Sumachs are very prone to suckering, especially the commonly grown Rhus typhina (stag's horn or velvet sumach). Damaged, heavily pruned or coppiced sumachs will be more prone to suckering.
However, there may also be some evidence that plants growing strongly such as in a warm summer can send up more suckers than normal. Established sumachs are drought tolerant.
Control
If the suckers are numerous, removal of the tree is the most satisfactory and advisable approach. Cut back the whole tree or shrub and treat the stump and suckers with weedkillers recommended for stump killing such as Roundup Tree Stump & Rootkiller, Deep Root Ultra Tree Stump & Weedkiller or SBK Brushwood Killer.
If there are only a few suckers, trace each one, severing as close as possible to its point of origin on the tree's root, then remove. Suckers under a lawn will require that the turf be peeled back to allow the root to be traced back to the parent plant. If removal is difficult, when the tree is in a neighbour's garden for example, sever to isolate the sucker from the parent tree by cutting through the root, then treat as above. If several large roots are severed, the health or stability of the tree may be affected. There may also be further sucker development at the point where roots are removed, giving a recurring sucker problem.
Simply mowing over suckers in a lawn will only aggravate the problem and is unlikely to significantly weaken the plant.
Prevention
Keeping a sumach in good health and keeping pruning to a minimum may help reduce the chance of suckering. Even fully healthy and undisturbed plants can start to sucker, however, and once suckering begins there is little that can be done to stop it.
Suckers are likely to come through geotextile fabrics or weed membranes but may be contained with a vertical barrier of an impenetrable material such as a paving slab, corrugated iron sheet, or a specially designed fabric manufactured by Dupont called 'Rootbarrier'. It is available from:
Greentech Limited, Sweethills Park, Nun Monkton, York YO26 8ET
Tel: 01423 332100
Fax: 01423 332101
e-mail: info@green-tech.co.uk
Website: www.green-tech.co.uk
Sumachs are not well suited to the small garden and should be planted where there is plenty of space for suckering. Site well away from lawns and manicured areas of the garden.