Stinkwort

Dittrichia graveolens (L.) Greuter

Synonyms - Inula graveolens.

Family: Asteraceae.

Names:

Dittrichia celebrates the German botanist M. Dittrich.
Graveolens is Latin for strong smelling.
Stinkwort - wort is from the Old English wyrt and means herb or plant used as a medicine and stink refers to the smell of the volatile oil secreted by glandular hairs on all parts of the plant.

Other names:

Camphour Inula (South Africa)
Kaapsekakiebos (South Africa)
Stink Weed.

Summary:

Stinkwort is an aromatic, erect, bushy, 25-60 cm tall, summer growing annual with many spreading leafy branches arising from a basal rosette of leaves. Oil secreted makes the plant sticky to touch and it is usually covered in dust and other light particles stuck to it. It has small, fluffy, yellow to white flowers with small outer radiating petal-like florets. The tiny seeds have a hat of hairs.
Originating from the Mediterranean region, it is now a common weed of pasture, roadsides and waste land. It flowers in late summer to early winter.
Stinkwort can cause stock losses and may cause dermatitis.

Description:

Cotyledons:

Two. Oval. Tip round. Base tapered. Hairless. Petiole shorter to about the same length as the blade.

First leaves:

Club shaped. Tip round. Base tapered. Hairs on upper surface. No petiole.

Leaves:

Alternate. Forms a basal rosette to 200 mm wide.
Stipules -
Petiole - None.
Blade - Oblong to lance shaped, often with small teeth, 20-100 mm long x 2-13 mm wide, soft. Veins usually indented on the upper surface. Edges hairy and curved or rolled inwards.
Stem leaves - May not have teeth, almost stem clasping, up to 60 mm long. Taper to a point at the tip.

Stems:

Erect, bushy, woody, rigid, aromatic, and oily to touch, 200-1300 mm tall with branches almost at right angles to the main stem and curving upwards. Dense glandular hairs and broad based hairs with thread like tips.

Flower head:

Many, small, bell shaped, 4.5-10 mm long x 3-5 mm wide, in long loose, leafy, pyramid like panicles surrounded by sticky bracts. On the ends of branches and on very short stalks in the leaf axils.

Flowers:

Bracts - Several rows surround the florets. Outer ones are leafy, green, narrow, sticky, and elliptical to triangular, 3 mm long x 0.5-1 mm wide, many glandular hairs and a few long hairs, tip has tiny hairs. Inner bracts are longer, 4-7 mm long x 0.7-1 mm wide with pale edges.
Florets - Ray florets, 10-12, outer, female with a short, erect, 3-toothed ligule, 4-7 mm long, slightly red or yellow and often just sticking out of the top of the flower head.
Disk florets, 10-12, inner, bisexual, yellow, tubular.
Ovary - Receptacle is flat or slightly convex, without bracts.
'Petals' - 10-12, yellow to red, 1-2 mm long.
Stamens -
Anthers - Tailed at the base.

Fruit:

Achene. Light brown, almost cylindrical, 2 mm long, downy with fine hairs. Narrowed to a neck at the top, then expanded into a small cup supporting the pappus.
Pappus of about 30 bristles, 3-4 mm long. Looks simple to the naked eye, but are fused together at their base and are barbed.

Seeds:

Enclosed in the fruit.

Roots:

Strong taproot with many laterals.

Key Characters:

Strong smell. Sticky to touch.

Biology:

Life cycle:

Annual. Germinates and grows in the late spring and summer forming small slow growing rosettes until warm weather occurs. The rosette then grows rapidly and the main stem emerges and branches to give the characteristic conical shape of the plant. Flowering starts around March and continues until frost or cold weather kills the plant.

Physiology:

Drought tolerant.

Reproduction:

By seed.

Flowering times:

March to April in SA.
Mainly late summer to autumn in NSW.
November to April in WA.

Seed Biology and Germination:

Seeds are short lived and probably don't survive more than 3 years.

Vegetative Propagules:

None.

Hybrids:

Allelopathy:

Population Dynamics and Dispersal:

Fluffy seed dispersed by wind, water, stock and machinery.
In pastures it is associated with low phosphate status or poor pasture growth. Seedlings are very sensitive to competition and usually only establish in relatively bare areas.

Origin and History:

Mediterranean.
Introduced into South Australia in contaminated wheat in the 1860's and recorded as a weed from Onkaparinga in SA around 1875. By 1890 it was classed as the worst weed of cereals in SA. Changing practices and increased fertility have now made it a minor weed of agriculture.

Distribution:

ACT, NSW, QLD, SA, VIC, WA

Courtesy Australia's Virtual Herbarium.

Habitats:

Climate:

Warm temperate and sub tropical areas. Open areas with an annual rainfall of 300-800 mm.

Soil:

Prefers light textured soils, depressions or winter flooded areas.

Plant Associations:

Significance:

Beneficial:

Fodder but low nutritive value.
Used as a Greek herbal medicine.
Dried plants used for smoking ham and bacon in Europe.

