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Species Review

Apocynum cannabinum, Indianhemp

Written
August, 2006
Contributors
Sonja Reeves - 1st Author

Reeves, Sonja L. 2006. Apocynum cannabinum, Indianhemp. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: https://research.fs.usda.gov/feis/species-reviews/apocan

DOI
10.2737/feis-species-review-apocan

AbbreviationCommon NameScientific NameClassificationStatus
Plants
APOCANIndianhempApocynum cannabinumLife Form: Plants/Forb
Kingdom: Plantae
Class: Dicot
Order: Gentianales
Family: Apocynaceae
Genus: Apocynum		Fed. Protected: No
Nativity: Native
Invasiveness: Noninvasive

Close up photo of a leafy green shrub with long, narrow leaves, and clusters of white flowers.
Photo of a plant with multiple, red stems and narrow green leaves in a field with brown grasses and mountains in the background.

Taxonomy

The scientific name of Indianhemp is Apocynum cannabinum L. (Apocynaceae) [72]. Hybridization is a common occurrence in this genus [3]. Apocynum × floribundum Greene is a hybrid of spreading dogbane (Apocynum androsaemifolium) and Indianhemp [3,70]. When information specific to Indianhemp is not available, information on the genus Apocynum is given.

Synonyms

  • Apocynumhypericifolium Ait.
  • Apocynum pubescens Mitchell ex R. Br.
  • Apocynum sibiricum Jacq.
  • Apocynum suksdorfii Greene [72]

Other Common Names

common dogbane, dogbane, hemp dogbane, prairie dogbane

General Distribution

Indianhemp occurs in North America [156]. It is found throughout all of the lower 48 United States and most of Canada, including Newfoundland. Historical populations in Maryland have been extirpated [72]. Plants Database provides a distributional map of Indian hemp.

States and Provinces

  • United States: AZ AR CA CO CT DE FL GA ID IL IN IA KS KY LA ME MD MA MI MN MS MO MT NE NV NH NJ NM NY NC ND OH OK OR PA RI SC SD TN TX UT VT VA WA WV WI WY DC PR VI
  • Canada: AB BC MB NB NF NT NS ON PQ SK

Site Characteristics

Indianhemp can grow in diverse environments [113]. It prefers damp locations along streams and ditches and in marshes, though it can be found growing less abundantly in drier locations such as thickets, open woods, and open ground [35,70].
Indianhemp is seldom found on soils low in fertility. It grows best on fertile, medium- to heavy-textured soils [116,160].

The following table describes site characteristics for Indianhemp throughout its distribution.

