Tall Weed With White Fluffy Seeds

As we roll into August, plenty of noxious weeds across the county are blooming and going to seed, and those of us in the weed world are doing our best to keep up. Here's what to watch out for this month: Starting off with regulated noxious weeds, first up is the infamous tansy ragwort (Senecio… Welcome to the famous Dave’s Garden website. Join our friendly community that shares tips and ideas for gardens, along with seeds and plants. If you’ve made it outside on a recent sunny day, you’ve probably noticed the abundance of flowers blooming in gardens, parks, forests, and throughout King County right now. Unfortunately, the noxious weeds are out there, too—many of them bolting, flowering, and even going to seed already. Below are some of the top regulated noxious weeds…

Weeds to Watch out for—August 2017

Tansy ragwort produces clusters of bright yellow daisy-like flowers—usually with 13 petals—at the ends of its stems.

Garden loosestrife’s 5-petaled, yellow, primrose-like flowers appear in clusters at stem ends between July and September.

Phragmites has purple-brown-silver seed head plumes at end of stalks, 6-20 inches long and up to 8 inches wide.

Brazilian elodea’s showy white flowers with 3 petals and yellow centers, fragrant, floating on water surface

Knotweed’s flower are small, creamy white to greenish white, appearing in showy, plume-like, branched clusters in leaf joints near stem ends in July and August.

Bull thistle has many 2-inch-wide, rose to purple flower heads with spines around base, clustered at branch ends. Photo courtesy of Jennifer Andreas, Washington State University Extension.

As we roll into August, plenty of noxious weeds across the county are blooming and going to seed, and those of us in the weed world are doing our best to keep up. Here’s what to watch out for this month:

Tansy ragwort (Senecio jacobaea) often grows in pastures, where it poses a serious threat to horses and cattle.

Starting off with regulated noxious weeds, first up is the infamous tansy ragwort (Senecio jacobaea). This Class B noxious weed is flowering and getting ready to seed right now. Tansy ragwort is especially worrisome because it’s toxic to horses and cattle, who are most likely to eat it when it’s dry and mixed with hay. Add to that the 150,000 seeds each plant produces, all of which can remain viable in the soil for up to 15 years, and you have one nasty plant.

You can identify tansy ragwort by:

  • First-year plants in low rosettes with ruffled leaves and often reddish stems
  • Second-year plants 2 to 4 feet (up to 6 feet) tall
  • Leaves dark green on top, whitish-green below
  • Mature ruffled leaves have deeply cut, blunt-toothed lobes
  • Clusters of small daisy-like flowers with orange-yellow centers and usually 13 yellow ray petals atop stems

Tansy ragwort produces clusters of bright yellow daisy-like flowers—usually with 13 petals—at the ends of its stems.

For more information on tansy ragwort identification and control, visit these pages:

You can also check out our July “Weed of the Month” post on tansy ragwort, and our recent post on noxious weeds and their look-alikes.

Spotted knapweed (Centaurea stoebe) in bloom. Photo by Matt Lavin / CC BY.

Next, spotted knapweed (Centaurea stoebe). This Class B noxious weed will also be blooming and starting to seed this month. A lover of well-drained soils in full sun, the short-lived perennial thrives in dry, disturbed sites throughout King County.

You can identify spotted knapweed by:

  • First-year plants in a basal rosette with deeply lobed, grayish-green leaves
  • Mature plants up to 5 feet tall with up to 20 upright branched stems
  • Stout taproot
  • Small, oval flower heads with pink or light purple flowers
  • Bracts that have distinct black spots with vertical lines below (bracts are those scale-like structures growing around the base of the flower head)

For more information on spotted knapweed identification and control, visit these pages:

You can also check out our June “Weed of the Month” post on spotted knapweed, as well as a number of other blog posts.

Garden loosestrife (Lysimachia vulgaris) infestation at Marymoor Park on Lake Sammamish.

A number of our riparian and aquatic weeds are also flowering and seeding right now. For instance, the resilient garden loosestrife (Lysimachia vulgaris), a Class B noxious weed, is currently blooming along King County’s shores. You can identify garden loosestrife by:

  • Round erect stems covered in soft hairs, growing 3-6 (sometimes 10) feet tall
  • 3-5 inch long, ovate leaves in whorls of 3 (sometimes 2 or 4) with hairy undersides
  • Showy, yellow, 5-petaled primrose-like flowers in clusters at stem ends
  • Flower bases ringed by green sepals with distinct orange-brown edges
  • Dry, egg-shaped capsules containing a few seeds each
  • Creeping red rhizomes up to 15 feet long
See also  Growing Weed From Seed For Dummies

Garden loosestrife’s 5-petaled, yellow, primrose-like flowers appear in clusters at stem ends between July and September.

