Purple Loosestrife Control In Michigan

Purple Loosestrife is a beautiful plant, but it poses a serious threat to the waters, wetlands and streams in Michigan.

Purple Loosestrife was brought to the eastern US in the early 1800’s from Europe for medicinal purposes and to be an ornamental landscape plant.

This seems to be a pattern with how many invasive plants come to our country. Someone long ago thought it would be a good idea to bring the seeds here to grow the plant for its beauty and or its uses in early medicine, but they were unaware of the future consequences of this seemingly innocuous action.

This plant has been very popular in the past and, because of its beauty, is still desired today with gardeners of all skill levels. The horticultural industry has made strides to engineer sterile variants of Purple Loosestrife, especially because this plant’s flowers are a favorite with pollinators such as honeybees and bumble bees. In Michigan the only variant that is allowed to be planted and cultivated are the sterile varieties.

This plant may be pretty, but it is also very destructive and harmful to our water habitats here in Michigan. Due to Purple Loosestrife being a prolific and opportunistic grower, this makes it very difficult to control. Each plant can produce 2.7 million seeds per year, and it can also grow 10,000 to 20,000 seedlings per square meter.

These plants pose an issue because they rapidly grow into dense stands. Purple Loosestrife stems are very stiff and collect silt and debris and the plants can quickly change shallow water habitats into dry terrestrial ones. Changing the hydrology of the area changes the plant diversity in this area negatively. There is also a concern with the plants growing along rivers where the stiff, dense growing stalks will slow the flow of water and directly affect wetland moisture levels.

 
Purple loosestrife starting to fill up a drainage ditch. | Steve Dewey, Utah State Univ., Bugwood.org

Michigan has an abundance of ideal growing environments for these plants. Purple Loosestrife grows in many soil conditions, and it can grow in many types of water. Purple Loosestrife grows mainly in shallow water, but it also grows in wet meadows, marshlands, ditches in lowlands, and prairie habitats.

Purple Loosestrife is a direct cause of reduction in recreational wetlands and waterways. This plant species is also known to clog irrigation systems, thus hindering cropland irrigation and crop growth.

These are many of the reasons why this invasive plant is classified as a Noxious Weed in 30 states and is on Michigan DNR’s “Report List” and is classified as a high risk weed.

We in Michigan aren’t alone in recognizing the invasive harm purple loosestrife poses. Mississippi and Ohio Invasive Plant Councils consider it one of the worst invasive plants in their states.

Another contributing reason for Purple Loosestrife to be on the “Report List” is how easily this plant’s seeds can be spread. Seeds can be spread via mud on aquatic life, livestock, humans and vehicle tires in mud. The seeds can also be dispersed by birds, wind and water. Sadly, these are not the only reasons this invasive plant has established itself in all US states except Florida and all of the southern provinces of Canada.

Another factor that makes Purple Loosestrife a prolific invasive plant is that it can grow in a variety of soil and light conditions. Purple Loosestrife thrives in open, wet areas with full sun, but it can also grow well in areas with up to 50% shade. It is a perennial aquatic weed that prefers very moist soil or standing water. It can also handle prolonged water logging and can survive in gravel where the water can be as deep as 6 inches below the surface.

Purple Loosestrife seeds, once dispersed, can survive dormant in the soil for many years and can germinate in a variety of environmental conditions. After the plant has established itself in an area, the rhizomic root system grows and in late spring new sprouts emerge from the ground near the parent plant. The sprouts establish themselves in the spring, then grow rapidly and flower in 8 to 10 weeks.

There are several control options when Purple Loosestrife has been found in an area. The control method options can vary depending on the size of the infestation found.

Manual control by hand digging of a single plant or a fairly small infestation is an option. When utilizing this method, caution must be taken when excavating the plant. When hand digging, one must make sure to dig out the entire plant and as much of the rhizomic root system as possible. To begin with this method, start with cutting off the flowering spikes to prevent the seeds from releasing and spreading while digging the plant out of the ground. Digging the plants from loose, sandy soil is the easiest, but in areas where it may be more difficult to dig out, caution must be taken with regards to the root rhizomes. Any damage done to the root rhizomes that are left in the ground can result in new sprouts from the broken roots.

There is a biological option to help with Purple Loosestrife infestations. Galerucella Beetles have been found to mainly feed on the buds, stems and leaves of Purple Loosestrife plants. The beetles feeding on the plant can help to weaken the plant and make it harder for it to reproduce. Doing a controlled release of these beetles can help to reduce the spread of Purple Loosestrife and help increase the biodiversity of the areas that the invasive plant is growing in. The beetles won’t eliminate Purple Loosestrife, but they can slow the rate at which the plant spreads. There is a downside to this control method, however, as it is human-dependent. To be effective, humans need to report the infestation location and then humans need to collect the beetles by hand and relocate them to the new infestation location. This is primarily done by volunteer stewards working with Michigan DNR.

A more permanent, and quicker, control option for dealing with a large area of Purple Loosestrife infestation is using targeted herbicide applications. Improvements have been made to herbicides and additives to make them environmentally friendly and safe for application to plants in standing water.

As with any herbicide application, extreme caution must be taken when applying a herbicide to any kind of water or wetland. That is why this type of application is only allowed to be done by properly licensed, experienced and permitted commercial pesticide applicators.

Properly licensed companies and applicators understand the best herbicide mixes and application rates that are safe for the non-target plants and yet still effective to treat the target plant.  Early locating, identifying and treatment are the keys to successful control of Purple Loosestrife, and any invasive plant. The optimal timing for treatment of Purple Loosestrife is late spring, right around late May or early June. While this is the ideal time for treatment, the treatment window does extend all the way through summer to the end of August.

Owen Tree Service is a MDARD (Michigan Department of Agriculture and Rural Development) licensed commercial pesticide applicator. We have seasoned, experienced and licensed commercial pesticide applicators on staff. Many of our senior applicators have spent the better part of 20 years identifying and treating invasive species along with other nuisance brushy plants throughout Michigan.

We work closely with chemical manufacturers to stay on top of the latest and most effective products as they are developed. We at Owen Tree keep in mind the big questions: is the product effective in controlling the target plant, and what is the application rate that can achieve that control and not affect non-target plants. Our goal in dealing with invasive plants is to have effective control of the target plant with minimal harm to the other surrounding non-target plants.

If you think you may have Purple Loosestrife or another invasive aquatic or upland plants growing on your property, feel free to contact our office and have one of our specialists come out to make a positive identification and develop a plan of action and control. Early identification and early treatment is the key to achieving control of any invasive plant.