PESTS OF BEANS AND PEAS

The pests of beans, southern peas, and English peas are a diverse group. Mites and beetles are usually the most common pests of beans. Aphids frequently infest English peas, and stink bugs and leaffooted bugs are nuisances of southern peas. Some aphids transmit virus diseases.

KEY TO PESTS OF BEANS AND PEAS

A. Pests that feed primarily on the foliage

  1. Insects that mine or eat holes in the foliage

    1. Bean leaf beetle - These reddish to yellowish-brown beetles are 5 to 6 mm long and often have three black spots on each wing cover (Fig. 43A). They have black margins and a black triangle on the front portion of the wings. Bean leaf beetles consume mostly young leaves although the outer wall of pods are sometimes attacked when vegetative growth ends.

    2. Mexican bean beetle - Copper red, dome-shaped Mexican bean beetles are 6 to 8.5 mm long; each wing cover has eight small black spots that form three rows across the body when wings are at rest (Fig. 43B). These beetles skeletonize leaves which become lace-like and eventually turn brown from their feeding.

    3. Vegetable leafminer - Colorless to bright yellow, vegetable leafminers are maggots which grow up to 3 mm long (Fig. 44). The head is pointed. These maggots make serpentine mines, slightly enlarged at the new end.

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

    1. Aphids - Aphids are soft-bodied, pear-shaped insects with a pair of dark cornicles (tailpipe-like appendages) and a cauda (tail) protruding from the abdomen; they may be winged or wingless - wingless forms most common (Fig. 45A to D). Aphids feed in colonies and cause discoloration, curling, and deformation of foliage. They often transmit virus diseases, and they excrete honeydew on which sooty mold grows.

      1. Bean aphid - Dark green to black, bean aphids have white appendages. They grow to 2.6 mm, and the cornicles are about the same length as the cauda (Fig. 45A). Nymphs are green; mature nymphs have five to seven pairs of white spots on abdomen.

      2. Cowpea aphid - Cowpea aphids are black with white appendages and up to 2.5 mm long (Fig. 45B). The cornicles are barely longer than the cauda. Nymphs are pale green to gray with a powdery coating.

      3. Melon aphid - Yellow to green, melon aphids have dark cornicles and cauda (Fig. 45C). They feed in colonies and wingless forms are most common.

      4. Potato aphid - Pink, mottled or light green, potato aphids have a dark stripe (Fig. 45D). Adults are up to 3.5 mm long, and the cornicles are slender and about twice as long as the cauda.

        1. Potato leafhopper - Spindle-shaped and up to 3 mm long, potato leafhoppers are green with yellowish to dark green spots (Fig. 46). They usually jump instead of fly when disturbed. Potato leafhoppers extract sap from the undersides of leaves causing them to crinkle and curl downward. Infested plants become yellow or bronzed and dwarfed.

        2. Thrips - Spindle-shaped and 1.2 mm or less in length, thrips are yellow, amber, brown, or black. Adults have two pairs of wings which are fringed and have brown crossbands (Fig. 47 A to C). Immature thrips are white or yellow with red eyes. Thrips are pests during hot, dry weather. They cause whitish flecks or streaks on leaves and blossoms, and they deposit black specks of excrement.

        3. Twospotted spider mite - Tiny (almost microscopic) pale to dark green, twospotted spider mites have two or four darkly colored spots. Adults and nymphs have eight legs (Fig. 48). Larvae have six legs. Females are oval and 0.3 to 0.5 mm long. Males are somewhat diamond shaped. Infested foliage becomes silvery because of pale yellow stipples. Leaves eventually become pale and die. Silken webs are spun on the underside of leaves as the mites feed.

        B. Insects that feed on pods

        1. Corn earworm - Early instars of corn earworms are cream colored or yellowish green with few markings. Later instars are green, reddish or brown with pale longitudinal stripes and scattered black spots (Fig. 49). Corn earworms are moderately hairy and grow to 44 mm long. They have three pairs of legs and five pairs of prolegs. They attack beans in fall and eat holes in pods.

        2. European corn borer - These caterpillars are grayish pink with a dark head and rows of small brown doughnut-shaped spots on the back (Fig. 50). European corn borers grow to about 26 mm long and bore into the pods.
        3. Cowpea curculio adult and larva (Fig. 51 A,B) - Adults are black humpbacked weevils 6 to 7 mm long. Larvae are pale yellow and have brown heads. Larvae are legless and grow 6 to 7 mm long. Curculios leave feeding scars - small holes in pods and peas; larvae feed inside green seeds.

        4. Stink bugs - Adults are green or brown shield-shaped insects up to 19 mm long; nymphs are pale green or green with orange and black markings (Fig. 52 A,B ). Stink bugs pierce buds, pods, and seeds and cause buds to be malformed and plants weakened.

          C. Insects which damage seeds and roots and bore in stems

        1. Bean leaf beetle larva - The whitish larva (up to 10 mm long) are dark at both ends and have three pairs of prolegs near the head (Fig. 53). They are minor pests of bean roots.

        2. Lesser cornstalk borer - These slender, bluish-green caterpillars are up to 19 mm long and have brown rings around the body, three pairs of legs near the head, and five pairs of prolegs on the abdomen (Fig. 54). Young larva bore into stems and sometimes disrupt the growing point.

        3. Limabean vine borer - Gray when young, these caterpillars later become bluish-green and sparsely covered with long yellowish hairs. Linnaean vine borer caterpillars grow up to 25 mm long and have three pairs of legs near the head and five pairs of prolegs on the abdomen (Fig. 55). They move from the leaves into stems, usually near nodes where they cause galls up to 70 mm long and 20 mm around to develop. Short, loose, silky frass tubes are connected to entrance holes.

        4. Seedcorn maggot - White to yellow-white maggots up to 7 mm long (Fig. 56) feed on seed contents causing poor germination and tall spindly seedlings. Seedcorn maggots have no legs. The head is pointed.

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