Herbicide Application Timing Critical to Control Exotic Hawkweeds

Herbicide Application Timing Critical to Control Exotic Hawkweeds

This article summarizes field studies established on meadow hawkweed at two sites near Santa, Idaho in 2009 by Dr. Tim Prather, University of Idaho. Selective herbicides such as Milestone® have shown to control hawkweeds and release grasses and desirable native forbs. Strategically timed herbicide applications can improve hawkweed control and promote establishment and maintenance of grass cover.


Read More

Managing Invasive Nightshades (Horsenettles) in Natural Areas and Pastures

NightshadeBanner-notext.jpg

By CELESTINE DUNCAN

 

Silverleaf nightshade (Solanum elaeagnifolium) and Carolina horsenettle (Solanum carolinense), also known as horse nettle or bull nettle, are deep-rooted, herbaceous, perennial plants in the nightshade family. Both plants are considered native to the Americas, although silverleaf nightshade may have been dispersed to new locations by Spanish or Portuguese colonists. They are well established throughout much of the U.S. (Figure 1). Carolina horsenettle is considered problematic in the Midwest, eastern U.S., and northeast Canadian provinces, whereas silverleaf nightshade is more problematic in the southern and western U.S.


Figure 1:  Distribution of silverleaf nightshade (top) and Carolina horsenettle (above) in the United States (USDA-NRCS Plants).

Nightshades-Fig1.jpg
Nightshades-Fig1b.jpg

Silverleaf nightshade is declared noxious in Arkansas, California, Hawaii, Idaho, and Nevada and is an “A”-designated weed for quarantine in Oregon and Washington. Carolina horsenettle is declared noxious in Alaska, Arizona (prohibited weed), Arkansas, California (“B”-list), Hawaii, Iowa, and Nevada (USDA-NRCS, 2018).

Silverleaf nightshade and Carolina horsenettle reproduce by seed, rhizomes, and root fragments. Plant stems die in the fall, and new shoots develop from adventitious buds on roots. Stems are 1 to 3 feet in height. Flowers have five petal-like lobes that are about 3/4 inch across, with bright yellow stamens (Sidebar). Flower color ranges from dark violet to blue for silverleaf nightshade, and white to light violet for horsenettle. Individual plants produce up to about 200 fruit that resemble small tomatoes, and each fruit contains from 40 to 120 seeds. Fruit remain on dead branches where they can be spread by machinery, wildlife, livestock, and wind. Seed remain viable for up to 10 years in soil. 

Impacts

Silverleaf nightshade and Carolina horsenettle have the potential to invade natural areas, pastures, and cropland.  Once established, plants form dense colonies from an extensive root system. Infestations reduce crop production, forage quality and quantity, and serve as a host for insects and plant diseases. Plants are adapted to a wide range of habitats, but thrive on disturbed land, including roads, ditch banks, rivers, livestock corrals, and overgrazed lands. 

Both plants contain glycoalkaloids, which are toxic to livestock. Although all parts of the plant are toxic, immature fruit have a higher concentration of glycoalkaloids than mature fruit, leaves, or stems. Damage to the intestinal tract and nervous systems in livestock can occur. In severe cases, ingestion can cause hallucinations, paralysis, and death. Cattle and horses are reported to be more susceptible to toxicity than sheep, while goats are apparently unaffected. Most grazing animals and wildlife avoid grazing the plants. 

Management

Several management methods have been investigated for both weeds. The key to effective control is stopping seed production and killing the root system. Quarantine and exclusion are regarded as the most important control strategies in areas where the plant is not established.

Herbicides

In field trials, silverleaf nightshade and Carolina horsenettle responded similarly to various broadleaf herbicide treatments. Results from studies conducted in the U.S. show that Milestone®, GrazonNext® HL, or Chaparral® specialty herbicides provided significantly better control 90 to 120 days after application than 2,4-D (Figure 2). On sites where other weedy broadleaf plants are present, GrazonNext HL at 1.5 to 2.1 pints per acre will provide more broad-spectrum control than Milestone at 4 to 7 fluid ounces and would be the most cost-effective treatment.  Applications of 2,4-D alone will suppress nightshade shoot growth and fruiting, but result in minimal damage to roots allowing plants to regrow. The optimum time to apply selective herbicides is when nightshades are actively growing at the bud to flower growth stage.

