FAQ

Check out the answers to our most frequently asked questions, below.
Click for a list of Loosestrife Control Contacts in North America

1. What is purple loosestrife?

2. Why should we want to control it?

3.  Isn't it good for anything?

4.  So how can we get rid of it?

5.  What are the control options?

6.  What is biological control?

7. How effective is biological control?

8. What natural enemies are approved for use?

9.  How long will it take for biological control to work?

10.  How safe is this approach?

11.  What will the beetles eat when the purple loosestrife is gone?

12.  What can I do?

1. What is purple loosestrife?     

Purple loosestrife (Lythrum salicaria) is a perennial plant native to Europe and Asia which has become widely established in the US and Canada.  It grows and reproduces prolifically in wetlands and other moist habitats.  Each mature 4-7 foot tall plant produces 30 or more beautiful purple flower spikes that bloom in late summer and can produce over 2.5 million seeds per year.

2. Why should we want to control it?   

For generations, wetlands were considered wastelands.  Throughout the US, wetlands were drained and filled until in some areas, virtually none remained.  Currently, the important roles that wetlands play as habitats for native plants and wildlife, flood control, recreation and enhanced water quality are widely recognized.  Purple loosestrife is degrading the quality of our precious remaining wetlands.

While undeniably beautiful, once it becomes established purple loosestrife frequently becomes the dominant vegetation by out-competing native plants.  As native plant communities are reduced, so too are wildlife species that depend on them.  Declines in ducks, geese and other wetland birds as well as muskrats, mink and some amphibians have all been noted.   There is also concern that purple loosestrife may reduce spawning habitat for some fish.

3. Isn't it good for anything?

 Purple loosestrife produces abundant nectar and is attractive to honeybees and other pollinators.  Butterflies can often be seen obtaining nectar at its blossoms.  The stiff erect stems are also used by redwing blackbirds as supports for nest construction.  In the past human beings greatly contributed to the spread of  purple loosestrife, planting it for its beauty and reported medicinal qualities. Although it is beautiful, we now know better than to let it spread uncontrolled across the countryside. It is illegal to sell or distribute purple loosestrife in many states, including the state of Michigan.

4.  So how can we get rid of it?

 For years, people have tried without success to eradicate purple loosestrife.  It is now clear that this is impossible and we must find ways to live with this plant.  Current efforts focus on two approaches to controlling but not eradicating purple loosestrife: 1) keeping it out of wetlands where it is not currently established and 2) where it is present, managing its density so that native plants and animals can prosper.

5. What are the control options?   

There are several, and your choice depends on the particulars of the infested site. The best control strategy is dictated by the density and extent of infestation.

New or  Localized Infestations:  In habitats where just a few isolated plants exist or the infestation is localized in a very small area (less than 1 acre), it is best to dig them up.  Be sure to get all the roots, but try not to overly disturb the surrounding soil or vegetation.  Plant cover is vital to keep loosestrife from re-invading.  All plant material should be dried and burned, or placed in a closed black plastic bag in the sun for several days where the high heat will kill the plant and seeds.  Any plant material left in the field can easily re-sprout. The best advice we have found about pulling purple loosestrife comes from Ontario Federation of Anglers and Hunters 1993 publication "A Universal Manual for Purple Loosestrife Control."

Where permitted, plants may be treated with an approved herbicide.  RODEO is an effective herbicide registered for use in wetland habitats.  However, it is non-selective and will kill most vegetation it contacts.  Spot sprays directed at the at the early flowering stage are most effective.  Broadcast sprays are not recommended.

Cutting of plants can be used as a holding action until other measures can be taken.  Flowering stalks can be cut to prevent seed formation and old flower heads removed as these may still contain viable seed. 

Established Infestations:  Where hundreds of mature plants exist, or the infestation is spread over several acres digging may be impractical, however, use of herbicides and cutting are still options to consider.  In established infestations where millions of purple loosestrife seeds are present in the soil, care must be taken not to spread them on muddy boots or equipment.  Disturbance of the soil and vegetation should be minimized so as not to open up new areas for loosestrife seedling establishment.

Learn to recognize purple loosestrife throughout the year.  Record areas where you see vegetative growth in the spring, the flowering plants in late summer, or the dry, erect stems in the winter. Plan ahead. In most instances where more than 500 mature plants occur, biological control is likely to be the only practical long-term management option.

