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Cut-leaved Crane’s-bill (Geranium dissectum) and Dove’s-foot Crane’s-bill (Geranium molle) are the two crane’s-bill species most commonly found as weeds of arable crops, although round-leaved crane’s-bill (Geranium rotundifolium) and small-flowered crane`s-bill (Geranium pusillum) may also be found as weeds. Many other Geranium species also occur in the UK, but rarely as arable weeds. Both cut-leaved and dove’s-foot crane’s-bill occur in a variety of habitats throughout most parts of the UK but cut-leaved crane’s-bill is the species more commonly encountered and has become increasingly common as an arable weed during the past 30 years. Cut-leaved crane’s-bill was the 8th commonest weed in a 2007/08 survey of arable fields on 28 farms in Southern England and was particularly frequent in winter broad-leaved crops, especially oilseed rape. This probably reflected the weakness of the herbicide programmes in that crop. [Reference: Lutman et al., (2009). Abundance of weeds in arable fields in southern England in 2007/08. Aspects of Applied Biology 91, Crop Protection in Southern Britain, 163 – 168.]
Cut-leaved crane’s-bill is a short/medium, semi-upright or sprawling hairy annual up to 60 cm tall with pink-purple flowers. The leaves are deeply dissected almost to the base and the fruits are hairy or downy. Dove’s-foot crane’s-bill is similar, but tends to be shorter, up to 40 cm tall, and the leaves are more rounded and less deeply dissected, usually only to about half-way to the base, and the fruits are hairless. The cotyledons (seed leaves) of both species are broader than long, slightly asymmetrical, long-stalked and noticeably hairy. The two species are hard to tell apart at the seedling stage but the second true leaf of cut-leaved crane’s-bill has additional, small secondary lobes which are absent in dove’s-foot crane’s-bill.
Cranesbills are moderately competitive species, with similar competitive abilities to groundsel, red dead-nettle and speedwells. It has been estimated that, on average, a population of 62.5 plants2 can cause a 5% yield loss in wheat crops. They may be more competitive in winter oil-seed rape. See other information sheet: How competitive are different weed species. In the past, cranesbill seeds were often serious contaminants of seed crops, especially clover, but improved seed cleaning has greatly reduced this risk.
As annual broad-leaved weeds, crane’s-bills are propagated solely by seeds. Both species flower from April to September with seeds being shed from June. The numbers of seeds produced per plant in a competitive crop situation is normally less than 500 but, in the absence of strong crop competition, many more (>2500 per plant) may be produced. Some seeds can germinate soon after shedding and consequently seedling emergence tends to be highest in August/September. This may help explain why crane’s-bills are often associated with early-sown winter oil-seed rape crops. However, some seeds shower greater dormancy, resulting in a more protracted germination period which tends to peak again in late spring
Seedlings can only emerge from seeds within the surface 5 cm of soil. Persistence of cut-leaved crane’s bill seed in the soil is generally considered to be relatively low (<5 years) compared with many other broad-leaved species. Seeds of dove’s-foot crane’s-bill are more persistent (> 5 years).
See other information sheet (Broad-leaved weeds: occurrence, agro-ecology and management) for the best approaches to integrated weed management of crane’s-bills. The limitations of these mean that control is largely dependent on herbicides on most farms, so maintaining the availability and efficacy of a wide range of herbicides is essential. It is worth emphasising that, as explained above, prevention of seed return over a period of years should greatly reduce the threat from cut-leaved crane’s-bill as the seedbank should decline more rapidly than for many other major broad-leaved weeds (e.g. charlock and poppy).
Herbicides and resistance
- Several herbicides are available for control of crane’s-bill, at least in major arable crops. However, with some of these, good control can only be achieved pre-emergence or by applications to young plants. Consequently, a primary aim must be to treat crane’s-bill plants while they are small.
- Some pre-emergence herbicides applied primarily for black-grass control in winter cereals, such as prosulfocarb, also give useful control of autumn emerging crane’s-bill but are unlikely to adequately control plants subsequently emerging in spring. Prosulfocarb can also be used to control crane’s bill in potatoes.
- In cereals, sulfonylurea herbicides such as metsulfuron+tribenuron can give good control of small plants but restrictions on application to after 1 February may mean that plants are too large for effective control. Sulfonylurea and related herbicides which can be applied in autumn, such as flupyrsulfuron or pyroxsulam+florasulam, may be a better option.
- The formulated mixture of chlorotoluron+diflufenican+pendimethalin can also control crane’s-bill species in cereal crops.
- The older synthetic auxin herbicides, such as MCPA and mecoprop, give poor control of crane’s-bills, but the new synthetic auxin herbicide halauxifen-methyl (‘Arylex’), formulated in mixture with fluroxypyr or florasulam, gives good control (although only small-flowered crane’s-bill is on the label).
- In winter oil-seed rape, clomazone+napropamide (pre-emergence only), and dimethenamid (only available in mixtures with metazachlor and/or quinmerac) can give good control of crane’s-bill post-emergence. Imazamox+quinmerac (applied before 9th true leaf stage of the crop) also gives control but can only be used in ‘Clearfield’ varieties.
- No cases of herbicide resistant crane’s-bill (or other Geranium spp.) have been detected in the UK or, indeed, worldwide. Consequently, crane’s-bill can be considered a ‘low resistance risk’ weed based on global experience but should not be consider a ‘no resistance risk’ weed due to the high dependency on herbicides for control. If resistance is suspected, collect a seed sample and have it tested.