State/Region/ProvinceSite Characteristics
ArizonaStreambeds in woodlands and riparian woodlands between 3,000 to 7,500 feet (910-2,300 m) [18,74]
CaliforniaDamp/moist places near streams, springs, and ditches below 7,000 feet (2,100 m), sometimes in deserts or a weed in orchards [28,63,101,102]
ColoradoRoadside ditches and floodplains between 3,500 and 7,500 feet (1,100-2,300 m) [61,145,146]
IllinoisPrairies, fields, abandoned fields and rocky woods [89,98]
KansasPrairies, streambanks, roadsides, and "waste grounds" [11]
MinnesotaPipestone National Monument: rock outcrops, woodlands, and tallgrass prairies [13]
MontanaHills, slopes, moist, shady areas, and disturbed areas [17,42]; sometimes found in wetlands, but also occurs in drier sites [115]
West-central MontanaAlong rivers below high water marks, on islands, and low banks. Often in half shade beneath tree canopies, also on gravelly, vernally moist to wet places, and on disturbed sites. Dry to moist valleys [81,82]
NevadaGravelly slopes, damp ditch banks or canyon bottoms from 2,800 to 6,500 feet (850-2,000 m) [73]
NebraskaOccurs in patches in field crops and may occur as a dense infestation throughout the field [160]; ravines and wet meadows [131]
New MexicoMoist, open, or "waste ground" between 3,500 and 7,500 feet (1,100-2,300 m) [91]
New YorkWet meadows and margins of bogs [126]. Rarely found on Fire Island (off Long Island, New York) on dry, open sandflats and sandy dredged material [44]
North CarolinaDisturbed areas, old fields, and roadsides [94]
OhioMoist to mesic fields and thickets, pond and stream margins, moist to mesic woodland openings and borders, railways, roadsides, and other "waste places" [5]
Oregon"Wastelands" and seldom cultivated areas, especially in orchards [139]
South DakotaBlack Hills Hills, streambanks, and railroad embankments [41,93]
TexasOpen or disturbed, often moist ground. Sandy, gravelly, or eroding clayey soils [38]
UtahRoadsides, fields, streambanks, and disturbed sites mainly in riparian communities between 3,200 to 7,700 feet (970-2,350 m). "Poorly kept" agricultural lands [57,152]
VirginiaLow woods [151]
WyomingHills, slopes, and disturbed areas [43]
Great PlainsPrairies, river floodplains, terraces, open or woodland waterways or lakeshores, disturbed roadsides or fields, ditches, and sparsely wooded slopes [58,70]
Intermountain westMoist to moderately moist, disturbed areas along roadsides and ditch-banks between 1,600 to 7,200 feet (500-2,200 m) [34]
Northern Great PlainsBorders of marshes, lakes, streams and other moist to wet places, often in disturbed areas [83]
Ozark MountainsGlades, prairies, open woods, and "waste ground" [33]
Pacific NorthwestA "serious" weed on "wasteland" areas that are infrequently plowed, occasionally a problem in orchards [64,65]
Western U.S.Grows on plains and foothills at elevations up to 7000 feet (2,100 m). Commonly found on gravelly or sandy fields, in meadows, and along creekbeds, irrigation ditches, and fence lines in cultivated pastures [69,140]
British ColumbiaCollected in draws and exposed banks [1]
Nova ScotiaGravelly beaches and cobbly or sandy stream banks [117]
Baja CaliforniaStreams and ditches, meadows, and hillsides [154]

Plant Communities

Indianhemp is not an indicator or dominant species in vegetation types. It is considered a characteristic (secondary) plant species in the wet-meadow vegetation of the Prairie Potholes in North Dakota [132]. In Virginia, Indianhemp is "particularly characteristic" of the Rocky Bars and Shores communities of the palustrine-alluvial floodplain communities [52]. Other communities where Indianhemp is known to occur:

  • Freshwater tidal marsh of the Merrimack River, Massachusetts in the high tide zone [25]
  • Weeping alkali grass (Puccinellia distans) association and seeps in canyons (vertical, loose, sandy soils) in Tsegi Canyon, Arizona [66]
  • Cultivated and uncultivated field crops [64,65,69,89,98,104,140,160]
  • Natural (vs. restored) prairie wetlands in northwest Iowa [124]

Botanical Description

This description provides characteristics that may be relevant to fire ecology, and is not meant for identification. Keys for identification are available [17,31,38,50,57,91,112,125,134,155,158].

Photo of a plant with multiple, red stems and narrow green leaves in a field with brown grasses and mountains in the background.
Photo Credit
Photo by Steve Dewey, Utah State University, Bugwood.org, some rights reserved.

Indianhemp (BY-NC 3.0).

Indianhemp is a native, perennial, broadleaf herb. In some cases, it is considered a weed [15,77,104,119]. It has an erect to ascending growth habit and reaches heights of 2 to 6 feet (0.6-1.8 m) from a spreading root stalk [15,28,77,119,156] Branching is opposite or sub-opposite [156]. The leaves are opposite, ovate to lanceololate, entire, and glabrous to sparingly pubescent beneath [5,15,28,119,156]. The flowers consist of 5 petals occurring in terminal clusters from the leaf axils [15,119]. The inflorescence of Indianhemp is a trichasial cyme. The lateral cymes of the trichasium can continue growing vegetatively to form a complete stem with their own terminal trichasiums [156]. The fruits are slender, pencil-like, hanging pods that are 4 to 8 inches (10-20 cm) long and occur in pairs. Seeds are flat, thin, and tufted with soft hairs [15,77,119]. Indianhemp leaves, stems, and roots all contain milky juice [14,15,28,119].