  Figure 2:   Percent control of horsenettle 90-120 days after application of various selective broadleaf herbicides.

Figure 2:  Percent control of horsenettle 90-120 days after application of various selective broadleaf herbicides.


Grazing

Livestock grazing favors invasive night-shades since animals will graze more desirable forage first. Nightshades are poisonous to most livestock; however, goats appear to be unaffected and may reduce flowering and seed production in a targeted grazing program. Do not graze plants when they are fruiting as seed passing through the gut of animals remains viable. If seed are present on a site with grazing livestock, hold animals for at least 7 days to allow seed to pass through before moving animals to a weed-free pasture.

Mechanical Control

Frequent mowing and cutting through-out the growing season may prevent flowering and seed production, while reducing root carbohydrate reserves in invasive nightshades. Cutting once during the growing season will not control either plant, since rosettes will grow below the height of mower blades. Tillage is not recommended, since viable rhizome fragments may be moved to new areas and start infestations. 

Biological Control

The native leaf-galling nematode (Ditylenchus phyllobius) has been used to reduce silverleaf nightshade density with some measure of success, but it is not host specific. The nematode needs to be integrated with other vegetation management practices. Biological control research is not being conducted due to concerns about possible attacks on non-target crops and closely-related native plants. 

Historical Uses

The genus Solanum is derived from the Latin word solamen (quieting), referring to the narcotic properties of many species in this genus. Nightshades are rich in solanine, a poisonous glycoalkaloid that causes gastrointestinal, neurological, and coronary problems. However, glycoalkaloids from the nightshade family have been shown to be effective in a variety of medical applications, including limiting growth of certain cancer cells and treating herpes complex viruses.

Native American tribes utilized silverleaf nightshade to treat a variety of ailments, including toothaches, respiratory problems, colds, eye and stomach ailments, sneezing fits, or constipation. The fruit was also mixed with milk, to produce a curdled beverage or cheese, a use that is still reported to occur in the desert southwest and Mexico.

Nightshades-Sidebar.jpg

References

Boyd, J W, D S Murray, and R J Tyrl. 1984. Silverleaf nightshade, Solanum elaeagnifolium, origin, distribution, and relation to man. Economic Botany 38:210-216.

Burch, Pat. Field Scientist, DowDuPont.

CABI Invasive Species Compendium. Solanum elaeagnifolium (silverleaf nightshade). Accessed January, 2018. Online: www.cabi.org/isc/datasheet/50516

DiTomaso, JM, GB Kaiser et al. 2013. Weed Control in Natural Areas in the Western United States. Weed Research and Information Center, Univ. of California. 544 pp. Online: wric.ucdavis.edu/information/natural%20areas/wr_S/Solanum.pdf 

Dow AgroSciences. Unpublished field data.

Eleftherohorinos IG; Bell CE; Kotoula-Syka E, 1993. Silverleaf nightshade (Solanum elaeagnifolium) control with foliar herbicides. Weed Technology, 7(4):808-811

Más EG; Lugo-Torres MLde, 2013. Malezas Comunes en Puerto Rico & Islas Vírgenes Americanas (Common Weeds in Puerto Rico & US Virgin Islands). USDA Servicio de Conservación de Recursos Naturales. Ârea del Caribe/Caribbean Area. Online: www.nrcs.usda.gov/wps/portal/nrcs/detail/plantmaterials/newsroom/feature/?cid=stelprdb1078250

PIER, 2014. Pacific Islands Ecosystems at Risk. Honolulu, USA: HEAR, University of Hawaii. Online: www.hear.org/pier/index.html 

Silverleaf Nightshade—Texas Beyond History. Online:
www.texasbeyondhistory.net/ethnobot/images/silverleaf.html

Thinakaran, J, E Pierson, M Kunta, JE Munyaneza, CMRush and DC Henne. 2015. Silverleaf Nightshade (Solanum elaeagnifolium), a Reservoir Host for ‘Candidatus Liberibacter solanacearum’, Volume 99 No 7. Pg 910-915. Online: doi.org/10.1094/PDIS-12-14-1254-RE 

USDA, NRCS. 2018. The PLANTS Database (plants.usda.gov, 20 January 2018). National Plant Data Team, Greensboro, NC 27401-4901 USA.