Garden loosestrife’s flowers appear in clusters at stem ends. Education Specialist Sasha Shaw holds a garden loosestrife plant on the Raging River.

For more information on garden loosestrife identification and control, visit these pages:

You can also check out our August “Weed of the Month” post on garden loosestrife, as well as a number of other blog posts.

Purple loosestrife (Lythrum salicaria) has magenta flowers clustered in tall, dense spikes.

The somewhat similar purple loosestrife (Lythrum salicaria), another Class B noxious weed, is also flowering. You can identify this wetland perennial by:

SOLVED: A tall weed with white fluffy flowers

Definitely not Ageratina havanensis – neither flowers nor leaves match.

Thank you both for replying.
Altagardener I am sure you are on the mark with the Conyza species

Conyza bonariensis is a weed species listed here in New Zealand and it looks similar to my photos.
I see Wikipedia now calls it Erigeron bonariensis

Of these, in the reference cited, Conyza bonariensis, C. canadensis, and C. parva resemble, superficially at least, the plant in question.

C. parva is said to be a synonym for C. canadensis (now Erigeron canadensis). (The others mentioned have also been put back into Erigeron.)

It’s very like what I know as Conyza bonariensis, distinguished by its the rather large, globular seedheads, not as numerous as in some other weedy spp, and almost linear upper leaves.
Altagardener, the Wikipedia article on Erigeron does not show much awareness of taxonomy. Its article on E. bonariensis cites Tropicos as a primary source for the name but Tropicos is neutral as to which name is accepted though citing usage under the ‘accepted names’ tab –
http://www.tropicos.org/Name/2702433
http://www.tropicos.org/Name/2702314
The USDA PLANTS database keeps these species in Conyza but GRIN has them under Erigeron!
The plot thickens as I check on genus Conyza in GRIN, as they cite 2 recent cladistic studies which appear to give support to its being merged under Erigeron
http://www.ars-grin.gov/cgi-bin/npgs/html/genus.pl?2902

I don’t generally use Wikipedia for plant info details, nor for nomenclature (far too many misidentified plant photos, which makes me suspect the accuracy in general) – it was the OP who referenced it.

Thanks for that lead altagardener. It’s not a database I have used much but looks like it can be relied on. And the entry linked straight to the Global Compositae Checklist, which is also new to me.

Thanks for all your help With the leads you have given me I am sure its Conyza parva.

. for which the accepted name is Erigeron canadensis.

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SOLVED: A tall weed with white fluffy flowers
SOLVED: A tall weed with white fluffy flowers
SOLVED: A tall weed with white fluffy flowers
SOLVED: A tall weed with white fluffy flowers
SOLVED: A tall weed with white fluffy flowers
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Noxious weeds to watch for in June

If you’ve made it outside on a recent sunny day, you’ve probably noticed the abundance of flowers blooming in gardens, parks, forests, and throughout King County right now. Unfortunately, the noxious weeds are out there, too—many of them bolting, flowering, and even going to seed already.

Below are some of the top regulated noxious weeds to keep an eye out for this month. Please let us know if you see one of these high-priority invasive plants, so we can make sure they’re controlled or eradicated in time! [Click here to go to the King County Noxious Weed List for the whole list!] Report locations and share photos with us easily on our new and improved Report a Weed online form.

1. Top priority: eradicate before seeds disperse

First up, weeds already going to seed or getting close. Catch them now before seeds disperse!

Many garlic mustard plants in King County are going to seed. Note the long, skinny seed pods on this one.

Garlic mustard (Alliaria petiolata), a Class A noxious weed, is a biennial or winter annual herb, can self-pollinate to produce 62,000 seeds and overtake a relatively undisturbed forest understory. Eradicating it before seeds mature is key. You can identify garlic mustard by:

  • Scallop-edged, rounded leaves (on rosettes) or toothed triangular leaves (higher up on mature plants) that feel smooth (hairless) and smell like garlic smell when crushed
  • Small, 4-petaled white flowers and long, skinny seedpods
  • Root bent in a distinct “s” shape
  • Highly variable form, maturing and setting seed at anywhere from a few inches to 6 feet tall
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Garlic mustard rosette leaves are more rounded or kidney-shaped, while mature plants have more triangular leaves. All leaves are lobed.

