Lepidium latifolium: A Case Study

1
Lepidium latifolium A Case Study
2
What is Lepidium Latifolium?

• Semi-woody plant that grows in dense masses of
  erect stems
• Grows 1-3ft tall, but can grow up to 8ft tall in
  wet growing conditions
• Leaves and stems are waxy
• Leaves are alternate with toothed to smooth
  blades (0.5 1.0 inches wide)
• Flowers are a brilliant white, arranged in dense
  panicles in clusters of 6 to8. (Young 1995)

3
Common Names.

• Whitetop
• Tall Whitetop
• Broadleaf Peppergrass
• Broadleaf Pepperwort
• Perennial Pepperwort
• Pepperwort
• Virginia Pepperweed
• USDA (2008)

4
Where is Lepidium latifolium from and where has
it naturalized to?

• Native to Eurasia and Northern Africa
• Believed to have been accidentally introduced to
  North America as a contaminant in Sugar Beet seed
  (Young et al., 2005)
• Has become naturalized in Australia, Mexico,
  Canada and the United States
• Within the U.S. Lepidium latifolium has been
  declared a noxious weed in 13 states and by the
  Bureau of Land Management (USDA, 2008)

Figure 1 Distribution of Lep. L. throughout
North America. (USDA, 2008)
5
Why is it considered invasive?

• Likes to establish near wetlands, riverbanks,
  riparian areas and flood plains (Renz et al,
  2004)
• Forms extremely dense clonal monocultures
• Has a tendency to out grow pre-existing
  vegetation by
• Consuming available nutrients and moisture
• Forming a dense canopy where light cannot
  penetrate
• Incredibly difficult to get rid of!
• (Donaldson, 1997 Young et al., 1997)

6
What makes it invasive?

• There are several properties that make perennial
  pepperweed a fierce competitor
• Has high rate of dispersion
• Reproduces by both seed and stoloniferous
  rhizomes these are generally carried by water to
  vulnerable downstream areas (Whitson et al.,
  1992 Donaldson, 1997)
• Produces 15 billion seeds/ha spread of seeds is
  facilitated by wind, animals, humans and vehicles
  (Eiswerth et al., 2005)
• Has an extensive root system
• Hypothesized that deep root system is what
  allows perennial peperweed to access water and
  gain a competitve advantage agiainst natives
  (Qualls et al., in prep)
• Has high phenotypic plasticity for survival
• Can tolerate shade, sun, and extensive flooding
  (Qualls et al., in prep)

7
Ecological Effects

• Influences soil properties and elemental cycling
• Blank et al., 2002
• Alters biogeochemical cycling so that affected
  sub soils are ameliorated
• Blank and Young, 2002

8
Ecological Effects Perennial pepperweed
Influences soil properties and elemental cycling

• In an experiment by Blank et.al. (2002) the
  effect of soil nutrient depletion on the growth
  of and competition between perennial pepperweed
  and Bromus tectorum was examined
• Species were grown individually and in
  combination
• When the perennial pepperweed flowered, the roots
  and aboveground mass of both species were
  harvested.
• Soils were then homogenized.
• Soil was re-planted with the same species
• This cycle was repeated for 3 growth cycles.

9
Ecological Effects Perennial pepperweed
Influences soil properties and elemental cycling

• (Blank et al., 2002)
• The Results
• After 3 growth cycles the boveground mass of the
  perennial pepperweed decreased significantly, and
  the growth potential of the perennial pepperweed
  was surpassed by that of the Bromus tectorum
• The Conclusion
• The data suggests that, as nutrients are
  biocycled to the upper layers of the soil, the
  monoculture stands of pepperweed may become
  nutrient limited and out-competed by plants with
  greater root densities.

10
Ecological Effects Perennial pepperweed
Influences soil properties and elemental cycling

• Figure 2 Root/Shoot ratios of Bromus Tectorum
  and Lepidium latifolium after each of three
  growth cycles (Blank et al., 2002).

11
Ecological Effects Perennial pepperweed alters
biogeochemical cycling so that affected sub soils
are ameliorated

• (Blank and Young, 2002)
• Tested the hypothesis that perennial pepperweed
  alters biogeochemical cycling relative to
  pre-existing vegetation such that sodium affected
  sub-soils are ameliorated
• Cycling and distribution of different elements
  were monitored for four years in sites that were
  both invaded with perennial pepperweed and sites
  that were not invaded but contained Elytrigia
  elongata.

