Small Grains and Forage

Occasional and Non-Economic Forage Pests

Blister beetles

Epicauta spp.

Appearance and Life History

There are several species of blister beetles that may be found in alfalfa. They include the gray, black, margined, and striped blister beetles. They all have relatively soft wing covers and are about 1/2 to 3/4 inch (13 to 19 mm) long. Eggs are laid in the soil and the larvae, which remain in the ground.

Gray blister beetle Gray blister beetle
Photo by University of Illinois
Black blister beetle Black blister beetle
Photo by J. Obermeyer
Margined blister beetle Margined blister beetle
Photo by B. Christine
Striped blister beetle Striped blister beetle
Photo by J. Obermeyer

Damage

Blister beetles are important in alfalfa production, not so much for their foliage feeding activity but because they contain the chemical cantharidin in their bodies. This substance is toxic to horses. These beetles can be consumed by horses when they feed on infested hay. As few as 25 to 50 beetles can kill a horse weighing 275 to 550 pounds (125 to 249 kg), respectively. Cantharidin can also decrease the digestibility of fibrous feeds by ruminants (eg., cattle and sheep).

Sampling Method

Blister beetles are gregarious and may aggregate in large swarms within alfalfa fields. If beetles are detected while sampling for other pests, infested areas should be identified and mapped. Caution should be used when sampling an area infested with these beetles. Cantharidin may cause blisters on a the skin.

Management Guidelines

Forage Insect Control Recommendations: E-series 220-W (PDF)

Defoliation by blister beetles in alfalfa is not of economic concern. Feed value and quality is decreased, and may be deadly to animals ingesting the hay. Beetles controlled by insecticides will still exude cantharidin if picked up while baling. Areas with blister beetles should be well-mapped and avoided during harvest. Infested areas should be harvested with a sickle-bar mower (do not use a conditioner) which allows the beetles to drop off the cut foliage and seek food and moisture elsewhere.

If control is necessary, contact your state Cooperative Extension Service or click here for control materials and rates.


Caterpillars (Miscellaneous)

Several species

Caterpillar larva Larva
Photo by J. Obermeyer

Appearance and Life History

Webworms, green cloverworm, armyworm, yellowstriped armyworm, loopers, and alfalfa caterpillar are among the many species of caterpillars that may be noted in an alfalfa field.

Damage

These caterpillars, all foliage feeders, are usually of little economic importance. Heavy damage, which is rare, causes fields to appear ragged. Some species can damage new seedings in the spring or fall, causing a stand reduction.

Leaf defoliation Leaf defoliation
Photo by J. Obermeyer

Sampling Method

Separate sampling should not be necessary for these defoliators. While sampling for normal pests, (i.e., alfalfa weevil and potato leafhopper) outbreaks of caterpillars may be noted. Since many of the occasional caterpillar pests are controlled by predators, parasites, and pathogens, they should be considered while sampling.

Management Guidelines

Forages Insect Control Recommendations: E-series 220-W (PDF)

No management guidelines have been established for these caterpillars in alfalfa. However, depending on the value of the crop and intended use, defoliation levels as low as 10% to 15% may be economic. Fall seedings especially need protection from larval defoliation and possibly plant death.

If control is necessary, contact your state Cooperative Extension Service or click here for control materials and rates.


Clover leaf weevil

Hypera punctata Fabricius

Clover leaf weevil larva Larva
Photo by Purdue University

Appearance and Life History

The adult, about 1/3 inch (8.5 mm) long, is a robust snout beetle that is dark brown flecked with black. The larva, 1/2 inch (13 mm) long when fully grown, is green with an off-white stripe down the middle of its back. It is very similar in appearance to the larva of the alfalfa weevil. To distinguish between larvae of these two species, carefully examine the head capsule. The alfalfa weevil larva has a black head while the larva of the clover leaf weevil has a brown head.

Damage

Larval feeding is similar to that of alfalfa weevil; ragged holes in leaves. Damage from this pest is considered insignificant compared to that of the alfalfa weevil.

Sampling Method

Sampling procedures are the same as for alfalfa weevil. Also, look for diseased larvae as you assess leaf feeding damage levels. Diseased larvae turn yellow and then brown.

