Management and Control
Due to the prolific nature of purple loosestrife, its ability to disperse long distances, and the diversity of public and private land owners involved, effective long-term control requires a coordinated and cooperative effort. Controlling loosestrife downstream from a major seed source is a futile effort. Therefore, we propose to target loosestrife on a watershed basis, beginning with the headwater regions and working towards the mouth. GLIFWC has been working in the Bad River - Chequamegon Watershed to control purple loosestrife since 1988 using an Integrated Pest Management (IPM) approach. The IPM program combines educational efforts to deter additional introductions, chemical control for small isolated populations, biological control for large infestations or where chemical is inappropriate, constant evaluation & monitoring of ongoing efforts and interagency coordination and cooperation.
Manual Control
Only for use on very small stands and isolated plants.
Cutting Flower Heads: removing the flower heads before they mature will prevent dispersal and additional plants in the future.
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Digging and Hand Pulling: small infestations consisting of young plants in loose soils can be successfully treated if the entire rootstock is removed. However, the roots of large plants or plants in compacted soils will break and grow into new plants, thereby exacerbating the problem.
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Chemical Control
For use on small to moderate stands and large stands where biological control is not suitable.
Herbicides: many sites have been effectively treated with varying formulations of Glyphosate (available commercially as "Roundup" and "Rodeo") or Triclopyr (available commercially as "Garlon 3A") depending on site characteristics. Consult your local resource agency for advice and possible permits prior to treating any loosestrife infestations with herbicide.
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Biological Control
Biological control is most effective on large stands of purple loosestrife that have more than 1,000 plants or cover more than an acre of land.
After undergoing an intensive screening process to ensure that biocontrol agents will not feed on native plants and agricultural crops, four biological control species were approved and introduced in North America. These species were a root-boring weevil, Hylobius transversovittatus; a flower feeding weevil, Nanophyes marmoratus; and two species of leaf eating beetles, Galerucella calmariensis and Galerucella pusilla. Hylobius transversovittatus weevils mine the stem and root tissue causing fatal damage to the plants' food storage and retrieval system. Nanophyes marmoratus weevils severely reduce seed production of purple loosestrife by feeding on their flowers. Galerucella spp. beetles feed heavily upon the leaves of the plant seriously affecting its ability to undergo photosynthesis causing high plant mortality, reducing shoot growth, preventing or delaying flowering and can reduce seed production.
The detrimental impact to purple loosestrife through biological control can be significant. The object is not to completely eradicate the weed, but to reduce and maintain its numbers at levels in balance with the native ecosystem. Purple loosestrife may still remain but it will no longer dominate the site, allowing native plants and animals to reestablish their own populations.
Due to an easy rearing process and their effectiveness of controling purple loosestrife, Galerucella beetles are used most often by both agencies and the general public. GLIFWC's past biological control efforts focused on rearing Galerucella beetles. After four years of rearing and releasing Galerucella beetles, populations have been established allowing us to collect beetles from established populations and move them to new infestations. For more information on GLIFWC's purple loosestrife program please contact Miles Falck.
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For more information on:
| Biocontrol Screening Process | Hylobius transversovittatus | Nanophyes marmoratus |
Life History of Galerucella calmariensis and G. pusilla
Galerucella calmariensis and G. pusilla are two European leaf-eating beetles from the family Chrysomelidae. There are also three native species of Galerucella in North America, Galerucella nymphaeae, G. stefanssoni, and G. quebecencis, however none of them have evolved with purple loosestrife as a host plant. Since the two European species are nearly identical both in their life cycles and their morphology they will be referenced together.
Identification
G. calmariensis and G. pusilla are light brown, sometimes with a darker margin of each elytron. They range from 3 to 6 mm in length, being about half as wide as they are long. "It is sometimes possible to differentiate between the two with some accuracy using spots on the pronotum (one mark for G. calmariensis and two tiny dots on G. pusilla) although variability is present here as well. Some insects of either species may exhibit no markings and adults emerging from pupation do not harden and develop markings for up to ten days from emergence" (Klepinger 5). In the field, Galerucella beetles can be distinguished from flea beetles (sometimes found on loosestrife in late summer) by their movement. Galerucella adults are slow and may fall off of plants when moved. Flea beetles are black, slightly larger, and will jump when disturbed (Laing 4).