12
Ecological Effects Perennial pepperweed alters
biogeochemical cycling so that affected sub soils
are ameliorated

• (Blank and Young, 2002)
• The Results
• Perennial pepperweed had significantly greater
  concentrations of of C, Ca, Mg, K, and S in above
  ground tissue that Elytrigia elongata
• Perennial pepperweed was increasing the
  solubility of Ca2
• The Conclusion
• The increased solubility of Ca2 lowered the
  ratio of sodium adsorption to the soil, and
  ameliorated the soils by decreasing dispersion,
  increasing aggregation of sodium and improving
  physical properties.
• Once sodic soils are ameliorated they will likely
  be able to support a richer and more productive
  community, if perennial pepperweed can be
  controlled.

13
Ecological Effects Perennial pepperweed alters
biogeochemical cycling so that affected sub soils
are ameliorated

• Figure 3 Biogeochemical fluxes of C, Ca, Mg, K,
  and S in Elytrigia elongata and Lepidium
  latifolium and calculated SAR (sodium adsorption
  ratios). (Blank and Young, 2002)
• Immiscibly displaced (aqueous-soluble) Mg2,
  Ca2, Na, K, and SO4-2 and sodium adsorption
  ratio (SAR) calculated from ID values, by plant
  (Lepidium latifolium community vs Elytrigia
  elongata community) and soil depth. Bars are 1
  standard error.

14
Control

• Very difficult to control through mechanical
  methods
• Deep tap roots, rhizomenous regeneration
• Very difficult to control through Chemical
  methods
• Waxy layer of cutin that protects leaves and
  stems
• Perennial pepperweed generally grows by water.
  Only two herbicides are safe for use by water and
  affective against broadleaf vegetation
• Glyphosate (N-Phosphonomethylglycine)
• 2,4-D (2,4-dichlorophenoxy acetic acid)
• No existing mechanisms for biological control

15
Control- tilling and herbicides

• In experiments by Young et al. (1998) control of
  perennial pepperweed was examined through use of
  tilling and herbicides over wide range of soils,
  over a 2 year period.
• Results
• Tillage with periodic disking had no permanent
  affect
• Applications of 2,4-D and Glyphosate had no
  permanent affect
• Applications of Chlorsulfuron was effective in
  destroying the perennial pepperweed 3 years
  after the initial application, the plants had not
  re-established

16
Control mowing and herbacides

• In a study performed by Renz and DiTomaso (2004)
  it was demonstrated that perennial pepperweed
  could potentially be controlled by mowing
  followed by an application of Glyphosate
• Mowed plants translocated more glyphosate from
  their basal leaves to their below ground tissue
  than un-mowed plants
• Mowed plants accumulated 6.7 of glyphosate
• Unmowed plants only accumulated .38 of
  glyphosate

17
Control mowing and herbacides

• Table 1 Average percent 14C-glyphosate
  recovered in various tissues of perennial
  pepperweed 48 hours after labeling (Renz et al.,
  2004)

18
Control - Flooding

• Study by Qualls et al. (in prep)
• When perennial pepperweed was subjected to 3
  months of flooding, with water above the plant
  tops the following ocurred
• Rapid die back of above gound tissue
• 17 of the root stock survived to re-sprout after
  the soil was drained
• Conclusion
• Perennial pepperweed appears to have a wide range
  of tolerance for survival

19
Control- Mowing and grazing by sheep

• In a study conducted by Allen et al. (2001) Sheep
  grazing and mowing were both examined as methods
  for the control of perennial pepperweed.
• Infested pastures were mowed or grazed for one
  season
• Results
• Pastures that had been grazed by sheep had a
  reduction in perennial pepperweed of 78
• Pasures that had been mowed had a reduction of
  48
• These results are contrary to grazing experiments
  using goats (Young et.al.,2000)

20
Control- Mowing and grazing by sheep

• Figure 4 Change in number of perennial
  pepperweed plants in mowed and grazed pastures
  after one season. (Allen, 2001).

21
Economic and Social Impacts

• A dynamic cost-benefit analysis for the control
  of perennial pepperweed was performed by Eiswerth
  et al. (2005)
• Costs and benefits for land that was used solely
  for grazing and for land that was used for both
  grazing and hay harvest were estimated by
  analyzing current costs for weed control (Table
  2), estimated future control costs, future
  forgone revenues, and by calculating the
  standardized benefits and costs for infested
  land.
• Results
• On land that is used for grazing only, it would
  take 15 years for the costs to equal the returns.
• On land that is used for both grazing and hay, it
  would take 5-6 years for the costs of control to
  equal the returns

22
Economic and Social Impacts

• Table 2 Predicted costs for weed control
  (Eiswerth et.al. 2005).