Indianhemp has 2 underground organs: the 1st are thick, branched, horizontal rhizomes that produce new aerial shoots at variable depths. The 2nd are slender, well-branched, vertical, absorbing roots [99]. These large roots/rhizome systems have been found as deep as 13 feet (4 m) below the soil surface and may extend up to 20 feet (6 m) in radial spread [76,104].

Raunkiaer Life Form

  • Hemicryptophyte
  • Geophyte [114]

Seasonal Development

Seasonal development of Indianhemp begins with emergence in late spring or early summer [69,140]. Established plants initiate growth in the spring from root crown and rhizome buds [116,160]. The lateral cymes continue to add vegetative tissue, prolonging the productive potential of the plant. In this manner Indianhemp may continue bloom and vegetative growth from spring until late in the autumn, giving it a distinct advantage over the much shorter periods of growth of the other Apocynum species [156].
The seasonal nonstructural carbohydrate levels of Indianhemp decline with vegetative growth in the spring, reach seasonal lows during flowering, and then increase until fall dormancy [14].

The following table details the different flowering periods of Indianhemp throughout its distribution.

State/Region/ProvinceAnthesis Period
ArizonaMay to August [74]
CaliforniaJune to August [101,102]
IllinoisMay to August [89,98]
KansasMid-May to mid-August [11]
NebraskaJune to August [131]
NevadaJune to August [73]
New MexicoMay to September [91]
North DakotaJune to July [26]
OhioJune to August [5]
TexasApril to July [38,46]
Utah - Unita BasinJune to August [57]
Great PlainsMay to September [58,135]
Intermountain westMay to August [34]
Northern Great PlainsJune to August, fruiting August to October [83]
Pacific NorthwestJune to September [64,65]
Nova ScotiaJuly to August [117]
Baja CaliforniaJune to July [154]

Phenological data for Indianhemp growing along a tall fescue (Festuca arundinacea) waterway at Lincoln, Nebraska is given below [122].

Growth Stage19771978
EmergenceApril 18April 29
BudMay 20June 2
Early flowerMay 26June 13
Full bloomJune 4June 21
Pod initiationJune 17not produced

Regeneration Processes

Indianhemp regenerates by seed and vegetative means. Regeneration is largely by vegetative means from rhizomes or from root crown buds located at the woody base of stems [15,55,104,119,147].

Close up photo of a leafy green shrub with long, narrow leaves, and clusters of white flowers.
Photo Credit
Photo by Miranda Kohout, iNaturalist.org, no rights reserved.

Indianhemp in bloom.

Pollination and Breeding System

Indianhemp is visited by 19 species of bees and wasps, 17 species of flies, 2 species of butterflies and/or moths, 1 species of beetle, and 2 species of bugs and/or aphids. However, it appears that these visits do not succeed in pollination. Successful transfer of pollen seems to occur only when the insect is trapped in the flower and struggles to escape, in turn collecting pollen [156]. Bees, butterflies, and flies were observed as nectar feeders on Apocynum flowers. Pollen was not observed on any of these insects after visiting the flowers [70]. Indianhemp does not self pollinate [70,156].

Apocynum flowers depend largely on cross-pollination for sexual reproduction [156]. Cross-pollination is frequent in the genus [3].

Seed Production and Predation

Indianhemp can produce numerous seeds [69,113]. A study by Shultz and Burnside [122] in Nebraska reveals that the number of seeds produced by an individual plant is dependent on the amount of competition for water, light, and nutrients. Grown without any competition Indianhemp produced up to 150 pods with 81 seeds per pod. When grown with soybeans (Glycine max), Indianhemp only produced 2 pods/plant on average [122]. Seed production in disturbed areas was around 600/plant [109].

Seed Dispersal

Indianhemp seeds are dispersed by wind and gravity [96,97,139]. The small seeds are specialized for dispersal over long distances. They have a very large, fine coma (a tuft of hairs on the seed) that facilitates wind dispersal [92,108,109,139,147].

