Do 17-Year Periodical Cicadas Damage Trees and Gardens?

Periodical cicadas are one of nature’s most fascinating phenomena, especially the 17-year periodical cicadas that emerge en masse in specific regions of the United States. Their synchronized appearance every 17 years has intrigued scientists, gardeners, and homeowners alike. But beyond their striking presence and loud chorus, a common question arises: Do 17-year periodical cicadas damage trees and gardens? In this article, we will explore the biology of these cicadas, their life cycle, how they interact with plants, and the real impact they have on trees and gardens.

Understanding 17-Year Periodical Cicadas

Periodical cicadas belong to the genus Magicicada and are known for their extraordinary long developmental cycles. Among these, the 17-year cicadas are particularly famous as they spend nearly two decades underground as nymphs before emerging simultaneously in large numbers.

Life Cycle Overview

• Nymph Stage: Periodical cicadas spend approximately 17 years underground feeding on xylem fluids from tree roots.
• Emergence: After 17 years, the nymphs emerge from the ground in massive groups, usually during late spring or early summer.
• Adult Stage: Once above ground, cicadas molt into adults, mate, and females lay eggs in tree branches.
• Egg Hatching: The eggs hatch within six to ten weeks; the young nymphs fall to the soil and burrow underground to begin the cycle anew.

This long life cycle is coupled with a synchronized emergence that helps overwhelm predators—a phenomenon called predator satiation.

How Do Cicadas Interact with Trees?

The interaction between periodical cicadas and trees happens mainly in two ways: feeding by nymphs on roots and egg-laying by females on branches.

Nymph Feeding

For most of their underground life, cicada nymphs feed on sap from tree roots using specialized mouthparts. While this feeding might sound harmful, it is generally considered to be harmless or only mildly stressful to healthy trees because:

• Most trees have extensive root systems that can tolerate moderate sap loss.
• Cicada nymphs feed at relatively low intensities compared to other root-feeding insects.

Therefore, root feeding by cicada nymphs rarely causes significant damage or long-term health issues for mature trees.

Egg-Laying Damage

The primary source of concern for gardeners and arborists comes from the egg-laying behavior of adult female cicadas. Females use a saw-like ovipositor to cut small slits into twigs and branches where they deposit their eggs. This process can lead to:

• Flagging: The dying or wilting of branch tips where eggs were laid.
• Twig Dieback: In severe cases, multiple egg scars can cause substantial twig loss.
• Stress on Young Trees: Smaller or younger trees with thinner branches may be more vulnerable to damage.

While this flagging can cause cosmetic damage and reduce fruit or flower production temporarily, it typically doesn’t kill mature healthy trees outright.

Impact on Gardens and Ornamental Plants

Gardens often feature a variety of plants including shrubs, fruit trees, ornamental trees, perennials, and annual flowers. Understanding how 17-year periodical cicadas affect different garden plants is crucial for managing expectations during an emergence.

Trees

• Mature Trees: Large shade trees like oaks, maples, hickories, and others tend to tolerate cicada egg-laying quite well. They may lose some twigs but generally recover quickly without lasting harm.
• Young Trees: Newly planted or smaller trees with thin branches are more susceptible to significant twig dieback. This may stunt growth temporarily or weaken structural integrity if many branches are affected.

Fruit Trees

Fruit trees such as apples, peaches, cherries, and plums can experience twig dieback during cicada emergences. This may result in:

• Reduced fruit yields for the current season due to loss of fruiting wood.
• Possible entry points for fungal infections through egg slits if secondary pathogens invade.

However, like shade trees, healthy fruit trees usually bounce back after a season or two without lasting damage.

Shrubs and Smaller Plants

Most shrubs and herbaceous plants are not targeted by periodical cicadas for egg-laying because their stems are either too thin or unsuitable for oviposition. Therefore:

• Shrubs like azaleas, rhododendrons, dogwoods etc., typically experience little to no direct damage.
• Herbaceous plants including perennials and annual flowers are unaffected by cicada feeding or egg-laying behaviors.

Should Gardeners Be Concerned?

The answer depends largely on what kinds of plants you grow and how much value you place on immediate aesthetics versus long-term health. Here are some key considerations:

For Mature Trees

If you have mature shade or fruit trees in your garden:

• Expect some twig dieback but no catastrophic damage.
• Pruning dead tips after emergence can improve appearance but is not essential for tree health.
• Avoid overreacting with insecticides; cicadas aren’t harmful pests requiring chemical control.

For Young Trees

Protecting small or newly planted trees is advisable:

• Use physical barriers like netting during peak emergence times (often 4–6 weeks) to prevent females from laying eggs.
• Delay planting new young trees until after a major emergence if possible.
• Provide extra watering and care post-emergence to help recovery.

For Vegetable Gardens and Flowers

Cicadas pose no threat to vegetables or flowering plants. No special action is needed here.

Managing Cicada Damage: Practical Tips

Though periodical cicadas’ impact is mostly cosmetic rather than lethal to plants, gardeners eager to minimize damage can adopt several strategies:

1. Netting Young Trees: Cover young trees with fine mesh netting starting just before expected emergence dates until adults die off.
2. Pruning Dead Twigs: Remove flagging branches about two months after emergence once egg hatching is complete; this encourages healthy regrowth.
3. Avoid Pesticides: Most insecticides are ineffective against cicadas due to their brief above-ground adult phase and large numbers; plus they disrupt beneficial insect populations.
4. Plant Selection: If planning new plantings before an expected emergence year, consider species less susceptible to twig flagging or delay planting young woody plants.
5. Watering & Fertilization: Maintain optimal tree health through proper watering and fertilizing—healthy trees withstand stress better.

Ecological Benefits of Periodical Cicadas

Before focusing purely on perceived negatives, it’s important to recognize that periodical cicadas contribute positively to ecosystems:

• Their emergence provides critical food for birds, mammals, reptiles, amphibians, and other insects.
• Nutrient cycling improves as dead adults decompose enriching soils.
• Root feeding stimulates new root growth in host trees.
• Their synchronized life cycle maintains natural predator-prey balances without overwhelming tree populations regularly.

Conclusion: Are 17-Year Periodical Cicadas Harmful?

In summary:

• Nymph feeding underground causes minimal harm to mature trees due to low sap removal intensity.
• Egg-laying does cause twig flagging, which primarily affects small branches leading to cosmetic damage and minor stress.
• Mature healthy trees generally recover quickly with no lasting effects.
• Young or newly planted trees need protection during mass emergences through netting or delaying planting.
• Other garden plants like shrubs, vegetables, flowers are largely unaffected.

Ultimately, while 17-year periodical cicadas can be a temporary nuisance causing visible branch damage in certain cases, they do not pose a serious long-term threat to most trees or gardens. Their predictable cycles also allow gardeners time to prepare protective measures if desired. Embracing their natural role in the ecosystem helps balance appreciation of these remarkable insects with practical plant care strategies.