As this is a perennial plant complete removal of the weed by hand is the best cultural control. If possible do this before it sets seed.
There are no specific recommendations for the control of herb bennet, although we assume that it is fairly resistant to most of the lawn herbicides available as this is the case for the closely related genus Potentilla.
Use a glyphosate-based weedkiller such as Round-up. Glyphosate is a non-selective, systemic weedkiller applied to the foliage. It is inactivated on contact with the soil, so there is no risk of damage to the roots of nearby ornamentals.
As glyphosate is not selective in its action, it is essential to avoid spray or spray drift coming into contact with garden plants. If treating weeds in the immediate vicinity of garden plants, apply carefully using a ready-to-use spray formulation in cool, calm weather. Branches or shoots can be held back, using canes, or by covering or screening while spraying, but make sure that the weed foliage has dried before releasing branches or removing the covering.
Glyphosate is most effective when weed growth is vigorous. This usually occurs at flowering stage, but before die-back begins.
In rough grassland:
If the weed is growing in grassy areas, then the herbicide SBK Brushwood Killer can be used, as this would leave the grass unharmed. The susceptibility of Geum urbanum to SBK is not known, but as the weedkiller gives good control of the closely related silverweed (Potentilla anserina) it is likely that Geum will also be knocked back. This herbicide is systemic, travelling from the weed foliage down into the root system. SBK will damage any broad-leaved plants however (e.g. wildflowers) and so should only be used in grass where such action is acceptable.
Spring or summer are usually the best seasons to obtain good control of perennial weeds. More than one application may be necessary to gain control. Seedlings will not be prevented from germinating so be sure to catch these either by hand weeding or with an herbicide when they appear. Always follow the manufacturer’s instructions when using weedkillers.
Inclusion of a weedkiller product does not indicate a recommendation or endorsement by the RHS. It is a list of products currently available to the home gardener.
Weedkillers for gardeners (Adobe Acrobat pdf document outlining weedkillers available to gardeners; see sections 1a and 4)
Chemicals: using spot and broad-scale weedkillers
Chemicals: using a sprayer
Chemicals: using safely and effectively
Weeds: non-chemical control