|Abstract or Summary
- Lepidium latifolium L. (perennial pepperweed, LEPLA) is an exotic invader
throughout western North America. At Malheur National Wildlife Refuge
(MNWR) in southeast Oregon, it has invaded about 10% of meadow habitats that
are important for wildlife. This study's objective was to determine the most
effective and least environmentally harmful treatment to control this weed and
restore native vegetation using integrated pest management techniques. During
summer 1995, nine 0.24-ha plots in three meadows infested with L. latifolium at
MNWR were randomly assigned to a treatment with metsulfuron methyl herbicide,
chlorsulfuron herbicide, disking, burning, herbicide (metsulfuron methyl or
chlorsulfuron) then disking, herbicide (metsulfuron methyl or chlorsulfuron) then
burning, or untreated. Changes in L. latifolium ramet densities and basal cover of
vegetation, litter, and bare soil were evaluated in 1996 and 1997. Sheep grazing
was evaluated as a treatment for reduction in flower production along roadsides
and levees during summer 1997. Revegetation treatments of seeding, transplanting
or natural (untreated) revegetation were attempted at plots treated with
chlorsulfuron, disking, chlorsulfuron then disking, and at untreated plots from
October 1996 through September 1997. Chlorsulfuron was the most effective
control treatment with greater than 97% reduction in L. latifolium ramet densities
two years after treatment. Metsulfuron methyl was an effective control (greater
than 93% reduction) for one year. Disking was ineffective. Burning was
ineffective at the one site where sufficient fine fuels existed to carry fire.
Herbicide treatments were associated with increased grass and reduced forb cover.
Disking was associated with reduced grass and litter cover. Disking combined with
either herbicide treatment was associated with reductions in all plant cover (49 to
100%), increased bare ground, and invasion by other weedy species such as
Cirsium arvense (L.) Scop. (Canada thistle, CIRAR) and Bromus tectorum L.
(cheatgrass, BROTE). Ungrazed L. latifolium averaged 4513 flowers per ramet.
Sheep grazing reduced L. latifolium flower production by at least 98%.
Revegetation treatments were unnecessary in sites treated with chlorsulfuron and
were ineffective at all treatment sites.