Zhu, X, H Wu, R Stanton, GE Burrows, D Lemerle and H Raman. 2013. Time of emergence impacts the growth and reproduction of silverleaf nightshade (Solanum elaeagnifolium Cav.). Weed Biology and Management, 13: 98–103. doi:10.1111/wbm.12015 


®™Trademark of The Dow Chemical Company (“Dow”) or an affiliated company of Dow.

Milestone, GrazonNext HL, and Chaparral specialty herbicides specialty herbicides are not registered for sale or use in all states. Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your state.

When treating areas in and around roadside or utility rights-of-way that are or will be grazed, hayed or planted to forage, important label precautions apply regarding harvesting hay from treated sites, using manure from animals grazing on treated areas or rotating the treated area to sensitive crops. Consult the label before purchase or use for full details. Always read and follow label directions.

Horseback Team Key to Protecting Jackson Hole Backcountry

  Dave Hanna managing invasive plants in Jackson Hole, WY.

Dave Hanna managing invasive plants in Jackson Hole, WY.


By CELESTINE DUNCAN. Photos by Dave and Karin Hanna.

 

Teton County Wyoming lies in the heart of the Yellowstone Ecosystem and is home to some of the most spectacular scenery on Earth. Rugged peaks, high-elevation lakes, meandering rivers, and broad meadows characterize the 2.7 million acres. More than 97 percent of the county is public land, including Grand Teton National Park, Bridger-Teton National Forest, the National Elk Refuge, and about 40 percent of Yellowstone National Park. 

 FIGURE 1: Multi-day trips into the Teton and Gros Ventre Wilderness are needed to monitor and treat invasive plants.

FIGURE 1: Multi-day trips into the Teton and Gros Ventre Wilderness are needed to monitor and treat invasive plants.

Each year more than three million tourists come to Teton County for hiking, wildlife viewing, and other recreational opportunities. With high public use and more than 1,270 miles of trails in the county, the opportunity for introduction and spread of invasive plants is high. 

Mark Daluge, Assistant Supervisor for Teton County Weed and Pest District, believes that trails serve as the primary vector for weeds into the backcountry. “Managing these areas is a real challenge due to remoteness, use restrictions, and a short growing season,” Daluge explains. 

Hiking crews historically controlled invasive plants in the backcountry; however, the work was inefficient, exhausting, and treated areas were limited to a half-day hike. Daluge explains, “Crews with backpack sprayers can cover about 2 to 3 miles a day and need to be near a water source. This greatly limits the miles of trails that can be covered in a season.”

Since 2004, contractors with horse-mounted equipment have been hired to monitor and control invasive plants along backcountry trails. The horseback crews are much more efficient and can cover about 13 or more miles of trail per day. They can also carry food, water, and camping supplies for multi-day trips (Figure 1). 

Partners with the Jackson Hole Weed Management Association provide funding for the project (Sidebar 1). The Teton County Weed and Pest District provides herbicide, GIS support, and contract oversight.  Priorities for monitoring and control are established based on risk for invasion, threat to native plant communities, and operating budget.

HorsebackSprayingHorses-Sidebar1.jpg

Dave and Karin Hanna, owners of Hanna Outfitting, have contracted weed management in the backcountry for the past 12 years. “We initially started using the Saddle-light sprayers, but over the years have adapted our equipment to better fit the steep terrain we are working in,” explains Karin Hanna (Figure 2). 

The Hannas switched from the standard 5-gallon canisters to 3-gallon canisters to reduce stress on the animals. Dave custom-builds their panniers to carry the smaller canisters, extra CO2 containers, herbicide concentrate, and supplies for emergency repairs in the field (Figure 3). Water for mixing the spray solution is dipped from streams and filtered before pouring into canisters.


  Figure 2 : Karin Hanna and pack mules managing invasive plants along trails in Grand Teton National Park.

Figure 2: Karin Hanna and pack mules managing invasive plants along trails in Grand Teton National Park.

  Figure 3:  Dave Hanna treating cheatgrass on steep hillsides in the backcountry.

Figure 3: Dave Hanna treating cheatgrass on steep hillsides in the backcountry.

The Hannas have five mules and four horses that they rotate throughout the summer season. All the stock is tolerant of packs, spray equipment, and most hazards—which include hikers, grizzly bears, and steep terrain. “The mules are more than 7 years old, so they have the maturity to handle stressful situations,” explains Karin. “Our best horses are ones that we introduced to the program when they were just two years old and trailed behind the more experienced animals. Growing up with the program adjusts the horses to the sounds of the spray equipment and demanding situations that occur in a typical work day.”

