The Control of Creeping Thistle (Cirsium arvense)
The species has fewer spines on the margins of the first leaves than the other thistles.
One of the worst weeds, it occurs abundantly in grassland, arable and waste land throughout the British Isles spreads by far-creeping roots which can really regenerate new plants from small pieces, and to a lesser extent by seed
Spear Thistle (Cirsium vulgare)
Spear thistle is a common biennial of the grassland and waste places throughout the British IslesThe most distinctive feature of this thistle is the second true leaf which can be very large and is a dull dark green with dense vertical whitish hairs on the upper surface.
Marsh Thistle (Cirsium palustre)
A biennial weed of wet pastures, common throughout the British Isles.
This thistle differs from the other species in having longer spines on the margins of the first true leaves and broader, less tapered leaf bases.
There are three types of thistle common in Ireland:
(1) Creeping Thistle (Cirsium arvense)
(2) The Spear Thistle (Cirsium vulgare)
(3) The Marsh Thistle (Cirsium palustre)
The Creeping Thistle
The creeping thistle is one of our most troublesome noxious weeds. It thrives equally well in reasonably fertile grassland and in tillage ground, but it is usually absent on soils of low fertility. Winter poaching and overgrazing in Spring encourages the spread of thistles. In grassland its prickly nature prevents animals grazing close to the base of plants. Stock forced to graze on heavily infested pastures may suffer skin eruptions about the mouth.
The creeping thistle is a perennial plant, the overground parts of which die down at the end of each growing season. It produces large numbers of seeds which have a very low vitality and only a small percentage are capable of germinating. In any event seed is not necessary for propagation, because the underground portions which resemble roots produce shoots which can give rise to thistle plants. When these are allowed to grow unchecked, they in turn produce their own roots which spread out underground, so that an ever-increasing area of land is infested each year. This spread of roots is extremely rapid, a small portion of a root being known to produce 18 m (60 feet) of root system in two years.
The root system of creeping thistle is, in fact, a reserve of food to enable the plant to survive the winter and produce plants the following Spring. The object of cutting is to exhaust the food reserves in the roots. If cutting is postponed until the plants have reached the flowering stage, the roots will have accumulated the additional reserves of food, and cutting then serves little useful purpose.
To eradicate the creeping thistle cutting must be systematic. Cut when the plants are 10-15 em (4-6 inches) high, usually early in June. At that stage the food reserves in the roots are at a very low ebb. Further efforts by the roots to produce fresh shoots will further deplete the food reserves. The fresh shoots should also be cut down and even a third cutting may be necessary. Cutting as outlined should eradicate the creeping thistle in about three years. There is no evidence whatever to support the belief that if cutting is delayed until autumn, rain will penetrate the hollow stem of the plant and cause the roots to decay.
On tillage and young leas, where soil disturbance has led to an abundance of young thistles, MCPA salt used at 1.4 kg per hectare, MCPB salt or 2-4D13-amine used at 2.25 kg per hectare, or 2-4-D amine used at 0.70 kg per hectare are all effective. On established pastures effective chemical control is more difficult. MCPA or 2-4-D amine used at 1.4 to 1.68 kg per hectare will give good control of top growth, but respraying is usually necessary. Both MCPA and 2-4-D amine retard clover growth, but MCPB and 2-4-DB do not suppress clovers. Best results are generally obtained if spraying is carried out in the early flower bud stage when the weeds are growing vigorously.
Spear and Marsh Thistles
Both these thistles are biennial plants. They are spread by means of fertile seeds which germinate in late summer or autumn and produce plants in rosette form close to the ground. In the following season the centre of the rosette grows up into one or more branched stems reaching heights of up to 1 m (3 feet). Both plants carry pale purple flowers and when seeds have been produced the plants die off. Seeds are scattered over wide areas by means of wind drift.
Since these plants depend entirely on their seed for regeneration, control is much easier than in the case of creeping thistle. Prevention of seeding is of crucial importance. This can be achieved by spudding out rosettes at a depth of about 5 em (2 inches) below ground-level or when spudding cannot be done, by cutting the stems while the flower heads are in the unopened bud stage. Cutting in consecutive years or spot treatment with a hormone type spray may also be used to control these thistles.
MAFF advice on control of injurious weeds specified in the Weeds Act 1959
Injurious weeds can be controlled using a number of chemical and cultural means. Care should be taken to choose the most appropriate method for each site circumstance. This applies particularly to sites of special conservation interest where control of the injurious weeds may risk damaging rare or valuable flora and fauna. In these situations expert advice should be sought before any action is taken.
Injurious Weed Control using Herbicides
N.B. This document is kept under review to check the continuing validity of the herbicide recommendations, and revisions are issued as necessary.
The application of herbicides is subject to regulations which must be observed when using products. These are summarised in theCode of Practice for the Safe Use of Pesticides on Farms and Holdings (available from MAFF Publications, quoting reference PB3528).
Instructions for use including operator and environmental protection, the crops or plants on which the product may be used, maximum dose, harvest interval and other details are shown on the product label. Each time a product is used you must READ THE LABEL AND FOLLOW THE INSTRUCTIONS. Some products are only available to operators who hold a certificate of competence as recognised by the Ministry of Agriculture, Fisheries and Food.
Non Selective Herbicide Treatment
Control of injurious weeds can be undertaken using a non-specific herbicide such as glyphosate either as an overall spray or using a height selective applicator or spot treatment.
