Docks

Occurrence

Both broad-leaved dock and curled dock are common and widely distributed throughout the UK. A hundred years ago, docks were the third most problematic weeds of arable crops (after couch and charlock) and the fourth worst weeds of grassland (after thistles, buttercups and Holcus spp.). However, docks are now considered minor weeds in most arable crops but remain a significant problem in meadows and pastures.

Identification

There are many species, and hybrids, of docks but only broad-leaved and curled dock are of widespread concern in agriculture.

• Broad-leaved dock has broad lower leaves with an elongated heart shape. The breadth of leaves is usually at least half their length. The flowering stems are well branched which often spread quite widely. Flowering starts in late June or July and the fruits, when fully ripe, are a reddish-brown colour and often remain in clusters on the stems.
• Curled dock has narrower leaves which are usually at least three times long as broad. The leaf margins are very wavy and convoluted. The flowering stems are much less branched and tend to be carried close to the main stem. Flowering starts in early June.

Agro-ecology

Both species are perennials and form long tap roots. Curled dock tends to be much shorter-lived than broad-leaved dock, and can behave as an annual or biennial in some situations with plants dying after flowering. Individual plants of broad-leaved dock can be very long-lived, especially in pastures. Both species occur in meadows and pastures but curled dock is the commoner species in arable crops. Both species produce large numbers of seeds (>25,000 per plant) which are very persistent in the soil – many can survive for over 20 years.

Most infestations arise from seeds but vegetative reproduction can occur from tap root fragments resulting from tillage. Seedlings are largely derived from seeds within 5 cm of the soil surface and may emerge in autumn or spring. Seedlings have a low competitive ability and consequently often only establish in open or disturbed patches in established vegetation. Once the deep taproots have developed, dock plants have an advantage over shallow rooted crops and grass. Well establish plants of broad-leaved dock show great resilience and can withstand damage resulting from grazing, trampling, cutting and tillage. Both species thrive under high soil nitrogen conditions but will also tolerate poor nutritional conditions.

Damage

Little information is available on the competitive ability of dock seedlings in arable crops and the ability to control seedlings with herbicides means that they are usually of little significance in conventional cropping situations. However, in pastures and meadows, docks may reduce grass productivity and be considered unsightly in amenity areas. These two species of docks are two of the five weeds classified as injurious under the Weeds Act 1959, the others being common ragwort, spear and creeping thistle.

Management Options

See other information sheet (Broad-leaved weeds: occurrence, agro-ecology and management) for best approaches to integrated weed management of broad-leaved weeds. Both dock species have protracted germination patterns with plants emerging in both autumn and spring.

• The protracted period of germination, combined with high seed persistence (> 20 years) in the soil, makes eradication impractical. Consequently, while preventing seed production is important in long-term weed management, this is likely to have less immediate impact compared with grass-weeds and other broad-leaved weeds with less persistent seeds.
• Rotations which include spring as well as autumn sown crops are unlikely to be as effective against docks as they are against autumn germinating grass-weeds such as black-grass, although they may enable the use of a wider range of herbicides.
• Dock seedlings are susceptible to competition, especially at the early growth stages, and a strongly competitive crop will assist other control measures.
• Cultivations may encourage some seeds to germinate, but many will remain dormant especially if deeply buried. Establishing spring crops by direct drilling or with minimal soil disturbance should reduce the numbers of dock seedlings emerging in the crop.
• Cultivations can fragment tap roots resulting in the formation of new plants. This can make infestations worse unless used in combination with herbicides or a programme of repeated cultivations.
• Fallowing is likely to be ineffective at reducing seedling populations due to the great persistence of dock seeds in the soil.
• Hoeing in row crops and harrowing can be effective in controlling many broad-leaved weeds, especially if carried out while weeds are small.
• Prevent importation and spread of seeds. The main method of long-distance dispersal is in contaminated crop seed, animal feed, straw and manure. Dock seeds can pass through cattle unharmed and will survive for several weeks in manure and slurry. German studies indicate that dock seeds are unlikely to survive in silage or anaerobic digestion (AD) processes.
• Cutting, mowing or grazing docks in grassland can prevent seed return but is likely to be ineffective at reducing established populations, unless carried out repeatedly for long periods.
• In pastures heavily infested with docks the best option may be to plough and reseed with grass. Docks are likely to regenerate both vegetatively and from seed, so a period of fallowing or arable cropping prior to re-seeding may help to reduce re-establishment.
• In grassland, minimising sward damage from trampling, poaching and uneven slurry application will prevent dock seedlings establishing in the disturbed patches.
• Control of docks is largely dependent on herbicides on most farms, so maintaining the availability and efficacy of a wide range of herbicides is essential.

Herbicides and resistance

• Synthetic auxin herbicides, such 2,4-D and MCPA, are effective at controlling dock seedlings in cereals and young grass swards. MCPB and 2,4-D are a safer option in grass/clover swards. The introduction of these herbicides in the 1940s and 1950’s was the primary reason for docks becoming much less important as weeds of arable crops. Many newer herbicides are more effective and have a wider weed spectrum.
• Sulphonylurea herbicides, such as metsulfuron-methyl, control docks in cereal crops.
• Fluroxypyr controls docks in a range of arable crops and also in grassland situations.
• Dimethachlor can be used to control docks in oilseed rape.
• Established dock plants are much less susceptible to herbicides. Fluroxypyr+triclopyr is a good option for controlling docks in established grassland. Applications must be made when weeds are growing actively, there is sufficient foliage for effective uptake and plants should not be cut for at least 28 days after spraying to ensure effective translocation to the tap roots. Repeat applications may be required to achieve full control.
• Glyphosate can be used to control docks non-selectively but will kill or severely damage other plants exposed to the spray. Can be effective on small patches if applied by knapsack or by weed wiper. Best applied when docks have produced a flowering stem but before seeds are set.
• No cases of herbicide resistance in either of these dock species has been reported anywhere in the world. However, resistance to ALS inhibitors has been reported in the closely related Rumex dentatus (Toothed dock) in India in 2014.
• Docks represent a low resistance risk compared with many other grass and broad-leaved weeds. However, if resistance is suspected, collect a seed sample and have it tested. The long persistence of dock seeds in the soil and their fecundity, mean that detecting resistance at an early stage is vital.