Detrimental:

Taints milk and meat but not usually grazed by stock.
Weed of pastures, crops, lucerne, fallows, roadsides, railways, slightly saline areas, summer moist areas, watercourses, summer crops and irrigated and disturbed areas.
Discolours wool but it comes out during scouring.
It is one of the most widespread weeds in Australia.

Toxicity:

Can cause severe dermatitis in humans especially if handled when in flower. Gloves should be worn when handling the plant as some people are quite sensitive and it may take several months for the dermatitis to clear. Some people are allergic to the aromatic oils produced by Stinkwort.
Can cause stock deaths if mature plants with seeds are grazed because fine hairs on seed induce pulpy kidney or the fatal bacterial entero-toxaemia.
Dogs may vomit when working in infested areas when it is in flower or seed.
Causes dermatitis in sheep and horses that may persist for some weeks after the stock are removed from the infestation.

Symptoms:

Pulpy kidney, sudden death.
Dermatitis.

Treatment:

Remove stock from infestation or provide alternative feed.
Don't graze areas that are in seed. Don't expose lambs or young sheep to infestations.
Wear protective clothing when working with the plant.

Legislation:

Noxious weed of New South Wales, South Australia, Victoria and Western Australia.

Management and Control:

For extensive areas of stinkwort it is often more profitable to vaccinate stock for pulpy kidney rather than killing it with herbicide. This reduces the economic impact of the weed.

Thresholds:

Eradication strategies:

Small areas can be mechanically removed. Plants in flower must be burnt as seed will develop from the nutrient reserves in the stem if left on the ground. Cultivation of larger plants is only effective if done before flowering.
Mowing reduces seeding but is effective only if is cut very close to the ground and repeated. Regrowth often occurs if adequate soil moisture is present.
Older plants are relatively tolerant of glyphosate, metsulfuron and hormone herbicides.
Heavy grazing (with older wethers) provides some control of young plants. The level of control may be improved by spraying with 1 L/ha 2,4-D amine plus wetting agent and heavily grazing 7 days later. Thick stands of Stinkwort reduce winter pasture growth which helps conserve moisture for Stinkwort growth next summer. Control programs should address the reasons why stinkwort has become a weed in a particular area. This may include rectifying soil nutritional deficiencies, lowering water tables and alleviating salinity, or introducing more suitable pasture species such as perennials to consume summer moisture, or controlling pasture pests and disease to reduce premature death of winter annuals.
Infestations upwind or upstream may need to be controlled to prevent re-infestation. Young plants can be controlled with 2 L/ha 2,4-D ester(800g/L) plus 1% spray oil or 40 mL 2,4-D ester(800g/L) plus 100 mL spray oil in 10 L water. Older plants are more difficult to kill and a mix of 100 mL 2,4-D ester(800g/L) plus 4 g Lontrel®750 plus 100 mL spray oil in 10 L of water will be needed for reasonable control.

Herbicide resistance:

Biological Control:

Related plants:

None.

Plants of similar appearance:

Fleabanes (Conyza species) are not sticky to touch and is not aromatic.
Kochia (Bassia scoparia) is larger and has three parallel veins on the leaf and is not aromatic or sticky.
Tumbleweed (Amaranthus albus) is not aromatic or sticky.

References:

Auld, B.A. and Medd R.W. (1992). Weeds. An illustrated botanical guide to the weeds of Australia. (Inkata Press, Melbourne). P100. Photos.

Black, J.M. (1965). Flora of South Australia. (Government Printer, Adelaide, South Australia). P921-922. Diagram.

Burbidge, N.T. and Gray, M. (1970). Flora of the Australian Capital Territory. (Australian National University Press, Canberra). P385, 387. Diagram.

Cunningham, G.M., Mulham, W.E., Milthorpe, P.L. and Leigh, J.H. (1992). Plants of Western New South Wales. (Inkata Press, Melbourne). P668. Photo.

Everist, S.L. (1974). Poisonous Plants of Australia. (Angus and Robertson, Sydney). P172. Diagram.

Gardner, G.A. and Bennetts, H.W. (1956). The toxic plants of Western Australia. (West Australian Newspapers Ltd, Perth). P194. 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). P96-97. Photo.

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

Lazarides, M. and Hince, B. (1993). CSIRO handbook of economic plants of Australia. (CSIRO, Melbourne). #458.1.

Marchant, N.G., Wheeler, J.R., Rye, B.L., Bennett, E.M., Lander, N.S. and Macfarlane, T.D. (1987). Flora of the Perth Region. (Western Australian Herbarium, Department of Agriculture, Western Australia). P677. Diagram.

Meadly, G.R.W. (1965). Weeds of Western Australia. (Department of Agriculture - Western Australia). P139-141. Diagram. Photo.

Parsons, W.T. and Cuthbertson, E.G. (1992). Noxious weeds of Australia. (Inkata Press, Melbourne). P281-283. Photos.

Wilding, J.L. et al. (1987). Crop weeds. (Inkata Press, Melbourne). P53. Diagrams. Photos.

Acknowledgments:

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