PESTS OF SWEET POTATO

The sweet potato flea beetle is the most common pest of sweet potatoes in North Carolina. Soil-inhabiting pests lower grades or make potatoes unmarketable and are most economically important. Tough the sweet potato weevil is the most damaging pest of this crop nationwide, it has only recently been founding in North Carolina and is a potential problem here.

Many pests attack sweet potato foliage. In the plant bed, this injury can be threatening. In the field, however, there is little evidence that foliar pests do enough damage to warrant treatment.

KEY TO SWEET POTATO PESTS

A. Pests that feed on aboveground plant parts

  1. Caterpillars with three pairs of legs and five pairs of prolegs

    1. Southern armyworm - Gray or nearly black larva up to 36 mm long with greenish or pinkish tint; lightly colored longitudinal stripes and paired triangular spots down back; pale yellow head capsule with bright reddish-brown markings (Fig. 208A,B); feeds on leaves, tender stems, and tips of branches; congregates round bases of plants during hot portion of the day

    2. Sweetpotato hornworm - First instar: white with black anal horn; later instars: green or brown with black angled marks down each side and black anal horn; body up to 90 mm long; head green or brown with black stripes (Fig. 209); defoliates plants; often hides near base of plant under large leaves

    3. Yellowstriped armyworm - Pale gray to black caterpillar up to 45 mm long with yellow-orange stripes along each side and paired triangular spots on the back of most segments (Fig. 210A); head capsule brown with black markings and a white inverted V (Fig. 210B); feeds much like southern armyworm

  2. Potato leafhopper - Spinkle-shaped pest up to 3 mm long; green body with yellowish to dark green spots (Fig. 211); usually jumps instead of flies; extracts sap from underside of leaf causing yellowing of leaf tips and margins; one of several leafhopper species attacking sweet potato

  3. Small fruit or vinegar fly - Small yellowish fly about 3 mm long with red eyes (Fig. 212); hovers around overripe or decaying produce; often found with small creamy maggots in the cracks of sweet potatoes

  4. Sweet potato flea beetle - Black oval beetle about 1.6 mm long with a bronze tinge, reddish-yellow legs, and deeply ridged wing covers (Fig. 213); leaves narrow channels or grooves in upper surface of leaves; injured areas turn brown and die

  5. Sweetpotato weevil adult and larva - Ant-like snout beetles are about 6 mm long with dark blue wing covers and red-orange legs and thorax (Fig. 217A); fat, legless, dirty white larvae are about 9 mm long with pale brown head (Fig. 217B); beetle makes small holes over surface of sweet potatoes particularly at stem end; larva tunnels inside filling tunnels with frass and causing sweet potatoes to turn bitter. Feed on foliage, but primarily on underground plant parts

  6. Tortoise beetle adult and larva - Oblong-oval, basically gold-colored beetle, up to 8 mm long, with various black or red markings on its flattened, shell-like body (Fig. 214A); larva with dull yellow, brown, or green body up to 12 mm long with black head, legs, spots, and spines; long spines on larval abdomen hold excrement (Fig. 214B); adult and larva chew leaves leaving them riddled with holes

  7. Spider mites - Tiny pale or reddish spider-like arthropods feed on the bottom of leaves (Fig. 215); heavily infested plants become yellowish, bronzed or burned in appearance

B. Pests that feed on belowground plant parts

  1. Sweetpotato flea beetle larva - Slender, white, cylindrical larva, up to 5 mm long, with 3 pairs of legs near head (Fig. 216); etches shallow, winding tunnels on surface of sweet potato roots and sweet potatoes; tunnels darken, split, and leave scars

  2. Sweetpotato weevil adult and larva - Ant-like snout beetles are about 6 mm long with dark blue wing covers and red-orange legs and thorax (Fig. 217A); fat, legless, dirty white larvae are about 9 mm long with pale brown head (Fig. 217B); beetle makes small holes over surface of sweet potatoes particularly at stem end; larva tunnels inside filling tunnels with frass and causing sweet potatoes to turn bitter

  3. White grub (spring rose beetle) - Dirty white grub up to 25 mm long with brown head and 3 pairs of legs near head (Fig. 218); leaves large, shallow feeding scars on sweet potatoes

  4. Wireworms - Several species of slender, wire-like larvae with 3 pairs of short legs near the head and a pair of prolegs at the tip of the abdomen; large shallow cavities in sweet potatoes - evidence of early injury; deep ragged holes - later injury

    1. Melanotus communis - Yellowish-brown with darker head; body up to 25 mm long; last abdominal segment with scalloped edges (Fig.219A )

    2. Southern potato wireworm - Cream colored or yellowish-gray with reddish-orange head; body up to 17 mm long; closed oval notch in last abdominal segment (Fig. 219B)

    3. Tobacco wireworm - White with brown head; body up to 19 mm long; V-shaped notch in last abdominal segment (Fig. 219C)

  5. Whitefringed beetle larvae - These yellowish-white legless, 12-segmented grubs, up to 13 mm in length, have small, pale heads. They gouge on roots, reducing marketable sweetpotatoes

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