What are tree suckers and why do they form?

There are many trees that develop tree suckers. Ornamentals such as lilacs on standards, crabapples, ornamental pear, and fruit trees often form suckers at their base. Tree suckers appear as shoots or branches directed upright at the base of a tree. They are a common maintenance issue in spring and during the growing season on many ornamental trees. Sometimes, they indicate the tree is stressed. On ornamentals, they are most often the result of a vigorous root system. Often an ornamental tree with attractive features is grafted onto a less desirable, but hardier and more robust root system. This robust root system can be more prone to suckering.

What should I do with the suckers?

It is best to keep up with pruning tree suckers as they occur during the growing season. The longer they are left to grow the thicker, more numerous, and more difficult they will be to cut. Removal often requires cutting back into the soil to determine the origin of the sucker and making your cut with sharp pruning shears. Making a cut at soil level and leaving a nub, often encourages more suckers. If suckers are left to grow, the upright branches can overtake the tree or shrub. In addition, the vigorous rootstock will take nutrients from the more desirable portion of the tree or shrub. Typically, the leaves, fruit, flowers, etc that are produced from rootstock suckers are inferior to the main upper ornamental portion of the tree of shrub.

Should I spray herbicide or sucker killer on the sprouts?

I have found no qualified recommendations for spraying an herbicide or sprout stopper on suckers. The risk of damage to the desirable part of the tree is too likely. Enough research has not been done on the effectiveness of any such products. The best defense is keeping the trees healthy, monitor frequently, and remove sprouts as they occur.