Description:
The cowpea aphid is easily distinguished from other aphids (pea picture and blue picture alfalfa aphids) in alfalfa largely because it is the only black aphid found infesting the crop. In general, it is a relatively small aphid, less than 2 mm long. Apterous and winged adults are usually shiny black while the smaller nymphs may appear to be a dull gray to black. The first half of the antennae is white, and the legs are usually a creamy white color with blackish tips.
Damage:
In alfalfa, these aphids obviously feed on young terminal growth, but can be found infesting leaves, blooms, and stems. In general, legumes can be seriously damaged, either by direct insect feeding or by the transmission of virus diseases. During the winter of 1998/1999, populations of cowpea aphid were common in the low desert stunting alfalfa and in some cases, causing serious injury. In California, damage was especially severe in the high desert where dormant alfalfa varieties are grown. When the alfalfa broke dormancy in the spring, plants failed to grow because of heavy aphid populations. High numbers of cowpea aphids can produce a significant amount of honeydew and sooty mold .
Description:
The pea aphid (Acyrthosiphon pisum) and blue alfalfa aphid (Acyrthosiphon kondoi) are very similar in appearance. They are typically 1/6 inch long and green in color. The antennae are used to distinguish between these two aphids. The pea aphid has narrow, dark bands at the tip of each antennal segment, whereas the blue alfalfa aphid has light green segments that gradually darken to the tip. Additionally, the pea aphid is characteristically yellowish green in color with a light brown thorax, shiny in appearance, and can be found over most of the plant. The blue alfalfa aphid is bluish green with a blackish brown thorax (if winged), waxy in appearance, and is typically found on young, tender shoots and terminal leaves of the alfalfa plant
Damage:
Aphids feed in groups, often on the growing tips of plants. They have piercing-sucking mouthparts that extract the plant sap (phloem). Excess plant sap is excreted as a sticky material called honeydew. Severe aphid infestations can retard growth, reduce hay yield, and may even kill alfalfa plants. Damage can also reduce the alfalfa’s feed value. Furthermore, a black fungus called sooty mold that grows readily on the honeydew excreted by aphids reduces palatability of the alfalfa hay. The pea aphid is the least serious pest of this complex, because it does not inject toxin into alfalfa plants as it feeds. Pea aphid damage is usually limited to cupping and curling of the leaves and severe burning of the foliage when populations are large. Blue alfalfa and spotted alfalfa aphid inflict more serious damage because they inject toxins into the plant as they feed. Toxins injected by the blue alfalfa aphid can stunt growth and cause yellowing of the entire plant. Infested plants have smaller leaves and shorter internodes than normal. The spotted alfalfa aphid injects a toxin while feeding on the alfalfa plant that causes vein clearing, yellowing, and severe stunting of plant growth. Susceptible plants can be killed when populations are heavy. Alfalfa that is stressed by lack of water or by cutting is not able to withstand as large an aphid population as healthy unstressed alfalfa.
Description:
The first sign of a potential alfalfa caterpillar (Colias eurytheme) outbreak is the influx of large numbers of yellow or white butterflies in late spring or early summer. The butterfly reaches 1 inch long with a 2 inch wingspan. Its wings are yellow, orange, or white with a black border on the upper surface and are solid white or yellow on the underside. When butterflies are seen flying over a field of tall alfalfa, they have probably just emerged from that field. They will remain to feed on flowers and mate, but the females will move into alfalfa less than 6 inches tall to lay eggs. White 1/ 16 inch long eggs are laid singly, standing on end on the upper leaf surface, and hatch into small ½ inch long, brown larvae with black heads in 3 to 10 days.
The alfalfa caterpillar soon turns green and grows rapidly to 1 ½ inches long in approximately 2 weeks, depending on the temperature. Seven generations occur between May and October. Older, larger caterpillars have a prominent white stripe which runs along each side of the body. The alfalfa caterpillar can be distinguished from the beet armyworm by its hairy or velvety green body surface. Viewed with a hand lens, the beet armyworm has a smooth body. The alfalfa caterpillar pupa hangs from alfalfa stems by silken threads or rests on leaves. The caterpillar overwinters as a pupa which changes from a gray green to yellow color as it transforms into the butterfly that emerges the following spring. The life cycle of the alfalfa caterpillar is closely synchronized with the hay cutting cycle, taking about one cutting cycle to complete. Four to seven generations occur between May and October.
