Tuesday, September 11, 2012

Beetles Take Bite Out Of Purple Loosestrife

For over a decade, I have been battling purple loosestrife, an aggressive wetland invasive plant that has cost the United States millions of dollars in damage, and is known to impede recreation and degrade wildlife habitat.  As a Conservation Educator for Hamilton County Soil and Water Conservation District, my efforts include manual management and a new biocontrol program.  On June 26, my coworker and I released 500 beetles along the Sacandaga River in the Town of Lake Pleasant to take a bite out of purple loosestrife.

Purple loosestrife (Lythrum salicaria) is an perennial native to Eurasia that was introduced to North America in the 1800s.  Colonists brought the plant over from Europe as an ornamental and for medicinal uses in tonics.  Also, ship ballast water containing seeds was emptied into ports.  Without the ecological checks and balances found in its home turf, purple loosestrife can quickly reproduce and spread.

A few years ago, I spotted gargantuan purple loosestrife plants growing along the shoreline of Sacandaga Lake while out for a drive.  I am 5’9” tall and monster steams doubled my height.  Because plants reach 10 feet and spread quickly, they out-compete native vegetation for light, growing space, water, and soil nutrients.

Showy, purple flowers bloom from July through September.  Preferred habitats include open, sunny areas with wet soils, but drier conditions are tolerated.  Mature plants have a high germination rate and can produce 2.5 million seeds in a growing season.  Broken plant fragments and roots have the ability to re-sprout.  Seeds and fragments are spread via wildlife, wind and water movements, mowing, humans, and vehicles.

Beauty can sometimes be a beast, and this is the case with purple loosestrife.  Gorgeous magenta flowers are desirable for gardens.  It may be pretty, but this invasive plant can replace native wetland vegetation including cattails and ferns, degrade wildlife habitat, decrease the natural food source for herbivores, and change the structure and function of wetlands including biochemical and hydrologic cycles.

Over the years, I have removed thousands of pounds of purple loosestrife from wetlands and roadside ditches.  Flowering stalks are

clipped before plants go to seed.  All vegetation is bagged and allowed to liquefy in heavy duty plastic bags before being delivered to a transfer station.  These efforts are much greater than me and my coworkers alone.  Many local landowners and volunteers have dedicated countless hours to help control this invader.

Manual management is time consuming and labor intensive, but through this new biocontrol program, Galerucella beetles do the work for us by chowing down on purple loosestrife.  These insects are voracious herbivores that are host specific to invasive loosestrife.  Intense studies show that so far, they do not adversely impact native vegetation.  Larvae and adults munch on the stems, leaves, and shoot-tips, slowing reproduction and growth.  Adults overwinter and emerge again in the spring to feed.  Galerucella beetles depend on purple loosestrife to complete their life cycle, and as plants die back, beetle populations crash.

For decades, purple loosestrife has grown along the Sacandaga River in the Town of Lake Pleasant, spreading downstream to form dense populations.  In July 2011, the District received a permit from the Department of Environmental Conservation and released 200 beetles at 2 priority sites along the river.  In September, some leaf damage was seen.  This May, sample sites were monitored for damage inflicted by overwintered beetles.  Some leaves of emerging purple loosestrife plants showed “shot hole” feeding.  This July, the permit was renewed and 500 more beetles were released at the same sites.  Monitoring was conducted in late August and leaf damage appeared on many plants.  Depending on the size of the infestation and the number of beetles, it could take as long as 5 years to suppress purple loosestrife.

This coming spring, the District hopes to begin a beetle rearing program.  Purple loosestrife plants will be collected, planted in pots, and placed in standing water in plastic pools.  The plants and pools will be covered in netting, and adult beetles will be released.  Each plant may produce 500 – 2000 beetles.  In June, cages will be transported to the release site where the netting will be removed, allowing beetles to make their way into the wild.

I have seen my manual management efforts hinder purple loosestrife populations, but new plants always pop up.  I am excited about

the new biocontrol program because the Galerucella beetles will take some of the load off the District in our efforts to reduce purple loosestrife populations.  As with all invaders, success is never seen overnight and control takes years of persistence.

Photos: Above, Conservation Technician Lenny Croote releases Galerucella beetles along the Sacandaga River to munch on purple loosestrife; Middle, Purple loosestrife grows along the Sacandaga River;  Below, monster purple loosestrife plants tower above 5’9″ Conservation Educator Caitlin Stewart.

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Caitlin Stewart manages the Hamilton County Soil and Water Conservation District. The District's mission is to manage and promote the wise use of Natural Resources in Hamilton County. Caitlin will be sharing the District's conservation-focused services, programs, and events. She’s been a full time resident of Hamilton County since 2008 and is an avid hiker, skier, paddler, and biker. She is obsessed with adventuring with her dog Artemis.

4 Responses

  1. Wally Elton says:

    Was away for a while and am catching up. Thank you for this informative and encouraging article. It is good to hear of some hope against at least one invasive.

  2. Caitlin says:

    Thank you for your comment! It is amazing to think that these little beetles are taking a great burden off our manual management efforts.

  3. Suzanne McGraw says:

    This excellent article gives hope that we can significantly reduce the purple loosestrife population.I would love to see a follow-up on how the beetles are working in 2014 and onward! Thanks for posting it!

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