Lesser Jack

Emex spinosa (L.) Campdera

Synonyms -

Family: Polygonaceae

Names:

Other Names:

Summary:

An oval, wavy leafed, hairless, rosette plant that develops prostrate stems with green flowers in spring that produce fruits that are 4-5 mm long bearing 3 sharp, rigid spines.

Description:

Cotyledons:

Two. Elongated spear shape. Tip pointed. Sides parallel to slightly convex. Base tapered. Surface hairless. No petiole.

First leaves:

First leaf oval with a round tip. Hairless.

Leaves:

Forms a loose rosette.
Stipules - Membranous sheath where the leaf joins the stem (ochrea).
Petiole - Longer than blade.
Blade - Triangular. Tip pointed. Sides convex to slightly lobed. Base indented. Surface hairless.
Stem leaves - Alternate, pointed tip, edges wavy, hairless

Stems:

Low lying, up to 750 mm long, branch from base, round, ribbed.

Flower head:

Flowers:

Small and white.
Ovary -
Perianth - white
Stamens -
Anthers -

Fruit:

Hard woody capsule, 4-5 mm long with a broad base and (6)8-10 pits on each face.

Seeds:

Triangular pyramid.

Roots:

Taproot.

Key Characters:

Petioles longer than the leaf.
Ochrea
Fruit is 3 spined and woody
8-10 pits on each face of the fruit.

Biology:

Life cycle:

Annual. Seeds germinate mainly in autumn to winter, the plant grows over winter to flower and set seed in spring.

Physiology:

Reproduction:

By seed.

Flowering times:

Spring.

Seed Biology and Germination:

Vegetative Propagules:

Hybrids:

Hybridises with Spiny Emex (Emex australis)

Allelopathy:

Population Dynamics and Dispersal:

Spread by seed. Seed is effectively dispersed by piercing and attaching to footwear, bags and machines. Spread in agricultural produce.

Origin and History:

Mediterranean, Asia Minor, South America, Canary Islands.

Distribution:

ACT, NSW, SA, VIC, WA.

Courtesy Australia's Virtual Herbarium.

Habitats:

Climate:

Temperate

Soil:

Plant Associations:

Significance:

Beneficial:

Detrimental:

Weed of crops, pastures and disturbed areas.

Toxicity:

May cause oxalate poisoning.

Symptoms:

Treatment:

Legislation:

Noxious weed of SA and WA.

Management and Control:

Control small patches and prevent movement of stock, men and machines through these patches.
Spray grazing provides moderate control. Broadstrike® plus diuron is giving good selective control in clover based pastures.

Thresholds:

Eradication strategies:

Manually remove isolated plants and burn them. Spray a 10 m area around them with a mixture of 1 L of Tordon® 75-D® in 100 L of water to help control seeds germinating later in the season.
Small areas should be fenced off to prevent stock, people and vehicles spreading the seed.
For large areas, shallow cultivate in late summer to encourage germination in autumn and then kill the seedlings with cultivation or herbicides. Deep ploughing is not recommended because it buries seed and induces dormancy, which may be broken when the seeds are returned to the surface in following seasons.
Plan for continuous pasture with tactical use of herbicides or plan to use herbicides in the cropping phase. Chemical application usually needs to be applied early and repeated to avoid young plants setting seed before control and to control late emerging seed.
Broadstrike plus diuron have given the best results in clover based pastures. A number of other herbicides and Spray Graze are useful in other situations.
In cereals, the sulfonylurea herbicides or dicamba provide the best control.
In bushland areas, wipe actively growing plants with a mixture of 1 L glyphosate(450g/L) plus 2 L water. For small areas, apply a mixture of 0.5 g metsulfuron(600g/kg) plus 100 mL Tordon® 75-D® in 1 L water to actively growing plants before flowering in spring or summer depending on when the Lesser Jack has germinated. On larger areas, Spinnaker® at 1 L/ha, or 10 mL per 10 L water for hand spraying, will provide reasonably selective control of small actively growing Lesser Jack and control seedlings for about a year. Inspect areas 3 times a year for several years and repeat control if seedlings emerge.

Herbicide resistance:

None reported.

Biological Control:

Several have been released but none have been very successful.

Related plants:

Spiny Emex (Emex australis) has a petiole which is shorter than the blade, the burrs and spines are about twice as big as Lesser Jack, have only 4 pits on each face of the fruit, are narrowed towards the base and has a more prostrate growth habit.

Plants of similar appearance:

Fiddle Dock (Rumex pulcher) and other docks look very similar to Lesser Jack when young but soon distinguish themselves with erect stems.

References:

Bodkin, F. (1986). Encyclopaedia Botanica. (Angus and Robertson, Australia).

Everist, S.L. (1974). Poisonous Plants of Australia. (Angus and Robertson, Sydney).

Harden, Gwen J. (1991). Flora of NSW. (Royal Botanic Gardens, Sydney). Volume . P. Diagram.

Hussey, B.M.J., Keighery, G.J., Cousens, R.D., Dodd, J. and Lloyd, S.G. (1997). Western Weeds. A guide to the weeds of Western Australia. (Plant Protection Society of Western Australia, Perth, Western Australia). P198.

Lamp, C. and Collet, F. (1990). A Field Guide to Weeds in Australia. (Inkata Press, Melbourne).

Lazarides, M. and Cowley, K. and Hohnen, P. (1997). CSIRO handbook of Australian Weeds. (CSIRO, Melbourne). #384.2.

Parsons, W.T. and Cuthbertson, E.G. (1992) Noxious weeds of Australia. (Inkata Press, Melbourne). P541.

Wilding, J.L., Barnett, A.G. and Amor, R.L. (1987). Crop weeds. (Inkata Press, Melbourne). P135. Diagrams. Photos.

Acknowledgments:

Collated by HerbiGuide. Phone 08 98444064 or www.herbiguide.com.au for more information.