Natural Areas and Purple Loosestrife

Importance and background of natural areas, including activities related to monitoring and controlling Purple Loosestrife.
Natural Areas and Purple Loosestrife - Articles


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Undisturbed wetlands are important beyond their actual size in "acres". They harbor an enormous biodiversity of plant and animal life, provide diverse resources of water, many kinds of food and shelter, as well as serve functions of buffer zones, flood control, and pollution filtration. Invertebrates and vertebrates may breed there, catch a snack during migration, over-winter or live year-round. It is the diversity of the non-living components and plant life that allow all this thriving and coming and going of the animal component.

IPM Aspects - We may not think of streams and wetlands as places where we have to be concerned about pests. However, there are any number of situations in which certain organisms become "pesty"' by virtue of upsetting the ecological balance in wetlands and streams. Many of these examples are so-called exotic or invasive species.

Forests and Parks

As with wetlands, forests and parks serve a relatively natural areas where a diversity of plants and wildlife live. Some of this diversity can be "used" by humans in the form of a renewable natural resource such as timber. Human also "use" these habitats for recreation and restoration of the spirit. Who has not walked down a pine-needle soft path, breathing in the aromatic forest air and quiet of the trees? And yet, these environments are challenged by pests as well. Too many deer in too small an area can seriously impair forest regrowth. The ravages of the gypsy moth are all to familiar. The invasive vine, kudzu, is smothering trees in forests in certain areas. Yet, to preserve the forest ecosystem diversity, one wishes to only suppress these populations, not eradicate them. This must be done with as little damage to the non-target species as possible.

Pest management in parks is also a particular challenge, because as a human destination and visitor site, parks (as with public gardens, campuses, historic sites and the like) have many "micro" habitats where pest management tactics must be used carefully.

The activities listed will give you and idea of what is involved in managing pests in these two natural areas.

Activity - Purple Loosestrife: Monitoring and Biocontrol


The Pest: Purple Loosestrife, Lythrum salicaria was imported from Europe in the early 1800s for its medicinal value and for the beautiful purple spikes of the blooming plant. Unsuspecting visitors to an infested wetland often admire the beauty of the marsh when loosestrife is in bloom, unaware that it has crowded out native plants and animals. Its vegetative dominance may increase the likelihood of listing additional native species under the Endangered Species Act. Interestingly, this species is still sold as an ornamental in nurseries in some states, though 24 states have listed it as a noxious weed and prohibit its sale. It is found in 42 of the contiguous states, and could well invade the remaining six. The plant is extremely difficult to eradicate and control has focused on preventing its spread or establishment. Besides loss of plant and animal biodiversity, estimated losses are $45 million per year in control and forage loss.
(From "Harmful Non-Native Species: Issues for Congress III", National Institute for the Environment, Washington DC)

The BioControl Agents:

There are currently 3 biological control agents cleared for release in the US. All three are beetles, and each specializes only on loosestrife and upon certain parts of the plant. Galerucella calmariensis and pusilla feed on the leaves and flowers and the larvae of the weevil Hylobius transversovittatus feeds on the roots.

Learning Objectives:

  1. Learn about wetland ecosystems
  2. Discover the situation with invasive species
  3. Measure and calculate plant species diversity
  4. Recognize and monitor for biocontrol agents
  5. Discuss management options for purple loosestrife

Materials Needed:

  • Rubber boots
  • Clipboards with data sheets
  • Hand lens
  • Watch with a second hand
  • Meter square sampling tool
  • Tape measure (meters)
  • Posts to mark the transect (PVC or metal) & hammer to pound them in
  • Vials and zip lock bags for collecting samples

Timeline: 2 - 3 hrs on site depending upon how many samples will be taken


  1. Locate and area where purple loosestrife has invaded a waterway (*and biocontrols released)
  2. Make a map of the area and estimate the extent of the loosestrife population at % of cover
  3. Look at the data sheet and fill out other particulars (time of day, weather conditions)
  4. Set up a transect in a straight line through the loosestrife infestation for about 70 meters
  5. If you are releasing biocontrol beetles, release them at the center of your transect
  6. At 7 meter intervals, set posts to act as the permanent corner for your meter square samples
  7. Set the meter square carefully around the base of the plants (don't scare insects off)
  8. First search the surface of the loosestrife plants for biocontrol insects for one minute, noting especially Galerucella adults, eggs and/or larvae (see samples and fact sheet for what they look like). Record your data on the data sheet.
  9. Next, make observations on the status and health of the purple loosestrife (PL)plants themselves; For the plants in your meter square note:
    • percent cover due to PL number of stems per quadrat
    • average height of stems (5) # of terminal buds of 5 tallest shoots
    • percent of stems flowering # & length of inflorescences
    • % of leaf area removed due to feeding # of flower buds per 5 cm
  10. Set out some meter square quadrants in adjacent areas at the same site where loosestrife has not spread yet. Count the number of different plant species, number of stems of each, percent cover and average height. Identify the plants if you can.


These data are useful over time to see if the loosestrife is spreading, or declining, either in number or vigor as a result of the biocontrol, if species composition is changing, which species are re-establishing as loosestrife declines, and whether or not biocontrol numbers are stable.
Comparisons of plant species diversity between loosestirfe areas and non-loosestrife areas can be made right away.

Discussion topics:

Species diversity: Discuss with the students the difference in species diversity observed in Step 8 and Step 9. What are the implications of that difference?

Management of Loosestrife: Students can discuss all the strategies they might consider employing to suppress Purple Loosestrife (or even if they would try to control it at all!) Are there any advantages to the plant? How do the advantages stack up against the disadvantages?

On repeated visits, students can discuss whether they are seeing any changes in PL population and to what that change might be attributed.