broadleaf dock, butter dock, cushy-cows, kettle dock, smair dock
Rumex obtusifolius L.
The two main dock species are the broad-leaved dock (Rumex obtusifolius) and the curled dock (R. crispus). They are common throughout the UK both as the true species and as hybrids. The hybrids may produce less seed but can be more vigorous than the parents and will sometimes infest whole fields. The presence of fertile hybrids has been reported, probably the result of backcrosses with a parent. Broad-leaved dock itself is a highly variable perennial species and many forms, varieties and subspecies have been described worldwide. Three subspecies have been distinguished in the UK.
Broad-leaved dock is found throughout Britain and there is no climatic limitation on distribution. It is the most abundant dock in grassland. Dock seedlings are poor competitors and can only establish in open or disturbed patches in standing vegetation. The presence of docks in grassland is often associated with the uneven application of slurry or manure that leaves bare patches. The openness of a sward after cutting for silage is also linked with dock establishment. Poor grass management leading to overgrazing and poaching allows dock seedlings to emerge and grow. Fewer broad-leaved docks are found on grassland grazed by sheep or subject to flooding but it may be frequent on trodden ground in pastures and in gateways. Broad-leaved dock is also found in arable crops, field margins and waste places.
Broad-leaved dock is able to grow on a range of soils except the most acid. Soils high in nitrogen or low in potassium are said to favour docks. However, some research has shown a clear link between increasing dock populations and increasing levels of soil potassium. But other studies concluded that increasing the potassium status did not favour docks.
There are some who would argue that docks in grassland are not weeds because they contribute to the herbage and hence do not need to be controlled. They may also contribute trace elements to a grazing animals diet. Broad-leaved dock is relatively high in phosphate and potassium levels in the leaves, and is particularly high in magnesium. Cattle fed on the herbage containing docks are said not to suffer bloat because tannins in the dock leaves precipitate out soluble protein in the rumen liquor.
In the UK, broad-leaved dock is a host for the potato eelworm, Ditylenchus destructor. Docks also serve as alternate hosts for the bean aphis and mangold fly, and encourage subterranean larvae such as those of the swift moth.
Broad-leaved dock flowers from June to October but flowering is delayed by early shoot removal. A large mature broad-leaved dock can produce up to 60,000 ripe seeds per year. The seeds become viable from the milk stage onwards and immature seeds will continue to develop on stems cut down just a few days after flowering. Broad-leaved dock can shed seed from late summer through to winter but the seeds may require a short after-ripening period before being ready to germinate. Seedlings of broad-leaved dock generally do not flower in the first year.
There is considerable variation in germination characteristics between seeds from different populations, different plants, different panicles on the same plant and seed from different positions on the same panicle. Some of this is due to seed size and seedcoat thickness, some to the time of ripening and some is due to maternal factors. Defoliation can also affect seed development and germination characteristics. Light, alternating temperatures, chilling, nitrate and seed scarification can all help to promote germination.
The seeds germinate any time that conditions are favourable but the main flushes of emergence are in March-April and July-October. Seeds germinate best on the soil surface or in the upper 10 mm layer of soil. However, in the summer when the soil is warmer seedlings appear to emerge from deeper in the soil. In a clay loam soil, seedlings emerged from between 0 and 70 mm deep. Germination is inhibited under a dense leaf canopy. Seedlings have a low competitive ability but once the deep taproot has developed the dock plant has an advantage over shallow rooted crops and grass. It then becomes more difficult to eradicate.
Established plants can withstand trampling and mowing. New shoots are quickly sent up after decapitation and repeated regeneration may lead to the development of large clumps. The underground parts of a dock consist of a vertical stem and a branched taproot with a transition zone between them. The underground stem may reach 5 cm in length and is kept below ground by root contraction. Broad-leaved dock overwinters as a rosette with small dark-leaves and stout taproot. In spring, new leaves develop rapidly and there is a vegetative phase of elongation.
Dock seed numbers in soil have been estimated at 5 million per acre. The seeds contain a chemical that inhibits microbial decay and are capable of surviving in undisturbed soil for over 50 years.
In pasture, individual plants of broad-leaved dock can be very long lived, forming compound crowns with multiple taproots. There is considerable confusion about the ability of docks to regenerate from these underground organs. Some authors maintain that true roots do not regenerate and only the stem and transition zone can regenerate. Others insist that all parts will form new shoots if detached from the parent.
In resown grass/clover infested with dock seedlings, cutting will reduce seedling numbers initially. Increasing the cutting frequency will reduced root biomass but may not improve seedling losses. Mowing has little effect on established docks but will prevent seed production. Frequent cutting aids seedling development and encourages regeneration of taproots and branching of the shoots of established plants, increasing the potential for future growth. It was reported that when the sward was cut frequently (5-7 cuts per year) the presence of docks had little effect on yield. When the sward was cut less frequently (3-4 cuts per year) total yields were reduced and the herbage contained a high proportion of dock foliage. In a pasture heavily infested with docks the best option may be to plough and reseed with grass but not immediately. The docks are likely to regenerate both vegetatively and from seed, and a period of fallowing or arable cropping may help to reduce re-establishment.
In any grassland it is prudent to avoid sward damage from trampling, poaching and uneven slurry application. Cattle slurry has a high content of potassium well in excess of the optimum needed for good grass growth and docks are able to take advantage of this. It is best to apply slurry early in the year at moderate rates or as a split application.
Docks are grazed off by cattle, sheep, goats and deer but not by horses. It has been suggested that sheep should be used to graze off seedling docks in the autumn and mature docks in March.
Leaflet available below: Organic management of docks in organic systems (2004)