Homeowners and nature enthusiasts often look up in alarm when the droning chorus of cicadas fills the air, wondering if these loud insects are silently killing the trees they cling to. While the sight of cicadas clinging to trunks and branches is undeniable, the direct threat to a healthy tree is generally minimal, overshadowed by the indirect and secondary damage caused during the egg-laying process. Understanding the mechanics of how cicadas harm trees requires looking beyond the noise and focusing on the precise physical injury inflicted by the female insect’s ovipositor.
The Mechanics of Tree Damage
The primary way cicadas harm trees is not through feeding, as the adults do not consume leaves or bark, but through the act of oviposition. Using their serrated, knife-like ovipositor, female cicadas cut slits into the branches of deciduous trees to deposit their eggs. This deliberate slicing action disrupts the flow of nutrients and water, effectively girdling the branch just beneath the bark. While a few cuts are insignificant to a mature tree, a heavy infestation can result in so many slits that the branch loses its ability to transport resources, leading to wilting, dieback, and ultimately branch death.
Target Species and Vulnerability
Not all trees are equally susceptible to cicada damage, and hardwoods are generally the prime targets for these insects. Deciduous trees such as oaks, maples, cherries, and fruit trees are preferred because their bark provides the necessary structure for the female to anchor herself and cut her egg-laying slits. Coniferous trees, like pines and spruces, are typically avoided. Young trees with thin bark and flexible new growth are far more vulnerable to suffering significant injury compared to large, established trees with thick, protective bark that can withstand the trauma better.
Visible Signs of Infestation
Identifying a cicada problem early is key to mitigating damage, and there are distinct visual indicators to watch for. The most obvious sign is the presence of "flagging," where the leaves and branches on a twig turn brown and die back, appearing as if they have been scorched by fire. This occurs directly above the slit where the female laid her eggs. Additionally, one might notice small, brown, wedge-shaped slits or scars on the branches, often in a straight line, which are the entry points created by the ovipositor.
Secondary Pests and Disease
The injury caused by cicadas creates an open wound that compromises the tree’s natural defenses, making it an easy target for secondary invaders. Fungi, bacteria, and wood-boring insects are often attracted to these fresh slits and can infiltrate the damaged tissue, accelerating the decline of the affected branch. This secondary infection is frequently the true culprit behind the tree's rapid deterioration, rather than the initial egg-laying itself, highlighting the importance of protecting the tree from opportunistic pathogens.
Management and Prevention Strategies
For valuable landscape trees, proactive protection is the most effective strategy against cicada harm. Wrapping the trunks and major branches of young trees in fine mesh netting or cheesecloth can physically prevent females from accessing the bark to lay their eggs. This barrier method is most effective when installed before the adults begin emerging and actively seeking hosts. Timing is critical, as the netting must be in place during the peak emergence and mating season to be successful.
Long-Term Recovery and Care
In cases where damage has already occurred, the tree often has the resilience to recover naturally, especially if it is mature and healthy. Pruning out the visibly dead or "flagged" branches is recommended to eliminate the unsightly damage and prevent the spread of disease from the open wounds. Ensuring the tree receives adequate water and mulch around the base during the recovery period helps reduce stress and encourages the growth of new shoots, allowing the tree to fill in and restore its canopy over time.