Over the last five years, the Hannas have inventoried and treated newly invading weeds on 4,723 miles of trail and hillsides, or an average of 945 miles per season. The Hannas track distance and treatment areas with a GPS, storing their data with the weed district. Noxious weeds targeted in the backcountry include spotted knapweed, musk thistle, houndstongue, yellow and Dalmatian toadflax, whitetop, and cheatgrass. Milestone® specialty herbicide  alone at 7 fluid ounces per acre or Opensight® specialty herbicide  at 2.5 ounces of product per acre control the majority of broadleaf weeds along the trail.

The horseback project is key to Teton County’s Early Detection Rapid Response (EDRR) program for areas that are at high risk for invasion. Riders can closely monitor about 150 feet on either side of the trail and can identify more remote satellite infestations with binoculars. That means each year at least 34,360 acres are inventoried and newly invading plants treated within the high-risk corridors. Based on these figures, the annual cost of protecting the backcountry is about $1.50 per acre, excluding herbicide and oversight expenses (Sidebar 2). 

Mark Daluge summarizes his thoughts on the program. “The horseback program is critical in the protection of pristine areas around Jackson Hole. By implementing EDRR in these areas on a consistent yearly basis, we can continue to protect the backcountry. Without this horseback program, we would never be able to treat and inventory the miles of single track trails, and difficult terrain areas would most likely be left untreated.”

For additional information on invasive plant management in the Greater Yellowstone Area:

HorsebackSprayingHorses-Sidebar2.jpg

®TMTrademark of The Dow Chemical Company (“Dow”) or an affiliated company of Dow.

Milestone and Opensight specialty herbicides are not registered for sale or use in all states. Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your state.

When treating areas in and around roadside or utility rights-of-way that are or will be grazed, hayed, or planted to forage, important label precautions apply regarding harvesting hay from treated sites, using manure from animals grazing on treated areas or rotating the treated area to sensitive crops. See the product label for details. State restrictions on the sale and use of Milestone and Opensight apply. Consult the label before purchase or use for full details. Always read and follow label directions.

The Most Popular Mobile Applications (Apps) for Invasive Plant Managers

The Most Popular Mobile Applications (Apps) for Invasive Plant Managers

In January 2018, a web-based survey on mobile applications was emailed to invasive plant managers to identify mobile-device applications currently used to support invasive plant management activities and share information on how individual apps ranked in terms of user satisfaction. Details on demographics and affiliation for this survey are available at here.

Read More

Midwest/East Region Summary: The Most Popular Mobile Applications for Invasive Plant Managers

Midwest/East Region Summary: The Most Popular Mobile Applications for Invasive Plant Managers

In January 2018, a web-based survey on mobile applications was emailed to invasive plant managers to identify mobile-device applications currently used to support invasive plant management activities and share information on how individual apps ranked in terms of user satisfaction. Results from midwestern and eastern states are summarized in this article.

Read More

West Region Summary: The Most Popular Mobile Applications for Invasive Plant Managers

West Region Summary: The Most Popular Mobile Applications for Invasive Plant Managers

In January 2018, a web-based survey on mobile applications was emailed to invasive plant managers to identify mobile-device applications currently used to support invasive plant management activities and share information on how individual apps ranked in terms of user satisfaction. Results from western states are summarized in this article.

Read More

Managing Autumn Olive in Natural Areas

Autumn olive is an invasive woody shrub or small tree that grows to about 20 feet in height. The plant is commonly found invading open and early-successional woodlands, abandoned agricultural fields, and edges of streams and rivers.

Read More

Autumn Olive and Russian Olive—What’s the Difference?

Autumn Olive and Russian Olive—What’s the Difference?

Autumn olive (Elaeagnus umbellata) and Russian olive (Elaeagnus angustifolia) are invasive, deciduous, woody shrubs or small trees that were introduced for landscaping, soil stabilization, and wildlife food/cover. Both plants became invasive in riparian areas, open forests, lake shores, and abandoned fields.

