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Home , Centaurea solstitialis

YELLOW STARTHISTLE solstitialis Sunflower Family ()

DESCRIPTION This winter annual (or some- duce almost 75,000 seeds in a times biennial) is considered to single season. Most seeds are be ’s worst . wind-dispersed, but they spread It is also found on disturbed sites and the greatest distance by being trans- annual grasslands, and affects access to ported in contaminated hay or seed recreation areas. loads, or attached to vehicles. They are Yellow starthistle form a basal spread to a lesser degree attached to ani- rosette as juveniles, then bolt in maturity. mals and humans. About 90 percent of Flowering plants are usually about 1–3 feet seeds are ready to germinate immediately tall, though some may be only a few inches after release. Germination frequently and single-stemmed while others are 5 feet takes place after the first fall rains, as tall and branching. Leaves and stems are seeds need moisture and light to ger- downy and gray-green. The leaves are minate. Seeds can remain viable in the alternate, 2–3 inches long, and pinnately soil for 3 years and possibly much lobed with triangular tips. longer. The develop terminally, the bud appearing like a small scaly ball with a halo IMPACT ANNUALS of stiff yellowish spines up to 1 inch long. A rapidly growing taproot enables yellow The composite inflorescence looks like a starthistle to outcompete native fuzzy ball of tiny petals. Flowers generally species, including purple needlegrass, for bloom from May to September, but in the summer soil moisture. Yellow starthistle Bay Area a few plants bloom at any time of year. may also produce allelopathic compounds that give it another competitive edge. The current REPRODUCTION level of infestation in California (estimated at Yellow starthistle reproduces solely by seed.The 22 million acres) has brought agricultural and plants produce two kinds of seeds: plumed and economic loss by reducing the quality and yield plumeless, both measuring roughly a quarter- of forage. It can be fatally poisonous to horses inch. Most seeds are plumed with a tuft of soft, and its spines deter other livestock from graz- white bristles that aid in wind dispersal. These ing. seeds are pale (cream to tan) and develop on the inner (disk) part of the . The plume- KEY FACTORS less, outer (ray) seeds are darker brown. They u High seed production. remain attached to the flower head until it drops on the ground. u Seed longevity is at least 3 years. Large plants can produce as many as 1,000 u Fast-growing and deep taproot. composite flower heads which together can pro- u Seedlings are somewhat shade-intolerant.

THE PLANTS: HOW TO REMOVE BAY AREA 87 A 1 percent dilution of dilution A 1 percent P -U with cattle,goats,and sheep to help to sheep cattle,goats,and with ISPOSAL Foliar spray. the at plants on sprayed be can stage.bolting spot use this for might You application. Graze seed production. and reduce plants contain plants, spiny goats mature eat but don’t Cattle come results Best picky! less are sheep and of number a large grazing by intensive from period of short a for animals time, preferably of end the from June, to May plants after just bolted.have grazing the suggests at Research rosette stage is counterproductive, leading to starthistle. in yellow an increase is This weed toxic to horses. late. sideways bolt starthistles Occasionally with flower heads much closer to the ground, or mowed plants may rebloom very low. You can the take off tops these with a shovel, hoe, mattock,or if numbers. in small is Cutting dry on soil, effective most otherwise a repeat later. weeks 4 roughly necessary is treatment OLLOW F 3 years least at last should program A removal longer,and probably intensity. lower though at areas. in nearby infestations new for Watch out in shading be helpful may Mulching seedlings.Some a 5-inch that experiments show u D clippings the leaving advise practitioners Some do as they (as long on-site mowing each from rein- from soil the protect seeds) to contain not species, invasive other by festation to and also pro- by seedlings starthistle yellow discourage viding extra shade. Plants with only buds and young, paleyellow flowers can be left on the ground. yellow, turn darker flowers pulled Once plants should be bagged, as they may produce viable seed. Dispose of the bags off-site where elsewhere. disperse seeds can’t Bay East bags District plastic clear uses Park Regional years. a few for in them plants the and leaves u WEED WORKERS’ HANDBOOK WEED WORKERS’ PTIONS O individual plants by hand in hand by plants individual dig (or cut with a hand scythe, cut (or brushcutter, or Mowing too early can encourage greater can encourage early too Mowing Heavy leather gloves are a must! Working a must! are gloves leather Heavy Continue to recheck and pull emerging Hand pulling is often difficult if plants or any cutting tool) after the plants have plants the after tool) cutting any or bolted and a small fraction of the buds (about 2 percent) have started to bloom. Make sure mow closeyou enough to the ground to get buds. lowest the 1–2 inches leave to Aim a second need mow to may ground.You above intervals. 4–6 week time at a third even or Mow Pull seed production, crucial time to the so it’s removal carefully. If there are no buds, too it’s early, if but bloomed mostly have flowers the too color,it’s losing their yellow bright and are with yellow starthistle,with yellow eventu- chemicals the be tasted. can and skin soak into ally harm to known not are toxins the Although humans, wash hands after working with this plant. plants through August, through plants later. even preferably in conjunction can be done Hand-pulling from plants mowing: keep with can mowing time pull. to have you setting seed until have stems more than a quarter-inch in diam- than a quarter-inch more stems have eter. spade, a narrow Use knife, soil other or root.Given the cut this or that free help to tool is an annual,weed of most can be the taproot left soil, in the if especially get to manage you of a half-inch to a quarter- the below the root root crown. May–June, when plants are bolting or as soon as possible afterwards. (Rosettes often break off from roots, which steadily,straight pull base and up. the resprout.) at plant Grasp the together, close dig- grow plants several Where ging or pulling smaller ones often makes it easy to pull others. Cuttinglateral roots and make also base the around soil the loosening it easier to pull. If cannot you pull up the plant, twist if or it cut off base. the at REATMENT u u u u u u T

ANNUALS 88 layer of wheat straw (or rice straw) stops all INTERESTING FACTS regrowth. This level of coverage might be Native to the Mediterranean, yellow starthistle expensive, however, and therefore only an was introduced to the US in the mid-1800s, option for small patches. probably as part of a shipment of contaminated grain or other crop seed.Beekeepers find it to be a valuable source of nectar for honeybees,which account for a large proportion of the thistle’s .

Notes ANNUALS

THE PLANTS: HOW TO REMOVE BAY AREA WEEDS 89