Additionally, no transportation, propagation, or sale of these plants is allowed. Failure to comply may result in enforcement action by the county or local municipality. Minnesota Noxious Weed Law. Canada thistle is native to Europe. It was introduced to North America in the s, probably in agricultural seed shipments and is now widespread throughout the United States and Canada.
Found growing in a wide range of habitats. Typically infests a variety of disturbed landscapes and is commonly found along roadsides, trails, natural areas, pastures, forest and field margins, mining locations, waste areas and unmaintained gravel pits. This plant establishes quickly after new road construction, housing and development projects, overgrazing of pastures, forestry clear-cuts, and destructive flooding events.
It conserves moisture, enriches the soil and prevents germination of new thistle. Apply vinegar. Fill an empty spray bottle with vinegar. No need to dilute as this makes it less efficient at killing weeds.
Cut off at the base of the stem. Spray one to two sprays of vinegar directly on the cut of each thistle plant. The cut allows the vinegar to spread to the roots more quickly, which in turn kills the plant more quickly. Saturating the unwanted plants once a week with this mixture helps control the problem. Do not spray the soil with vinegar. Application beyond designated timing or using higher than labeled rates may result in crop injury. Use caution at application to prevent drift to sensitive crops.
An option for Canada thistle in row crops and fallow that includes both tillage and herbicides is known as the rosette technique. The thistles then will regrow as rosettes only. Research at NDSU has found herbicide absorption and translocation to the roots of Canada thistle is greater when applied to the rosette growth stage than when applied to bolted plants, making fall treatment of rosettes the most cost-effective method for long-term Canada thistle control.
The rosette technique for Canada thistle control in fallow includes the use of tillage and fall-applied herbicides, while control in row crops includes in-crop herbicide treatments, tillage and fall-applied herbicides. Periodic tillage in fallow is used to control Canada thistle shoots and other weeds until late July, when the day length is less than 15 hours. Herbicides used for Canada thistle control then are applied to rosettes in late September or early October. Cultivation should be continued until canopy closure in soybeans and until early July in corn.
Research at NDSU has found that cultivation until late June prevented more than 90 percent of Canada thistle from bolting in corn and soybeans. A second option in soybeans is to apply a split application in lieu of tillage. Herbicides then are applied in the fall following harvest for Canada thistle control. The rosette technique controls Canada thistle in both fallow and row crops during the season, and maximizes the number of rosettes for better herbicide absorption and translocation in the fall.
Fall is the preferred time for applying herbicides for biennial thistle control. Fall treatment allows more time for herbicide application than in the spring, and thistle control generally is best with fall treatments. Seedlings that emerge in summer after tillage or previous herbicide applications will not bolt but remain in the rosette stage.
Biennial thistles are most susceptible to herbicides in the rosette form. Herbicides should be applied as late as possible in the fall, but prior to a killing frost to allow for maximum seedling emergence and rosette size. Seedlings that emerge after spraying will remain vegetative until the following spring and can be treated then. Long-term eradication of biennial thistles is difficult because of the large number of seeds each plant can produce.
For perennial thistle control in noncropland, herbicides may be applied in the summer or fall, when thistle is at or beyond the bud stage of growth. Perennial thistle control usually is greater when treatment is applied in the fall rather than the spring.
Grazing restrictions vary with herbicide and application rate, so read the label carefully before using. I nsect biocontrol agents have been released on both musk thistle and Canada thistle with limited success.
The seed weevil Rhinocyllus conicus was introduced from Eurasia to control musk thistle by reducing seed production. Larvae develop in the flower head and consume the seed as it develops.
The weevils can reduce seed production by nearly 80 percent, but they are attracted more to early-blooming than late-blooming flowers. The late-season flowers produce seeds with little damage from the weevil, which sustains the musk thistle population. Five to 10 years are often needed for an insect to reach a population high enough to reduce seed production.
However, the resulting damage to various thistle populations has been minimal to date. Another weevil introduced for musk thistle control is Trichosirocalus horridus, which feeds on the apical meristem of the thistle rosette and developing stems. The feeding causes multiple stems to be formed, instead of a single stem, when the plant bolts. The multiple stems produce small flowers with few seeds, which is beneficial to the R. However, even with the two biological agents working together, musk thistle is only partially controlled.
