Wireworms: Hidden Pests in Sweet Potato Fields

Written by: Alex Gannon, UF

Introduction

Wireworms are click beetle larvae (Elateridae) that are soil pests affecting sweet potato and potato crops not only in Florida but around the world. There are many different species of click beetle larvae that are usually found 4 to 6 inches deep in the soil. Within these species of click beetles many can be pest while others are beneficial. Species in Florida known for their pest status include Conoderus rudis and Conoderus scissus. A beneficial species of click beetle is Alaus oculatus which are the eyed click beetle that are very common. The larvae are can range in color from white, yellow, orange, and brown. They have many larval stages and can last up to 4 years in the soil. This pest can go dormant in the soil during each larval stage which can cause the assumption that the field will have no damage. Today, research is being conducted for species in different regions on how to prevent extensive damage.

Tobacco wireworm larvae (Conoderus falli) R.J. Reynolds Tobacco Company, www.insectimages.org

Damage

Wireworms tend to aggregate in the soil near the outer edges of the field. Due to this aggregation, most of the damage can be seen on the outer edges of sweet potato fields but that does not mean damage is not present throughout. The larvae will chew round holes resembling that of a pencil tip. Depending on the time of feeding, the sweet potato will heal causing scars or will be ragged and more pronounced if later feeding occurs. This damage will make sweet potato unsuitable to sell in stores so the product will be sold cheaper at a farmers market.

Photo Credit: E. Coleman. Keys.lucidcentral.org

Management

Many of the management practices deal with cultural control due to the toughness to apply insecticides deeper in the soil. Wireworms can burrow lower than the chemical residue that is utilized in the soil. Due to this issue it is a good idea to track the life cycle of the pest. The larvae are usually inactive in the spring and an increased activity is observed beginning of fall and mid-July. It is recommended to remove previous crop residue and deeply plow the field to kill the larvae. Bait traps can easily be made for wireworms to determine what type of damage and if applications of insecticide need to be applied. The link for more management strategies can be found below and how to make the bait traps.

http://www.aces.edu/pubs/docs/A/ANR-1104/ANR-1104.pdf