Weed with cotton like seeds

Narrow leaf cotton bush: what you should know

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What you should know about narrow leaf cotton bush (Gomphocarpus fruticosus).

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What you should know about narrow-leaf cotton bush

Narrow-leaf cotton bush (Gomphocarpus fruticosus) is in the family Asclepiadaceae which contains many toxic weeds and garden plants. The members of this family typically have thick white sap, which gives rise to the common name of the milkweed family. Some other plants in the family are rubbervine (Cryptostegia grandiflora), calotrope (Calotropis procera), moth plant (Araujia sericifera), redhead cotton bush (Asclepias curassavica) and stapelia (Orbea spp.).

Narrow-leaf cotton bush and the closely related balloon cotton bush (G. physocarpus) get their common names from the silky white thread-like attachments on their seeds. Narrow-leaf cotton bush is also known as swan plant because of the shape of its seed pods. Balloon cotton bush has more rounded seed pods. Narrow-leaf cotton bush is native to South Africa and Ethiopia and was introduced to Australia as a garden plant. It is a weed right across Australia, as well as parts of New Zealand and the Mediterranean basin. Narrow-leaf cotton bush is a food plant for the brightly coloured caterpillars (larvae) of the wanderer butterfly (Danaus plexippus). The wanderer is native to North America but has now established in Australia, due to the presence of narrow-leaf cotton bush and other introduced plants that provide food for its larvae. Narrow-leaf cotton bush is a declared plant but is still found in cultivation.

Why narrow-leaf cotton bush matters

Narrow-leaf cotton bush is a common weed in the south-west of Western Australia. It invades run down or low fertility pastures where it displaces useful species such as clover. Narrow-leaf cotton bush and its close relatives contain cardiac glycosides, which are toxic to humans and livestock. Stock wouldn’t normally eat the plant because its acrid latex makes it extremely unpalatable but it may cause problems as a contaminant of hay or chaff. The main symptom of narrow-leaf cotton bush poisoning is severe gastroenteritis, which shows up as severe congestion of the alimentary canal. Narrow-leaf cotton bush also invades riparian areas where it competes with native plants.

What to look for

Narrow-leaf cotton bush is a shrub growing up to two metres in height. It can form dense thickets covering many hectares. The opposite leaves are 6–18mm wide and 5–12.5cm long. The creamy white flowers are about 1cm across and have a short corolla tube. The flowers form in drooping clusters from October to April. The distinctive seed pods are puffy, swan-shaped structures up to 6cm long and covered in soft spines. It could be confused with balloon cotton bush, which also reaches 2m in height, but has more rounded seed pods. There are hybrids of these two species that produce intermediate seed pods. Narrow-leaf cotton bush is most prevalent on the Darling Scarp and the Swan Coastal Plain between Perth and Bunbury, though it may be found from Gingin to Esperance.

Life history of narrow-leaf cotton bush

Narrow-leaf cotton bush spreads by seeds, which usually germinate in spring or autumn, but can germinate at any time in warm, moist conditions. Seedlings have the ability to resprout from the crown or root if the above ground parts of the plant are damaged. The plants grow through summer and usually flower in the second year from October to April.

What you can do about narrow-leaf cotton bush

Practice good biosecurity to avoid introducing narrow-leaf cotton bush or other weeds and pests to your property. Do not cultivate narrow-leaf cotton bush as a garden plant and avoid purchasing soil or other landscaping supplies that could be contaminated with weed seeds or bulbs. Take particular care when purchasing fodder – cheap hay is not a bargain if it is full of weed seeds or toxic plants. Ensure contractors entering your property have clean equipment to avoid the introduction of new weeds – install a washdown bay if necessary. If you have narrow leaf cotton bush on your property, take care to prevent it spreading to other properties. Control small infestations before they spread. Join forces with your neighbours and local government authority to remove narrow-leaf cotton bush and other weeds. Narrow-leaf cotton bush has a shallow root system so small infestations can be dealt with by hand pulling – make sure you get all the roots to prevent suckering. Take appropriate measures to avoid contact with the toxic sap, such as wearing rubber gloves and overalls, and washing hands thoroughly before eating. Contact with the sap could cause a rash or other symptoms for which medical advice should be sought.

Destroy any seeds in a way to avoid spreading the plant. Larger infestations are best dealt with by a combination of spraying, slashing, burning and pasture management. Burning heavy infestations of cotton bush is an effective, low cost option which damages seed on and near the soil surface. The reduction in the soil seed bank allows increased pasture production. Ploughed firebreaks can provide an ideal seedbed for narrow-leaf cotton bush and other weeds, so chemical firebreaks may be better. Chemical firebreaks have the added advantage of providing a firm surface that can be used as an access track or an escape route in the event of fire.