Seed Banking

Seed dormancy of Indianhemp is unclear, though viability of Indianhemp seed declines rapidly in soil [23,113]. Burial studies indicated that the seeds are not long-lived and that the seeds do not persist after 1 year in the soil [12,24]. In Pennsylvania Indianhemp has been found in the aboveground vegetation and not in the seed bank [84]. Conversely, Indianhemp emerged from the seed bank of a Delaware River freshwater tidal wetland [86]. Further research is needed on the seed dormancy of Indianhemp.

Germination

Germination ability of Indianhemp seed depends on burial depth and seed age. A long-term study done by Burnside and others [23] tested the viability of seeds buried at a depth of 8 inches (20 cm). At the 1st study site there was 74% seed germination at year 0, 22% seed germination after burial of 1 year, and 0% in years after that. At the 2nd site germination rates were 74% at year 0, 52% after year 1, 13% in year 2, and 1% in year 4 and 6 [23]. In another laboratory study the greatest germination occurred when seeds were buried at 0.4 inch (1 cm), and germination declined greatly at greater depths [116].

A study by Everetts and Burnside [48] comparing temperature and germination of Indianhemp seed revealed that successful germination occurred between 59 ºF to 95 ºF (15-35 ºC). The highest germination rate occurred at 95 ºF (35 ºC).

Stratification inhibited Indianhemp seed germination in a greenhouse study done by Greene and Curtis [59]. After 3 months of stratification 0% of the seeds germinated, while 10% of unstratified seed germinated.

Seedling Establishment and Growth

A study by Everetts and Burnside [48] comparing Indianhemp seedling development and temperature found seedling establishment occurred at 59 ºF to 95 ºF (15-35 ºC). Indianhemp could not establish seedlings at or below 50 ºF (10 ºC) or at or above 100 ºF (40 ºC) [48]. Best establishment occurs on moist sites [108].

Vegetative Reproduction and Regeneration

Apocynum species spread by cloning [70]. Indianhemp reproduces by rhizomes or sprouting from the root crown [15]. Aerial shoots arise from adventitious rhizome buds. Rhizomes spread extensively, forming new plants at "considerable" distances [76,99]. Seedlings are capable of sprouting within 10 to 41 days of emergence [15,119].

Successional Status

Indianhemp is most often referred to as an early successional species. It colonizes disturbed sites, abandoned agricultural fields, and prairie pot hole wetlands [75,100,108]. On restored prairies in Arkansas, Indianhemp established during the 2nd year after disturbance, declined during the 3rd year, and generally disappeared or was greatly diminished by the 4th growing season, when it was overtopped by other species [36].
Indianhemp is occasional in older (20 to 30 years) jack pine (Pinus banksiana) and mixed-hardwood stands in New Brunswick [88].

Immediate Fire Effects

Fire likely top-kills Indianhemp. It is probably resistant to fire-induced mortality because of its deep root and rhizome system.

The development of new Indianhemp plants 100 days following severe fire in Ontario, on a site previously dominated by white spruce and quaking aspen, resulted from rhizome and root crown sprouts [27].

Postfire Regeneration Strategy

  • Rhizomatous herb, rhizome in soil
  • Geophyte, growing points deep in soil
  • Secondary colonizer (on-site or off-site seed sources) [133]

Fire Adaptations

Indianhemp has an extensive, deep root and rhizome system, and sprouts from the root crown and rhizomes after top-kill by fire. For example, populations near Ottawa, Ontario, sprouted from both rhizomes and root crowns following severe fire [27]. Indianhemp also reproduces from wind-blown seed [96,97], so postfire establishment from seed is possible. The ability of Indianhemp to colonize disturbed areas may give it an advantage on burned soils.

Plant Response to Fire

There are conflicting results as to how Indianhemp responds to fire. Johnson and Knapp [71] stated that populations of Indianhemp increased with increased fire frequency on tallgrass prairie in Kansas [71]. However, Tester [137] found a nonsignificant negative effect of burn frequency on Indianhemp in an oak savanna of east-central Minnesota [137].

