Are 17-Year Periodical Cicadas Harmful to Agricultural Crops?

Periodical cicadas, particularly those emerging every 17 years, have fascinated scientists, farmers, and nature enthusiasts for centuries. Their synchronized mass emergence is one of the most spectacular natural phenomena in the insect world. However, for those involved in agriculture, the question often arises: Are 17-year periodical cicadas harmful to agricultural crops? In this article, we will explore the biology and behavior of 17-year periodical cicadas, their impact on crops, and what farmers can do to mitigate any potential damage.

Understanding 17-Year Periodical Cicadas

What Are Periodical Cicadas?

Periodical cicadas belong to the genus Magicicada. Unlike annual cicadas that appear every year, periodical cicadas have a unique life cycle that spans either 13 or 17 years underground as nymphs. After this long developmental period, they emerge en masse as adults for a few weeks to mate and lay eggs before dying off.

The 17-year periodical cicadas are native primarily to the eastern United States and are divided into several distinct broods. Each brood emerges in a specific geographical area during a particular year, which means that massive swarms can appear suddenly but only occur every 17 years in each location.

Life Cycle Highlights

Nymph Stage: The cicada nymphs live underground for 17 years, feeding on xylem fluids from tree roots.
Emergence: When ready, they tunnel to the surface en masse, typically during late spring.
Adult Stage: Adults live above ground for about four to six weeks.

Reproduction: Females lay eggs in slits they cut in small branches or twigs of trees.
Egg Hatching: Nymphs hatch from eggs and drop to the ground to burrow and begin their long development cycle again.

This life cycle is crucial when considering how cicadas interact with agricultural crops.

The Relationship Between Cicadas and Agriculture

Feeding Behavior and Crop Impact

The primary concern with cicadas in agricultural settings relates to their feeding and egg-laying behaviors:

Feeding: Both nymphs and adults feed on plant fluids. Nymphs extract sap from roots underground, while adults feed on xylem fluids from twigs and branches. However, cicadas generally do not feed on crop fruits or leaves directly.

Egg-Laying (Oviposition): Female cicadas use their ovipositors to cut slits into small diameter branches (often less than half an inch thick) where they deposit eggs. This can cause “flagging,” where affected twigs wilt and die.

Which Crops Are at Risk?

Cicada damage is generally more pronounced in woody plants rather than herbaceous crops like vegetables or grains. The following types of crops are more vulnerable:

Orchard trees: Apples, peaches, cherries, pears, plums.
Vineyards: Grapevines may also experience damage.
Nursery stock: Young trees and ornamental shrubs.

Herbaceous crops such as corn, wheat, soybeans, or vegetables usually escape damage since cicadas do not feed or lay eggs on herbaceous stems.

Extent of Damage Caused by Periodical Cicadas

Root Feeding: Minimal Agricultural Impact

Although nymphs feed underground on roots for 17 years, this feeding is generally minimal and does not significantly harm mature plants or crops. The root systems of established trees and crops are extensive enough to tolerate the nymph feeding without visible stress.

Egg-Laying Damage: The Main Concern

The most notable damage occurs when females cut slits into small branches for egg laying:

This results in twig dieback or “flagging.”
Young trees or nursery stock are particularly sensitive because their smaller branches are more abundant relative to mature trees.
In orchards with young trees (less than five years old), heavy egg-laying can lead to branch breakage or reduced growth.

Mature orchard trees generally withstand the damage with minor loss of some twigs but no significant decrease in yield.

Impact on Crop Yields

Studies show that:

Yield losses due to periodic cicada emergence are usually negligible for mature fruit trees.

Large orchards rarely experience economic loss severe enough to warrant control measures unless trees are very young or under stress.
Herbaceous crop yields remain unaffected due to lack of feeding activity on these plants.

Case Studies and Scientific Research

Several research projects across affected regions provide valuable insights:

A study by the USDA found that fruit tree saplings suffered some branch dieback but recovered after emergence events without significant yield loss.
Research conducted by state agricultural extensions often reports that long-term economic damage from 17-year cicadas is minimal if proper management and monitoring are practiced.
In contrast, some nursery operators reported higher mortality rates in young nursery stock during heavy emergence years but were able to manage losses by protective netting or other means.

Managing Cicada Impact in Agriculture

While periodical cicadas are not major agricultural pests, preventive steps can help reduce potential damage during emergence years.

Timing and Monitoring

Farmers should:

Know when local broods are expected based on historical emergence schedules.

Monitor young orchard blocks closely during emergence years (late spring).
Use branch inspections to identify early signs of egg-laying damage.

Protective Measures

For vulnerable crops like young orchard trees:

Physical barriers: Netting or row covers can prevent adult cicadas from reaching branches during peak emergence.
Pruning: Removing damaged twigs shortly after hatching can help reduce stress on trees.
Avoid unnecessary irrigation stress which might weaken trees’ ability to recover from flagging.

Chemical Control Options

Chemical control is generally discouraged because:

Cicada emergence is brief (a few weeks).
Broad-spectrum insecticides may harm beneficial insects including pollinators.

However, targeted insecticide sprays might be considered for very valuable nursery stock under heavy infestation after consulting local extension recommendations.

Ecological Importance of Periodical Cicadas

It’s worth noting that periodical cicadas play an important ecological role:

They aerate soil through their burrowing activity as nymphs.

Serve as a food source for numerous predators such as birds, mammals, reptiles, and other insects.
Provide nutrient pulses when large numbers die off simultaneously.

Thus, their presence contributes positively to ecosystem health despite occasional minor impacts on agriculture.

Conclusion

In summary:

17-year periodical cicadas are not significantly harmful to most agricultural crops.
Herbaceous crops like grains and vegetables remain largely unaffected.

Woody crops such as orchard trees may experience localized branch dieback due to cicada egg-laying but usually recover without major yield loss.
Young orchard plantings and nursery stock face greater risk but can be managed with physical barriers and good cultural practices.

Farmers should remain informed about local emergence schedules and monitor vulnerable crops during peak periods. By understanding the biology of these fascinating insects, growers can minimize any negative impacts while appreciating their unique role within natural ecosystems.

Ultimately, while momentarily disruptive during emergence years, 17-year periodical cicadas do not pose a lasting threat to agricultural productivity.