Sweetpotato Weevil

R. A. Roberts.

The sweetpotato weevil occurs in parts of Alabama, Florida, Georgia, Louisiana, Mississippi, South Carolina, and Texas. Very likely it is of Asiatic origin. Our first record of it in this country was in 1875 in Louisiana.

The adult weevil is about one-fourth inch long and resembles a large ant. The head, snout, and wing covers are a dark, metallic blue. The prothorax and legs are reddish orange. The adult has well-developed wings and is capable of limited flight. The small eggs are yellowish white. The larvae are white, legless grubs about three-eighths inch long. The pupa is white and somewhat smaller.

The adult places its eggs in small cavities, which it punctures in the stem of the plant near the ground or directly into the sweetpotato. The eggs hatch in about a week. Then the grubs feed in the vine or potato for 2 or 3 weeks. The pupa is formed within the vine or stem or within the potato and this stage lasts a week or longer, after which the adult emerges. The adult may live for several months. The time required for the development of all the stages varies according to the season or the conditions under which potatoes are stored. In a year six to eight generations may be produced.

The adult weevils damage sweetpotato plants by feeding on leaves, vines, and roots and by pitting the potatoes with feeding and egg-deposition cavities. The larvae, which feed in both the vines and the potatoes, do the most injury. Men of the Louisiana State University and the State Extension Service estimated the loss to the commercial crop of sweetpotatoes in Louisiana in 1946 to be nearly 3 million dollars. In 1950 this loss was reduced to 250 thousand dollars. Growers of sweetpotato plants in Georgia in 1945 had losses of about 1 million dollars. Eradication measures have prevented subsequent severe losses to these plant growers. The weevils even in light infestations can cause great damage because they can impart a bitter taste to the sweetpotato after only slight feeding and thus destroy much of its value.

CONTROL OR ERADICATION depends on strict adherence to the recommended procedures and constant care by the grower to prevent reinfestation. The principle of control is to deny the weevil the host plants in which to feed. Strict sanitary, cultural, and storage practices are required. The use of insecticides to destroy and prevent weevil populations helps.

In areas of noncommercial sweet-potato production where weevil infestations are light and where non-planting zones can be established, the weevil can be eradicated if it is deprived of its food for about a year. If weevils are found on a property no sweetpotatoes should be bedded, grown, or stored within a zone extending 1/2 to 1 mile from the point of infestation. The procedure has resulted in eradication of the weevil when practiced on a single farm or on a community basis.

When a nonplanting zone is established, all remaining sweetpotatoes in the zone should be disposed of by February 1 (or earlier, if possible) by dehydration, feeding to livestock, or burning. The place where the potatoes were stored should be thoroughly cleaned and the debris burned. Thereupon the storages should be dusted with a 10 percent DDT dust at the rate of 1 pound to each 1,600 square feet of surface area. A spray may be used, consisting of 8 pounds of 50 percent DDT wettable powder to 100 gallons of water, applied 1.5 gallons to each 1,000 square feet. The treatment will eliminate any remaining weevils.

Potatoes still in the ground when the infestation is found should be removed from the premises at harvest time and disposed of in such a way as to prevent infestation of other properties. None should be stored within the restricted zone. Before the potatoes are plowed out, vines should be cut off at the surface of the ground and burned when dry. All potato roots, crowns, small sweetpotatoes, and scraps in the field should be destroyed by cultivation and by grazing livestock on the field after harvest. The old potato field should be plowed at least twice during the winter in order to expose any roots or potatoes missed. No volunteer sweetpotato plants should be permitted in the field or elsewhere on the property. These may be grubbed out or destroyed with a weed killer.

Sweetpotato weevil.

After the end of the 1 year non-planting period, potatoes may be grown again. In the new plantings in zones that have been out of production, it is important that weevil-free planting stock be used.