Glossy nightshade.
Glossy nightshade. Contributed

Glossy nightshade one of Australia's worst weeds

Glossy nightshade (Solanum americanum)

Solanum americanum is commonly known as American black nightshade, small-flowered nightshade or glossy nightshade.

It is probably native to Europe, and is now a worldwide common weed.  

Solanum americanum is widespread and very common in most coastal wetter parts of Australia on the east coast, south coast, west coasts, and northern coasts.

Glossy nightshade (Solanum americanum) is a weed of disturbed urban areas, cultivation, crops, pasture, gardens, stock yards, disturbed woodlands, stream banks, wetlands and eroded areas.

Up to 178,000 seeds can be produced by one plant and the seeds are often spread by birds and other animals that can eat the ripe fruit.  Fruit and seeds can also be spread on shoes, tractor implements and vehicles by humans. 

It is readily spread by birds into bushland and flowers for most of the year.

The numerous seeds can germinate producing thickets of plants which crowds out other garden, crop, or native plants.

Solanum americanum is one of Australia's worst and widespread weeds of intensive agriculture. 

It competes vigorously for space, sunlight, and nutrients especially with related Solanaceae crop species such as tomatoes, egg plants, and potatoes.  Glossy nightshade (Solanum americanum) is known to host a number of insects, nematodes, fungi, and viruses that are a threat to crops.

The known threats it is a host for include diseases such as anthracnose,Cercospora, blight, leaf spot and powdery mildew, at least 13 nematode species, 3 bacterial diseases, 7 fungal diseases including Rhizoctonia and over 30 crop viruses. 

It can be competitive in pea crops and is a particular problem since its black berries cannot be distinguished from peas by the processing equipment. The purple juice of the berries also stains wool.

In beans crops, mechanical harvesting ruptures the berries causing staining of the beans and adhesion of soil results in degraded quality of beans.

It occurs occasionally during the establishment stage of pasture and can outcompete grasses and other pasture plants due to cattle not usually eating it.  But in periods of drought or lack of grass cattle will eat it and become poisoned. 

The green berries are highly poisonous and has caused the death of children and pet animals. 

Ripe berries and foliage may cause poisoning. 

Livestock can also be poisoned by high nitrate levels in the leaves. 

This is because of high levels of the glycoalkaloids; solanine and solamargine. 

Other toxins present in the plant include chaconine, solasonine, solanigrine, gitogenin and traces of saponins, as well as the tropane alkaloids scopolamine (hyoscine), atropine and hyoscyamine.

Symptoms of glycoside poisoning in humans include abdominal pain, vomiting, constipation or diarrhoea, blood stained faeces, loss of appetite, and death. 

Alkaloid poisoning in humans and animals includes drowsiness, breathing difficulty, salivation, trembling, staggering.

Description
Glossy nightshade (Solanum americanum) is 1 to 1.5 metres tall and is an annual or short-lived perennial shrub.

The leaves are green, hairy to almost hairless, smooth-edged to coarsely blunt-toothed, alternate, and broadly to narrowly egg-shaped with a pointed tip.

The stems are mostly erect, well-branched, and green to tinged purple in colour. 

The Alternate leaves vary greatly in size, up to 10 cm long and 7 cm broad, with a 4 cm petiole and smooth margin.

The flowers are in small, umbel-like clusters below the leaf axils. 

The individual flowers are small, drooping, and have 5 often reflexed (bent backwards toward the stem), white to purplish lobes and a beak of yellow stamens and a longer style. 

Star shaped flowers are about 1 cm diameter.
Flowering occurs throughout the year, but mainly from autumn through to spring.

Fruit is a shiny black berry with a strongly reflexed green calyx and numerous disk-shaped seeds, 5 to 10 mm in diameter.

Management

Hand pulling when the soil is moist but it has a strong tap root and can break off above ground.

It is important to bag pulled plants due to the numerous seeds.

Bags of plants can be left in the sun to destroy seeds by high heat.

Spraying with Glyphosate herbicide will kill plants but not always the seeds.

It can develop resistance to herbicides.



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