Damage:
Alfalfa caterpillars consume large portions of foliage or entire leaves. Larger larvae are the most destructive. In contrast to beet armyworms, alfalfa caterpillars do not skeletonize leaves and will consume the leaf midrib, nor do they cause flagging in which alfalfa terminals dry up and turn whitish-grey in color. Alfalfa caterpillar feeding damage is most severe when eggs are laid in recently cut fields, and large populations of developing larvae defoliate the crop before it reaches maturity. When infestations occur in half to full grown plants, growers can harvest early to avoid serious damage.
Description:
Beet armyworm (Spodoptera exigua) caterpillars are smooth skinned with few or no hairs on the body, may be olive green to almost black in color down the middle of the back, and have a yellow stripe on each side of the body. They usually have a conspicuous black dot on each side of the second body segment behind the head and just above the second pair of legs, a white colored dot at the center of each spiracle, and reach a length of about one inch. In contrast, the western yellow striped armyworm has a black dot on its first abdominal segment, a brown colored dot at the center of each spiracle, and an inverted “Y” marking that is white to orange in color on the front of its dark brown head. The alfalfa caterpillar can be distinguished from the beet armyworm by its velvety green smooth surface and a single prominent white stripe along each side. The common armyworm, which is occasionally found in corn and sudangrass, differs from the beet armyworm in that it is dark green to light grey with two orange stripes along each side. Additionally, the common armyworm lacks the inverted Y-shaped mark found on the front of the head of the western yellow striped armyworm.
Damages:
Young beet armyworms skeletonize foliage, leaving the veins of leaves largely intact. Heavy feeding and leaf skeletonization on the tips of the stalks by early instars can cause distinct flagging visible from a distance as terminal leaves turn white. Comparatively, the alfalfa caterpillar eats the entire leaf of alfalfa, and although the alfalfa weevil also skeletonizes leaves, it is not present in alfalfa during the summer when armyworm damage occurs.
Early in the season, beet armyworm populations may move to seedling cotton. The caterpillars eat all but the epidermal leaf layer producing a windowed effect. Later in the season, they characteristically bore into the cotton plant terminals and feed on squares, blossoms, and green bolls. Their damage to cotton fruit is recognized by extensive feeding and holes chewed in adjacent bracts and leaves.
Description:
The Egyptian alfalfa weevil (EAW), Hypera brunneipennis (The Egyptian strain of H. postica) is a major winter pest of AZ alfalfa. EAW adults are small (0.25 inch) and gray-brown with ridges on their hardened forewings. They have a distinct, extended snout. EAW may be confused with clover root curculio, a non-economic weevil, which looks similar to but is about two-thirds the size of EAW and has a short, blunt snout. Young EAW larvae are yellow-green with a brown head. They are often difficult to find because they hide in tightly folded young leaves. The older larvae are darker green with a white line down the center of their back and a distinct brown head capsule. Fully-grown larvae are 0.25 inches long. EAW larvae may be confused with syrphid larvae (a valuable natural enemy), which lack a head capsule on their tapered head, or with lepidopteran larvae (summer pests), which have legs and rarely occur simultaneously in the field; EAW is legless.
Damages:
EAW is active December–April. Adults aestivate (summer hibernation) under loose bark or other sheltered place. In late fall or early winter, adults emerge and migrate to alfalfa fields. Females insert eggs into alfalfa stems. Once hatched, the larvae feed on leaves and terminal buds, causing skeletonization, bronzing and stunted growth. Larvae are the most damaging stage. Adult weevils also feed on alfalfa leaflets and stems but generally do not cause significant damage. EAW is most damaging to the second cutting, but may also damage the third.
_3.jpg?sfvrsn=d3cd518d_10)
