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Identifying and removing invasive Purple Loosestrife

There have been reports this summer of an aquatic invasive species (AIS) called purple loosestrife on both North and South Center Lakes. It is important that this invasive species is removed early before it spreads!


Identifying purple loosestrife

Purple loosestrife grows to an average of 5 feet. The perennial herb blossoms between July and August. It produces purple flowers, thus the name purple loosestrife. The flowers are held by spiky sepals found at the tip of the branches, which contain some spikes.


The leaves are arranged in a whorled or opposite pattern and they are smooth. They are rounded or heart-shaped. The leaves are around 2-3 inches long.



Removing purple loosestrife

The MN DNR has 3 recommended ways of removing these invasive plants:


1) Digging, Hand-pulling and Cutting

In areas where there are few plants and easy access, manually removing the plants in recommended. Purple loosestrife can be cut or pulled without a permit in Minnesota. It is important to dispose of the plants away from the water. Allow the plants to dry out, then burn if possible.


Pulling purple loosestrife by hand is easiest when plants are young (up to two years) or in sand. Older plants have larger roots that can be eased out with a garden fork. Remove as much of the root system as possible, because broken roots may sprout new plants.

Removing flowering spikes will prevent this year's seeds from producing more plants in future years-remember each mature plant can produce over 2 million seeds per year. Also, remove last year's dry seed heads, as they may still contain seeds. Finally, cut the stems at the ground to inhibit growth.


Proper disposal of plant material is important. Put all plant pieces in plastic bags (vegetation rots quickly in plastic) and take the bags to a sanitary landfill site. Be sure the landfill site doesn't require bags to be broken open for composting. Composting is not advised, as purple loosestrife seeds may not be destroyed and the thick, woody stem and roots take a long time to decompose. If facilities exist in your area, incineration is an effective way to dispose of plant material.


2) Chemical Control

Herbicide can be used to spot treat small infestations of purple loosestrife. A DNR permit is required to spray purple loosestrife in public waters and protected wetlands in Minnesota.


However, there is no fee for this permit.

Details on controlling purple loosestrife with herbicides.



3) Biological control

Leaf-eating beetles Galerucella spp. are available for control of purple loosestrife. They can be used on a variety of site types and on small sites with as few as 20 plants.


Contact the DNR at 500 Lafayette Road, Box 25, St. Paul, MN 55155 for information on how to obtain beetles by field collecting or rearing your own with a beetle rearing kit.

Details on biological control of purple loosestrife.





References

Invasive Garden

Minnesota DNR article on purple loosestrife

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