Digitaria insularis (L.) Mez ex Ekman, Poaceae

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Present on Pacific Islands?  yes

Primarily a threat at high elevations?  no

Risk assessment results:  High risk, score: 20 (Go to the risk assessment)

Other Latin names:  Trichachne insularis (L.) Nees.

Common name(s): [more details]

English: sourgrass

Habit:  grass

Description:  "Large perennial grass with more or less erect culms, branching up to 1.5 m tall; cataphylls densely-soft-hairy; sheaths apically carinate, longer than internodes, hirsute; ligule 3-4 mm long; blades 10-30 cm long, 2-12 mm wide; margins finely scabrid; panicles 15-30 cm long, slender, congested, tawny to whitish, the branches steeply ascending; spikelets 3.5-4 mm long; first glume 0.5 mm long, glabrous; second glume and sterile lemma both densely silky-hairy with hairs longer than spikelet; fertile lemma dark, 3-3.5 mm long; caryopsis beaked, pale, 1.5 mm long" (Stone, 1970; p. 226).

Description from GrassBase.

Habitat/ecology:  Infests disturbed areas in mesic and dry natural areas, roadsides and waste areas up to 300 m elevation. In Hawai‘i, "naturalized in abandoned fields, disturbed sites, and along roadsides, 0-340 m"  (Wagner et al., 1999; p. 1531). "Forms dense stands in mesic pastures and disturbed forests.  Infests disturbed areas in mesic and dry natural areas, roadsides, and waste areas"  (Motooka et al., 2003). In New Guinea, "a weed of grazing land, headlands and roadsides; not a serious problem in cultivation" (Henty & Pritchard, 1975; p. 38).

Propagation:  "Large volumes of wind-dispersed seed.  Vegetative propagation from runner fragments."  (Waterhouse & Mitchell, 1998; pp. 67-68).

Native range:  Tropical America.

Presence:

