PESTS OF POTATO

Irish potatoes re attacked by most of the insects which infest closely related solanaceous plants like tomato, eggplant, and pepper. However, since potatoes are grown for their edible tubers, they must receive greater protection from soil-inhabiting pests. Wireworms, tuberworms, white grubs, and vegetable weevils are pests for which growers should watch.

KEY TO POTATO PESTS

A. Pests that feed externally on the upper plant

  1. Chewing pests that make holes in leaves

    1. Blister beetles - Several species of slender, elongate beetles up to 19 mm long; have prominent heads; bodies variously colored but usually black, black with yellow margins, or black and yellow striped (Fig. 171A to C); stringy black excrement on heavily infested plants; foliage ragged; plants sometimes stunted

    2. Colorado potato beetle - Yellowish-brown, oval, convex beetle up to 14 mm long with 5 black longitudinal stripes on each wing cover and several black spots on pronotum (area behind the head) (Fig. 172); feeds on leaves and terminal growth

    3. Flea beetles - Various species of tiny, darkly colored beetles 2.5 to 4.5 mm long; solid-color body or dark with pale yellow stripe on each wing cover (Fig.173); tiny round holes in foliage

  2. Sap-sucking pests that cause discoloration, deformation, or abscission

    1. Aphids - Soft-bodied, pear-shaped insects with a pair of dark cornicles and a cauda protruding from the abdomen; may be winged or wingless - wingless forms most common; feed in colonies; cause discoloration or mottling of the foliage; often transmit virus diseases; excrete honeydew on which sooty mold grows

      1. Green peach aphid - Pale yellow to green, wingless adult up to 2.4 mm long; winged adult with dark dorsal blotch on yellowish-green abdomen; cornicles over twice as long as cauda and slightly swollen toward tip; yellow-green nymphs with 3 dark lines on abdomen (Fig. 174A to C)

      2. Potato aphid - Adult and nymph both solid pink, green and pink mottled, or light green with dark stripe; adult up to 3.5 mm long; long slender cornicles about twice as long as cauda (Fig. 175)

    2. Potato leafhopper - Spindle-shaped pest, up to 3 mm long; green body with yellowish to dark green spots (Fig. 176); usually jumps instead of flies; extracts sap from underside of leaf causing leaf to crinkle and curl upward; also causes yellowing of leaf tips and margins (hopperburn)

B. Pests that feed on underground plant parts, bore into stems, or mine in leaves and petioles

  1. European corn borer - Cream to light pink caterpillar with reddish-brown to black head; body up to 26 mm long with several rows of dark spots; has 3 pairs of legs near head and 5 pairs of prolegs (Fig. 177); bores into stem; tangled frass and silk near entrance hole; stem may break, plant may yellow or wilt readily

  2. Potato tuberworm - Creamy white (young) or green to pink (mature) caterpillar up to 19 mm long with dark brown head; 3 pairs of legs near head and 5 pairs of prolegs (Fig. 178); mines in older lower leaves causing grayish papery blotches; tunnels in exposed tubers or those close to soil surface, filling tunnels with excrement; entrance holes usually near the eyes and surrounded by a pink coloration

  3. Vegetable weevil and larva - Adult - dull grayish-brown weevil, about 6.4 mm long, with short, stout snout and light V-shaped mark on wing covers (Fig. 179A); larva - pale green, legless, up to 10 mm long, with dark mottled head (Fig. 179B); both feed at night making large open holes in surface of potatoes. Feeds primarily at night on underground plant parts, but sometimes consumes buds and foliage

  4. White grubs - Several species of creamy white grubs with a distinct brown head capsule, three pairs of legs near the head, and slightly enlarged abdomen; body C-shaped and up to 50 mm long (Fig. 180); sever roots and stems of potatoes; leave large, shallow circular holes in tubers

  5. Wireworms - Several species of slender, wire-like larvae with three 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. 181A)

    2. Southern potato wireworm - Cream colored or yellowish-gray with reddish-orange head; body up to 17 mm long; oval notch in last abdominal segment (Fig. 181B)

    3. Tobacco wireworm - White with brown head; body up to 19 mm long; V-shaped notch in last abdominal segment (Fig. 181C)

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