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Control options

Seedlings, plants less than 1m tall

Minor infestations or small patches of young seedling plants can be sprayed with glyphosate or physically removed by grubbing or hand pulling. At this growth stage they are unlikely to have seeded and can be disposed of by drying and burning. Larger infestations are effectively controlled using glyphosate to ensure all seedlings are controlled before they mature and produce seed.

Mature plants more than 1m tall

Small areas can be sprayed or physically removed by grubbing or pulling. Plants that have been removed will dry out quickly and should be burnt or deep buried. Mature plants with seed pods attached have the potential to spread seed and infest new areas when moved away from their original location and should be disposed of as close to the infestation as possible. Large infestations of mature plants can be managed and controlled using various techniques including slashing, burning and spraying. All methods reduce the potential for plants to produce seed. Slashing and burning must be followed up with herbicide treatment to control regrowth and seedlings. Spraying with glyphosate mixed with metsulfuron methyl is very effective in controlling larger cotton bush plants and is best applied by a high volume hand lead sprayer. Plants should be sprayed until the leaves are wet, almost to the point that liquid is running off. The table below provides the amount of glyphosate herbicide per 10L knapsack or 100L tank mix for products that contain 360, 450 or 540g/L or 680g/kg of glyphosate. Other herbicides used for the control of narrow-leaf cotton bush include triclopyr and metsulfuron methyl. In bushland areas, wipe the leaves with a mixture of 1L glyphosate plus 2L water before flowering when the plants are actively growing in spring to early summer. The larvae of the wanderer butterfly occasionally cause stem and leaf damage to cotton bush, however it is not sufficient to kill infestations of the plant.

Summary of control options for narrow leaf cotton bush seedlings and immature plants (

Glyphosate (sold under various trade names).

Use with a wetting agent.

Amount of product for 10L sprayer

Amount of product for 100L tank

Time of application

More information and other control methods

Slash established bushes during winter and burn. Cultivate or grub regrowth.

Use Roundup®Biactive or Razor around sensitive aquatic areas.

Triclopyr (sold under various trade names).

Use crop-oil such as Uptake @ 500mL 100L, or DC-Trate @ 1L/100L.

Amount of product for 10L sprayer

Amount of product for 100L tank

Time of application

Use in place of glyphosate to preserve grass pasture.

More information and other control methods

Summary of control options for narrow leaf cotton bush mature plants (>1m tall)

Glyphosate + metsulfuron (sold under various trade names).

Use with a wetting agent.

  1. glyphosate 360g/L
  2. glyphosate 450g/L
  3. glyphosate 540g/L
  4. glyphosate 680g/kg

+ metsulfuron methyl 600g/kg

Amount of product for 10L sprayer

Amount of product for 100L tank

  1. 1000mL + 10g
  2. 800mL + 10g
  3. 650mL + 10g
  4. 500g + 10g

Time of application

Treat actively growing plants (i.e. Spring to December)

Lower the rate of metsulfuron methyl (1g/100L) in areas where sensitive native species occur.

More information and other control methods

Physically remove or slash plants if there is potential for off target damage to sensitive plant species. Treat regrowth and seedlings with glyphosate.

Further information

For more information on narrow leaf cotton bush, search this website or contact the Pest and Disease Information Service.

Weed with cotton like seeds

The first step in developing an effective weed management program is being able to properly identify the weed species that are infesting a field. But why? Why is weed identification so important? Simply stated, because not all weeds are created equal. Species differ with respect to their emergence timing, life history traits, competitive interactions with the crop, potential to harm livestock, and sensitivity to available herbicides, among other characteristics. Consequently, the type and timing of weed control events need to be designed to target problematic species so that control is maximized, weed seed return to the soil seedbank is minimized, and crop yields are protected.

Unfortunately, weed identification is not a simple task, especially when it comes to members of the Asteraceae, one of the largest plant families in the world. Several species of Asteraceaeare found throughout California in many different agricultural and non-agricultural environments; these include: hairy fleabane (Erigeron (Conyza) bonariensis), horseweed (Erigeron (Conyza) canadensis), annual sowthistle (Sonchus oleraceus), prickly lettuce (Lactuca serriola), and common groundsel (Senecio vulgaris). This blog post has been developed to help you distinguish among these species.