Management Guidelines

Forages Insect Control Recommendations: E-series 220-W (PDF)

Control is usually not needed due to high clover leaf weevil mortality from diseases. A scouting program for alfalfa weevil will also catch outbreaks of this occasional pest. Refer to the alfalfa weevil defoliation guidelines for treatment levels.

If control is necessary, contact your state Cooperative Extension Service or click here for control materials and rates.


Clover root curculio

Sitona hispidulus Fabricius

Clover root curculio Adult Larva
Photo by University of Kentucky

Appearance and Life History

This grayish-brown weevil is about 3/16 inch (4.7 mm) long with a short blunt snout. The larva is white, grub-like, and about 1/4 inch (6 mm) long.

Damage

In the fall, the early larval instars feed in the nitrogen fixing nodules and on lateral roots. In the spring, the later instars feed on the surface of the taproot. Root feeding is characterized by extensive scarring of the epidermal layer. These lesions may allow for entry of plant pathogens which can cause wilt and root rot. Late instar feeding damage can be extensive enough to girdle the taproot and may result in plant death. Larval damage is more commonly found in older alfalfa stands.

Adults, which emerge in June, cause crescent-shaped notches along the edge of alfalfa and clover leaves. This damage is rarely of concern.

Sampling Method

Sampling procedures have not been established for this insect.

Management Guidelines

Forages Insect Control Recommendations: E-series 220-W (PDF)

Because extensive damage by this pest is most likely to occur in older alfalfa stands, it is suggested that one rotate crops.

If control is necessary, contact your state Cooperative Extension Service or click here for control materials and rates.


Fall armyworm

Spodoptera frugiperda J.E. Smith

Fall armyworm larva Larva
Photo by J. Obermeyer

Appearance and Life History

Fall armyworm larvae are smooth-skinned worms that vary in color from light tan or green to nearly black. They have three yellowish-white narrow lines down their backs. On each side of their bodies and next to the yellow lines is a wider dark stripe. Next to this is an equally wide, wavy, yellow stripe, splotched with red. Full-grown larvae are about 1-1/2 inches (38 mm) long. To differentiate this larva from other armyworm species or corn earworm one needs to look at the head of the insect. The fall armyworm's head has a white, inverted Y-shaped suture usually visible between the eyes.

Damage

Although severe damage to alfalfa is uncommon, heavy infestations can cause complete defoliation from mid to late summer. Fall seedings can be completely destroyed.

Sampling Method

If you find a substantial fall armyworm population and/or their damage during regular field surveys, take sweep samples with a sweep net and carefully examine stems in order to ascertain the extent of the infestation and injury. Walk the field in an "M" pattern. Take 20 continuous sweep samples in each of 5 field areas. At the completion of each series of sweeps, count and record the number of fall armyworms in the net to determine the average number of larvae per sweep.

Examine 5 stems at each sampling site and record information on the following three factors:

  1. percentage of foliage showing feeding damage
  2. stage of development of the plant
  3. stem length

Management Guidelines

Forages Insect Control Recommendations: E-series 220-W (PDF)

No management guidelines have been established for fall armyworm in alfalfa. However, depending on the value of the crop and intended use, defoliation levels as low as 10% to 15% may be economic. Fall seedings should be protected if the stand is threatened.

If control is necessary, contact your state Cooperative Extension Service or click here for control materials and rates.


Grasshoppers

Melanoplus spp.

Adult grasshopper Larva
Photo by Purdue University

Appearance and Life History

Grasshoppers are general feeders on grasses and weeds and often move to cultivated crops. Their populations vary from year to year. Crop damage is likely to be greatest in years when dry weather accompanies high populations. Drought reduces natural vegetation forcing the insects to move to cultivated crops.

Grasshoppers are gray, green, to brown insects, up to 1-3/4 inches (44 mm) long. They have large hind legs designed for jumping and prominent heads topped by large compound eyes. Nymphs are similar in appearance, except that they lack developed wings.

Typically, grasshopper populations develop in uncultivated areas such as pastures, roadsides, or fence rows. They move into alfalfa fields when their preferred hosts, grasses, are no longer available or attractive. In some cases, grasshoppers hatch from eggs laid within alfalfa fields.

Damage

Grasshopper damage is characterized by irregular holes extending from the margin of leaves inward. Injury to the growing tips of alfalfa plants may also occur.