Indianhemp was found on all 5 burned study plots 100 days after fire in a white spruce-quaking aspen site in Ontario [27]. Indianhemp also produced new spring growth within days following a prescribed burn in a tallgrass prairie in Kansas [71].

Prescribed burns were implemented in consecutive years in an oak savanna in east-central Illinois. The 1st fire resulted in a "hot, intense" fire, and the fire the following year was not as hot or intense. Indianhemp increased on burned sites but only in the 2nd postfire year [67]. It increased in percent cover on both control and burn plots studied after a prescribed fire on a mid-elevation wetland in southeastern Arizona [51].

Conversely, the findings of Bowles and others [19] indicate that Indianhemp populations did not survive after 8 dormant-season prescribed burns on graminoid fens in Cook County, Illinois. Indianhemp plants were recorded on the study plots before burning, but were not present after 5 years [19]. On study plots dominated by post oak, winged elm (Ulmus alata), and white ash (Fraxinus americana) in southern Illinois, Indianhemp was observed during prefire sampling and not found in postfire months 5 or 6 (burns characterized as "moderate, at best") [62]. In a sedge-beaked spikerush-Kentucky bluegrass (Carex spp.-Eleocharis rostellata-Poa pratensis) wetland near Tucson, Arizona, Indianhemp density increased more on control plots than burned plots. Indianhemp increased on high-frequency repeat spring burns (every 2-3 years), medium-frequency repeat spring burns (every 5-7 years), and unburned control plots [51]. However, analyses of variance failed to demonstrate a significant (p=0.70) effect of burning on Indianhemp cover.

Fire Regimes

The extensive distribution of Indianhemp places it in a wide range of fire regimes. Plains and mountain grasslands where Indianhemp occurs have short fire-return intervals and could burn in any year if fuels are cured [20]. Indianhemp is found in communities with mixed-severity and understory fire regimes as described by Brown and Smith [20]. The following table provides fire return intervals for plant communities and ecosystems where Indianhemp occurs.

For additional fire regime information, search FEIS for this species by entering the species name on the Advanced Search page and selecting “Fire Regime” as the publication type.

Community or EcosystemDominant SpeciesFire Return Interval Range (years)
Maple-beechAcer-Fagus spp.684-1,385 [30,144]
Maple-beech-birchAcer-Fagus-Betula spp.>1,000 [144]
Nebraska sandhills prairieAndropogon gerardii var. paucipilus-Schizachyrium scoparium<10
Bluestem-Sacahuista prairieAndropogon littoralis-Spartina spartinae<10
Sagebrush steppeArtemisia tridentata/Pseudoroegneria spicata20-70 [106]
Basin big sagebrushArtemisia tridentata var. tridentata12-43 [120]
BirchBetula spp.80-230 [136]
Plains grasslandsBouteloua spp.<35 [106,157]
Blue grama-needle-and-thread grass-western wheatgrassBouteloua gracilis-Hesperostipa comata-Pascopyrum smithii<35 [106,118,157]
Blue grama-buffalo grassBouteloua gracilis-Buchloe dactyloides<35 [106,157]
Grama-galleta steppeBouteloua gracilis-Pleuraphis jamesii<35 to <100 [106]
CheatgrassBromus tectorum<10 [107,153]
Black ashFraxinus nigra<35 to 200 [144]
Green ashFraxinus pennsylvanica<35 to >300 [47,144]
Wheatgrass plains grasslandsPascopyrum smithii<5-47+ [106,111,157]
Great Lakes spruce-firPicea-Abies spp.35 to >200
Northeastern spruce-firPicea-Abies spp.35-200 [45]
Jack pinePinus banksiana<35 to 200 [30,45]
Shortleaf pinePinus echinata2-15
Shortleaf pine-oakPinus echinata-Quercus spp.<10 [144]
Longleaf-slash pinePinus palustris-P. elliottii1-4 [103,144]
Longleaf pine-scrub oakPinus palustris-Quercus spp.6-10 [144]
Interior ponderosa pine*Pinus ponderosa var. scopulorum2-30 [7,10,85]
Red pine (Great Lakes region)Pinus resinosa3-18 (x=3-10) [29,53]
Eastern white pinePinus strobus35-200 [136,144]
Virginia pinePinus virginiana10 to <35
Virginia pine-oakPinus virginiana-Quercus spp.10 to <35
Sycamore-sweetgum-American elmPlatanus occidentalis-Liquidambar styraciflua-Ulmus americana<35 to 200 [144]
Eastern cottonwoodPopulus deltoides<35 to 200 [106]
Quaking aspen-paper birchPopulus tremuloides-Betula papyrifera35-200 [45,144]
Quaking aspen (west of the Great Plains)Populus tremuloides7-120 [7,60,95]
Mountain grasslandsPseudoroegneria spicata3-40 (x=10) [6,7]
Rocky Mountain Douglas-fir*Pseudotsuga menziesii var. glauca25-100 [7,8,9]
Oak-hickoryQuercus-Carya spp.<35 [144]
Oregon white oakQuercus garryana<35 [7]
Oak savannaQuercus macrocarpa/Andropogon gerardii-Schizachyrium scoparium2-14 [106,144]
Post oak-blackjack oakQuercus stellata-Q. marilandica<10 [144]
Little bluestem-grama prairieSchizachyrium scoparium-Bouteloua spp.<35 [106]
*fire return interval varies widely; trends in variation are noted in the species review

