Quick Facts

Quick facts

• Sourgrass (Digitaria insularis) is a large, upright perennial grass, growing up to 1.5 m tall.
• It is doubtfully naturalised in Queensland, at St Lucia on the Brisbane River.
• In the Pacific region, it prefers disturbed areas in wet or dry natural areas, roadsides and waste areas up to 300 m in altitude.
• It produces large volumes of wind-dispersed seed.
• It can be controlled by chemical means.

What Does It Look Like?

What is it?

Sourgrass (Digitaria insularis) is a large perennial grass with more-or-less upright, branching stems, growing up to 1.5 m tall. The new growth is densely soft and hairy. The flat leaf blades are 10–30 cm long and 2–12 mm wide and the leaf margins are finely rough to the touch.

The inflorescence is 15–30 cm tall, tawny to white or gray, somewhat closed, silky and slender, with many slightly drooping branches (Motooka et al. 2003; Clayton et al. 2006; PIER 2008).

For further information and assistance with identification of Sourgrass, contact the herbarium in your state or territory.

Flower colour

Yellow, White

Growth form (weed type/habit)

Grass

Where it currently grows? Preferred habitat

In the Pacific Islands, Sourgrass prefers disturbed areas in wet or dry natural areas, roadsides and waste areas up to 300 m altitude (Motooka et al. 2003; PIER 2008).

Are there similar species?

Sourgrass is one 220 species of Digitaria worldwide, with 41 native or naturalised species found in Australia. The use of keys and descriptions for the species occurring in Australia, such as in Sharp & Simon (2002), can provide help in identification of the correct species.

For further information and assistance with identification of Sourgrass, contact the herbarium in your state or territory.

Why Is It A Weed?

What are its impacts?

Agriculture: Sourgrass forms dense stands in mesic (moist) pastures and disturbed forests and it is also a weed of grazing land. In Hawaii it is a serious weed of pineapple fields. It is also a principal weed in Paraguay and Venezuela. It is not a desirable pasture grass as it is unpalatable to stock and rapidly displaces more palatable species (Waterhouse & Mitchell 1998; Motooka et al. 2003; PIER 2008).

How does it spread?

Sourgrass produces large volumes of wind-dispersed seed. Vegetative propagation from runner fragments is also possible (PIER 2008).

What is its history in Australia?

It is not known how or when Sourgrass arrived in Australia, however there is one herbarium record from Brisbane in 1984 (Queensland Herbarium 2008).

How To Manage It?

Best practice management

Sourgrass is sensitive to herbicides, although grazing management, i.e., avoidance of overgrazing of palatable species, is considered to be a more practical control measure in pastures (Motooka et al. 2003; PIER 2008).

Please see the Australian Pesticides and Veterinary Medicines Authority for chemical information http://www.apvma.gov.au 

Does it have a biological control agent?

NO

When does it grow? (lifecycle/growth calendar)

Sourgrass is a perennial grass, which produces large quantities of fertile seed (PIER 2008).

Where Is It Found?

Which states and territories is it found?

QLD

What areas within states and territories is it found?

Sourgrass is present in Queensland, but there is no evidence that it has naturalised. There is one specimen in the Queensland Herbarium, from St Lucia on the Brisbane River (Queensland Herbarium 2008).

Where does it originate?

Sourgrass is native to tropical America (PIER 2008).

National And State Weed Listings

Is it a Weed of National Significance (WONS)?

NO

Where is it a declared weed?

NT

Government weed strategies and lists – Weeds Australia

Is it on the National Alert List for Environmental Weeds?

NO

Government weed strategies and lists – Weeds Australia

Is it on the Agricultural Sleeper List?

NO

Government weed strategies and lists – Weeds Australia

Names And Taxonomy

Main scientific name

Digitaria insularis

Other scientific names (synonyms)?

Andropogon insularis L.

Does it have other known common name(s)?

Cotton Grass, Feather-top Grass