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Activity - Purple Loosestrife: Monitoring and BioControl
E&E IPM Standard: 4A, 4B, 7B. 10B, 12B
Skills: Observing, measuring, data collection &interpretation, math
Introduction:
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 http://www.cnie.org)
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. More detailed fact sheets on these species are attached.
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
Procedure:
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 quadrats 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.
Analysis:
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.