Fire Management Considerations

The current body of research provides no clear direction for using fire as a management tool for Indianhemp populations. The results of studies done to date, 2006, are conflicting. Further research is needed on the fire ecology of Indianhemp.

Federal Status

None

Other Status

None

Importance to Wildlife and Livestock

Indianhemp is poisonous to all livestock, although domestic sheep are affected more than other animals [15,33,35,69,110,119,123,129,140]. However, actual cases of livestock poisoning from Indianhemp are rare [15,35]. Traces of Indianhemp were found in rumen samples of pronghorn and white-tailed deer in Montana, but no animals were observed eating it [2,32].

Indianhemp is a primary host for 2 species of leaf beetle [40]. It is also a host plant for Chrysochus auratus (a root beetle) in Iowa. Chrysochus auratus mating and ovipositing occur on Indianhemp throughout the summer. Once hatched, the larvae drop to the ground and tunnel to the roots of the host plants, where they feed and overwinter [130].

Butterfly gardeners grow Indianhemp because it is a valuable native nectar plant [68].

Palatability and Nutritional Value

Indianhemp is unpalatable at all seasons, even to livestock that are virtually starving [46]. Animals usually avoid Indianhemp because of the bitter, sticky, milky-white juice; however, domestic sheep may eat large quantities if other forage is scarce [69,140].

All parts of Indianhemp, fresh or dried, are poisonous because of the toxic glycoside it contains [33,35,69,123,140]. The levels of the glycoside, cymarin, in Indianhemp are disputed. Knight [77] claims the levels of cymarin are low and Majak [90] states that there are high concentrations. Death from Indianhemp poisoning may occur 6 to 12 hours after animals eat the plant. A lethal dose for domestic sheep is about 0.5 to 1 ounce/100 pounds of body weight. A lethal dose for cattle and horses is about 0.5 to 0.75 ounce/100 pounds of body weight [69,140].

Cover Value

Cover of Indianhemp for wildlife has been rated as follows [39]:

AnimalUtahMontana
ElkPoor—
Mule deerPoor—
White-tailed deer—Fair
PronghornPoor—
Small mammalsFair—
Small nongame birdsFair—
Upland game birdsPoor—
WaterfowlPoor—

Value for Rehabilitation or Restoration of Disturbed Sites

There is value in using Indianhemp for the rehabilitation of disturbed sites. It grows very well in disturbed areas. It is, for example, common on American badger-disturbed sites [108,109]. It is also recognized as a worthwhile native landscaping plant because it spreads rapidly by vegetative means and can help suppress weeds [37].

Other Uses

Indianhemp is known for its importance to early Native Americans. The strong, fibrous root and stem fibers were used to make fish nets, rope, thread, baskets, cloth, and bags [1,4,15,28,35,78,105,121,128,138,156].