Erigeron bonariensis – Hairy fleabane:

Hairy fleabane (also called asthma weed and flax-leaf fleabane)is an annual (sometimes biennial) herb that is not native to California. According to the USDA’s PLANTS database (https://plants.usda.gov), the species can be found in California, Arizona, Nevada, Oregon, and Washington, and across the southern US to as far north as Virginia. Biotypes of fleabane can emerge fall through spring with the earlier emerging plants over-wintering as rosettes. Leaves are a grey-green in color, hairy, and are arranged alternate to each other. While the first leaves produced are roughly oval- to spatula-shaped, later leaves tend to be more linear with entire to weakly-toothed margins. Leaves of hairy fleabane are also twisted, crinkled or wavy in appearance. At bolting, hairy fleabane produces a many branched stem (0.5 to 3 feet [0.15 to 0.9 m] in height) upon which numerous cream- to yellow-colored flowers are held. Lateral branches can be longer in length than the main stem. Flowering occurs, predominantly, mid-summer through fall. The resultant seedheads resemble those of dandelions, although they are much smaller in size (0.2 to 0.3 inches [5 to 7 cm] in diameter). Individual seeds possess a pappus (0.12 to 0.16 inches [3 to 4 mm] in length) on one end that facilitates wind-dispersal. Hairy fleabane plants produce taproots along with fibrous lateral roots. Hairy fleabane populations with resistance to glyphosate and with resistance to both glyphosate and paraquat have been confirmed in California.

Hairy fleabane leaves are grey-greenish in color and are often wavy, crinkled, or twisted. Photo by L. M. Sosnoskie.

At bolting, hairy fleabane sends up a many branched stem upon which flowers are produced. From: Weeds of California and Other Western States by J. M. Ditomaso and E. A. Healy. Photo by J. M. DiTomaso.

Hairy fleabane seedheads. Individual seeds each possess a pappus, a tuft of hair that aids with wind dispersal, which gives the seedheads their fuzzy appearance. Photo by L. M. Sosnoskie.

Erigeron canadensis – Horseweed:

Horseweed, also known as marestail,is an annual (sometimes biennial) herb that is native to California and most other parts of North America. According to the USDA’s PLANTS database, the species has been found in all 50 states and most of Canada. The pattern of horseweed germination and emergence is like that of hairy fleabane, were seedlings can emerge from the fall through early spring. At the seedling stage of development, horseweed and hairy fleabane resemble each other, morphologically; differences become more apparent past the 12 to 15 leaf stage. Not unlike hairy fleabane, horseweed leaves are alternate and are arranged in a rosette; however, horseweed leaves are typically a darker shade of green, as compared to fleabane. Upon bolting, plants send up a single, erect stem that can reach heights of 10 feet (3 m). Unlike hairy fleabane, lateral branches are shorter than the main branch. Cream- to yellow-colored are produced in dense panicles from mid-summer to fall. Like hairy fleabane, horseweed produces seeds that possess a pappus (0.10 to 0.12 inches [2.5 to 3 mm] in length) that facilitates wind dispersal. Whereas single hairy fleabane plants have been estimated to produce up to 20,000 seeds per plant, horseweed plants can produce more than 200,000. Horseweed plants produce taproots along with fibrous lateral roots. Horseweed populations with resistance to glyphosate and with resistance to both glyphosate and paraquat have been confirmed in California.

Horseweed (L) and hairy fleabane (R) rosettes. Hairy fleabane leaves are grey-greenish in color and are often wavy, crinkled, or twisted as compared to horseweed. Photo by L. M. Sosnoskie.

Bolting horseweed. Notice the single erect non-branching stem. Photo by L. M. Sosnoskie.

Horseweed growth habit. At bolting, horseweed sends up a single, erect stem upon which flowers are produced. Horseweed stems can reach heights up to 10 feet. For comparison, Lynn Sosnoskie, an author of this post, is 5’3” tall. Photo by D. D. MacLean.

Sonchus oleraceus – Annual sowthistle:

Annual sowthistle is not native to North America but has become naturalized throughout the US and Canada. The first true leaf is round to egg-shaped although following leaves become spatulate with prickly margins. Older leaves are deeply lobed with the terminal lobe being large and triangular in shape. Stems are erect and hollow between nodes and can reach heights of 4 feet [1.2 m]. Leaves on the stems are clasping at the base. Broken or cut leaves and stems will exude a white sap. Because annual sowthistle can be both a summer and a winter annual, flowers can be produced year-round when conditions are favorable. Flowers (0.5 to 1 inch [1.2 to 2.5 cm] in diameter) resemble those of dandelions except they are a light yellow in color. Like other species in the Asteraceae family, the pappuses (0.2 to 0.3 inches [5 to 8 mm] in length) attached to individual seeds give the seedhead it’s cotton ball-like appearance. Seeds are wind-dispersed. Annual sowthistle produces a short and think taproot with many lateral roots.

