Cicadas are a familiar summer sound, but when populations surge, they can pose a real threat to the health of ornamental and fruit trees. The damage is not caused by the insects chewing leaves, but by the female’s behavior when preparing to lay eggs. Understanding the cycle and the specific mechanisms of harm is the first step in protecting valuable landscape specimens.
How Cicadas Cause Structural Damage
The primary culprit for tree damage is the female cicada, which possesses a saw-like ovipositor. She uses this tool to cut slits into the ends of small branches to deposit her eggs. This process interrupts the flow of nutrients and water, effectively girdling the branch and causing it to wilt, turn brown, and often break off. While the insect itself feeds on fluids, the physical trauma from egg-laying is what creates lasting structural problems for the tree.
Symptoms to Watch For
Identifying an infestation early can save a tree from permanent decline. The most obvious sign is the presence of small, branch-like structures that look like they have been snipped with pruning shears, but are scattered randomly across the canopy. These are the egg-laying sites. Additionally, you might notice premature browning of leaves on affected branches or an increased number of branches dying back from the tips during the growing season.
Branch Flagging
In arboriculture, the specific pattern of damage is often called "flagging." This occurs when a distinct section of a branch turns brown and dies due to the cicada's girdling action. While a healthy tree can often compartmentalize this damage and push growth from nearby buds, severe flagging across a significant portion of the canopy can stress the tree and make it vulnerable to disease or secondary pests.
Which Trees Are at Risk?
Not all trees face the same level of danger. Cicadas show a distinct preference for thinner, more flexible new growth. Therefore, young trees and saplings are the most vulnerable, as their branches are the perfect size for egg deposition. Fruit trees like cherry, apple, and peach are particularly attractive targets, as are ornamental varieties such as maple, oak, and dogwood. Mature trees with thick, bark-heavy branches are generally more resilient and rarely suffer fatal damage.
Protecting High-Value Trees
For valuable landscape trees or young orchards, proactive measures can be highly effective. One of the most reliable methods is to cover the tree with fine-mesh netting, such as bird netting, during the peak emergence period in late spring and summer. This physical barrier prevents the females from accessing the branches. The netting must be secured tightly around the base of the trunk to prevent cicadas from crawling underneath.
Recovery and Long-Term Care
If a tree has already been damaged, removing the affected branches is the best course of action. Pruning should occur in the late winter or early spring to remove all the dead flagging and allow the tree to redirect its energy to healthy growth. Fertilizing can be beneficial to support recovery, but watering during dry periods is the most critical step to ensure the tree regains its vigor and can withstand future cycles.
Understanding the Cycle
It is important to note that the cicadas causing damage are typically the annual, or "dog-day," variety, which emerge every year. The more famous periodical cicadas, which emerge in massive numbers every 13 or 17 years, cause widespread damage but are less predictable. Regardless of the type, the key to tree protection lies in vigilance during the summer months and implementing physical barriers before the females begin their egg-laying process.