Sampling Method

If substantial numbers of grasshoppers and/or their damage are found during regular field surveys, estimate the extent of the infestation. In 10 areas of the field, estimate the number of grasshoppers leaping from an area of approximately 1 square yard (90 cm square). Move in a zigzag pattern, rather than in a straight line, through areas where counts are to be made.

Estimate the average percentage of alfalfa foliage that has been consumed by grasshoppers, the average plant height, and the average stage of plant development.

Management Guidelines

Forages Insect Control Recommendations: E-series 220-W (PDF)

No management guidelines have been established for grasshoppers in alfalfa. However, depending on the value of the crop and intended use, defoliation levels as low as 10% to 15% may be economic.

If control is necessary, contact your state Cooperative Extension Service or click here for control materials and rates.


Mexican bean beetle

Epilachna varivestis Mulsant

Adult mexican bean beetle Adult
Photo by Purdue University

Appearance and Life History

The Mexican bean beetle is primarily a pest of beans. The beetle and larva of this insect, however, can feed on the foliage of clovers and alfalfa.

The Mexican bean beetle is a lady beetle, one of the few destructive species of this primarily beneficial family of insects. The adult beetle is oval shaped, about 5/16 inch (8 mm) long and 1/4 inch (6 mm) wide, and copper colored with 16 black spots on its back. Females lay yellow, oval-shaped eggs in a cluster on the underside of leaves. From these eggs hatch yellow larvae with branched spines that cover their soft bodies. The larva passes through 4 instar stages, the final instar reaching a length of 1/3 inch (8.5 mm), before transforming into a bright yellow pupa. The pupa is usually found attached to the underside of a leaf.

Emerging in early spring from overwintering sites such as woodlands adjoining bean and alfalfa fields, adult beetles may congregate in nearby alfalfa fields if their preferred host, beans, have not yet emerged. Late in the season beetles may enter alfalfa fields after bean plants are no longer attractive.

Damage

Mexican bean beetle feeding on alfalfa foliage appears similar to extensive alfalfa weevil damage. The beetles skeletonize the leaf tissue, producing a shredded appearance to the leaves. Extensive beetle feeding can cause an alfalfa field to take on a grayish appearance.

Sampling Method

If you find a substantial Mexican bean beetle population and/or their damage during regular field surveys, take sweep samples with a sweep net and carefully examine plants in order to ascertain the extent of the infestation and injury. Walk the field in an "M" pattern. Take 20 continuous sweep samples in each of 5 field areas. At the completion of each series of sweeps, count and record the number of Mexican bean beetles in the net to determine the average number of adults and larvae per sweep. Also, randomly pick 5 stems in each sample area. Examine each stem, recording information on the following three factors:

  1. percentage of foliage showing feeding damage
  2. stage of development of the plant
  3. stem length

Management Guidelines

Forages Insect Control Recommendations: E-series 220-W (PDF)

No management guidelines have been established for Mexican bean beetle in alfalfa. However, depending on the value of the crop and intended use, defoliation levels as low as 10 to 15% may be economic.

If control is necessary, contact your state Cooperative Extension Service or click here for control materials and rates.


Plant bugs

Several species

Appearance and Life History

Plant bugs range from 1/4 inch (6 mm) to 3/8 inch (10 mm) long. They have flattened, oval bodies and vary in color from pale yellow or green to tan or brown. Plant bug nymphs look very much like the adults, except that they are smaller and lack wings. After they hatch from eggs, the nymphs are pale green. Shortly after feeding begins, they become darker in color.

Tarnished plant bug Tarnished plant bug
Photo by J. Obermeyer
Alfalfa plant bug Alfalfa plant bug
Photo by J. Obermeyer
Plant bug nymph Plant bug nymph
Photo by J. Obermeyer
Slight and severe plant bug damage to seed Slight and severe plant bug damage to seed
Photo by Purdue University

Damage

Both the adults and nymphs use their piercing-sucking mouthparts to feed on leaves, stems, flowers, and seed pods of alfalfa. In addition to the physical damage to the plant caused by their feeding, the toxin they inject into the plant can cause cell death, which may lead to a deformed plant. Plant bugs are mostly of concern to alfalfa seed producers.

Sampling Method

In seed alfalfa, if plant bug populations appear large while sampling for potato leafhopper, resample to estimate the extent of their infestation. Take 20 sweeps with a sweep net in each of 5 areas of the field. Examine and count the net contents after each set of sweeps for plant bugs. Measure the stem length at each sample area.