Annual sowthistle seedling. Note the spatula-shaped (spoon-shaped) leaves with finely-toothed margins. Photo by L. M. Sosnoskie.

Mature rosette of annual sowthistle. Leaves are deeply lobed with the terminal lobe being triangular in shape. Photo by L. M. Sosnoskie.

Leaves of annual sowthistle on flower stems are clasping at the base. Photo by L. M. Sosnoskie.

Lactuca serriola – Prickly lettuce:

Prickly lettuce is not native to North America but has become naturalized throughout the US and Canada. The species is classified as a winter and summer annual and sometimes a biennial. The first leaves are football-shaped; later leaves are elongated and club-shaped with weakly-toothed margins or are deeply- and pinnately-lobed with rounded indentations. The midrib vein is pronounced and covered with a row of prominent spines on the underside. Plants exist as a basal rosette (with alternating leaves) before sending up a single flower stalk that can reach heights of 6.5 feet (2 m). The stems are covered with stiff hairs that give them a spiny appearance and are branched at the terminal apex. Stems and leaves exude a milky sap when cut or broken. Flowers (0.3 to 0.4 inches [8 to 10 mm] in diameter) are pale yellow; flowering occurs, typically, from April to October. Like other members of the Asteraceae, prickly lettuce seeds possess pappuses (0.16 to 0.2 (4 to 5 mm) in length) that facilitate wind dispersal. Plants produce deep tap roots with fibrous lateral roots.

Young prickly lettuce rosette. Photo by L. M. Sosnoskie

Spines on the underside of the midrib vein of a prickly lettuce leaf. Photo by L. M. Sosnoskie.

A mature Prickly lettuce stem exhibiting prickly/spiny stems and deeply lobed leaves with prominent midrib veins. From: Weeds of California and Other Western States by J. M. Ditomaso and E. A. Healy. Photo by J. M. DiTomaso

Senecio vulgaris – Common groundsel:

Common groundsel is not native to North America but has become naturalized throughout the US and Canada. The species is, predominantly, a winter annual and sometimes a summer annual. The youngest leaves are egg-shaped with shallowly-toothed edges, the base of the leaves may be purple on the underside. Following leaves are alternately arranged in a rosette, are usually more deeply (but irregularly) lobed, and may also be hairless to hairy. At maturity, plants may send up a single stem or else a series of branches from the base; stem heights can reach 2 feet (0.6 m). The plant has often been described as having a ‘ragged’ or ‘scraggly’ appearance. Common groundsel produces small, yellow flowers in clusters. Individual flowers are surrounded by green bracts with black tips. Flowering can occur throughout the year. Like other members of the Asteraceae, a pappus, a tuft of hair that aids with wind dispersal, is attached to each seed. Common groundsel plants produce small taproots with fibrous lateral roots. The presence of common groundsel can be problematic for alfalfa and forage producers; the species produces pyrrolizidine alkaloids, that can lead to liver damage in livestock following consumption. Even hay with a small amount of contamination can be problematic as pyrrolizidine alkaloid poisoning can accumulate in the livestock over months of feeding.

Common groundsel leaves demonstrating deep, but irregular, lobed patterns. Photo by L. M. Sosnoskie.

Common groundsel at the bolting stage. Photo by L. M. Sosnoskie.

Mature groundsel plant displaying a many-branched habit, flowers in clusters, and fuzzy seedheads. Photo by L. M. Sosnoskie.

While similar in general appearance (i.e. alternate leaves arranged as a basal rosette, flowers produced on upright stems, and seeds with pappuses that allow for wind dispersal), hairy fleabane, horseweed, annual sowthistle, prickly lettuce, and common groundsel all possess unique morphological and phenological characteristics that differentiate them from one another. Properly identifying these and other species is the first step in developing a safe and effective weed management program in crop production systems. For example, the type and timing of herbicide applications are directly influenced by the emergence patterns of the target species as well as their sensitivity to available products. For instance, the presence of glyphosate-resistant weeds like hairy fleabane and horseweed may reduce the value of glyphosate as a stand alone active ingredient. Identifying the presence of poisonous plant species is also critical for some producers. Repeated consumption of common groundsel, can result in irreversible liver poisoning of livestock; consequently, a quick and proper ID of this species is important for limiting animal exposure to toxic alkaloids. Many tools are available to assist growers, PCAs, and other crop consultants with weed identification; this includes the reference materials listed below. Your local county farm advisors can also be an extremely useful resources for determining the identity of suspect species.