The issue: Purple loosestrife

Purple loosestrife (Lythrum salicaria), a semi-aquatic, creeping perennial from Europe, was introduced to the U.S. as an ornamental plant. While it is semi-aquatic and is most often found along ditches, streams and rivers, and in ponds and lakes, it will invade cropland, pastures and home gardens. It destroys the ecology of wetlands.

Purple loosestrife grows up to eight feet tall. The showy, spike, flower stalks have beautiful pink to magenta flowers from June through September. One plant may produce 2.5 million seeds. The opposite leaves are lance-shaped, entire, and sessile—usually two or three at each node.

Purple loosestrife reproduces by seed and rhizomes. Killing the root and eliminating seed production is essential for control. The seeds may remain viable for several years in field conditions. Seeds may spread through water, wind, feather, fur, boats, muddy boots, vehicle tires, and clothing.

Integrated pest management options:

· Prevention: Keep ditch banks free of seed-producing weeds; identify and control new weed infestations; clean farming, recreational, and construction equipment and machinery between fields.

· Mechanical: Hand-pull small patches, removing as much root as possible. Cut and bag seed heads.

· Cultural: Don’t overgraze pastures; manage land to provide good competition from desirable plants; drain swampy areas if possible.

· Biological: Two have been approved for release in Idaho—a leaf-feeding beetle, Galerucella spp., and root weevil, Hylobius transversovittatus, combine to give a good one-two punch.

· Chemical: Spring for seedlings, early bloom for mature plants before seed formation; glyphosate, metsulfuron, imazapyr, triclopyr. Be sure the weed and landscape or crop situation are listed on the label. Always read and follow herbicide label directions.

Combine them:

Combine different IPM options over a period of years to help improve the effectiveness of your efforts.

For more information, contact Ron Patterson, University of Idaho Extension horticulture/agriculture educator in Bonneville County, at 208-529-1390 or