or clothes.
Protect Pollinators
- Apply in the early morning or evening when bees are less active.
- Kill weeds before they flower. Avoid spraying flowering plants.
- Do not spray on bees or insects.
Protect Plants You Want to Keep
- Glyphosate and similar herbicide ingredients damage both grass and broadleaf plants.
- Minimize spraying of foliage, stems, exposed roots, or the trunks of desirable shrubs or trees to avoid harm.
- Follow the label to avoid damaging the roots of trees and shrubs.
Avoid Wet, Windy, or Hot Weather
Use during favorable weather for best results.
- Don’t spray when it’s raining or when rain is expected in the next 24 hours.
- Wind causes spray to drift that can get on you and desired plants.
- Herbicides may be less effective in hot weather if the target plants are moisture-stressed.
- Some herbicides can turn into a vapor in hot weather and damage nearby plants.
Don’t Spray into Water
- It’s illegal to apply herbicides in a stream or slow moving/wetland pool.
- You need a product registered for aquatic areas. This includes waterways, ditches, drains, and other places where water collects.
Storage & Disposal
- Store in a secure area away from children.
- Don’t put unused herbicide products in the trash.
- Never pour down any drain or waterway.
- Take unused herbicides to a hazardous waste facility.
Call 1-800-CLEANUP (1-800-253-2687) to find out where to dispose of herbicides.
For the Portland metro region in Oregon, contact Metro’s Recycling Information. Call 503-234-3000, email or visit Metro’s website
More about:
About Using Pesticides on School Grounds in Oregon
If using pesticides on school grounds, there are special rules in Oregon. See School Integrated Pest Management (Oregon Department of Agriculture).
NEED HELP?
The National Pesticide Information Center (NPIC) can answer questions about pest control chemicals.
1-800-858-7378 or npic@ace.orst.edu
Consider using a licensed pest or weed control company. Learn How to Hire a Pest Control Company.
Your local Extension Specialist in Oregon and other states can suggest other methods.
Invasive Species Alert
- Invasives are non-native species that spread aggressively and alter the environment.
- Controlling purple loosestrife is costly.
- Please do your part to control it on property you manage. Purple loosestrife can spread beyond your property and have an adverse impact on your neighbors.
If you think you’ve found purple loosestrife in the grey areas of this map, please report it to the Oregon Invasive Species Hotline at: 1-866-INVADER (1-888-468-2337) or use their online reporting form.
Invasive species data @ 2022, iMapInvasives (NatureServe)
View Larger Map >
The map shows the distribution of purple loosestrife (Lythrum salicaria) in Oregon. If you find purple loosestrife in a new area (orange shows already reported cases), please report it.
Content provided by Weston Miller, Jessica Green and J. Jeremiah Mann. Pesticide safety information edited by Kaci Buhl.
Peer review facilitated by OSU Department of Horticulture.
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