Sweet Potato Weevil Control: How to Identify, Prevent and Get Rid of Sweet Potato Weevils

Cylas formicarius, the scientific name of sweet potato weevil, is the most common pest that affects sweet potato. They demonstrate concealed feeding habits, which makes it quite difficult to control their population. Their infestation normally causes 20 to 50% of damage in most commercial plantations. When the infestation is heavy, it can damage up to 100% of the crops. To prevent such from happening, it is vital to learn the fundamentals of how to get rid of sweet potato weevils.

The adult sweet potato weevil has a striking color and form, which makes it easier to notice as against the younger stages. It has a thin and elongated head, legs, and body, which makes it look like an ant. It is shiny and smooth, but when you look closely, you will notice that they grow short hairs. Their color will be different on the various parts of the body. The abdomen is metallic blue, the head is black, and the legs, thorax, and antenna can range from orange to reddish brown.

The larvae, meanwhile, will have an average length of 8 millimeters. They do not have legs and they have sub-conical abdomen. When in the form of eggs, the length is .65 millimeter and the width is .46 millimeter on average. They are soft and translucent white, which turns to cream when they are about to hatch.

Sweet Potato Weevil

A sweet potato weevil on a leaf

Sweet Potato Weevil’s Habitat

The sweet potato weevil has a global distribution, which means that regardless of where in the world you are from, this pest can be a problem. The adults are often feeding on the lower surface of the leaf. Most of them are active during the night, which makes it more difficult to detect their presence. It is most destructive during the larval stage. At such point, it feeds on the mature stems and storage roots of the host plant. The eggs, on the other hand, are laid on the juncture of the stem of the host plant, as well as its roots.

Identifying Sweet Potato Weevil’s Damage

Plants Affected

From the name of the pest, it is pretty much obvious that the main host is sweet potato. Most of its host plants are from the Convolvulaceae family, which includes great bindweed, cupid’s flower, and a variety of species of morning glory.


Watch out for the following symptoms, which can be indicative of the presence and infestation of sweet potato weevil:

  • The leaves will show signs of external feeding. The edges and the surface will appear as if it has been chewed. There will be small holes. Eventually, the leaves will wilt, dry, or discolor. This is because the pest affects the ability to the leaf to photosynthesize, and hence, making it short of the nutrients that are necessary for survival.
  • External feeding will also be apparent on the roots of the host plant. It will lead to the production of terpenes, which will give the crop an unpleasant odor and taste, making it unmarketable.
  • The stems will also show visible signs of damage, including feeding, rotting, and distortion. In some cases, it will be dry and weak, making it unable to support the host plant.

Results of Infestation

In case of severe infestation, it can lead to up to 100% of losses of host crop, making it a serious concern amongst many commercial growers. High weevil density can cause the plant to die and will negatively affect the crops. This deprives the host of the nutrients that are necessary for survival. The infestation on the plant’s storage roots will make it unfit for human consumption. Hence, it will probably result in significant economic losses.

Damaged Potato

Evidence of pests damaging the crop

How to Get Rid of Potato Weevil

Natural and Organic Solutions

For effective and safe elimination of sweet potato weevil, the following are some of the best solutions you might want to consider:

  • Among others, mulching is one of the solutions that can be promising, which does not only control current population, but will also prevent their appearance in the future. It aids in the prevention of cracks and in the improvement of the moisture of the soil. It also makes the ground more attractive for natural enemies.
  • Be sure as well to destroy crop residues that are in the garden or plantation. This will kill the eggs even before they hatch or eliminate the larvae before they spread infestation to the healthy plants.
  • You will also benefit from using biological controls in the eradication of sweet potato weevils. Among others, entomopathogenic nematode will be effective as a natural enemy. They are roundworms with a soft body and can naturally occur on the soil. They help in biological suppression by killing the larvae of the pest.
  • Another simple solution that you should not ignore is to sprinkle ash on the top of the sweet potato plant. This provides a protective barrier and will kill the insects that get in contact with the ash.
  • It is also a good idea to use sex pheromone trap. Sex pheromone is a chemical that adult sweet potato weevils release to attract males. There are commercial products that mimic its odor. It will also be useful in monitoring the presence of the pest, and hence, you will know where to concentrate.
  • Beauveria Bassiana, a fungal pathogen, is also an effective solution for the control of sweet potato weevil. It will be deadly for weevils and other pests, but will not be toxic to humans and beneficial insects. It can be available in the form of a spray, or in some instances, it is one of the main components of a sex pheromone trap.

Chemical Solutions

Chemical insecticides also present a promising solution, although there are some who stay away from it. It has a bad reputation because of its toxicity, making it bring more harm than good. It kills not only sweet potato weevils, but even beneficial insects and natural predators. Some of the active ingredients for the chemical treatment of this pest include Diazinon and Carbofuran. To be specific, some of the products that contain these active compounds include Basudin, Spectracide, Furadan, Furacarb, Knox Out and Yaltox.

How to Prevent Sweet Potato Weevil

Crop rotation and inter-cropping are two of the preventive measures that can deliver a high level of effectiveness. It will be good to grow the sweet potatoes only once after every five years. Also, as much as possible, do not plant within the same location in a period of two years.

Field sanitation is another prevention method that will work. Get rid of infested vine and decaying vegetation within the plantation. See to it that it is free from leaf litter.

Proper timing of planting and harvest will also be essential. As much as possible, do this when the pest is not that active, which is commonly during the dry months.

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