Pennisetums. Friends and Foes

By Admin on 20-07-2015

Pennisetums are warm season grasses that are native to many parts of the world, including Australia. Pennisetum range in form from grasses suitable for lawns ie kikuyu (Pennisetum clandestinum) to medium/large tussocks that have been used in gardening. The Australian species is Pennisetum alopecuroides, and it is a tussock form. Bluedale grow and supply 4 cultivars of alopecuroides as well as the common form. We also sell one species from Africa. Let’s call these species Friends.

Now for the FoePennisetum setaceum is from Africa and south western Asia. It is highly invasive and will germinate readily in gardens, bushland, even cracks in the footpath. Not the sort of plant you want to have around! setaceum has been declared a Class 5 weed in NSW (restricted weed which must not be sold, bought or knowingly distributed throughout the entire state) and Class 3 weed in Qld (environmental weed). It is yet to be classified in other states.

 

Native Pennisetums used in landscaping and supplied by Bluedale

The cultivars and common form of alopecuroides supplied by Bluedale are regularly used in the landscape industry and include:
 

· Nafray® Pennisetum alopecuroides ‘PA300’

· Purple LeaTM Pennisetum alopecuroides ‘PAV400’ (see first picture)

· PennstripeTM Pennisetum alopecuroides ‘PAV300’

· Cream LeaTM Pennisetum alopecuroides

· Pennisetum alopecuroides(common form)


P. alopecuroides is known as Swamp Foxtail Grass. Its distribution ranges from tropical Queensland to the south of New South Wales mainly along the coast. P. alopecuroides naturally occurs in moist conditions and boggy areas. Importantly, Harden (1993) classifies alopecuroides as a native Australian species, however to confuse the issue, many sources indicate it may not be indigenous to Australia, having been transported here prior to European settlement.
 

Pennisetum varieties flower in late summer and autumn. Unfortunately, it follows that in areas with warm moist winters, such as tropical Qld and northern NSW, some cultivars, namely ‘Nafray’ and ‘Purple Lea’, can self-seed. Bluedale believe in responsible gardening and would not recommend growing either of these cultivars in such areas. To complicate things further, modern gardeners and landscapers will need to consider global warming and the resulting warmer winters some of us are already experiencing when using any plant that produces seed in abundance. The same can be said of gardens with warm winter micro-climates, coastal gardens and irrigated gardens.

When grown in other areas, an uncharacteristically warm and moist winter can see some self-seeding. In this case, we recommend thick, quality mulch and vigilance. Beware of coarse mulch such as pine bark as this leaves gaps and exposed soil suitable for seed germination. Seed heads can be removed before seed is set and unwanted seedlings spray very effectively with glyphosate.

In Bluedale’s experience, ‘Pennstripe’ is yet to produce viable seed. It is also the first variegated Australian native grass available. ‘Cream Lea’ has also proven to be non-invasive. There are no reports from Bluedale customers of ‘Cream Lea’ self-seeding.

 

Pennisetum ‘Rubrum’

Pennisetum ‘Rubrum’ is a commonly grown ornamental cultivar grown from the species Pennisetum advena native to Africa, the Middle East and East Asia. Both tall and dwarf forms are available. It is completely sterile and does not have a rhizome. ‘Rubrum’ will therefore not become a weed.

 

Our Foe Pennisetum setaceum

 

P. setaceum is also called Fountain Grass (see second picture). In an ideal world setaceum would not be available for sale in Australia. Over the past few years Bluedale has however, seen projects where this weed has been supplied to unsuspecting landscapers as the native form. The take home message here is be sure you/your contractors source plants from a reliable supplier. If in doubt, ask. Beware of plants produced by ‘backyard growers’ and sold at places like local markets.

P. setaceum flowers most of the year and produces an abundance of viable seed, which is mainly dispersed by wind but can also be spread by vehicles, humans, livestock, water and possibly birds. Where the native form has 10 – 30% seed viability, P. setaceum has close on 100%. Notably seed has been reported to remain viable for at least 7 years. It was likely brought into Australia as an ornamental grass and has been living it up here ever since.

According to the NSW Department of Primary Industries, P. setaceum is difficult to eliminate. Control may need to be repeated several times a year. The long-lived seeds mean continued monitoring aft­er treatment is essential. Control should initially be directed to outlying populations followed by treatment of the core area. Small infestations of fountain grass can be removed by uprooting and removing/destroying seed heads. Extensive infestations of fountain grass are probably best controlled with herbicides, combined with mechanical techniques.

The invasive behaviour of setaceum is likely to be the first step in its identification. Other features include:

· upright tufted grass with very narrow leaves and flowering stems growing up to 1 m or more tall

· long spike-like seed -heads (6-30 cm long) are reddish, pinkish or purplish in colour

· flowers are always present

· P. setaceum has a hairy peduncle (flower stalk) compared with the hairless peduncle of P. alopecuroides

· seed-heads contain large numbers of densely packed stalk less flower spikelet clusters

· each flower spikelet cluster is surrounded by numerous feathery bristles (12-26 mm long) and one significantly larger bristle (16-40 mm long)

· its mature seed-heads turn straw-coloured or whitish and the seeds are shed with the featherybristles still surrounding them.
 

If in doubt about identification, contact your local council or post a specimen to your nearest botanic gardens (most botanic gardens have a plant identification service that charges a small fee).

 

REFERENCES

Harden, G. J. (Ed) 1993 ‘Flora of New South Wales Volume 4’ Copywrite Royal Botanic Gardens and Domain Trust. Published by New South Wales University Press, Kensington, NSW Australia.

NSW Primary Industries Biosucurity (part of Department of Primary Industries) Weed Alert Brochurehttp://www.dpi.nsw.gov.au/agriculture/pests-weeds/weeds/profiles/fountain-grass

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