Introduction:
Creeping sowthistle (Sonchus oleraceus) Weed.
Sonchus oleraceus is an annual herb native to Eurasia and northern Africa. It has been introduced to a wide range of countries around the world. It is a common weed in disturbed areas and is a major problem in agricultural systems mainly due to its role in harbouring diseases and pests. It produces large numbers of seeds that are dispersed by wind.
Description:
Sonchus oleraceus is a dicotyledonous winter annual plant in the family Asteraceae. It has a rosette morphology that produces all its leaves, followed by a terminal flowering bud. It has two types of mature leaves: rosette leaves grow in circles from a common centre close to the ground; cauline leaves grow on the upper part of the stem. Leaves are thin and soft, measuring up to 35cm long and 12cm wide. Leaves are lanceolate to oblanceolate in shape, hairless and dark green in colour with pale white to purple veins. Stems are five angled and hollow and dark-green in colour (sometimes have a reddish-purple tinge), and emit a milky sap when cut. Plants can grow to 1m or greater in height.
Flowers are inflorescences (capitula), and are yellow and 5-6mm in diameter. Capitula are borne on stalks at the end of branches. Flowers open from 6am to 11am. The fruit is an achene that is 2.5-4mm long and 1mm wide, compressed and obovoid in shape. Achenes have 3-5 ribs and are rugose in texture. Mature seeds have a white feathery pappus (5-8mm long), that collectively form a white puff ball similar to dandelion. A single plant can produce over 8,000 seeds that are wind dispersed.
Occurs in:
Ruderal/disturbed, water courses.
Creeping sowthistle (Sonchus oleraceus) Distribution in north America shown in green.
Habitat description:
Sonchus oleraceus can grow on most soil types. It prefers disturbed areas such as fields, pastures, gardens, roadsides, edges of yards, construction sites, waste areas, farmland and recently burned fields. It grows at altitudes of up to 2650m. On Inaccessible Island S. oleraceus is recorded to occur on footpaths, landslides, depressions left by shifting boulders, old settlements/cultivations and rivers.
General impacts:
Annual sowthistle (Sonchus oleraceus) is a major problem as invaders of many crops, particularly of open vegetable fields. It is particularly problematic in winter crops and in tillage systems throughout southern Australia, South-East Queensland and Northern New South Wales. It uses valuable stored soil moisture during fallow periods, which reduces the yield of future crops.
S. oleraceus is also an important alternative host of pests and diseases of crops. It is a known host of a wide range of viral diseases including watermelon mosaic virus (WMV), pepino mosaic virus (PepMV), tomato spotted wilt virus (TSWV) and alfalfa mosaic virus (AMV). It is the host for the economically significant castor whitefly (Trialeurodes ricini), Bemisia whiteflies, cotton bollworm (Helicoverpa armigera and the nematode Radopholus similis. It is also likely to be an important host for downy mildew (Bremia lactucae), one of the worst diseases of lettuce which is an important vegetable crop worldwide.
Management information:
Close up of the Creeping sowthistle (Sonchus oleraceus) Weed.
Physical Control: Small or isolated populations of Sonchus oleraceus may be manually removed while plants are young, prior to seed set. The taproot must be removed, as resprouting can occur if left in the soil. Slashing is often ineffective as flowers continue to be produced. Minimal tillage of crops is recommended as this will maintain most of the seed bank close to the soil surface, which favours seed germination, enhances emergence and promotes seed decay and predation. If the seedlings are controlled effectively for a 6-12 month period, this type of control should greatly reduce the seed bank. Mulching and soil sterilisation methods can complement other management efforts.
Grazing: Grazing of Sonchus spp. by cattle and sheep effectively suppresses infestations in pastures, and weakens plants allowing other control methods to be more effectively used. They also make excellent feed for livestock.
Chemical Control: For control of Sonchus spp. (asper and oleraceus), a pre-emergent herbicide containing isoxaben can be used, herbicidal soaps when the plants are young, or glyphosate when plants are mature. Zollinger and Parker recommend 2,4-D, clopyralid, dicamba, glyphosate, and picloram for control of Sonchus spp., while Rice 2,4-D, DCPA, diethatyl-ethyl, MCPA, amitrole, atrazine, bromoxynil, chlorsulfuron, dicamba, dichlorprop & 2,4-D, diuron, glyphosate, isoxaben (Snapshot), norflurazon, oryzalin, oxyfluorfen, paraquat, Ornamental Herbicide II, napropamide, simazine and tebuthiuron.
Biological Control: Biological agents are currently being researched as a possibility for managing S. oleraceus and other Sonchus species in Australia. Sonchus species have previously been the target of biological control in Canada. Preliminary surveys for biological control agents have been made in southern France and northern Europe. Currently the rust fungus Miyagia pseudosphaeria and an unidentified eriophyid mite species are two widespread organisms in Australia with potential for control. The CSIRO project will focus on determining the impact of these potential control agents on related native Australian species ( Sonchus hydrophilus and Actites megalocarp and on weedy S. oleraceus and S. asper.
Sourced From:
