Problem type: Miscellaneous
Name of problem: Epicormic shoots and suckers
Plant name(s): Deciduous trees and shrubs
Symptoms / Characteristics:
Clumps of shoots are produced along the trunk or shoots grow from the ground around the base of the tree.
Epicormic shoots are sprouts that emerge from dormant buds along the trunk or branch of a tree. They are also called water sprouts. They often form in response to the sudden exposure to light in a forest setting but in the urban area they are more often associated with stress to the tree. Trees with severe die-back due to winter injury, drought and salt spray often produce many such sprouts as a means of compensating for the loss of leaf surface due to the stress or injury. Certain species are more prone than others and deciduous species are much more prone to such sprouting than gymnosperms (most evergreens). Oak and basswood tend to produce a large number whereas maple species and ash produce relatively few.
Suckers are sprouts that form from the roots of existing trees. They tend to form new trees or shrubs in the process. In species of aspen and poplar, the suckers may form at some distance from the tree and are a natural process of reproduction. They are especially prevalent after a disturbance such as occurs when mature trees are cut down. This type of sucker is also commonly produced by chokecherry and apple. They can become a nuisance in lawns.
Suckers may also be produced at the base of the trunk of a tree. This type of sucker is commonly found in plants that tend to form clumps of woody stems rather than a single stem. Examples include Amur maple, basswood and lilac. The formation of sucker shoots in this situation can become a problem when the shoot of a cultivar having certain characteristics such as a particular leaf colour or fruit flavour is grafted on a rootstock that does not exhibit these quality characteristics. In the case of apple, if the top dies back to the graft union for some reason, and a sucker from the rootstock develops into a replacement tree, the fruit will usually be of poor quality. In the case of Dropmore basswood (a hybrid between the European little leaf linden and American basswood), the rootstock is usually American basswood and because of the tendency to sucker, American basswood trees may continually develop at the base of the original tree.
Control / Preventions:
The best control for epicormic sprouts is prevention, by keeping the tree healthy. However, once formed they can be removed by pruning. A formulation of naphthaleneacetic acid (NAA), a form of the plant hormone auxin, has been used to control both epicormic shoots and suckers. For suckers in lawns it is important to mow frequently enough to prevent them from becoming too large. For suckers at the base of trees, frequent pruning is probably the simplest means of control. To prevent excessive suckering after cutting down aspen trees for example, a glyphosate herbicide may be used to treat the stump; from there the herbicide is translocated by the roots to the suckers. This should be done when the cut is relatively fresh as the herbicide will not translocate well in an old stump. The procedure is as follows: Drill 2 or 3 holes in the stump about 5 to 8 cm deep and 2 to 3 cm in diameter. Pour in glyphosate herbicide concentrate (i.e., not the ready to use type) to the top of each hole about 2 times per week for the first few weeks and then about once per week thereafter until the sucker sprouts begin to die. Glysphosate herbicides will kill anything green so care must be taken not to make contact with other vegetation in the area.