A second control method, such as herbicide treatment, is needed to stop the spread of the weed. Two biological control agents have been introduced for Canada thistle control, and a third was introduced accidentally. To date, none have been effective at reducing the weed on a large scale. The Ceutorhynchus litura weevil first was released in North Dakota in the s. The larvae feed on the underground parts of Canada thistle for a short time, but little, if any, noticeable effect on an infestation has been observed.
The effects of the weevil must be supplemented by using additional control methods, such as mowing or applying herbicides. A gall-producing fly, Urophora cardui, causes meristematic galls, but does little long-term damage to the perennial thistle. The Canada thistle bud weevil Larinus planus was an accidental introduction into North America.
The insect feeds on developing flowers to prevent seed production. Although L. The painted lady butterfly Vanessa cardui can be a very effective biological control agent, but only on an intermittent basis. Larvae of the butterfly feed on Canada thistle plants and can eliminate an infestation. However, the insect generally is found in only southern states, such as Arizona and New Mexico, and will build up populations large enough to migrate north only once every eight to 11 years.
The insect will migrate north as far as Canada, and those fortunate enough to reside within the migratory pathway will see a dramatic decrease in the Canada thistle population. Unfortunately, the insect feeds on many plants, including crops such as soybeans and sunflowers, and is not a candidate for long-term biological control of Canada thistle. Publications Accessibility. Rod Lym, Professor, Plant Sciences. MUSK THISTLE Musk thistle is one of the more common biennial noxious thistles and is relatively easy to identify because it often grows in excess of 6 feet tall, has very large flowers that tend to droop, and the flower has very characteristic brown bracts that resemble pine cones Figure 2A.
Figure 4A. Bolted Canada thistle with cluster flowers and waxy, wavy leaves. Figure 4B. Canada thistle rosette form with spiny tips and wavy leaves. Figure 5A.
Flodman thistle flowering plant showing deeply toothed leaves. Filed under: crops , crops-weeds. Each year, the foliage dies back in late autumn and regrowth reappears in spring. There appear to be widely differing views on the importance of seed production in the spread of creeping thistle.
Individual plants bear only male of female flowers dioecious from July onwards, plants are insect pollinated and male and female plants need to be within about 30 m of each other for high levels of cross-pollination to occur.
Most seeds are retained in the heads and are not shed until these drop to the ground very close to the mother plant. Seed production is highly variable and viability is often low, probably due to inefficient pollination. Average seed production in an arable crop situation is typically about seed per plant. Seeds tend not be highly persistent in cultivated soil and the seedbank may be low even where dense patches of thistle occur.
However, some seeds may persist for over 5 years, especially if undisturbed. Seeds mainly germinate in April or May. Overall, it appears that localised spread within or between fields is largely by vegetative means, due to lateral growth or movement of root fragments, rather than by seed movement.
However, spread by seed may be more important than generally assumed as thistles soon appeared on set-aside land, even where previously absent. In contrast, spear thistle and smooth and prickly sow-thistle are spread only by seeds with seedlings emerging in both autumn and spring. Seedlings are largely derived from seeds within 3 cm of the soil surface. The seeds are not highly persistent in the soil, but some may survive several years especially in undisturbed soil.
Perennial sow-thistle spreads by underground roots but, in contrast to creeping thistle, these are largely confined to the surface 15 cm. Spread by seed is also important and these are dispersed by wind. Seeds may survive up to 5 years in soil and seedling emergence is largely confined to the spring. Most information is available for creeping thistle. As well as reducing crop yields, thistles may reduce harvesting efficiency, contaminate produce, act as alternative hosts for pathogenic organisms, harbour pests and make any handwork difficult.
Creeping and spear thistle are two of the five weeds classified as injurious under the Weeds Act , the others being broad-leaved dock, curled dock and common ragwort. See other information sheet Broad-leaved weeds: occurrence, agro-ecology and management for best approaches to integrated weed management of broad-leaved weeds. If you joined with a network, select it below, if not use the email and password you set when joining.
Thanks for choosing to join Croprotect, we just need a few details from you in order to create your account. Creep Thistle croprotect Pricklysow croprotect. Occurrence Both creeping and spear thistle are widely distributed throughout the UK. Identification Creeping thistle is a perennial with extensive creeping underground roots whereas spear thistle is a biennial with a very deep tap root.
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