6.  What is biological control?

Biological control is when humans use a pest's natural enemies to reduce its density and the damage that it causes.  These natural enemies may be predators, parasites or pathogens.  Most people are familiar with the use of predators such as lady beetles to help control insect pests.  Fewer are aware that biological control can also be used to help manage plants like purple loosestrife.

When purple loosestrife arrived in North America, it came without the natural enemies that attack it in its native home.  Without these natural enemies, loosestrife populations can grow largely unchecked.  Scientists know that in its native range, purple loosestrife is a part of wetland ecosystems, but never becomes the dominant vegetation.  By careful study, they found several species of insects which feed on purple loosestrife, keeping its population in balance with other vegetation.  The process of identifying, studying and establishing these natural enemies where loosestrife has invaded, is known as importation biological control.      

7.  How effective is biological control?

Biological control has been practiced in the US for over 100 years with both successes and failures.  In this country, most of the effort has gone into the control of insect pests.  Farmers in Michigan are very familiar with the highly successful control of two exotic insect pests, the cereal leaf beetle and the alfalfa weevil, using parasites imported from Europe.  The alfalfa weevil project is estimated to save US agricultural producers $10 million per year in reduced pesticide usage and increased yields.  Control of Klamath weed, another European invader of rangelands in the western US was also highly successful in just a few years.  However, in other cases natural enemies have failed to establish or never built-up to sufficient numbers to impact the pest.  Fortunately, in the case of purple loosestrife, some of these hurdles have already been overcome.

8.  What natural enemies are approved for use against purple loosestrife?

Three species of plant feeding beetles, Galerucella calmariensis, Galerucella  pusilla and Hylobius transversovittatus show the greatest promise as biological controls for purple loosestrife.  The Galerucella leaf beetles feed on bud, leaf and stem tissue causing defoliation and prevention of flowering/seed production.  Continued defoliation leads to plant death.  Hylobius is a weevil whose larvae mine in root tissue weakening and ultimately killing the plant.   These insects have undergone extensive testing to determine their safety and effectiveness, receiving USDA approval in 1992.  At the request of the Michigan Department of Natural Resources (MDNR), the Michigan Department of Agriculture reviewed and approved the release of these insects.  The MDNR's releases of Galerucella in 1994 have established well and are beginning to show impacts.  The result of 1996 releases of Hylobius are still uncertain.

9. How long will it take for biological control to work?

Most estimates range from 5-15 years for large impacts of these beetles to be realized.  However, recent results from  Ontario and Minnesota indicate that Galerucella can  have had a dramatic impact on purple loosestrife infestations is as little as three years.  Larger releases and better rearing techniques may help to shorten the time to impact. 

10.  How safe is this approach?

Before introduction of any weed biological control agent it must pass several tests to determine its level of host specificity and establish that it is free of unwanted diseases or parasites.  The Galerucella and Hylobius beetles were tested against 47 plant species that are either closely related to purple loosestrife, occur in the same habitat or are important economic species.  Based on this testing these species were considered to be host specific to purple loosestrife and approved for release by the USDA.  Galerucella and Hylobius beetles are also harmless to humans and pets.

11.  What will the beetles eat when the purple loosestrife is gone?

Because they survive exclusively on purple loosestrife the number of the beetles in any area is expected to rise and fall based on the amount of loosestrife present.  As the plant becomes less common, the beetles will have a harder time finding food, they will produce fewer offspring, and as a consequence, their population will decline.  Experts believe that these natural enemies cannot eliminate purple loosestrife but they can severely reduce its density.  Once established, the beetles will continue to control loosestrife on a permanent basis.

12.  What can I do?

Get started. Enlist a friend and brainstorm ideas so you can begin to understand the problem and its solutions as a part of the larger picture.

Conduct a survey:  A "Loosestrife Locator Survey" of your neighborhood or township can determine if purple loosestrife is present, where it occurs and the level of infestation.  Consider enlisting the help of local 4H, scouts, schools, service organizations, conservation groups etc. to broaden your coverage. Send for a copy of the Biological Control of Purple Loosestrife 4H Manual.

Formulate a management plan:  Consider your options for hand digging, cutting flowers or spot spraying. Read all you can Talk to adjacent landowners about a coordinated effort. Make contacts with others to share resources. In Michigan, call a regional CBC network site.

If you are an educator, contact The Purple Loosestrife Project office for more information, including suggested activities for kids.

13. Where can I get beetle rearing cages?

The person who sews our cages is:
Marisol Soto
msolsoto@hotmail.com
(517) 394-0847