Read More

Managing Garlic Mustard in Natural Areas

GarlicMustard-banner.jpg

By CELESTINE DUNCAN


  FIGURE 1:  Distribution of garlic mustard in the U.S. and Canada  (USDA-NRCS Plants; EddMaps)

FIGURE 1: Distribution of garlic mustard in the U.S. and Canada (USDA-NRCS Plants; EddMaps)

Garlic mustard (Alliaria petiolata) is a cool-season, invasive, herbaceous plant that is invading temperate forests throughout much of North America (Figure 1). The plant is native to Eurasia and northern Africa, and was introduced into the U.S. for food and as a medicinal plant. It is well established in the upper Midwest and eastern U.S., and is reported across the northern half of the U.S., Alaska, and parts of Canada. 

Garlic mustard is shade tolerant and can move into stable forest understory where it rapidly out-competes native vegetation. Once established, the plant is capable of forming near-monotypic stands that suppress growth and recruitment of native plants and tree seedlings. Research has shown that garlic mustard can interrupt the associations that plants form with mycorrhizal fungi. 

Garlic mustard is a biennial or short-lived perennial that can grow to about 3 feet in height. Seeds germinate early in spring, and new seedlings produce numerous kidney-shaped basal leaves that remain green throughout winter (Figure 2). In the second year, plants develop a vertical stem with alternative leaves that are more triangular or heart-shaped (Figure 3). All foliage produces a garlic-like odor when crushed. Stems often branch near the top and have individual flowers that alternate up the stem. Flowers have four white petals about ¼ inch long, four sepals, and six stamens. Fruits are long and linear, and individual plants can produce up to 8000 seed. 

  FIGURE 2:  Garlic mustard seedlings produce numerous round- to kidney-shaped basal leaves that remain green throughout winter.  Photo by Mark Renz, University of Wisconsin.

FIGURE 2: Garlic mustard seedlings produce numerous round- to kidney-shaped basal leaves that remain green throughout winter. Photo by Mark Renz, University of Wisconsin.

  FIGURE 3:  Garlic mustard stems bolt in the second growing season, and have alternative, heart-shaped leaves and white flowers.  Photo by Chris Evans, University of Illinois, Bugwood.org.

FIGURE 3: Garlic mustard stems bolt in the second growing season, and have alternative, heart-shaped leaves and white flowers. Photo by Chris Evans, University of Illinois, Bugwood.org.


Management

Garlic mustard is difficult to eradicate once plants have established and produced seed. Since the plant quickly invades disturbed sites, management efforts should strive to reduce soil and vegetation disturbance. Early detection and removal of new infestations before they produce seed will reduce the need for long-term management. If plants have produced seed, the site must be monitored and germinating seedlings removed for at least 10 years if eradication is the goal. 

Garlic mustard spreads from established infestations along an invasion front. Small, satellite infestations often occur along trails, roads, or forest edges by seed transport. Management priority should be given to removal of these satellite infestations.

Herbicides

Field trials were conducted on garlic mustard to compare efficacy of Vastlan® and Garlon® 4 Ultra specialty herbicides to Accord® XRT II herbicide. Results of the study showed that both Garlon 4 Ultra and Accord XRT II provided excellent control of garlic mustard 38 days after application (Figure 4). Garlon 4 Ultra is a selective herbicide that will control garlic mustard and allow desirable grasses to thrive. Apply Garlon 4 Ultra at 16 to 32 fluid ounces of product per acre (oz/A), or as a spot application of 1.25 percent volume to volume (% v/v). Applications should be made to foliage in spring when plants are in the rosette growth stage. Use caution when applying herbicide solution near stems of desirable woody plants as injury may occur.

Accord XRT II applied at 1 to 1.5% v/v provides effective control of garlic mustard seedlings and rosettes. Accord XRT II is a non-selective herbicide, which can kill or damage most plants that are contacted by the spray solution. Garlic mustard must be actively growing to absorb the herbicide. Applications of Accord XRT II in late winter and early spring can often be timed for periods when few if any other plants beside garlic mustard are actively growing. 


  FIGURE 4:  Percent control of garlic mustard 38 days following application of several herbicides. Application rates are shown as percent volume to volume (v/v).

FIGURE 4: Percent control of garlic mustard 38 days following application of several herbicides. Application rates are shown as percent volume to volume (v/v).