Indianhemp is known to have many medicinal purposes. The glycoside, cymarin, was used as a cardiac stimulant, a diuretic, a diaphoretic, a febrifuge, a rheumatism remedy, and a treatment for gall stones [35,69,78,128,140]. The dried milky fluid in the stems can be used as a chewing gum substitute [78].

The fragrant flowers attract honeybees for nectar, making a "superior," almost colorless honey [33].

There may be potential for using Indianhemp as a hydrocarbon-producing crop as an energy alternative [21].

Other Management Considerations

Indianhemp is considered a serious weed problem in agricultural fields in the Midwest and can cause decreases in yield [14,22,76,104,116,147,148,149,150,160]. Infestations tend to occur in agricultural crops where no-tillage systems have been implemented, which allow for Indianhemp's rhizome and root system to become well established [56,147,148,149]. Reductions in yield are reportedly due to allelopathic influences of Indianhemp [122,159]. Indianhemp is also considered a weed species in nurseries, plantations where Christmas trees are grown, and in orchards [64,65,80].
Indianhemp increases on grazed pastures in South Dakota [87].

Control: Many management strategies have been used to try to control Indianhemp, with different levels of success. Complete control is difficult due to Indianhemp's persistent and extensive root and rhizome system [104].

Integrated management: A successful management program to control Indianhemp likely includes a combination of cultural, mechanical (tillage including the usage of plows, disks, or cultivators), and chemical methods [119] as well as an appropriate schedule for implementing these methods. There is widespread agreement that timing of control methods is critical and can make weed management very difficult [56,104,147,149]. Fall herbicide treatments have provided better control than spring treatments. The spring treatments can effectively control Indianhemp, but the timing often occurs when the most damage can be done to other herbs [14,116,160]. Becker [15] states that herbicide application timing should coincide with late bud to early flower set, or beyond. Mechanical methods such as mowing, cultivation, or tilling practices should be implemented at mid- to full-flower, before root carbohydrate levels begin, to recover to maximize carbohydrate depletion [14].

Physical/mechanical: Mechanical control has been shown to decrease and increase infestations. Numerous Indianhemp sprouts occurred on study plots that had the soil scraped off. The scraping and deep plowing destroyed most of the perennating tissues except for the some deeply buried rhizomes. The following year Indianhemp continued to spread and increase in height. A steady decrease was observed in the following years, until it was absent or of little importance [75]. Buhler and others [22] state that Indianhemp can be controlled by tillage systems. Tillage can reduce infestations if done frequently (every 2 to 3 weeks) enough to deplete underground root reserves [119]. Increases in infestations where tillage practices are used have been attributed to tillage equipment moving parts of the root systems to new areas and by breaking dormancy of underground buds, resulting in new shoot growth [122,160].

Chemical control has also had mixed success. The seedlings are "easily controlled" by most soil-applied herbicides including 2, 4-D and glyphosate. Once seedlings become established, control becomes much more difficult [15]. A broad range of herbicides was reported to be effective (80% to ≥92%) on Indianhemp seedlings in a greenhouse study in Delaware [142]. Depending on the herbicide, applications made during the vegetative stage of growth provide a shorter-term control than applications made during the early reproductive stage. Applying herbicides during the early reproductive stage provides the longer-term control but can be harmful to other herbs [104]. Applications of the "traditionally safe" herbicides sulfometuron methyl and imazapyr were used on Indianhemp in eastern white pine plantations were unsuccessful [80]. Glenn and Anderson [56] report good Indianhemp control with herbicide applications of one or more of the following: 2, 4-D, dicamba, nicosulfuron, and triclopyr; however, regrowth from the root crown occurred occasionally. Herbicide treatments reduce the vigor of Indianhemp plants but often do not kill them [160].

Table A1— Forest and range ecosystems, Bureau of Land Management (BLM) physiographic regions, Kuchler plant associations, Society for American Foresters (SAF) forest cover types, and Society for Rangeland Management (SRM) rangeland cover types in which this species occurs.