Many shiny geranium plants are forming seed capsules (the crane’s-bill-like shapes next to the flowers), though they aren’t dispersing their seeds quite yet.

Shiny geranium (Geranium lucidum), a Class B noxious weed, is an annual herb that grows in disturbed areas such as roadsides, as well as in shady woodlands and forest openings. This weed is already starting to form seed capsules, though it isn’t dispersing seeds yet. You can identify it by:

  • Reddish, smooth stems that can reach 20 inches tall
  • Shiny, round to kidney-shaped leaves with 5-7 lobes, usually shiny (not fuzzy)
  • Leaves often turn red in sun or as plants are going to seed
  • Tiny pink-purple 5-petaled flowers that appear in pairs at stem ends
  • Keeled sepals
  • Seeds in long capsules that look like cranes’ bills
  • Does not smell bad like herb Robert and is not covered with soft hairs like Dove’s foot geranium

Shiny geranium can invade a variety of areas, from roadsides to woodlands. Photo by Matt Below.Photo by Matt Below.

2. In full flower

The next group of weeds are now in full flower and before long will go to seed. Make sure you eradicate them from your property before they do.

Milk thistle’s large, pink-purple flower head with broad, spiny bracts around its base is in full bloom right now. Photo by Dan Sorensen.

Milk thistle (Silybum marianum) is a Class A noxious weed that grows 2 to 6 feet tall and is a winter annual or biennial that grows mostly in rural parts of King County. You can identify it by:

  • Shiny green leaves with distinct milky-white marbling
  • Spines on leaf edges and stems
  • Large, pink-purple flower heads appearing singly at stem ends
  • Broad, fleshy, spiny bracts around base of flower head

Milk thistle’s large, pink-purple flower head with broad, spiny bracts around its base. Photo by Dan Sorensen.

A bee enjoys an orange hawkweed flower. Be sure to time your noxious weed control so that it has the least impact on pollinators and other animals that might be using the plant.

Orange hawkweed (Hieracium aurantiacum) and yellow hawkweed (Hieracium caespitosum) are two Class B perennial herbs that readily invade roadsides, pastures, grasslands, and other areas throughout King County. Both weeds spread via seeds and stolons. You can identify them by:

  • Hairy, unlobed leaves in rosettes at the base of hairy, almost leafless stem
  • Black, ball-shaped, tightly-clustered flower buds followed by orange (H.aurantiacum) or yellow (H. caespitosum) blooms (look like little dandelion flowers)
  • Milky juice inside all plant parts
  • Fluffy, dandelion-like seed heads
  • Fuzzy white stolons (runners)

Dalmatian toadflax grows especially well in disturbed areas with rocky soil, such as around train tracks. Photo by Sasha Shaw.

Dalmatian toadflax (Linaria dalmatica ssp. dalmatica), a Class B noxious weed, is a perennial plant that grows to 3 feet tall and mostly grows in disturbed areas in western Washington. It spreads by both seed and spreading roots. You can distinguish it by:

  • Multiple stems that grow from one woody base
  • Bluish green, heart-shaped, waxy leaves that wrap around each stem
  • Bright yellow, snapdragon-like flowers growing in rows at stem ends

Sulfur cinquefoil is blooming now, displaying its pale yellow flowers with 5 heart-shaped petals and darker yellow centers.

Sulfur cinquefoil (Potentilla recta) is another Class B noxious weed and perennial herb that reaches 3 feet tall. You can distinguish it by:

  • Palmately lobed leaves with 5-7, long, toothed leaflets
  • Upright, hairy, leafy, mostly unbranched stems (hairs stick straight out from stems unlike on the similar native species graceful cinquefoil, Potentilla gracilis)
  • Pale yellow flowers with 5 heart-shaped petals and darker yellow centers

3. Budding or starting to flower

At a bit earlier stage in their life cycles, the following plants are either budding or just starting to bloom.

Tansy ragwort plants are bolting, and some are even starting to form flowers.

Tansy ragwort (Senecio jacobaea), a Class B noxious weed, is a biennial found throughout King County that is toxic to horses, cattle and other animals. It quickly takes over disturbed areas, thriving in sites with full sun and dry to somewhat wet soils. You can identify it by:

  • Ragged, ruffled leaves that are dark green on top and light-green below, with deeply cut, blunt-toothed lobes
  • First year plants are basal rosettes; second year plants have 2 to 4-foot-tall flowering stalks
  • Clusters of numerous small daisy-like flowers with 13 yellow ray petals and yellow-orange centers
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Tansy ragwort often spreads in pastures and fields where it out-competes grass. It is toxic to horses, cattle and other animals.