Physical and Mechanical Control

Individual garlic mustard plants can be controlled by digging. Cutting the entire taproot with a sharp shovel or spade 1 to 2 inches below the soil surface will control plants. Soil disturbance should be minimized to reduce garlic mustard reinvasion. Mowing or cutting of above-ground growth should be done as low as possible to reduce flowering and seed production. If garlic mustard is flowering, it is important to remove all cut stems since viable seed may be produced even if the stem is severed from the root. Because mechanical cutting does not remove the root crown, it may be necessary to cut multiple times in a growing season to prevent seeds from developing on secondary stems that sprout from the rootstock. Mowing may impact desirable non-target vegetation.

Prescribed Fire

The effectiveness of fire as a control tool for garlic mustard differs based on site characteristics. Research shows that dormant-season fires do not control garlic mustard; however, fires conducted after garlic mustard emergences but prior to emergence of desirable plants may be effective. Repeated burns (fall, spring, spring; or spring, spring, spring), have been used to maintain garlic mustard in a reduced condition and stimulate herbaceous species richness and cover. Integrating herbicide treatments with fire may be more effective than fire alone.

Biological Control

Research is underway to develop biological control of garlic mustard. Currently, six species are identified as possible candidates for biological control agents. Future biological controls will be an essential component of integrated management of garlic mustard.


References

  1. Becker, R. and others. 2013. Biology and biological control of garlic mustard. Forest Health Technology Enterprise Team FHTET-2012-05. Online: www.stewardshipnetwork.org/sites/default/files/garlic_mustard_biocontrol.pdf
  2. Blossey, B., V. Nuzzo, H. Hinz, E. Gerber. 2001. Developing biological control of Alliaria petiolata (M.Bieb.) Cavara and Grande (Garlic mustard). Natural Areas Journal 21: 357-367.
  3. DiTomaso, JM, GB Kyser et al. 2013. Weed Control in Natural Areas in the Western United States. Weed Research and Information Center, Univ. of CA. 544pp.
  4. Dow AgroSciences, Unpublished field data. 
  5. EDDMapS. 2018. Early Detection & Distribution Mapping System. The University of Georgia — Center for Invasive Species and Ecosystem Health. Online: www.eddmaps.org/; last accessed February 1, 2018.
  6. Evans, JA, AS Davis, RA Lankau, AS Davis, S Raghu, DA Kabdus. Soil-mediated eco-evolutionary feedbacks in the invasive plant Alliaria petiolata. Functional Ecology, 2016; DOI: 10.1111/1365-2435.12685
  7. Nuzzo, V.A. 1991. Experimental control of garlic mustard [Alliaria petiolata (Bieb.) Cavara and Grande] in northern Illinois using fire, herbicide and cutting. Natural Areas Journal. 11: 158-167.
  8. Nuzzo, V.A., 1996. Impact of dormant season herbicide treatment on the alien herb garlic mustard (Alliaria petiolata (M.Bieb.) Cavara and Grande) and groundlayer vegetation. Transactions of the Illinois State Academy of Science. 89: 25-36.
  9. Nuzzo, V.A., W. McClain, and T. Strole. 1996. Fire impact on groundlayer flora in a sand forest. The American Midland Naturalist. 136: 207-221.
  10. Pardidi, EA, JM Drake, JM Chase, and TM Knight. 2009. Complex population dynamics and control of the invasive biennial Alliaria petiolata (garlic mustard). Ecological Applications.19:2. pp387-397.
  11. USDA, NRCS. 2018. The PLANTS Database (plants.usda.gov, 1 February 2018). National Plant Data Team, Greensboro, NC 27401-4901 USA.

®™Trademark of The Dow Chemical Company (“Dow”) or an affiliated company of Dow. 

State restrictions on the sale and use of Garlon 4 Ultra specialty herbicide and Accord XRT II apply. Consult the label before purchase or use for full details. 

Vastlan specialty herbicide is not registered for sale or use in all states. Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your state. 

Always read and follow label directions.

Active ingredients for herbicide products mentioned in this article: Vastlan specialty herbicide (triclopyr-amine), Garlon 4 Ultra (triclopyr-ester), and Accord XRT II (glyphosate).

Identification & Management of Purple Loosestrife

PurpleLooseleaf-banner.jpg

By CELESTINE DUNCAN


  FIGURE 1:  Distribution of purple loosestrife in Canada and the United States.  Adapted from USDA, NRCS Plants and Wilson et al.