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Life Cycle in the Midwest
In spring, overwintering adults emerge from soil and litter below or nearby old loosestrife plants to feed for several days on new foliage before reproduction. Adult feeding has a characteristic "shot-hole" appearance, where they eat clear through the leaf tissue. Females lay egg masses, usually consisting of 2-10 eggs, which can be found on leaves, at leaf axils, or even placed low on the stem. The eggs are round, the size of a pin-head, and white to cream colored. Masses have a thin, black, stringy deposit (frass left by the female) across the tops of the eggs, giving it a "salt and pepper" appearance. Egg-laying peaks in May and June, but will continue into mid-July. Each female is capable of producing 500-1500 eggs (Corrigan 1).
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Seven to ten days after laying, larvae begin to emerge and migrate to shoot tips. First instar larvae feed primarily upon apical meristems while later instars are less discriminant and will feed more heavily on leaves. This type of feeding differentiation helps to reduce competition among larvae. The first two instars are very small and will probably not be seen. Third instar larvae are much larger, with full-grown larvae about ¼ inch in length. Larvae are yellow to orange and have black stripes across the width of their body. Larvae have a characteristic feeding, "window-paning", where where they eat the upper layer of the leaf while leaving the lower layer behind. Feeding generally begins at the top of the plant and works its way down. If larval feeding leads to the complete defoliation of plants, they will migrate to other nearby plants. The larval stage lasts for about three weeks, after which they move down into the soil or litter to pupate. Where high water levels are persistent, larvae may pupate by burrowing into the stem's aerenchyma tissue. They remain as pupae for about two weeks, during which they do not feed and are not mobile.
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Mid-summer, pupating insects begin to emerge as adults to feed and harden. After 7-10 days, the adults move back into the soil and litter to overwinter. This emergence typically lasts from July through September. The total maturation time from egg to adult is about 30-40 days.
Galerucella spp. Impacts
The Galerucella beetles can cause significant damage to purple loosestrife, but it may take 5 to 10 years after the insects become established before populations will be large enough to have such an impact (Malecki et al. 1993). The potential complete defoliation of a plant through combined adult and larval feeding leads to photosynthetic suppression, while first instar larval feeding seriously affects shoot-tips, often rendering a plant incapable of flowering.
Adult shot-hole feeding patterns and larval window-paning, creates leaf damage that greatly reduces the photosynthetic capability of purple loosestrife. This may reduce quantities of starch being stored in the roots and can interfere with the plant's ability to overwinter. Photosynthetic inhibition results in reduced stem height and root length, both essential to overall plant vigor. The feeding of first instar larvae on the apical meristem, reduces plant growth and can prevent flowering. The resultant weakening of loosestrife populations in an area provides an opportunity for native plant species such as cattails, grasses and sedges to return.
Galerucella species are more suited to flooded sites than H. transversovittatus as the adult beetles can fly between plants and all three stages are capable of floating, allowing currents and wind to move them to nearby plants. However, pupation is difficult for Galerucella under conditions with long-term standing water (Klepinger1 6).
Galerucella beetles are susceptible to some insecticides, and sites which will be sprayed with insecticides against adult mosquitos should not be used (Klepinger3 23).
Instructions for the Outdoor Rearing of Galerucella beetles
Materials needed:
| ITEM | QUANTITY |
| Wading pool (6' diameter) | 1 |
| Wire tomato cage (42")* | 10-12 |
| Soil-less planting mix (40qt.) | 2 |
| Time Release fertilizer (2.5 lb.) | 1 |
| 1-4 gallon pot | 8-12 |
| 6' metal posts (or clothesline posts) | 4 |
| Heavy duty string | 1 |
| Sleeve cage | 8-12 |
| Aspirator* | 1 |
| *Optional | |
Collecting and Potting Purple Loosestrife Rootcrowns
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In order to rear beetles, you will need purple loosestrife plants. New, bigger plants are easily grown using old rootcrowns. Rootcrowns are used to grow plants rather than using seeds because the rootcrowns will produce multiple, hardy stems quicker and with much less effort. Collect in the early spring from an older, established stand to ensure larger and healthier rootstock.
