Common Problems With Honey Locust Trees

The honey locust, Gleditsia triacanthos, is a popular choice for street and garden planting, valued for its delicate, fern-like foliage that casts a light, dappled shade. Its tolerance for a wide range of climates and soil conditions enhances its appeal. While many modern cultivars are bred to be low-maintenance, the honey locust is susceptible to a variety of issues. These problems range from insect infestations and diseases to environmental or structural weaknesses.

Common Pests Affecting Honey Locusts

A variety of pests can affect honey locusts, with some of the most common including:

• The nymphs of the honey locust plant bug, Diaphnocoris chlorionis, hatch in spring as leaf buds open and feed on new growth. This feeding causes leaves to appear distorted, stunted, or covered in yellow spots. Heavy infestations can lead to premature leaf drop.
• The adult honey locust pod gall midge, Dasineura gleditchiae, lays eggs in developing leaflets. The larvae’s feeding causes leaflets to swell and form a pod-like gall. While this damage is primarily cosmetic, severe infestations can cause small branches to die back, and the ‘Sunburst’ cultivar is particularly susceptible.
• Honey locust spider mites (Platytetranychus multidigituli) become a problem during hot, dry weather. These tiny arachnids feed on leaf cells, causing a stippled or yellowed appearance and, in large numbers, significant defoliation. Their presence is confirmed by fine webbing on the undersides of leaves.
• The larvae of flatheaded borers tunnel beneath the bark, feeding on the cambium layer. This disrupts the transport of water and nutrients, which can weaken or kill branches and, in severe cases, the entire tree. Borers are often attracted to trees already stressed by drought or injury.

Prevalent Diseases in Honey Locust Trees

Cankers are localized areas of dead tissue on the bark. Thyronectria canker is a common type, appearing as sunken lesions that can girdle branches or the main trunk, leading to yellowing foliage and branch dieback. The fungus often enters the tree through wounds from pruning, storm damage, or lawn equipment.

Powdery mildew appears in hot, humid weather as a white to grayish powdery growth on leaf surfaces. While visually unappealing, it develops late in the season and does not cause serious harm to an established tree. Management involves raking and disposing of fallen leaves to reduce fungal overwintering.

Leaf spot diseases are fungal infections that cause spots or blotches on the leaves, which can lead to premature defoliation. Leaf spots are often a cosmetic issue that does not threaten the tree’s long-term survival. Ensuring good air circulation through proper pruning helps reduce the incidence of these diseases.

Structural and Environmental Concerns

Beyond pests and diseases, honey locusts can face several structural and environmental challenges.

• The wood is somewhat brittle, making it susceptible to breakage during high winds or ice storms. This is a consideration for trees planted near homes or in high-traffic areas. Proper pruning to develop a strong central leader and well-spaced branches can help mitigate this risk.
• While most landscape cultivars are thornless, the native species has formidable, branched thorns up to three inches long on its trunk and lower branches. This is an important distinction, as the native, thorny version is generally not suitable for home landscapes due to the hazard they present.
• Non-sterile varieties produce large quantities of long, brown seed pods that drop in the fall, creating significant litter on lawns and sidewalks. This mess is a primary reason for the popularity of seedless cultivars like ‘Moraine’ and ‘Shademaster’.
• The thin bark on younger trees makes them vulnerable to sunscald. This winter injury occurs when sunlight warms the bark on a cold day, and a subsequent rapid temperature drop kills the activated tissue. This creates a sunken or cracked area on the trunk, typically on the south or southwest side.