Cicadas are one of nature’s most dramatic events, emerging en masse after years spent underground, but their presence can cause concern for homeowners with vulnerable trees. The primary damage to trees is not caused by feeding, but by the female’s reproductive process. When laying eggs, the female uses a knife-like organ called an ovipositor to slice slits into the bark of small, pencil-sized twigs and branches. This egg-laying (oviposition) weakens the branch tips, which can lead to dieback and breakage. It is the synchronized, massive emergence of periodical cicadas, with their 13- or 17-year life cycles, that poses a threat to young or high-value trees.
Determining When Control is Necessary
Most mature, healthy trees are naturally resilient and require no intervention to withstand a cicada emergence. Established trees with trunk diameters exceeding two inches can easily tolerate the loss of small branch tips. For these larger trees, the damage is essentially a form of natural pruning that does not affect their long-term health. Intervention is warranted almost exclusively for newly planted trees, those under four years old, and high-value ornamental trees whose branches fall within the cicada’s preferred egg-laying diameter of approximately 3/16 to 1/2 inch.
The clearest visual sign that egg-laying has occurred is a condition known as “flagging.” Flagging appears as brown, wilted, or dead leaves and twigs at the ends of branches because the oviposition slits interrupt the flow of water and nutrients. Homeowners should inspect trees for these longitudinal slits to confirm the tree is actively being targeted. If a vulnerable tree is showing heavy signs of fresh damage, protective action is needed immediately.
Non-Chemical Protective Strategies
The most effective and recommended method for protecting vulnerable trees from cicada damage is the use of physical barriers. This strategy prevents the female cicada from accessing the branches required for egg-laying. Fine-mesh netting, ideally with openings no larger than 1/4 inch, should fully enclose the tree’s canopy. Tulle, a lightweight fabric mesh often used for crafts, is a readily available and functional material for this purpose.
The netting must be installed before the adults emerge, typically when soil temperatures reach 64 degrees Fahrenheit. Drape the material over the entire tree, from the top of the canopy down to the trunk. Securing the netting tightly around the base of the trunk ensures that cicadas cannot crawl up from the ground and bypass the barrier. The barrier should remain in place for the duration of the emergence (four to six weeks) and must be removed once the adult cicadas have died off to prevent girdling or other damage to the tree.
Evaluating Insecticide Use
Chemical control is generally discouraged in residential settings due to its low effectiveness against massive emergences and significant environmental risks. The sheer volume of periodical cicadas means new insects continuously fly in from adjacent areas, quickly replacing any killed by a spray application. Furthermore, insecticides are only effective against adults actively laying eggs and do not prevent damage already caused.
Contact insecticides, such as pyrethroids, offer a quick knockdown effect and may be used in commercial nurseries or on extremely high-value trees, but they require repeated application every few days during the peak egg-laying period. These frequent applications harm beneficial insects, including pollinators and natural predators, and may lead to secondary pest outbreaks like spider mites. Systemic insecticides, applied to the soil, are largely ineffective against adult cicadas because they primarily target root-feeding nymphs, which are not the life stage causing branch damage. For the average homeowner, the environmental cost and minimal return on investment make insecticides an unsuitable option.
Tree Recovery After Cicada Emergence
Once the adult cicadas have died off, attention should shift to helping the tree recover from the wounds caused by oviposition. The most important post-emergence action is the timely pruning of any branches showing “flagging.” Pruning the dead or dying tips back to the nearest healthy lateral branch or bud prevents secondary infections from entering the weakened wood.
Pruning must be done carefully to remove all portions of the branch containing the egg slits. Ensure a clean cut at least six to twelve inches below the visible damage. Removing the damaged wood also prevents cicada nymphs from hatching and dropping to the ground, potentially reducing the population for the next emergence cycle.
Beyond pruning, maintaining the tree’s overall health is crucial for recovery. This includes ensuring proper watering, especially during dry periods, and applying mulch to conserve soil moisture and reduce stress. While the damage may look severe, providing good care allows even heavily-hit young trees to heal and generate new growth.