Controlling the spread of purple loosestrife is crucial to protecting vital fish, wildlife and native plant habitat. Purple loosestrife can easily spread if improper control methods are used. The following simple guidelines will ensure that your efforts to control the spread of purple loosestrife are effective.
The best time to control purple loosestrife is in late June, July and early August, when it is in flower, plants are easily recognized, and before it goes to seed. Once flower petals start to drop from the bottom of the spike, the plant begins to produce seed. Control activities can continue during this time, but require greater care so seeds are not shaken from the plant. At sites where plants have gone to seed, remove all of the flowering spikes first by bending them over a plastic bag and cutting them off into the bag. Further cutting of stems or pulling can now take place without fear of spreading the tiny seeds.
Be aware that your clothes and equipment may transport the small seeds to new areas. Thoroughly brush off your clothes and equipment before leaving the site.
Keep site disturbance to a minimum. Wetlands provide habitat for many native song birds, waterfowl, mammals, amphibians, and fish which depend on native wetland vegetation. Wetlands are also home to many rare and delicate plants. Take care not to trample or damage native vegetation when controlling purple loosestrife.
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.
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.
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.