Pacific
Country/Terr./St. & Island group	Location	Cited status & Cited as invasive & Cited as cultivated & Cited as aboriginal introduction?	Reference & Comments
Commonwealth of the Northern Mariana Islands (US) Northern Mariana Islands	Saipan Island	introduced	Fosberg, F. R./Sachet, Marie-Hélène/Oliver, Royce (1987) (p. 38) Managaha Island.
Commonwealth of the Northern Mariana Islands (US) Northern Mariana Islands	Tinian Island	introduced	Fosberg, F. R./Sachet, Marie-Hélène/Oliver, Royce (1987) (p. 38)
Commonwealth of the Northern Mariana Islands (US) Northern Mariana Islands	Tinian Island		Bishop Museum (Honolulu) (1946) (voucher ID: BISH 124245) Taxon name on voucher: Digitaria insularis (L.) Mez ex Ekman
Commonwealth of the Northern Mariana Islands (US) Northern Mariana Islands	Tinian Island		Bishop Museum (Honolulu) (1985) (voucher ID: BISH 540172) Taxon name on voucher: Digitaria insularis (L.) Mez ex Ekman
Commonwealth of the Northern Mariana Islands (US) Northern Mariana Islands	Tinian Island		Bishop Museum (Honolulu) (1980) (voucher ID: BISH 588179) Taxon name on voucher: Digitaria insularis (L.) Mez ex Ekman
Commonwealth of the Northern Mariana Islands (US) Northern Mariana Islands	Tinian Island		Bishop Museum (Honolulu) (1980) (voucher ID: BISH 588180) Taxon name on voucher: Digitaria insularis (L.) Mez ex Ekman
Fiji Fiji Islands	Fiji Islands		Waterhouse, D. F. (1997) (p. 61)
Guam Guam Island	Guam Island	introduced invasive	Stone, Benjamin C. (1970) (p. 226)
Guam Guam Island	Guam Island	introduced	Fosberg, F. R./Sachet, Marie-Hélène/Oliver, Royce (1987) (p. 38)
State of Hawaii Hawaiian Islands	Hawai‘i (Big) Island	introduced invasive	Wagner, Warren L./Herbst, Derral R./Sohmer, S. H. (1999) (p. 1531)
State of Hawaii Hawaiian Islands	Kaho‘olawe Island	introduced invasive	Wagner, Warren L./Herbst, Derral R./Sohmer, S. H. (1999) (p. 1531)
State of Hawaii Hawaiian Islands	Kaua‘i Island	introduced invasive	Wagner, Warren L./Herbst, Derral R./Sohmer, S. H. (1999) (p. 1531)
State of Hawaii Hawaiian Islands	Lāna‘i Island	introduced invasive	Wagner, Warren L./Herbst, Derral R./Sohmer, S. H. (1999) (p. 1531)
State of Hawaii Hawaiian Islands	Ni‘ihau, Lehua Islet	introduced invasive	Wood, K. R./LeGrande, Maya (2006) (p. 26) Voucher cited: K.R. Wood & VanderWerf 9875 (BISH, PTBG, US)
State of Hawaii Hawaiian Islands	Maui Island	introduced invasive	Wagner, Warren L./Herbst, Derral R./Sohmer, S. H. (1999) (p. 1531)
State of Hawaii Hawaiian Islands	Moloka‘i Island	introduced invasive	Wagner, Warren L./Herbst, Derral R./Sohmer, S. H. (1999) (p. 1531)
State of Hawaii Hawaiian Islands	O‘ahu Island	introduced invasive	Wagner, Warren L./Herbst, Derral R./Sohmer, S. H. (1999) (p. 1531)
Japan (offshore islands) Bonin (Ogasawara) Islands	Bonin (Ogasawara) Islands	introduced	Kato, Hidetoshi (2007)
Marshall Islands Ralik Chain	Bikini (Pikinni) Atoll	introduced	Fosberg, F. R./Sachet, Marie-Hélène/Oliver, Royce (1987) (p. 38)
Marshall Islands Ralik Chain	Bikini (Pikinni) Atoll		Bishop Museum (Honolulu) (1946) (voucher ID: BISH 127176) Taxon name on voucher: Digitaria insularis (L.) Mez ex Ekman
Marshall Islands Ralik Chain	Enewetak (Ãnewetak, Eniwetok) Atoll	introduced	Fosberg, F. R./Sachet, Marie-Hélène/Oliver, Royce (1987) (p. 38)
Marshall Islands Ralik Chain	Enewetak (Ãnewetak, Eniwetok) Atoll	introduced invasive	St. John, Harold (1960) (p. 323) Voucher cited: Fosberg 24328, Lane 57-138
Marshall Islands Ralik Chain	Enewetak (Ãnewetak, Eniwetok) Atoll	introduced invasive	Fosberg, F. R. (1955) (p. 5) Voucher cited: Fosberg 24328 (US)
Marshall Islands Ralik Chain	Enewetak (Ãnewetak, Eniwetok) Atoll		Bishop Museum (Honolulu) (1957) (voucher ID: BISH 576848) Taxon name on voucher: Digitaria insularis (L.) Mez ex Ekman
Marshall Islands Ralik Chain	Enewetak (Ãnewetak, Eniwetok) Atoll		Bishop Museum (Honolulu) (1946) (voucher ID: BISH 697533) Taxon name on voucher: Digitaria insularis (L.) Mez ex Ekman
Marshall Islands Ralik Chain	Kwajalein (Kuwajleen) Atoll	introduced invasive	Fosberg, F. R. (1955) (p. 5) Voucher cited: Fosberg 26502 (US)
Marshall Islands Ralik Chain	Kwajalein (Kuwajleen) Atoll		Bishop Museum (Honolulu) (1946) (voucher ID: BISH 124244) Taxon name on voucher: Digitaria insularis (L.) Mez ex Ekman
Papua New Guinea Papua New Guinea (eastern New Guinea Island)	Papua New Guinea (eastern New Guinea Island)	introduced invasive	Waterhouse, B. M./Mitchell, A. A. (1998) (pp. 67-68)
Papua New Guinea Papua New Guinea (eastern New Guinea Island)	Papua New Guinea (eastern New Guinea Island)	introduced invasive	Henty, E. E. (1969) (p. 76) Becoming common in the lower Markham Valley, where it was first noticed in 1952.
Philippines Philippine Islands	Philippine Islands	introduced invasive	Waterhouse, B. M./Mitchell, A. A. (1998) (pp. 67-68)
Solomon Islands Solomon Islands	Solomon Islands		Swarbrick, John T. (1997) (p. 91)
Solomon Islands Solomon Islands	Solomon Islands	native	Hancock, I. R./Henderson, C. P. (1988) (p. 66)
United States (other Pacific offshore islands) Midway Atoll	Midway Atoll	introduced invasive	Wagner, Warren L./Herbst, Derral R./Sohmer, S. H. (1999) (p. 1531)
United States (other Pacific offshore islands) Midway Atoll	Sand Island	introduced invasive	Starr, Forest/Starr, Kim/Loope, Lloyd (2008) (pp. B-8)
United States (other Pacific offshore islands) Wake Islands	Wake Island	introduced invasive	Fosberg, F. R. (1959) (p. 9) Voucher cited: Fosberg 34476
United States (other Pacific offshore islands) Wake Islands	Wake Island	introduced invasive	Fosberg, F. R./Sachet, M.-H. (1969) (p. 5) Voucher cited: Sachet 894
United States (other Pacific offshore islands) Wake Islands	Wake Island	introduced invasive	Fosberg, F. R. (1955) (p. 5) Voucher cited: Fosberg 34476 (US)
Vanuatu New Hebrides Islands	Vanuatu (Republic of)		Waterhouse, D. F. (1997) (p. 61)

