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  1. Agricultural IPM
  2. Field Crops
  3. Alfalfa
  4. Insects
Alfalfa Insects
Section Shortcuts
Lygus Bug
Cowpea Aphid
Aphid Complex
Alfalfa Caterpillar/Butterfly
Beat Armyworm
Egyptian Alfalfa Weevil
Lygus Bug
Lygus Image Gallery
Lygus Publications

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Cowpea Aphid

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 .

Aphid Image Gallery
Aphid Publications

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Aphid Complex

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.

Aphid Complex
Aphid Image Gallery
Aphid Publications

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Alfalfa Caterpillar/Butterfly

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.

Alfalfa Caterpillar-Butterfly

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Beet Armyworm

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.

Beet Armyworm Image Gallery
Beet Armyworm Publications

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Egyptian Alfalfa Wevil

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.

Coleoptera Curculionidae (Egyptian Weevil?)_3

Weevil Image Gallery
Weevil Publications

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Alfalfa Insect Publications
  • Nov 2015
    Cowpea Aphid in Alfalfa
    Publication (PDF, 248KB)
    Authors: John Palumbo and Barry Tickes
    Recent outbreaks of cowpea aphid in alfalfa are more than a local phenomena. Large populations of cowpea aphids have been reported throughout Arizona. The reason behind these outbreaks are unknown. This article hopes to bring some insight by discussing the cowpea aphid, the damage it causes, and suggestions on controlling it.
  • Jan 2014
    Summer Slump in Alfalfa
    Publication (PDF, 425KB)
    Authors: Mike Ottman and Ayman Mostafa
    “Summer slump” is a decline in growth of alfalfa usually beginning in July in areas where maximum daily temperature exceeds 100 °F, such as the low elevation deserts of Southwestern U.S. This article discusses some of the causes behind this and potential impacts.
  • Jul 2013
    Stink bugs in cotton, alfalfa, and other Arizona crops
    Publication (PDF, 510KB)
    Authors: Peter Ellsworth and Lydia Brown
    In Arizona, we have many species of stink bugs; the species pictured above are encountered in cotton, alfalfa, and other crops. Some are occasional or potential pests of cotton. In the article the Brown Stink Bug (BSB), Eushistus servus, is discussed which has been a pest of cotton, especially in the past few years.
  • Feb 2013
    Insect Management on Desert Produce Crops: Western Flower Thrips 2013
    Publication (PDF, 306KB)
    Authors: John C. Palumbo
    Western flower thrips are major pests to lettuces, cabbage, and spinach because of the damage they cause to these plants. This article describes their development, Economic Damage, and suggestions for their management.
  • Apr 2008
    Alfalfa Weed Control in the Low Deserts of Arizona
    Publication (PDF, 443KB)
    Authors: Barry Ticks and Mike Ottman
    Alfalfa is a vigorous crop that is very competitive with weeds. However, chemical weed control is often necessary even in well managed alfalfa since the marketplace has a low tolerance for weeds in alfalfa hay.
  • Jul 1999
    Growing Alfalfa for Seed in Arizona
    Publication (PDF, 29KB)
    Authors: Stephen H. Husman
    Due to worldwide shortages of non-dormant alfalfa seed, production opportunities and acreage have increased recently in central Arizona. This article gives some suggestions regarding growing alfalfa for seed in Arizona.
  • Aug 1998
    Alfalfa Aphid Complex
    Publication (PDF, 83KB)
    Authors: Tim C. Knowles
    Aphids feed in groups, often on the growing tips of plants. This article describes the complex of Aphids that can be found on alfalfa and discusses damages, monitoring, control, and when to treat for them.
  • Aug 1998
    Beet Armyworm
    Publication (PDF, 74KB)
    Authors: Tim C. Knowles
    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. This publication details the Beet Armyworm. It's description, biology, damages it causes, and methods of controlling it are discussed.
  • Aug 1998
    Alfalfa Caterpillar/Butterfly
    Publication (PDF, 72KB)
    Authors: Tim C. Knowles
    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. This article discusses their biology, the damages they cause, types of control, and when to treat for them.

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Alfalfa Insect Presentations
  • Oct 2019
    Alfalfa Production: Getting a Good Start
    Presentation (PDF, 4.8MB)
    Authors: Mike Ottman
    Location Presented: Parker and Blythe
  • Sep 2013
    Nutrient Management and Plant Density Recommendations For LA PAZ county Alfalfa Growers
    Presentation (PDF, 2.38MB)
    Authors: Shawna Loper
    Location Presented: Parker, AZ

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