Giant hogweed (Heracleum mantegazzianum), a Class A noxious weeds, is a perennial that usually grows in urban areas, especially where there’s rich, damp soil. This plant is poisonous, and touching its sap can cause severe blisters or even scars, so it’s good to know how to recognize it. You can identify it by:

  • 8-15-foot-tall, hollow, ridged stems with reddish-purple blotches and stiff white hairs
  • 3-5-foot-wide, deeply incised, compound leaves
  • Surface of leaf underside is hairless, with hairs only on ribs
  • 2-foot-wide umbrella-shaped flower clusters

Spotted knapweed will soon be blooming. Its silver-gray hue is a good way to identify it even without flowers. Photo by Tricia MacLaren.

Spotted knapweed (Centaurea stoebe), a Class B noxious weed, is a biennial or short-lived perennial that often appears in disturbed areas, especially those with full sun and well-drained soils. You can identify it by:

  • 5-foot-tall, upright, branched stems
  • Medium-green, somewhat silver-gray, often deeply lobed leaves
  • Small, oval flower heads with light purple to pinkish, thistle-like flowers
  • Bracts at base of flower head have triangular black spots
  • Stout taproot

Spotted knapweed’s small, oval flower head with light purple to pinkish, thistle-like flowers. Note triangular black spots on bracts at base of flower head.

Meadow knapweed is starting to bloom, revealing its oval, pink to reddish-purple flower heads. Up close, look for the comb-like fringes near bract tips around the flower head base.

Meadow knapweed (Centaurea jacea x nigra), another Class B noxious weed related to spotted knapweed, is loner-lived perennial that grows in not only disturbed sites, but also riverbanks, pastures, moist meadows, forest openings, and other areas. You can identify it by:

  • 4-foot-tall, upright, branched stems
  • 4-inch-long, slender, often shallowly lobed basal leaves and smaller, unlobed stem leaves, all coarse and tough
  • Single oval flower heads with pink to reddish-purple flowers at branch ends
  • Bracts at base of flower head have comb-like fringe near tip

Meadow knapweed’s oval flower heads with pink to reddish-purple flowers grow singly on stems. Bracts at base of flower head have comb-like fringes near their tips.

Meadow knapweed reaches 4 feet tall, with upright, branched stems. Stem leaves are unlobed and smaller than basal leaves.

4. Plants to keep an eye on

Plants in this final group are putting their energies into growing right now. They won’t go to seed until later this summer, but keep a tab on them and make sure you’re ready to control them when the time comes.

While not 8 feet tall yet, many policeman’s helmet plants are large enough to spot. Look for large, oblong or egg-shaped leaves with serrated edges, growing opposite or whorled in groups of 3 on stems.

Policeman’s helmet (Impatiens glandulifera), Class B noxious weed, is a 3 to 8-foot-tall annual that grows especially well in moist areas, such as wetlands, streams, and damp woodlands. You can identify it by:

  • Upright, hollow, watery, purple-reddish tinged stems
  • Large, oblong or egg-shaped leaves with serrated edges, growing opposite or whorled in groups of 3
  • White to pink to purple 5-part flowers that resemble an English policeman’s helmet
  • Stem base and exposed roots often reddish

Policeman’s helmet has large, oblong or egg-shaped leaves with serrated edges, opposite or whorled in groups of 3.

Purple loosestrife is bolting right now. Look for 4-6-sided stems and simple, smooth-edged leaves appearing opposite or whorled on stems.

Purple loosestrife (Lythrum salicaria), Class B noxious weed, is a deep-rooted, rhizomatous perennial found mostly in damp areas, such as freshwater and brackish wetlands, as well as lakes and streams. It spreads through both vegetative growth and seeds. You can identify it by:

  • Stiff, 4-6-sided stems that reach 6-10 feet tall
  • Simple, smooth-edged leaves that grow opposite or whorled on stems
  • Tall spikes of small magenta flowers with 5-7 petals
  • Woody taproot

Garden loosestrife is growing tall. Look for softly hairy stems and leaves along with lance- or egg-shaped leaves usually arranged in whorls of 3.

Garden loosestrife (Lysimachia vulgaris) is another Class B noxious weed and deep-rooted perennial often found in wet areas, although it’s not related to purple loosestrife (despite the common names). Garden loosestrife spreads primarily via creeping rhizomes. You can identify it by: