Where Have All the Purple Flowers Gone?
by Sharon Moen
The Munger Landing area of the St. Louis River looked decidedly purple two years ago. This past August, it was green — a native rush-sedge-and-arrowhead-green — accented by a foreground of yarrow blossoms and red raspberries.
What changed the color of this place? Hunger.
Smallish beetles with largish appetites for purple loosestrife did what the children, parent volunteers, and agency staff hoped they would when they released them into this cove in the summers of 2000 and 2001.
"I can't believe the difference," said Shari McCorison, 4-H Program associate for the University of Minnesota Extension Service. "I'm seeing probably only about fifteen percent of the loosestrife I remember from last year and very little flowering."
Fingering a tattered plant, peppered with holes and browning leaves, she called out to the group of volunteers, "Just look at this! I think it is safe to say that this bio-control project is a success!"
In fact, the purple loosestrife biological control project was so successful that many of last-year's roots, which volunteers dug from Munger Landing and planted in kiddy pools, failed to sprout. The roots presumably perished during the winter due to reduced starch reserves. Blame the beetles and their ability to strip photosynthetic tissue from a loosestrife plant. Fewer healthy loosestrife plants growing in the volunteers' backyard beetle nurseries, coupled with an unusually cold spring, made the 2002 purple loosestrife control project more challenging but no less important.
"The beetles have done a splendid job," said McCorison, "but they're not done yet and neither are we."
Meet the Hero
Black-margined loosestrife beetle
Eating the shoots, buds, and other above-ground parts of purple loosestrife plants
Descendants from Northern Germany gained USDA approval for release in North America in 1992. Now helping to reduce purple loosestrife infestations in over 30 states and 6 provinces.
Focused and short.
Feeding by larvae strips the photosynthetic tissue off plants and at high densities (>2-3 larvae/cm shoot) they can defoliate entire purple loosestrife plants. Adult and larval leaf damage greatly reduces a plant's photosynthetic capability, reducing starch stores in the roots and thereby increasing winter plant mortality. Less severe attacks can reduce shoot growth, inhibit flowering, eliminate seed production, and impede root growth. Attacks also increase the branching pattern of purple loosestrife; attacked plants are shorter and appear "bushier" than unattacked individuals.
This year 55 volunteers raised roughly 100,000 black-margined loosestrife beetles, or Galerucella calmariensis, and released them in other loosestrife-ridden areas of the St. Louis River (Indian Point, Clough Island and Oliver Bridge). The beetles are host-specific; they eat purple loosestrife and nothing else.
Eradicating purple loosestrife once it has populated an area is a Herculean task; current control efforts focus on reducing its ability to dominate an ecosystem by releasing the beetles in infested wetlands and minimizing loosestrife's spread through public education.
Purple loosestrife is a lovely plant that is still popular with beekeepers and their bees, but it belongs in Europe and parts of Asia, not here. About 200 years ago, people deliberately and accidentally introduced this now-pesky perennial in North America. It spread rapidly throughout the continental United States and Canada, overpowering native wetland vegetation.
The leaf-chewing, bud-eating beetles that now live along the St. Louis River are native to Europe and Asia. They have been chomping away at purple loosestrife in North America since 1992 when, after years of quarantine and research, the US Department of Agriculture approved their use as a purple loosestrife control agent. Over five million of these beetles have been released in Minnesota's infested wetlands. Researchers report that larval and adult beetles have defoliated about 80 percent of some loosestrife populations.
Minnesota Sea Grant cooperates with the University of Minnesota Extension Service 4-H Program, the Minnesota Department of Natural Resources, and the St. Louis River Citizens Action Committee on the biological control of purple loosestrife along the St. Louis River. The Minnesota efforts are part of a larger project involving the Michigan and Illinois-Indiana Sea Grant programs. Funding was provided by a grant from the US National Oceanic and Atmospheric Administration to the National Sea Grant College Program through an appropriation by Congress based on the National Invasive Species Act of 1996.