Occurrence

A hundred years ago, these two closely related weed species, charlock and wild radish (runch), along with couch, were the most troublesome weeds of arable crops (Common weeds of farm and garden, H C Long, 1910).  In 1897, the value of copper sulphate at controlling charlock was discovered accidentally and this became the most widely used selective herbicide in the UK in the early 20th century – 30 years before MCPA and 2,4-D were discovered.  These synthetic herbicides revolutionised control of many broad-leaved weeds but, despite being very effective on charlock, this weed remains one of the commonest weeds of arable crops today.  Charlock and wild radish are a particular problem in brassica crops such as oilseed rape due to a lack of selective herbicides.

Charlock was the 7th commonest weed in a survey in 2007/08 of 28 farms in Southern England (Lutman et al., 2009).  It was particularly frequent in oilseed rape reflecting the weaknesses of the herbicide programmes in this crop.  Wild radish was much less common and not amongst the 20 commonest species.  

Identification

Charlock and wild radish are similar types of plants with roughly hairy stems (in contrast to mainly hairless oilseed rape) but can be distinguished by the following characteristics:

  • The first true leaf of wild radish has a more pointed tip than charlock and is rough to the touch
  • Subsequent leaves of wild radish have one of more independent lobes at the base of the blade whereas leaves of charlock tend to be more entire, although often indented
  • In charlock the flower sepals droop horizontally whereas in wild radish they remain erect
  • There are much more obvious constrictions between seeds in ripe pods of wild radish
  • Charlock has bright yellow flowers whereas petals of wild radish may be yellow, mauve or white, often with lilac veins.  Consequently, flower colour is a useful, but not a reliable, diagnostic characteristic.

Damage

Charlock and wild radish are two of the most competitive broad-leaved weeds and 12 plants/m2 typically causes a yield loss of 5% in cereals, similar to poppy and mayweeds.  See how competitive are different weed species.  Many seeds can be produced in favourable conditions and these can last for more than five years in the soil.  Both species can act as alternative hosts for a range of crop pests and pathogens, including the beet cyst nematode.

Management recommendations

Both charlock and wild radish have protracted germination patterns with most emergence occurring in spring but with a significant amount of autumn germination too, especially with wild radish.  Autumn emerging charlock plants may be killed by low winter temperatures but wild radish tends to be more frost-tolerant.

  • The protracted period of germination combined with high seed persistence (> 5 years) in the soil makes eradication from crops difficult.  Consequently, while preventing seed production is important in long-term weed management, this is likely to have less immediate impact compared with control of grass-weeds.
  • Rotations which include spring as well as autumn sown crops are unlikely to be as effective against charlock and wild radish as they are against autumn germinating grass-weeds such as black-grass, although they may enable the use of a wider range of herbicides.
  • 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 charlock and wild radish emerging in the crop.
  • Fallowing or grass leys are likely to be less effective than against grass-weeds due to the much greater persistence of charlock and wild radish 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.
  • Charlock and wild radish are susceptible to competition, especially at the early growth stages, and a strongly competitive crop will assist other control measures.
  • Prevent importation and spread of seeds in combine harvesters, grain, balers, seed, straw, manure and cultivation equipment.
  • Rogue plants, or spray off patches, in early summer wherever possible.  This should be done before seeds start shedding.
  • Try not to become totally reliant on herbicides for control of charlock and wild radish – integrate their use with non-chemical methods wherever possible.  This is difficult as there are fewer, effective non-chemical options and the highly competitive nature of these species means that infestations must be reduced as much as possible.
  • Control of charlock and wild radish 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

  • Sulfonylurea herbicides (e.g. metsulfuron and flupyrsulfuron), triazolopyrimidines (e.g. florasulam) and many synthetic auxin herbicides (e.g. 2,4-D, MCPA & mecoprop) generally give very good control of charlock and wild radish in cereal crops.  Note that the new Dow herbicide ‘Pixxaro’, containing the two synthetic auxin herbicides, halauxifen-methyl (‘Arylex’) + fluroxypyr, lists charlock, wild radish and volunteer oilseed rape as being tolerant, so is not a good option for controlling these brassica weed species.
  • These brassica weeds are a particular problem in brassica crops such as oilseed rape due to lack of selectivity.  However, the recent introduction of the ALS inhibitor imazamox, as found in the product ‘Cleranda’, allows excellent control of weeds such as charlock and oilseed rape volunteers in ALS-resistant Clearfield® varieties of oilseed rape.
  • Consider whether you have become over-dependent on one mode of action for control of charlock and wild radish throughout your rotation – especially ALS inhibitors.
  • Although many ALS inhibiting herbicides (e.g. sulfonylureas such as metsulfuron and triazolopyrimidines such as florasulam) are highly effective on charlock and wild radish, they are from a resistance-prone class of herbicides.
  • No cases of herbicide resistant charlock or wild radish have been detected in the UK so far but the UK Weed Resistance Action Group considers charlock to be one of the weeds most likely to evolve resistance here in future
  • The threat is very real as resistance in these species has been identified in nine countries worldwide, including Italy and Spain in Europe.  Most cases of resistance are to the ALS inhibiting herbicides but resistance to auxin type herbicides (e.g. 2,4-D) has also been recorded.
  • It may also be significant that charlock was the first ALS resistant broadleaved weed in the world (in Canada) to show enhanced metabolic resistance, which is much more commonly found in grass-weeds.  However, ALS target site resistance has also been demonstrated in charlock and wild radish in other countries, as well as in chickweed, poppy and mayweed in the UK. 
  • Use other modes of action in mixture, sequence or in rotation wherever possible to reduce the risk of resistance.  Be aware that using several herbicides with different modes of action may not prevent resistance if charlock and wild radish are only being controlled effectively by one active ingredient, despite many others being applied.
  • Try to ensure that high resistance risk species such as charlock and wild radish, as well those other species with confirmed resistance in the UK (chickweed, poppy, mayweed), are controlled effectively with at least two, and preferably three or more different herbicide modes of action over the course of a crop rotation.  Consider using non-ALS and non-auxin herbicides to control charlock and wild radish to reduce the risk of resistance (e.g. chlorotoluron+DFF+pendimethalin).
  • Autumn applied pre-emergence herbicides are unlikely to effectively control spring emerging charlock and wild radish.
  • If resistance is suspected, collect a seed sample and have it tested.  The long persistence of charlock and wild radish seeds in the soil, their competitiveness and fecundity, mean that detecting resistance at an early stage is vital.

Discuss Charlock

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