Management Guidelines

Forages Insect Control Recommendations: E-series 220-W (PDF)

If there is an average of 3 adults and/or nymphs per sweep on 3-inch (7.6 cm) seed alfalfa or over 5 adults and/or nymphs per sweep on seed alfalfa over 3 inches (7.6 cm) tall, a treatment may be advisable.

If control is necessary, contact your state Cooperative Extension Service or click here for control materials and rates.


Spotted alfalfa aphid

Therioaphis maculata Buckton

Aphids on leaf Adult
Photo by Purdue University

Appearance and Life History

Large populations of spotted alfalfa aphid most often occur during hot, dry periods. They reproduce rapidly during these times and can quickly become a problem. Large populations may also develop when insecticides used to kill other alfalfa pests and with little to no activity against aphids kill aphid predators and parasites.

Spotted alfalfa aphid is small (1/10 inch [2.7 mm] long), active, and pale yellow or green. It has 4 to 6 conspicuous rows of spots on its upper abdomen. Each spot is tipped with a short spine. The winged form has smoky colored wings.

Damage

This aphid injects a toxic salivary secretion into plants causing yellowing at the feeding site and along the leaf veins as the toxin is translocated. Severe infestations can cause general yellowing and stunting of plants. In addition, spotted alfalfa aphid secretes honeydew upon which a sooty mold develops. This reduces hay quality and makes harvesting difficult.

Sampling Method

If spotted alfalfa aphid populations appear large while sampling for potato leafhopper, resample to estimate the extent of the aphid infestation. Take 20 leaf sweeps with a sweep net in each of 5 areas of the field. Examine the net contents after each set of sweeps for aphids and determine the stem length in each area. Also count and record aphid predators, such as lady beetles and larvae and lacewing larvae while walking through the field. Use the following rating system to rank spotted alfalfa aphid abundance.

If large to extremely large populations are encountered, examine 25 randomly selected stems and count the number of spotted alfalfa aphids on each stem. Be aware that the aphids may fall from stems as they are picked. Count all parasitized (gray to brown and balloon-like) aphids separately. Determine the number of healthy and parasitized aphids per stem. Also examine each stem and record length and growth stage.

Management Guidelines

Forages Insect Control Recommendations: E-series 220-W (PDF)

Treatment may be advisable if:

  1. percentage of foliage showing feeding damage
  2. stage of development of the plant
  3. stem length

If control is necessary, contact your state Cooperative Extension Service or click here for control materials and rates.


Variegated cutworm

Peridroma saucia Hübner

Variegated cutworm Variegated cutworm
Photo by W. Cranshaw

Appearance and Life History

The variegated cutworm is often confused with armyworm because it feeds on the foliage. Although most damage is done at night, this cutworm will feed in the daytime, especially on cloudy or partly cloudy days. If the larvae are not found on damaged plants, they may be in loose soil or under crop debris.

The fully grown variegated cutworm larva is about 2 inches (50 mm) long and ranges in color from almost black to light greenish-yellow or tan. Distinctive light yellow diamond-shaped spots are visible in a line down the middle of its back. There are three to four generations per year.

Damage

The variegated cutworm larva will feed on alfalfa stems and leaves. It will also cut the stems of young alfalfa plants. Variegated cutworm is usually of greater economic importance on new alfalfa stands than on established stands.

Early detection, is very important since controls, if warranted, are most effective on young cutworms.

Sampling Method

Young larvae may be captured while sweeping with a sweep net during regular field surveys. If substantial numbers of variegated cutworms or their damage are noted, sample to determine the extent of the infestation and damage. Walking the field in a M-shaped pattern, count the cutworms in an area of approximately 1 square foot (0.09 square meters) in 10 locations in the field. Closely examine the alfalfa plants and plant litter within the sampling area. Determine the average number of larvae per square foot (0.09 square meters) for the field.

Record the length of several cutworms and estimate the percentage of alfalfa foliage consumed. Finally, estimate the average plant height and stage of growth of the plants within the field.

Management Guidelines

Forages Insect Control Recommendations: E-series 220-W (PDF)

No management guidelines have been established for variegated cutworm in alfalfa. However, depending on the value of the crop and intended use, defoliation levels as low as 10% to 15% may be economic.

If control is necessary, contact your state Cooperative Extension Service or click here for control materials and rates.