Quick Facts

Quick facts

• Silk Forage Sorghum (Sorghum hybrid cv. Silk) is a vigorous, upright, tussocky perennial grass growing to 3.5 m high.
• It prefers growing in fertile soils in warm areas and is a weed along roadsides and fence lines, especially in New South Wales.
• It is a successful forage plant but can also invade both dry land and irrigated cropping areas. It has the potential to poison stock, become a road safety hazard and to harbour disease and insect pests.
• It looks very similar to Columbus Grass (Sorghum × almum) and its seeds and flower clusters are indistinguishable from both Columbus Grass and Johnson Grass (S. halepense).
• Control measures include repeated cultivation, mowing and heavy grazing combined with slashing, burning and then spraying the regrowth with herbicide.

What Does It Look Like?

What is it?

Silk Forage Sorghum (Sorghum hybrid cv. Silk) is a vigorous, upright, tussocky perennial grass growing to 3.5 m high and living 3–5 years. It has smooth stems, arising from weakly spreading rhizomes (underground stems). The leaves grow to 50 cm in length and 2 cm in width, with relatively smooth, slightly toothed margins. The ligule (the structure where the leaf sheath and blade meet), is membranous, becoming covered with short, soft hairs with age (Parsons & Cuthbertson 2001).

The flower head is pale greenish to dark red-brown, open, branching and pyramid-shaped to 30 cm long. The flower clusters are arranged in pairs along, or in triplets at the ends of, branchlets. One of each pair or triplet is stalkless and fertile and the others are stalked and sterile. The fertile cluster is 5–7 mm long, often with a bristle, which is usually lost by the time the pollen is released (Anon 1978; Parsons & Cuthbertson 2001). The roots are fibrous and freely branching out to 1 m (Parsons & Cuthbertson 2001).

For further information and assistance with identification of Silk Forage Sorghum contact the herbarium in your state or territory.

Flower colour

Red, Green

Growth form (weed type/habit)

Grass

Where it currently grows? Preferred habitat

Silk Forage Sorghum prefers growing in warm areas on fertile soils. It is especially suited to the fertile, heavy clay soils in sub-tropical, summer rainfall areas of Queensland and northern New South Wales (Anon 1978). It often occurs as a weed along roadsides, fence lines and between cropping paddocks (Parsons & Cuthbertson 2001).

Are there similar species?

Silk Forage Sorghum is very similar to Columbus Grass (Sorghum × almum). They grow to a similar height, whereas Johnson Grass (S. halepense), a much more aggressive weed than either of the former, grows to only 2 m (Parsons & Cuthbertson 2001). The seeds and flower clusters of Silk Forage Sorghum are indistinguishable from both Columbus Grass and Johnson Grass in mixed samples (Parsons & Cuthbertson 2001).

Why Is It A Weed?

What are its impacts?

Agriculture: Silk Forage Sorghum is a successful forage plant. It is drought resistant, highly productive and has a long growing season. (Parsons & Cuthbertson 2001). It can invade both dryland and irrigated cropping areas (Liverpool Plains Shire Council 2006). It also has the potential to poison stock as well as become a road safety hazard by obscuring signs and curves (Parsons & Cuthbertson 2001).

Silk Forage Sorghum has the potential to harbour disease and insect pests of annual grain and forage sorghums. It can be an early flowering second host to the sorghum midge, Contarinia sorghicola, resulting in an early increase in midge population to the detriment of the later flowering annual sorghums (Parsons & Cuthbertson 2001).

In New South Wales, Silk Forage Sorghum has been declared noxious in areas where sorghum is grown for seed, mainly because of its potential to outcross with other forage sorghums and annual grains, and also because its seeds cannot be distinguished from those of Johnson Grass (Sorghum halepense), a much more serious weed (Parsons & Cuthbertson 2001).

How does it spread?

Dispersal of Silk Forage Sorghum is by seed and short rhizomes. The seeds float on water, stick to wool, fur and fabric and pass through the digestive tract of animals relatively unharmed. They are also spread in hay and grain. Rhizome fragments can be spread during cultivation during road grading (Parsons & Cuthbertson 2001).

What is its history in Australia?

Silk Forage Sorghum was selected, in Australia, from progeny of a hybrid plant resulting from cross-pollination between Sorghum halepense × S. roxburghii cv. Krish and S. arundinaceum as a useful forage plant. It was registered as a forage plant in 1978 and it has been widely grown in New South Wales and Queensland (Anon 1978).

How To Manage It?

Best practice management

Non-chemical control: Control measures for Silk Forage Sorghum are similar to those for Columbus Grass (Sorghum × almum) and Johnson Grass. Repeated cultivation, mowing and heavy grazing can be used to exhaust the rhizomes. This may be combined with slashing and burning, spraying the regrowth with herbicide, followed by sowing with a competitive pasture mixture (Parsons & Cuthbertson 2001).

Chemical control: The Liverpool Plains Shire Council requires all owner/occupiers of land within their jurisdiction to either treat Silk Forage Sorghum with a herbicide registered for such control in the manner specified on the label and/or mechanically remove all Silk Forage Sorghum root material, in order to comply with the New South Wales Noxious Weed Act 1993 and their own management plan (Liverpool Plains Shire Council 2006).

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)

Seeds germinate at from spring to late summer provided there is moisture. The vigorous seedling growth produces high forage yields within 6–8 weeks. Plants flower late December–January to April and seeds ripen until winter frosts or cool temperatures stop growth. Most seed is retained in the head but those that fall may germinate immediately. Growth slows or stops in winter depending on the temperature and vigorous new growth from stem buds or rhizome buds occurs the following spring (Parsons & Cuthbertson 2001).

Where Is It Found?

Which states and territories is it found?

NSW, QLD

What areas within states and territories is it found?

Silk Forage Sorghum occurs in New South Wales and Queensland. It has been declared noxious in 40 council areas in New South Wales, and is prevalent in the Macquarie and Lachlan River valleys and in the Riverina (Parsons & Cuthbertson 2001).

Where does it originate?

Silk Forage Sorghum was developed in Australia from progeny of a hybrid plant resulting from cross-pollination between Sorghum halepense Pers. × S. roxburghii cv. Krish and S. arundinaceum (Anon 1978; Parsons & Cuthbertson 2001). S. halepense or Johnson Grass is a weedy perennial plant of Mediterranean origin and was introduced to Australia as a fodder plant in the 1800s (Parsons and Cuthbertson 2001). S. roxburghii is a synonym for S. bicolor (GRIN 2008)) and is a short lived fodder plant of African origin (Jacobs et al. 1993). The cultivar Krish was developed by CSIRO Australia and registered in 1967 (Cook et al. 2005). S. arundinaceum is also of African origin (GRIN 2008) and is a weed of sugar cane (Lazarides 2002). Silk Forage Sorghum has also been successfully grown in Brazil and Argentina (Anon 1978).

National And State Weed Listings

Is it a Weed of National Significance (WONS)?

NO

Where is it a declared weed?

NSW, WA

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

Sorghum ssp. hybrid cv. Silk (Reg. No. A-9d-5)

Other scientific names (synonyms)?