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Weed Control - Purple Loosestrife

Purple Loosestrife is a favorite forage for several species of weed feeder insects. In 1996, Weber County and the USU Extension Service went into the loosestrife nursery business. The instructions were to dig purple loosestrife crowns from their natural habitat along the river banks just as an inch or two of new growth had occurred. Then the weeds were potted and placed in plastic wading pools to mimic the wetlands in which they are most at home.

Cloth Netting was sewn into four foot tall cylindrical cages to be placed over metal frames set into the potted weeds. Now the only wild card was whether or not the transplanting into pots was done correctly so as to end up with a nursery full of healthy, growing loosestrife. The potting was a success with only 2 out of 25 failing to grow.


Pictured on the left are pots with the hoped for new growth. Next, the cages and netting were placed over the young plants and we watched as they rapidly grew to fill the enclosures. Our friends at Cornell University were notified of our prospering nursery and our request for a few hundred of their prize beetles. We got the ok on the work done so far and a shipment was on the way. We were on alert status as the shipment had to be released into the plant enclosures immediately upon arrival.

Five Hundred Galerucella calmariensis L. and Galerucella pusilla Duft arrived and were carefully divided and introduced to the potted purple loosestrife. The photo to the right shows the nursery at the stage in which the beetles were introduced. During the next six weeks or so, our original stock of Galerucella calmariensis L. and Galerucella pusilla Duft went through a life cycle under the netting.

The ravaged plants were evidence that the beetles ate well! When the beetles were no longer observed in the enclosures it was time to return the purple loosestrife plants back to the river bank. This was a sign that the insects had laid their eggs for the next generation of weed feeders. The Next chore was to truck the heavy, wet potted loosestrife back to the marsh like edges of the Weber River where we wanted the beetles to hatch and prosper among the established purple loosestrife. The comment was made that there was no nasty swarm of hungry mosquitoes in the air when the loosestrife crowns were gathered in April! We were not so fortunate, however, during transplanting back to the wild in July. The mosquitoes ruled the humid landscape as they tried to drive us from their house! Ms Pat Bean, a beat reporter from the Ogden Standard Examiner in her summer dress and flats and her photographer hung in with us long enough to get a story (Thursday, July 4th 1996 issue) though. James Barnhill estimated that some 10,000 Galerucella calmariensis L. and Galerucella pusilla Duf eggs were introduced to the wild, clinging to the hand raised purple loosestrife as it was replanted there.

In Addition, 1,000 Hylobius transversovittatus weevil eggs were painstakingly introduced in the same area by cutting a mature loosestrife stalk, gouging out some pulp, placing an egg or two into the hollow and sealing the stem with clay. In September of 1996, James took the first monitoring data on the purple loosestrife release site as per our agreement with Dr. Bernd Blossey at Cornell University. He reported finding Galerucella feeding damage to be fairly significant in close proximity to the release site. Also found Hylobius larvae feeding near the base of stems that eggs had been placed in. With this data, we received a mini-grant for $200 from USU's Integrated Pest Management project to be used in the continuing biological control of purple loosestrife.

Additional data gathered has not been as encouraging as the knapweed project in North Fork. We continue to find insects among the purple loosestrife and expect them to build in numbers. Our second year hatch may have been diminished by placing too many transplants in the annual flood plane rather than in somewhat higher ground. We learned much and are satisfied with our efforts. It will probably take a few years for their numbers to reach significant Levels. We continue to spray the purple loosestrife on the Monastery ground in Huntsville and along accessible drainage's in northern and western Weber County.

The Preferred method of control for our purple loosestrife is with weedfeeder insects (as described above). However, where the weed is accessible, we will use chemical control as well. Each year, more manufacturers include loosestrife in their labeling. We like Garlon® 3A as it does not take out grasses under the target plants. Garlon® 3A can also be used near some waterways with caution. Quoting from the Garlon® 3A label:
"It is permissible to treat non-irrigation ditch banks, seasonally dry wetlands, flood plains, deltas, marshes, swamps, bogs and transitional areas between upland and lowland sites. Do not apply to open water such as lakes, reservoirs, rivers, streams, creeks, salt water bays or estuaries."
We also use Rodeo® and an approved surfactant on purple loosestrife where underlying grass damage doesn't matter or it is desirable. The cost per gallon of applied herbicide is a bit more with the Rodeo® also.