Selective Herbicide Treatment
Injurious weeds can be controlled using selective herbicides. Although most products are generally used as an overall spray, some can also be applied through a selective height applicator or as a spot treatment to improve their selectivity.
The following shows the most favoured active ingredients for the control of each injurious weed specified under the Weeds Act 1959. These active ingredients may be available alone or in mixtures with other chemicals and qualified advice should be obtained to determine the most appropriate product especially when mixed populations of weeds occur.
N.B. Herbicides (marked *) are referred to by active ingredient not product name
- SPEAR THISTLE (Cirsium vulgare)
Spear thistle occurs widely on lowland and upland grassland and waste places. The weed competes effectively with crops for water, light and nutrients. It is biennial and only spreads by seed. Mature plants are normally 30-50 cm tall, with flowers from July through to late autumn. Large numbers of seeds are produced which can be blown by wind across farm and field boundaries.
CONTROL The plants can be cut each year before mid-July to prevent shedding of viable seed. It is also possible to remove them by digging. Long-term control is possible from herbicide treatment; spear thistle is susceptible to clopyralid* and moderately susceptible to MCPA* herbicides. Where clover is an important constituent of the sward, a mixture of MCPA* and MCPB* herbicides is more appropriate.
- CREEPING OR FIELD THISTLE (Cirsium arvense)
Creeping thistle can quickly dominate vegetation in grassland or waste ground. The weed forms dense patches which suppress crop plants.
Mature plants extend 30-100cm in height, with flowers from July into late autumn each year. The plants produce only a few viable seeds which can be blown by wind. However, invasion is more often by spread of the plants’ underground root systems.
CONTROL Cultivation is not an effective means of control as the number of root pieces which can throw up new shoots is increased. Control on arable land therefore is usually by use of a range of herbicides depending on the field crop grown.
On grassland, cutting at flower stem extension but before opening of the flower buds will prevent seed spread for a particular season. Repeated cutting at the same growth stage over several years may “wear down” an infestation.
MCPA* herbicide applied during the early bud stage will kill the aerial parts of the plant, but repeat treatments the following year may be necessary for complete control. One application of the herbicide clopyralid* is normally sufficient to achieve an acceptable level of control.
- BROAD-LEAVED DOCK (Rumex obtusifolius) AND CURLED DOCK (Rumex crispus)
Broad-leaved dock thrives in high nitrogen environments, open swards and where there is heavy treading by stock. Curled dock occurs more commonly on arable and waste land.
Both species produce many seeds which can remain viable in soil for decades. Buds on pieces of tap-root broken by soil disturbance or treading will produce new plants. The two species are similar in appearance but leaf shape differs, as reflected in their names. Hybrids are common between the species and this can hinder identification. Flowering for both species is from late June until early autumn with inflorescences reaching over 100 cm in height.
|MCPB* for grass clover reseeds
Mecoprop* or MCPA* for grass reseeds without clover
|Asulam* for grassland with clover
Fluroxypyr*, 2,4-D*, triclopyr*, or thifensulfuron for grassland without clover
|MCPB* for grass clover reseeds
|Asulam* for grassland with clover
Fluroxypyr*, 2,4-D, MCPA*, mecoprop* or triclopyr* for grassland without clover
p* or MCPA* for grass reseeds without clover
- COMMON RAGWORT (Senecio jacobaea)
This is the only ragwort species specified in the Weeds Act 1959; other species of Senecio are not so widespread as common ragwort. Flowering is from late June onwards to early autumn when the characteristic yellow inflorescences usually extend between 30-100 cms in height.
The weed occurs in neglected grass fields, on uncropped ground and sand dunes. It prefers light soils of low fertility, particularly in over or under- grazed pasture. Common ragwort is biennial when undisturbed but can develop perennial characteristics following cutting or treading.
POISONOUS TO LIVESTOCK Cattle and horses are particularly susceptible to poisoning by common ragwort but sheep are also susceptible. Palatability of the weed increases when plants are conserved in hay or silage or treated with herbicide. An added problem is that livestock cannot easily reject fragments of ragwort in conserved herbage and its poisonous alkaloids are unaffected by the conservation process.
CONTROL Although short-term action can be undertaken to clear existing plants, reinfestation will be rapid unless overall husbandry is improved, particularly for uncropped ground and grassland.
Cutting: Cutting and stem removal at the early flowering stage reduces seed production but does not destroy the plant. Cut plants left lying in the field are a serious risk to grazing animals and may still set seed. These should be removed and burned within theCode of Practice for the Protection of Air (available from MAFF Publications, quoting reference PB0618).
Pulling (and digging): Pulling or digging can also prevent seed spread but may not give long-term control. Plants should be removed and burned within the Code of Practice for the Protection of Air (see above).
Herbicides: No single herbicide treatment will completely eliminate a ragwort infestation due to successive germinations of the weed. Treatment with selective herbicides can be made to the plant rosettes usually late spring and in the autumn before frost damages the foliage. The most effective material for overall spraying is 2,4-D* but this will damage clover and a number of other plant species.
WHICHEVER METHOD OF CONTROL IS SELECTED, REMEMBER NOT TO TURN GRAZING ANIMALS INTO THE FIELD UNTIL ANY TREATED RAGWORT PLANTS HAVE DIED AND DISINTEGRATED. DO NOT ALLOW RAGWORT TO BE HARVESTED IN HAY OR SILAGE FOR LIVESTOCK FEED.
Revised May 2000