FIGURE 1: Distribution of purple loosestrife in Canada and the United States. Adapted from USDA, NRCS Plants and Wilson et al.

Purple loosestrife (Lythrum salicaria L.) is a perennial, rhizomatous forb that invades riparian areas and other waterways throughout most of the U.S. and southern Canada (Figure 1). The plant was first introduced into North America in the early 1800s as an ornamental and subsequently escaped cultivation. It is currently reported in all U.S. states, except Florida and Hawaii, as well as in nine Canadian provinces.

  FIGURE 2:  Flowers are bright rose to purple and are the most identifiable characteristic of the plant. They are arranged on a spike.  Photo by Steve Dewey, Utah State University, Bugwood.org.

FIGURE 2: Flowers are bright rose to purple and are the most identifiable characteristic of the plant. They are arranged on a spike. Photo by Steve Dewey, Utah State University, Bugwood.org.

Purple loosestrife spreads primarily from seed, but new plants can also establish from root fragments and stem cuttings. Aerial shoots arise in spring from buds at the top of the root crown and can grow to more than 8 feet in height. Stems are square-shaped, five- or six-sided, and can be either smooth or covered with downy hairs. Bright rose to purple flowers are the most identifiable characteristic of the plant. Flowers are arranged on a spike, which can be a few inches to 3 feet long (Figure 2). The seed capsule is two-celled and contains very small seeds, with individual plants producing about 2.7 million seeds. Root crowns can spread to about 20 inches in diameter in a mature plant.  

Management

Successful management of purple loosestrife requires integrating various control methods.  Pulling and digging can be effective on individual plants that are not well established. Selective herbicides alone and in combination with biological control agents can effectively contain and control estab-lished infestations.

Herbicides

Field studies conducted on purple loosestrife show that Vastlan® specialty herbicide at 1 to 1.5 percent solution (4 to 6 quarts of Vastlan per acre) will provide good control of loosestrife for up to one year following application (Table 1). 

  TABLE 1:   Percent purple loosestrife control with Milestone® or Vastlan® specialty herbicides, compared to Rodeo® herbicide the season of application and one year following application. [ 1 ]  (DAA=Days After Application)

TABLE 1:  Percent purple loosestrife control with Milestone® or Vastlan® specialty herbicides, compared to Rodeo® herbicide the season of application and one year following application. [ 1 ]  (DAA=Days After Application)

[ 1 ] Data averaged from two field trials for 64-80 DAA; and from one site 377 DAA. Total application volume ranged
from 30 to 50 gallons per acre.

[ 2 ] Percent solution is based on “spray to wet” total application volume of about 100 gallons per acre.


A non-ionic surfactant approved for use in aquatic environments should be added to the spray mixture at 0.25 percent volume to volume (1 quart in 100 gallons of water).  

Purple loosestrife often establishes and flourishes on non-irrigation ditches and seasonally dry wetlands. On these sites, Milestone® specialty herbicide applied at 7 fl oz/A, or at the spot treatment rate of 14 fl oz/A, will provide good to excellent control for a year or more after application (Table 1). The addition of  1 pint per acre of 2,4-D with Milestone at 7 fl oz/A provides additional control.

  FIGURE 3:  Purple loosestrife control with Rodeo® at 6 quarts per acre (top) compared to Milestone® at 7 fluid ounces per acre (above). Both treatments provided good control of purple loosestrife, but Rodeo damaged desirable grasses.  Photos by Dow AgroSciences.

FIGURE 3: Purple loosestrife control with Rodeo® at 6 quarts per acre (top) compared to Milestone® at 7 fluid ounces per acre (above). Both treatments provided good control of purple loosestrife, but Rodeo damaged desirable grasses. Photos by Dow AgroSciences.

Rodeo® at 1 to 1.5 percent solution (4 to 6 quarts Rodeo per acre) will control purple loosestrife (Table 1). However, it is important to note Rodeo is non-selective and will injure or kill desirable grasses (Figure 3). Vastlan and Milestone are selective herbicides that will control broadleaf plants but will not kill cattail or desirable grasses at the recommended application rate. 

Herbicides should be applied at the bud to mid-flower growth stage.   Plant foliage should be thoroughly wetted with the herbicide solution during application. Follow-up applications will be needed a year after treatment to control seedlings and any regrowth that may occur from mature crowns.