Forest and Range Ecosystems (Garrison et al. 1977)

  • FRES10 White-red-jack pine
  • FRES11 Spruce-fir
  • FRES12 Longleaf-slash pine
  • FRES14 Oak-pine
  • FRES15 Oak-hickory
  • FRES16 Oak-gum-cypress
  • FRES17 Elm-ash-cottonwood
  • FRES18 Maple-beech-birch
  • FRES19 Aspen-birch
  • FRES20 Douglas-fir
  • FRES21 Ponderosa pine
  • FRES28 Western hardwoods
  • FRES29 Sagebrush
  • FRES32 Texas savanna
  • FRES33 Southwestern shrubsteppe
  • FRES36 Mountain grasslands
  • FRES38 Plains grasslands
  • FRES39 Prairie

BLM Physiographic Regions (Bernard and Brown 1977)

  • 1 Northern Pacific Border
  • 2 Cascade Mountains
  • 3 Southern Pacific Border
  • 4 Sierra Mountains
  • 5 Columbia Plateau
  • 6 Upper Basin and Range
  • 7 Lower Basin and Range
  • 8 Northern Rocky Mountains
  • 9 Middle Rocky Mountains
  • 10 Wyoming Basin
  • 11 Southern Rocky Mountains
  • 12 Colorado Plateau
  • 13 Rocky Mountain Piedmont
  • 14 Great Plains
  • 15 Black Hills Uplift
  • 16 Upper Missouri Basin and Broken Lands

Kuchler Plant Associations (Kuchler 1964)

  • K011 Western ponderosa forest
  • K012 Douglas-fir forest
  • K026 Oregon oakwoods
  • K038 Great Basin sagebrush
  • K053 Grama-galleta steppe
  • K054 Grama-tobosa prairie
  • K056 Wheatgrass-needlegrass shrubsteppe
  • K063 Foothills prairie
  • K064 Grama-needlegrass-wheatgrass
  • K066 Wheatgrass-needlegrass
  • K067 Wheatgrass-bluestem-needlegrass
  • K068 Wheatgrass-grama-buffalo grass
  • K069 Bluestem-grama prairie
  • K074 Bluestem prairie
  • K081 Oak savanna
  • K082 Mosaic of K074 and K100
  • K084 Cross Timbers
  • K093 Great Lakes spruce-fir forest
  • K095 Great Lakes pine forest
  • K096 Northeastern spruce-fir forest
  • K098 Northern floodplain forest
  • K100 Oak-hickory forest
  • K101 Elm-ash forest
  • K104 Appalachian oak forest
  • K111 Oak-hickory-pine
  • K112 Southern mixed forest

SAF Cover Types (Eyre 1980)

  • 1 Jack pine
  • 16 Aspen
  • 17 Pin cherry
  • 18 Paper birch
  • 20 White pine-northern red oak-red maple
  • 37 Northern white-cedar
  • 39 Black ash-American elm-red maple
  • 40 Post oak-blackjack oak
  • 46 Eastern redcedar
  • 61 River birch-sycamore
  • 63 Cottonwood
  • 70 Longleaf pine
  • 71 Longleaf pine-scrub oak
  • 75 Shortleaf pine
  • 76 Shortleaf pine-oak
  • 78 Virginia pine-oak
  • 79 Virginia pine
  • 83 Longleaf pine-slash pine
  • 95 Black willow
  • 107 White spruce
  • 108 Red maple
  • 210 Interior Douglas-fir
  • 217 Aspen
  • 222 Black cottonwood-willow
  • 233 Oregon white oak
  • 235 Cottonwood-willow
  • 237 Interior ponderosa pine
  • 252 Paper birch

SRM Rangeland Cover Types (Shiflet 1994)

  • 101 Bluebunch wheatgrass
  • 401 Basin big sagebrush
  • 411 Aspen woodland
  • 601 Bluestem prairie
  • 602 Bluestem-prairie sandreed
  • 604 Bluestem-grama prairie
  • 606 Wheatgrass-bluestem-needlegrass
  • 607 Wheatgrass-needlegrass
  • 608 Wheatgrass-grama-needlegrass
  • 609 Wheatgrass-grama
  • 610 Wheatgrass
  • 731 Cross timbers-Oklahoma

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