Pacific Rim
Country/Terr./St. & Island group	Location	Cited status & Cited as invasive & Cited as cultivated & Cited as aboriginal introduction?	Reference & Comments
Colombia Colombia	Colombia (Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
Costa Rica Costa Rica	Costa Rica (Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
Ecuador (Mainland) Ecuador	Ecuador (Republic of) (continental)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
El Salvador El Salvador	El Salvador (Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
Guatemala Guatemala	Guatemala (Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
Honduras Honduras	Honduras (Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
Nicaragua Nicaragua	Nicaragua (Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
Panama Panama	Panama (Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
Perú Perú	Perú (Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)

Control: 

Physical:  Grazing management in pastures (Motooka et al., 2003).

Chemical: Sensitive to glyphosate (Motooka et al., 2003).

Additional information:
Excerpt from the book "Weeds of Hawaii‘s Pastures and Natural Areas; An Identification and Management Guide" (Motooka et al., 2003). (PDF format).

Additional online information about Digitaria insularis is available from the Hawaiian Ecosystems at Risk project (HEAR).

Information about Digitaria insularis as a weed (worldwide references) may be available from the Global Compendium of Weeds (GCW).

Taxonomic information about Digitaria insularis may be available from the Germplasm Resources Information Network (GRIN).

References:

Bishop Museum (Honolulu). 1946. Voucher specimen #BISH 124244 (Fosberg, F.R. 26502).

Bishop Museum (Honolulu). 1946. Voucher specimen #BISH 124245 (Fosberg, F.R. 24922).

Bishop Museum (Honolulu). 1946. Voucher specimen #BISH 127176 (Taylor, W.R. 46-1499).

Bishop Museum (Honolulu). 1946. Voucher specimen #BISH 697533 (Fosberg, F.R. 24328).

Bishop Museum (Honolulu). 1957. Voucher specimen #BISH 576848 (Lane, A.E. 57-138).

Bishop Museum (Honolulu). 1980. Voucher specimen #BISH 588179 (Fosberg, F.R. 59881).

Bishop Museum (Honolulu). 1980. Voucher specimen #BISH 588180 (Fosberg, F.R. 59850).

Bishop Museum (Honolulu). 1985. Voucher specimen #BISH 540172 (Raulerson, L. 8732).