Purple loosestrife is often difficult to locate until the plant blooms. Clipping, bagging and removing flower heads from the infested site may be necessary to stop seed production at mid-flower growth stage and beyond. 

 


Biological Control

Biological control agents alone and in combination with herbicides can be used on large, well-established purple loosestrife infestations. 

Four species of beetles were introduced into the U.S. and Canada to control purple loosestrife. Galerucella pusilla and G. calmariensis are leaf-eating beetles that affect growth and seed production by feeding on leaves and new shoot growth of purple loosestrife plants. Hylobius transversovittatus is a root-boring weevil that deposits its eggs in the lower stem of purple loosestrife plants. The flower-feeding weevil, Nanophyes marmoratus, reduces seed production of purple loosestrife. The two Galerucella spp. have been the most successful of the four agents in establishing and reducing purple loosestrife density in the U.S.

Long-Term Management and Treatment

Loosestrife produces a vast quantity of seed that can germinate following herbicide application. Once the original infestation is controlled, new plants must be managed for several years. Long-term monitoring, vigilantly controlling newly emerging plants, and encouraging a desirable plant community will reduce reinvasion potential of purple loosestrife.


References

  1. Dow AgroSciences Unpublished Field Data.
  2. Lym, R. 2008. Purple loosestrife control with aminopyralid applied alone or with 2,4-D or triclopyr.  Western Society of Weed Science Research Progress Report. ISSN-0090-8142. Pp 139-140.
  3. Merentz, Joe. USDA-APHIS, Personal communication. January 2018.
  4. Nelson, LS, KD Getsinger, and JE Freedman. (1995) Selective Control of Purple Loosestrife with Triclopyr. Wetlands Research Program Technical Report WRP-SM-4. 
  5. Peterson, Vanelle. Field Scientist (retired). Dow AgroSciences.
  6. Wilson, LM, M Schwarzlaender, B Blossey and CB Randall. Biology and Biological Control of Purple Loosestrife. Forest Health Technology Team. Online bugwoodcloud.org/resource/files/6225.pdf.
  7. USDA, NRCS. 2018. The PLANTS Database (plants.usda.gov, 2 January 2018). National Plant Data Team, Greensboro, NC 27401-4901 USA.

® ™ Trademark of The Dow Chemical Company (“Dow”) or an affiliated company of Dow. Milestone and Vastlan specialty herbicides are not registered for sale or use in all states. Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your state. 
Label precautions apply to forage treated with Milestone and to manure from animals that have consumed treated forage within the last three days. Consult the label for full details. Always read and follow label directions.

Active ingredients for herbicide products mentioned in this article: Milestone specialty herbicide (aminopyralid), Vastlan specialty herbicide (triclopyr-amine), Rodeo (glyphosate), and 2,4-D (2,4-Dichlorophenoxyacetic acid).

Native and Exotic Thistles: Who's Jekyll, Who's Hyde?

Native and Exotic Thistles: Who's Jekyll, Who's Hyde?

There are five common exotic thistles (exluding Centaurea spp., both the starthistles and knapweeds) in the western U.S. that are problematic to some degree across a variety of habitats.

Read More

Studies explore the influence of plant-pollinator interactions on native plant communities threatened by invasive plants

Studies explore the influence of plant-pollinator interactions on native plant communities threatened by invasive plants

Two field studies in Montana and Illinois explore the influence of plant-pollinator interactions on native plant communities threatened by invasive plants.

Read More

Understanding Performance of Your ATV-Mounted Boomless Spray Nozzles

Understanding Performance of Your ATV-Mounted Boomless Spray Nozzles

All-terrain vehicles (ATVs) with small-capacity spray tanks and boomless nozzle systems are well adapted to uneven terrain and are thought to have potential to spray 25 to 30-foot swaths using a centrally located single or dual nozzle arrangement. This article summarizes field studies by Robert Wolf and others at Kansas State University to evaluate the effectiveness of spray nozzles on ATVs.

 

Read More

Spotted Knapweed Management with Herbicides

Spotted Knapweed Management with Herbicides

Spotted knapweed (Centaurea stoebe) is a tap-rooted perennial forb that spreads by seed. Seedlings and mature plants over-winter in a rosette stage and resume growth in early April. Spotted knapweed blooms from mid to late July through mid September.

Read More