For seedlings A watch should be kept out as, in the first growing season, their tuberous roots can usually be lifted out easily with a hand trowel.
For mature plants, the best approach is to dig out the tuberous root where the situation permits, tracing back the stems to the crown of the tuber which may be 7.5-10cm (3-4in) below soil level. Even if only some of the tuber is removed, this may be sufficient to prevent further regrowth. However, given the tendency for bryony to appear in tight spaces, digging out may not be an option.
An alternative method is to lay the long, trailing, leafy stems, still attached to the rootstock, on a hard surface, such as a path or bare earth (not grass), then spray with the non-selective herbicide glyphosate (e.g. Scotts Roundup, Bayer Garden Rootkill Weedkiller or Doff Knockdown Super Strength Glyphosate Weedkiller). This should succeed in checking it, but there may be regrowth the following season. This weedkiller is best applied between July and mid-September rather than in early spring.
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 in cool, calm weather or the gel formulation (Scotts Roundup Gel). 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.
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 section 4)
Chemicals: using a sprayer
Chemicals: using safely and effectively
Chemicals: using spot and broad-scale weedkillers
Weeds: non-chemical control