Fosberg, F. R. 1955. Northern Marshall Islands Expedition, 1951-1952. Land biota: vascular plants. Atoll Research Bulletin No. 39. Pacific Science Board, National Academy of Sciences, Washington. 22 pp.

Fosberg, F. R. 1959. Vegetation and flora of Wake Island. Atoll Research Bulletin 67. Pacific Science Board, National Academy of Sciences, Washington. 20 pp.

Fosberg, F. R./Sachet, M.-H. 1969. Wake Island vegetation and flora, 1961-1963. Atoll Research Bulletin No. 123. Smithsonian Institution, Washington. 15 pp.

Fosberg, F. R./Sachet, Marie-Hélène/Oliver, Royce. 1987. A geographical checklist of the Micronesian monocotyledonae. Micronesica 20:1-126.

Hancock, I. R./Henderson, C. P. 1988. Flora of the Solomon Islands. Research Bulletin No. 7. Ministry of Agriculture and Lands, Honiara. 203 pp.

Henty, E. E. 1969. A manual of the grasses of New Guinea. Department of Forests, Division of Botany, Botany Bull. No. 1. Lae, New Guinea. 215 pp.

Henty, E. E./Pritchard, G. H. 1975. Weeds of New Guinea and their control. 2nd edition. Department of Forests, Division of Botany, Botany Bull. No. 7. Lae, Papua New Guinea. 180 pp.

Kato, Hidetoshi. 2007. Herbarium records of Makino Herbarium, Tokyo Metropolitan University. Personal communication.

Motooka, Philip/Castro, Luisa/Nelson, Duane/Nagai, Guy/Ching, Lincoln. 2003. Weeds of Hawaii‘s Pastures and Natural Areas; An Identification and Management Guide. College of Tropical Agriculture and Human Resources, University of Hawaii at Manoa. 184 pp.

Motooka, Philip/Ching, Lincoln/Nagai, Guy. 2002. Herbicidal Weed Control Methods for Pasture and Natural Areas of Hawaii. Cooperative Extension Service, College of Tropical Agriculture and Human Resources, University of Hawai‘i. CTAHR free publication WC-8.

St. John, Harold. 1960. Flora of Eniwetok Atoll. Pacific Science 14(4):313-336.

Starr, Forest/Starr, Kim/Loope, Lloyd. 2008. Botanical survey of Midway Atoll. Prepared for: United States Fish and Wildlife Service. 27 pp. plus appendices.

Stone, Benjamin C. 1970. The flora of Guam. Micronesica 6:1-659.

Swarbrick, John T. 1997. Weeds of the Pacific Islands. Technical paper no. 209. South Pacific Commission, Noumea, New Caledonia. 124 pp.

U.S. Dept. Agr., Agr. Res. Serv. 2011. National Genetic Resources Program. Germplasm Resources Information Network (GRIN). Online searchable database.

Wagner, Warren L./Herbst, Derral R./Sohmer, S. H. 1999. Manual of the flowering plants of Hawaii. Revised edition. Bernice P. Bishop Museum special publication. University of Hawai‘i Press/Bishop Museum Press, Honolulu. 1919 pp. (two volumes).

Waterhouse, B. M./Mitchell, A. A. 1998. Northern Australia Quarantine Strategy: weeds target list. Second edition. Australian Quarantine & Inspection Service, Miscellaneous Publication No. 6/98. 110 pp.

Waterhouse, D. F. 1997. The major invertebrate pests and weeds of agriculture and plantation forestry in the Southern and Western Pacific. The Australian Centre for International Agricultural Research, Canberra. 93 pp.

Wood, K. R./LeGrande, Maya. 2006. An annotated checklist and new island records of flowering plants from Lehua Islet, Ni‘ihau, Hawai‘i. In: Evenhuis, Neal L. and Eldredge, Lucias G., eds. Records of the Hawaii Biological Survey for 2004-2005. Part 1: Articles. Bishop Museum Occasional Papers 87:19-29.