The following is information on sucker control in woody plants.
Many ornamental trees and shrubs will produce suckers from the stem area at the base of a plant, some from the roots. In multi-stem shrubs, these suckers will provide new stems and can serve as a means to rejuvenate plants (remove old stems, keep some new stems). However, in most trees and single stem shrubs, suckers are a drain on plant food reserves and can attract pests. In grafted plants, suckers from rootstocks will be different from the desired ornamental plant. Sucker removal by hand pruning can be time consuming in nurseries and large landscapes.
There are some chemical aids to reduce or eliminate suckers. Naphthaleneacetic Acid (NAA), a growth regulator, is labeled for some non-residential uses on ornamental plants. Apply in the dormant season or before new shoots are 12’’ long. Pelargonic acid (Scythe) is a non-selective herbicide that can be applied to suckers of woody plants. It can be used in landscapes and nurseries. Use a 5-10% solution. One caution is not to use glyphosate (Roundup and many other trade names) for sucker control or around plants with suckers. The glyphosate will be translocated into the root system of the plant and while you may not see any affect to the main plant this year, in the following year, the glyphosate will be mobilized from the root system and translocated to growing points causing poor leaf out, yellowing, reduced growth or stunting.
Gordon Johnson, Extension Agriculture Agent, UD