Effective Sucker Management in Apple Orchards

Root Suckers

Root and crown suckers are unwanted vegetative growths that can be treated much like perennial weeds, with one important distinction: every measure must be taken to avoid damaging the mother plant. This means suckers can be controlled through physical or chemical methods that lead to their burndown or elimination, provided the treatment does not cause damage beyond the sucker’s base (the rootstock or trunk).

Suckers require timely management. If left unchecked, they can harbor pests, serve as entry points for disease, absorb herbicides meant for the orchard floor, interfere with daily orchard management, and eventually they can overtake the orchard entirely.

While a small number of suckers is a normal occurrence, excessive growth often points to underlying orchard management issues. This can include poor rootstock selection, incompatibility between the rootstock and scion, or physical damage to the trunk.

Sucker removal is typically achieved through mechanical or chemical means. Each approach carries its own set of advantages and disadvantages, which are outlined below.

Physical Removal

Mechanical removal is generally reserved for orchards with very low sucker production due to the high labor costs involved. The primary physical methods are cutting or flaming.

While cutting is straightforward, it comes with a significant drawback: severing a sucker often stimulates the growth of multiple new suckers just below the cut line. Flaming, on the other hand, can be highly effective at destroying the tissue, but the equipment is expensive, and the process is often dangerous and impractical in most commercial orchard settings.

Chemical Control

Chemical control is usually the preferred option due to its speed, efficiency, and lower cost. Chemical removal strategies fall into three main categories: plant growth regulators, chemical desiccants, and herbicides.

The inherent challenge with chemical control is that products effective at killing suckers are logically quite capable of injuring the mother tree. Maximum caution and precise application are required to prevent drift or translocation to the desirable plant tissues of the mother tree.

Plant Growth Regulators (NAA)

First and foremost, it is crucial to note that there are currently no plant growth regulators registered in Canada for sucker control. Therefore, applying them for this purpose is illegal under Canadian regulations.

NAA (1-Naphthaleneacetic acid) is frequently mentioned in US-based literature, where specific formulations are registered for sucker management. However, using NAA improperly can trigger severe physiological disorders in the tree. The concentrations required for sucker control are magnitudes higher than those used for chemical fruit thinning, and the formulations are entirely different. For these reasons, Canadian growers must avoid using NAA for sucker management unless a specific product has been registered for this purpose.

Chemical Fertilizers as Desiccants

Certain liquid fertilizers, when applied at high concentrations, can rapidly dehydrate suckers and even suppress some weeds. Specifically, undiluted solutions of Urea Ammonium Nitrate (UAN) have been used with great success, achieving burndown levels comparable to conventional herbicides.

Because UAN works solely by dehydrating plant cells, it is only effective on soft, green tissue and leaves absolutely no residual effect. Maintaining control usually requires two to three applications per season.

If UAN is used as a desiccant, its high nitrogen content must be accounted in the overall orchard fertility program. For example, a single application of UAN (28-0-0) applied at 200 L/ha will add approximately 17 kg/ha of actual nitrogen to the orchard, assuming a 30% spray coverage area.

Herbicides

Currently, there are only two products explicitly registered in Canada for orchard sucker control: Beloukha (pelargonic acid) and Aim (carfentrazone-ethyl).

While other herbicides registered for apple orchards may suppress or burn down suckers, they are not strictly registered for this use and their applications should be targeted primarily at weed control. Conversely, when Beloukha or Aim are applied to suckers, growers get the added benefit of weed burndown.

Regardless of the chemistry used, control is always most effective on young, green, unlignified tissue. If suckers are allowed to develop woody bark, mechanical removal will be required.

Aim (carfentrazone-ethyl)

Aim is a Group 14 herbicide. For optimal control, it should be applied to fresh, green suckers in combination with a non-ionic surfactant (NIS). Because Aim has no systemic activity, it only kills the tissue it directly touches. Complete, thorough coverage of the sucker is mandatory for satisfactory results. The maximum allowable number of applications per year is two. As a highly effective contact herbicide, strict drift management is required to protect the mother tree’s green tissue and fruit.

Beloukha (pelargonic acid)

Beloukha is a naturally occurring organic acid that rapidly destroys plant cell walls and has no systemic effect. It is a preferred option for growers seeking a “greener” alternative to synthetic herbicides, although it’s not currently registered for organic production. Achieving effective control requires high application rates and repeated treatments, which can make it more expensive than conventional products.

Other Burndown Herbicides

Several herbicides registered for orchard weed control, such as glufosinate (Ignite), diquat (Reglone), and flumioxazin (Chateau), can result in partial or complete sucker burn-down. Although sucker control is not their primary registered use, their activity on suckers provides a useful secondary benefit when managing orchard floor weeds. Some growers coordinate these weed control applications with sucker control products (e.g., Aim + Ignite) to manage both weeds and suckers simultaneously. This approach can take advantage of additive effects that provide a very strong burndown effect, achieving a broader spectrum of weed control along with effective sucker control.

Spraying Glyphosate on suckers

Glyphosate should not be applied directly to suckers. Even early in the season when it might be relatively safe, any small amount of glyphosate that translocates into the mother tree can have severe, long-lasting consequences, so it’s better to avoid it. These effects, such as reduced winter hardiness and increased susceptibility to diseases like canker, are often not immediately visible.

Furthermore, it is never safe to apply glyphosate near suckers after mid-summer. Late-season applications will easily translocate down into the mother tree’s root system, potentially causing permanent, catastrophic damage. Finally, if you remove suckers mechanically, you must wait 7 to 10 days before applying glyphosate to the orchard floor, as the herbicide can be readily absorbed through the fresh wound tissue.