Signs of 17-Year Periodical Cicada Damage on Trees and Shrubs

Periodical cicadas, particularly the 17-year variety, are fascinating yet sometimes destructive insects. Emerging en masse every 17 years, these cicadas create a natural spectacle but can also cause noticeable damage to trees and shrubs. Understanding the signs of 17-year periodical cicada damage is essential for homeowners, gardeners, and arborists alike to mitigate harm and protect valuable plants.

What Are 17-Year Periodical Cicadas?

Before diving into damage signs, it’s important to know what 17-year periodical cicadas are. These insects belong to the genus Magicicada and have an extraordinary life cycle that lasts 17 years underground. After this long subterranean development phase, they emerge synchronously in staggering numbers during late spring to early summer.

Unlike annual cicadas, which appear every year in smaller quantities, periodical cicadas’ synchronized mass emergence overwhelms predators and ensures successful reproduction. However, their activity during this brief surface period can lead to physical damage on woody plants.

Cicada Life Cycle and Interaction with Plants

Periodical cicadas spend most of their lives as nymphs feeding on xylem fluids from tree roots underground. When mature, nymphs tunnel out of the soil and climb on nearby vegetation to molt into adults. Adult males then sing loudly to attract females.

Female cicadas lay eggs by cutting slits or “oviposition wounds” into small branches or twigs of trees and shrubs. This process is crucial for their reproductive cycle but often results in visible damage.

Common Signs of 17-Year Periodical Cicada Damage

1. Flagging of Twigs and Small Branches

One of the most obvious signs of cicada damage is “flagging,” where newly laid eggs cause dieback of small branches and twigs. The female’s egg-laying cuts disrupt the plant’s vascular tissues, leading affected parts to brown and wither.

• Appearance: Twigs look dry, brittle, and brown from the tip back toward the main branch.
• Location: Usually found on smaller branches between one-quarter inch and one-half inch in diameter.
• Timing: Appears within weeks after cicadas have laid eggs during late spring or early summer.

2. Egg Scars or Slits on Branch Bark

Female cicadas use a sharp ovipositor to make slits in the bark for egg deposition. These slits appear as small vertical cuts or scars on young branches and twigs.

• Appearance: Parallel rows or clusters of tiny cuts approximately 1/4 inch long.
• Affected Plants: Young trees or shrubs with thin bark are more vulnerable; mature hardwoods can also show these scars but usually suffer less damage.

3. Reduced Leaf Growth and Premature Leaf Drop

The physical stress from egg-laying wounds may cause affected branches to produce fewer leaves or shed leaves earlier than usual.

• Symptoms: Sparse foliage or yellowing leaves on flagged branches.
• Impact: Although usually not fatal, this reduced leaf health can weaken overall plant vigor temporarily.

4. Increased Vulnerability to Secondary Pests and Diseases

Open wounds from cicada egg-laying expose trees and shrubs to pathogens such as fungi and bacteria. These secondary infections can exacerbate damage, especially if environmental conditions favor disease development.

• Signs: Cankers, oozing sap, fungal fruiting bodies near oviposition sites.
• Concern: Secondary infections may delay recovery or cause branch dieback beyond initial flagging.

5. Physical Presence of Cicada Nymph Shells

While not a direct sign of damage, finding empty exoskeletons (molted shells) clinging to tree trunks or twigs signals recent cicada emergence nearby.

• Appearance: Light brown, hollow shells stuck firmly on bark surfaces.
• Implication: Indicates potential for egg-laying damage if adults remain active in the area.

Which Trees and Shrubs Are Most Affected?

Periodical cicadas prefer certain hosts when laying eggs. Typically, they choose deciduous hardwood trees with softer wood where oviposition is easier. Commonly affected species include:

• Maples (Acer spp.)
• Oaks (Quercus spp.)
• Dogwoods (Cornus spp.)
• Birches (Betula spp.)
• Willows (Salix spp.)
• Ash (Fraxinus spp.)
• Fruit trees like cherries (Prunus spp.) and plums

Shrubs with slender stems may also sustain some egg-laying damage if located near tree hosts.

Long-Term Impact on Trees and Shrubs

For mature healthy trees, cicada damage is usually superficial and temporary. Most recover fully after a growing season by producing new shoots from undamaged buds below flagged areas. However:

• Young saplings or stressed plants might suffer more serious consequences due to loss of significant branch material.
• Repeated infestations can weaken trees over time.
• Combined with drought or other environmental stressors, cicada damage may lead to decline or mortality in vulnerable plants.

Prevention and Management Strategies

Though you cannot stop periodical cicadas from emerging every 17 years, you can take steps to protect valuable trees and shrubs:

Physical Barriers

Use fine netting with mesh sizes smaller than adult cicadas (around 1/8 inch) to cover smaller trees during peak emergence periods. This prevents females from reaching branches to lay eggs.

Pruning

Remove flagged branches promptly after egg-laying is detected but before nymphs hatch (usually late summer). Pruning limits secondary infections and encourages healthy regrowth.

Avoid Planting Vulnerable Species Near Known Brood Areas

If possible, avoid planting sensitive young trees in regions where 17-year periodical cicadas are expected to emerge soon.

Maintain Tree Health

Healthy trees withstand insect stress better. Proper watering, mulching, fertilization, and pest control improve resilience against cicada damage effects.

When Is Cicada Damage Most Likely?

Emergence events are predictable due to the rigid life cycle but localized depending on broods, groups of periodical cicadas that appear in specific geographic areas every 17 years. The last major emergences occurred in:

• Brood X (2021) across parts of the eastern U.S.
• Other broods emerging at different years regionally.

During these years, expect increased reports of twig flagging and egg scars in affected zones.

Conclusion

The spectacular mass emergence of 17-year periodical cicadas brings brief noise and activity that can leave behind distinct signs of damage on trees and shrubs. By recognizing symptoms such as twig flagging, egg slits in bark, premature leaf drop, and nymph shell presence, gardeners and arborists can better assess injury severity.

Although mature healthy plants generally recover well post-cicada outbreaks, young or stressed vegetation may require targeted care including protective barriers or pruning. With proper understanding and management techniques, it is possible to reduce long-term harm while appreciating these remarkable insects’ unique role in ecosystems.

Understanding the lifecycle timing helps prepare for each emergence cycle, turning a potentially damaging event into an opportunity for education about nature’s intriguing rhythms.