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Locate rootstock by looking for groups of dead stems from the previous year's growth. Use a spade to dislodge the clumps and break apart larger rootcrowns. They should fit in the pots being used. Knock away loose soil, and cut away all but about six inches of the dead stems. Live, healthy rootcrowns have a tan to brown color, are pink to whitish in the inside, and are somewhat flexible. Rootcrowns which are dead will be charcoal-black in appearance and brittle. Rootcrowns may be potted immediately, or stored outdoors for a short time. Be sure to keep them moist until you are ready to plant. Collection of rootcrowns will need to take place about 12 weeks prior to the date you plan to release new beetles.
Fill the pots halfway with potting mix and time-release fertilizer. The slow-release fertilizer will provide the plants with needed nutrients throughout the summer (prepare extra pots incase some of the plants do not grow or do as well). Add a rootcrown to each pot and finish filling the pots with potting mix. Be sure that the tops of the rootcrowns are still pointing up when you plant them. Several smaller rootcrowns can be combined to provide the desired six or more healthy stems per pot. Do not press the potting mix into the pot - beetles will move into the top inch of soil to pupate, so this area should remain loose. The first time, water the plants from the top to settle the soil and determine whether more should be added (the pot should be filled to within an inch of the top). Afterwards, water plants by filling the pool only. Watering from the top could affect larval pupation in the top layer.
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Setting up the Rearing Cages
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Place a tomato cage in each pot, pushing them all the way to the bottom. Tie off one end of the sleeve and slide it over the tomato cage and down onto the upper lip of the pot. Place the drawstring in the groove along the upper lip and pull it tight around the pot. It is essential that you have a tight fit between the cage and the pot. If you can't get it tight, or there is no groove, use tape to secure the sleeve cage.
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Place the wading pool outdoors on level ground in full sunlight where air movement is not greatly restricted. Put
the potted plants into the wading pool, evenly spacing them so that air can move freely between the cages. Add
water to the pool, but do not water the tops of the pots again. Support the pots so that they can remain
upright in a wind. The tops of the cages can be tied or pinned to a clothesline overhead (where a clothesline is
unavailable, use four sturdy poles and rope or wire to create one).
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Maintaining the Plants
The most important thing is that the plants have enough water at all times. Keep about three inches of water in the pool. Too much water gives the pots enough buoyancy to easily tip over, so cut an overflow hole into the side of the pool 5 inches from the bottom to prevent this when heavy rainfall occurs. Periodically check that the sleeve cages are still tightly secured around each pot. After several weeks the plants should be ready to receive the Galerucella beetles.
Infesting Plants with Beetles
You should collect/receive enough beetles to add 15-25 adults to each plant. Beetles must be promptly placed on the plants to avoid starvation. Be careful to not expose beetles to temperature or humidity extremes while transporting. To avoid escapees, put the container into an empty sleeve cage and remove 10-12 beetles at a time. Untie the string at the top of the sleeve cage you want to infest with beetles and shake them into the cage. Securely close the cage top. Do this for each rearing pot. The beetles are very good at hiding so many may not be readily visible. Divide extra beetles among the pots.
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Double check the drawstring and if it does not fit securely against the pot use a large rubber band or heavy tape to secure it. Periodically check that the bottoms of the sleeve cages are secured tightly against the pots.
Soon after they are added, the Galerucella adults will begin feeding on the plants. They will begin mating soon after. It may take up to two weeks for females to start laying eggs in small groups on the stems and leaves. Females lay eggs for several weeks. Eggs can be tough to spot through the netting, but eventually you will become an expert at spotting them.
Eggs hatch within two weeks. Larvae are yellow to orange and have black stripes across the width of their body. The first two instars are very small and will probably not be seen. Third instar larvae are much larger, with full-grown larvae about ¼ inch in length. Larvae take about 3 weeks to become full grown. Last instar larvae crawl to the soil and burrow just under the surface where they change into a pupa. They pupate about two weeks, after which the new adult beetles crawl out of the soil and begin to look for food.
