Prevent Sweet Potato Weevil From Giving You the Slip

Prevent Sweet Potato Weevil From Giving You the Slip

Sweet potato weevil

The sweet potato weevil is a formidable foe for growers to contend with.
Photo by Bonnie C. Wells

Pest Specs

The sweet potato weevil is considered to be the most serious pest of sweet potato, with losses ranging from 5% to 97%. It occurs in tropical regions worldwide and is found throughout the Southeast U.S. from North Carolina to Texas. It causes damage in the field and in storage crops. The pest is around the whole year and most numerous in the fall and late spring.

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Identification

The adult is striking in appearance. The head is black; the antennae, thorax, and legs orange to reddish brown; and the abdomen and elytra are metallic blue. The snout is long and slightly curved.

Adults are secretive, feeding on the lower surface of leaves, and often go undetected. Adults can fly, but rarely do so.

Heavy infestations may cause yellowing of the vines, but problems are easily overlooked and damage not apparent until tubers are harvested. The main damage to sweet potato is mining of the tubers by larvae. Infested tubers are riddled with cavities and unfit for food. In addition, the damage caused by tunneling permits entry of soilborne pathogens.

Survival and Spread

A complete life cycle requires one to two months and up to eight generations may occur in South Florida. All stages can be found throughout the year if suitable hosts are available.

Eggs are deposited in cavities created by the female in roots or stems. After hatching, the larva burrows directly into the tuber or stem of the plant. The larva is legless, white in color, and displays three instars.

The mature larva creates a small pupal chamber in the tuber or stem. The pupa is similar to the adult in appearance. Initially, it is white, but becomes grayish in color with darker eyes and legs.

The weevil feeds on plants in the morning glory family. Among vegetable crops, only sweet potato is a suitable host. Native weeds can be important hosts.

Florida sweet potato field with weevil trap

Pheromone traps are set up in this field to help growers and researchers monitor sweet potato weevil activity.
Photo by Bonnie C. Wells

Management Methods

Sanitation is important for sweet potato weevil management. Discarded tubers and unharvested tubers can support large weevil populations and should be eliminated. Destruction of alternate hosts also is recommended.

Several natural enemies are known. Among predators, ants seem to be most important. Diseases, especially the fungus Beauveria bassiana, can inflict high levels of mortality under conditions of high humidity and high insect density, but field conditions are rarely conducive for control.

Pheromone traps show promise for monitoring of adult population density and might have potential for mating disruption and trapping.

Applications of insecticides are typically applied to the soil at planting to prevent injury to slips. Systemic insecticides are preferred. Due to the long duration of the crop, pre-plant applications are commonly followed by one or more insecticide applications to the plant or soil at mid-season.

Several strains of entomopathogenic nematodes, including Steinernema and Heterorhabditis, penetrate the soil and tubers, killing weevil larvae. At least in the soils of South Florida, the infective nematodes are persistent, remaining active for up to four months. In some cases, nematodes are more effective than insecticides at reducing damage.

Consult UF/IFAS recommendations for currently labeled insecticides for sweet potato weevil control in Florida.