23
Economic and Social Impacts

• Figure 5 Predicted costs and foregone net
  revenues for infested land. L1, cumulative
  foregone net hay harvest and grazing revenue at
  30 weed expansion rate L2, cumulative foregone
  net hay harvest and grazing revenue at 15 weed
  expansion rate L3, cumulative foregone net
  grazing-only revenue at 30 expansion rate L4,
  cumulative foregone net grazing-only revenue at
  15 expansion rate C1, cumulative cost to
  control the infestation at 70 control rate C2,
  cumulative cost to control the infestation at 80
  control rate C3, cumulative cost to control the
  infestation at 90 control rate (Eiswerth
  et.al.2005)

24
Conclusions

• Perennial pepperweed is very difficult to
  control at the moment it is hopeless for
  eradication
• It should have become a top priority for
  eradication 30 to 40 years ago
• May still be possible to thwart the continued
  spread of Perennial pepperweed through education,
  prevention, rapid response, and diligence in
  monitoring and treatment
• Hopefully an effective bio-control agent will be
  found!
• Or, perennial pepperweed may eventually eradicate
  itself through its currently observed patterns of
  nutrient cycling
• However! If I were to recommend a treatment for
  control, I would recommend a regiment that
  consists of grazing by sheep and mowing for areas
  that are accessible to livestock. For areas that
  are inaccessible by livestock, would recommend a
  treatment of mowing/weed-wacking followed by
  glyphosate spot application.

25
References

• Allen JR, Holcombe DW, Hanks DR, Surian M,
  McFarland M, Bruce LB, Johnson W, Fernandez G
  (2001) Effects of sheep grazing and mowing on
  the control of perennial pepperweed (Lepidium
  latifolium). American Society of Animal Science
  52
• Blank RR, Young JA (2002) Influence of the
  exotic invasive crucifer Lepidium latifolium,
  on soil properties and elemental cycling. Soil
  Science167821-829
• Blank RR, Qualls RG, Young JA (2002) Lepidium
  latifolium plan nutrient competition- soil
  interactions. Biol. Fertile Soils 35458-464
• Birdsall JL, Quimby PC, Svejcar TJ, Young JA
  (1997) Potential for Biological Control of
  Perennial Pepperweed (Lepidium latifolium)
• Chen H, Qualls RG, Miller GC (2002) Adaptive
  responses of Lepidium latifolium to soil
  flooding biomass allocation, aerenchyma
  formation, adventitious rooting and ethylene
  production. Environmental and Experimental
  Botony 48 119-128
• Donaldson, SG (1997) Flood-Borne Noxious Weeds
  Impacts on Riparian Areas and Wetlands.
  California Exotic Pest Plant Council 1997
  Symposium Proceedings
• Eiswerth ME, Singletary L, Zimmerman JR, Johnson
  WS (2005) Dynamic Benefit-Cost analysis for
  Controlling Perennial Pepperweed (Lepidium
  latifolium) A Case Study. Weed Technology
  19237-243
• Lipa JJ (1974) Survey and Study of Insects
  Associated with Cruciferous Plants in Poland and
  Surrounding Countries Final Report. Inst. Of
  Plant Prot., Lab. Of Biol. Contr., Miczurina 20,
  Poznan, Poland, 310pp
• Qualls JR, Walker M (In preparation) Competition
  for Water by Tall Whitetop

26
References Continued

• Renz MJ, DiTomaso JM (2004) Mechanism for the
  enhanced effect of mowing followed by glyphosate
  application to re-sprouts of perennial
  pepperweed (Lepidium latifolium). Weed Science
  5214- 23
• United States Department of Agriculture (2008)
  Plants Profile Lepidium latifolium.http//plants
  .usda.gov/java/profile?symbolLELA2, November
  18, 2008.
• Whitson TD, Burrill LC, Dewey SA, Cudney DW,
  Nelson BE, Lee RD, Parker R (1992) Weeds of the
  West. Western Society of Weed Science. Newark,
  CA, 630pp
• Young, JA (1995) Perennial Pepperweed.
  Rangelands 17121-123
• Young JA,Palmquist DE, Wotring SO (1997) The
  invasive nature of Lepidium latifolium a
  review. Plant Invasions studies from North
  America and Europe p. 59-68. Leiden,
  Netherlands Backhuys
• Young JA, Palmquist DE, Blank RR (1998) The
  Ecology and control of Perennial Pepperweed.
  Weed Technology 12402-405
• Young JA, (1999) Lepidium latifolium L. ecology
  and control. USDA, Agricultural Research
  Service. National Symposium on Tall
  Whitetop-1999, Alamosa, Colorado. pp. 43-45.

27
Questions?