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.
Estimate the size and density of the infestation, and use the following chart to choose one or more appropriate loosestrife control options.
In areas too heavily infested to pull, cut or dig plants, these control techniques can still be used to control plants that may sprout as a result of seeds escaping the area. Watch drainage ditches or streams leading from heavily infested areas, as new purple loosestrife colonies are likely to become established there. Pulling, cutting, or digging plants in these more manageable infestations will limit the spread of purple loosestrife beyond the area of heavy infestation.
Key to Chart Symbols
Glyphs used in the accompanying chart.
Digging and Pulling, Chemical Control, Cutting, and Biological Control
Digging & Hand Pulling: Pulling purple loosestrife by hand is easiest when plants are young (up to two years) or when 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.
Cutting: 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.
Biological Control: In areas of severe purple loosestrife infestation, manual and chemical control efforts are ineffective and may in fact contribute to the problem. However, the use of specially selected insects that feed on purple loosestrife is being studied to determine the effectiveness of this method for long-term control in these higher density areas. Biological control is discussed in more detail in a following section.
Chemical Control: If an infestation is in a dry, upland area, and on your own property, an approved herbicide can be applied to individual plants by selective hand spraying. Broadcast spraying is not recommended as it kills all broad-leaved plants, leaving the area open to further invasion from nearby sources of purple loosestrife. This also provides an opportunity for seeds present in the soil to sprout.
Chemical control is used in the United States to control purple loosestrife near or in water, however, as of 1996, no herbicide has been approved for this type of application in Canada. NOTE: In the U.S. a permit is required; call a state natural resource agency for more information.
Things to Keep in Mind
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 it has not yet gone 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.
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.
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 loosestrifes.