The combination of extensive defoliation, new beetles at the top of the cage, and few larvae remaining on the plant indicate that the beetles are ready for release into a wetland. It will take about 6 to 8 weeks from introduction to reach this stage. Do not wait for all of the new adults to emerge. There will probably not be enough food left on the plant for them to survive for very long. If the plant is heavily defoliated and there are still more than 50 larvae on the plant, it may be necessary to supplement feeding with shoots from another pot or backup plant. Place freshly cut shoots in a container of water and add them to the cage. Larvae will move onto the new shoots to feed.
Making the Release
Once the beetles are ready for release, the entire pot must be transported to the release site. Do not lay the plants on their side during transport, and do not leave the beetles inside of a vehicle for a prolonged period of time.
At your release site, choose a location which is not frequently disturbed. Also, beetles prefer areas that receive full sunshine each day. Place potted plants next to purple loosestrife plants already growing in the release area. Space the pots around a 10 meter square area. Set the potted plants where they will remain upright so that the unemerged insects in the pots will be able to safely complete development and emerge. Remove the sleeve and cage from the pot. Invert the sleeve and shake the beetles off of it. Gently place larvae in the sleeve onto purple loosestrife plants. Remaining beetles and larvae will move to new plants. Leave the pots intact for several weeks, until all of the adults have had time to emerge. Don't forget to return at a later date to collect the pots.
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Mark the release site to help you locate the area in the fall and following years to monitor the progress of your release. Be sure to record the exact location of the release site with a diagram and with measurements from permanent landmarks (trees, docks, etc.). It is very important to have multiple means of relocating the release site since large plants, vandals, ice, or heavy snow can easily remove or obscure other markers you will place.
These instructions are based upon Section Two of the Cooperator's Handbook, Rearing and Releasing Natural Enemies to Control Purple Loosestrife, through The Purple Loosestrife Project at Michigan State University. January 1999. pp.14-18.
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Illinois Natural History Survey: Center for Ecological Entomology - Biological Control of Purple Loosestrife Program
Invasive Plants of the Eastern United States - Purple Loosetrife
University of Minnesota - Biological Control of Purple Loosestrife: A Guide for Rearing Leaf-feeding Beetles
North Central Region Agricultural Experiment - Biological control of purple loosestrife using leaf-feeding beetles
USACE: Aquatic Plant Information System - Galerucella spp.
Biological Control Screening Links:Illinois Natural History Survey: Center for Ecological Entomology - Summary of no-choice Host Specificity Tests for Galerucella calmariensis.
Invasive Plants of the Eastern United States - Purple Loosetrife
USACE: Aquatic Plant Information System - Process of Biocontrol
USGS: Northern Prairie Wildlife Research Center - Spread, Impact, and Control of Purple Loosestrife (Lythrum salicaria) in North American Wetlands: The Case for Biological Control
http://www.dnr.state.mn.us/invasives/aquaticplants/purpleloosestrife/biocontrol_gc.html Hylobius transversovittatus Links:Agriculture Canada - Hylobius transversovittatus Goeze. Root-feeding weevil
Cornell University - Biological Control: A Guide to Natural Enemies in North America - Hylobius transversovittatus
Minnesota Department of Natural Resources - Hylobius transversovittatus
Montana War on Weeds - Hylobius transversovittatus Goeze: Root-boring Weevil
USACE: Aquatic Plant Information System - Hylobius transversovittatus
Nanophyes marmoratus Links:Manitoba Purple Loosestrife Project - Biological Control of Purple Loosestrife (Lythrum salicaria) in Manitoba with Nanophyes marmoratus
Minnesota Department of Natural Resources - Nanophyes marmoratus
Montana War on Weeds - Nanophyes marmoratus: Seed Weevil
University of Connecticut: Integrated Pest Management Program - History of Nanophyes marmoratus Life
USACE: Aquatic Plant Information System - Nanophyes marmoratus