Hackberry psyllids, often called jumping plant lice, are small insects that feed exclusively on hackberry trees (Celtis species). Their feeding activity results in noticeable galls on the leaves and produces a sticky, sugary substance known as honeydew. This honeydew often drips onto cars, patios, and outdoor furniture, creating a significant nuisance for homeowners. Effective management requires understanding the psyllid life cycle and targeting treatments at the correct time.
Identifying the Pest and Its Impact
The clearest sign of a psyllid problem is the appearance of galls on hackberry leaves. Different psyllid species create distinct structures, such as the Hackberry Nipple Gall Psyllid, which produces cone-shaped protrusions, and the Hackberry Blister Gall Psyllid, which forms rounded swellings. These galls act as protective shelters where the young psyllid nymphs develop after eggs hatch in the spring. Adults emerge in the late summer or fall and become a nuisance by clustering on homes and window screens.
The sticky honeydew excreted by feeding psyllids is another major indicator of infestation. This sugary residue can lead to the development of black sooty mold. Despite the galls and honeydew, these pests rarely pose a serious threat to the overall health of a mature hackberry tree. The damage is predominantly aesthetic, though severe infestations can occasionally cause premature leaf drop. Established trees are resilient enough to tolerate the damage and fully recover their canopy the following year.
Non-Chemical Management Techniques
Non-chemical methods can help reduce the current population and mitigate the nuisance when an infestation is noticed. A strong jet of water can be directed at the foliage to physically dislodge the psyllids. This technique is most effective on smaller, accessible branches to knock the insects off the tree and surrounding surfaces. Regular hosing also washes away sticky honeydew, minimizing the growth of sooty mold.
Pruning is another physical control method, useful for smaller, heavily infested trees or lower branches. Removing and disposing of leaves and twigs covered in dense galls reduces the number of developing psyllids. This mechanical removal should be done before adult psyllids emerge from the galls in late summer. Encouraging natural enemies, such as lady beetles and lacewings, provides biological control, as these insects prey on psyllids.
Choosing the Right Chemical Treatment
Chemical intervention is most effective when timed to target the insects before they form protective galls. Once nymphs are sealed inside the gall structures, most contact insecticides cannot reach them, making treatment ineffective. Management strategies must focus on killing overwintering adults or newly hatched nymphs. This approach uses two main chemical types applied when the tree is dormant or just beginning to grow.
One approach involves dormant oil, a horticultural oil applied in late winter or very early spring before the buds break. The oil works by suffocating adult psyllids overwintering in bark crevices and killing eggs laid on the branches. Applying dormant oil close to bud break ensures maximum contact with emerging pests before the leaves unfurl. This treatment is a good option for smaller trees where thorough coverage of all bark and branch surfaces is possible.
For larger hackberry trees, where spraying the entire canopy is impractical, systemic insecticides offer a manageable solution. These products, often containing imidacloprid or dinotefuran, are applied as a soil drench or injected directly into the trunk. The tree’s vascular system absorbs the chemical and distributes it to the leaves, rendering the foliage toxic to feeding psyllid nymphs. Systemic treatments are best applied in late fall after leaf drop or in early spring to allow the tree enough time to absorb the insecticide before eggs hatch.
Long-Term Tree Care and Prevention
Promoting the health of the hackberry tree is key to increasing its natural resilience against psyllid damage. Healthy, vigorous trees are better equipped to tolerate galls without suffering significant stress or defoliation. Proper watering, especially during drought, is a cultural practice that helps maintain tree vigor. Trees under drought stress are more susceptible to pest issues.
Fertilization should be managed carefully to support steady growth without encouraging excessive new foliage. Psyllids are attracted to soft, succulent new growth for egg-laying and feeding, so high-nitrogen fertilizers should be avoided. Applying organic mulch around the tree base helps conserve soil moisture, moderate temperature, and improve soil health. These cultural practices reduce the tree’s susceptibility and complement targeted control efforts.