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 Ca 2+  The Conclusion: –The increased solubility of Ca 2+ 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) Mg+2, Ca+2, 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 14 C-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 Science167:821-829  Blank RR, Qualls RG, Young JA (2002) Lepidium latifolium: plan nutrient competition- soil interactions. Biol. Fertile Soils 35:458-464  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 19:237-243  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 52:14- 23  United States Department of Agriculture (2008) Plants Profile: Lepidium latifolium.http://plants.usda.gov/java/profile?symbol=LELA2, November 18, 2008. http://plants.usda.gov/java/profile?symbol=LELA2  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 17:121-123  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 12:402-405  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?