Key to Asparagus Pests
Although there are only about 1,000 acres of commercial production in North Carolina, asparagus is grown in home gardens. One of the most expensive vegetables, asparagus is a gourmet item. Asparagus has relatively few pests. Asparagus aphids, asparagus beetles, caterpillars, and slugs damage plants.
A. Insects that feed on exposed berries, buds, shoots, or leaves.
- Asparagus aphid – Pale green and powdery, asparagus aphids (Figure 1) feed on leaves and bracts causing infested plants to become stunted or to die.
- Asparagus beetle – These hard-bodied chewing insects are about 6 to 9.5 mm long and are smooth, shiny, and slightly elongated. The antennae are less than half the length of the body. The tarsi appear four-segmented. They feed on meaty above-ground plant parts and leave brown scars on buds.
- Asparagus beetle larvae – These larvae are soft-bodied, plump, humpbacked, wrinkled, and sluggish. They grow to about 9 mm long and have three pairs of legs near the head and fleshy prolegs on most abdominal segments. They secrete a black fluid which stains the plant.
- Asparagus beetle grub – The body is dark gray and the head and prolegs are black. They feed like adult beetles and scar the buds (Figure 4).
- Spotted asparagus beetle larvae – The body is pale yellow to orange; they feed primarily on berries (Figure 5).
- Beet armyworm – These 30-mm-long caterpillars are soft-bodied, green to black with three lightly colored stripes running the length of the body. There is a black spot on each side of the body on the second segment behind the head. It has three pairs of legs and five pairs of prolegs (Figure 6). Beet armyworms damage buds, young leaves, and tender tips causing the stalks to curl and become deformed.
B. Insects that feed on roots or lower stems and usually are hidden in the soil
- Beet armyworm – (See above for description.) Beet armyworms usually feed on the foliage but occasionally they feed on roots or lower stems.
- Cutworms – Several kinds of fat, soft-bodied, basically gray, black, or brown caterpillars (40 to 50 mm long when fully grown) feed on asparagus roots. Cutworms have three pairs of legs and five pairs of prolegs (Figure 7A-C). Cutworms occasionally feed above ground on spears and ferns when young, but older larvae burrow in soil during the day and sever plant stems at night. They curl up when disturbed.
- Asparagus miner – Small maggots mine in the stems close to the ground (Figure 8) opening the plant up to disease-causing organisms.
- Grasshoppers – Fullgrown grasshoppers (Figure 9) are 19 to 33 mm long. They feed on spears, consume foliage, and gnaw and girdle asparagus stems.
Asparagus aphid, Brachycorynella asparagi (Mordvilko), Aphididae, HEMIPTERA
The powdery, pale green asparagus aphid is only a few millimeters long. Like other aphids, it is a pear-shaped, soft-bodied insect with a pair of tailpipe-like appendages (cornicles) on its abdomen.
Distribution – The asparagus aphid is native to eastern Europe and the Mediterranean area. The first infestation in North America was noticed in New York in 1969. Since that time, the aphid has been reported in New Jersey, Delaware, Rhode Island, Maryland, Pennsylvania, Virginia, North Carolina, and Washington.
Host Plants – Asparagus is the only known food plant of this aphid.
Damage – Asparagus aphids feed on cladophylls (modified leaves) and under bracts. They extract sap through their needle-like mouthparts. Heavily infested seedlings may form rosettes or shrivel and die. Similar infestations on older plants may cause severe dwarfing. Fortunately, predators, parasites, and diseases have kept this aphid from becoming a serious pest in most areas.
Life History – The biology of the asparagus aphid has not been formally studied in North America. It probably overwinters as eggs in North Carolina. In spring aphids resume development. Most species of aphids are prolific and produce live young without mating. New generations continue to be produced as long as warm, dry weather continues and host plants are available.
Asparagus aphids are subject to control by at least 31 species of natural enemies (predators, parasites, and diseases). As a result, chemical control is rarely necessary. Should large aphid populations develop, consult your state agricultural extension or the current North Carolina Agricultural Chemicals Manual for up-to-date recommendations.
Adult – About 6 to 9.5 mm long, asparagus beetles are smooth, shiny, and slightly elongated. The common asparagus beetle has a metallic blue head and bluish-black wing covers, each with three yellowish squared spots and reddish outer margins. The area just behind the head is red-orange or tan and has six black spots on each wing cover.
Egg – The dark brown, bullet-like egg of the common asparagus beetle is about 1.5 mm long and attached by one end to the host plant. The spotted asparagus beetle egg is greenish and glued on its side to the host plant.
Larva – The larvae of both species are plump, humpbacked, wrinkled, sluggish, and about 9 mm long when fully grown. The dark gray larva of the asparagus beetle has a black head and black distinctly fleshy prolegs; that of the spotted species varies from pale yellow when newly hatched to orange when mature (Figure A).
Pupa – The yellowish pupa is protected by a tough silken cocoon embedded with soil particles.
Distribution – Both species of asparagus beetles occur throughout the United States and Canada wherever asparagus is grown.
Host Plants – Asparagus is the only food plant of these beetles.
Damage – As soon as asparagus shoots appear in spring, they may be attacked by asparagus beetles. The beetles eat shoots and leaves but are particularly damaging when they gnaw the tips of buds causing them to scar and turn brown. In dry seasons, asparagus shoots may be blackened by hundreds of eggs from these beetles. The larvae of the common asparagus beetle damage plants much like the adults but also secrete a black fluid which stains the plant. Larvae of the spotted species, on the other hand, feed on developing berries, each larva often consuming three or four. Damage to the berries, however, is of little economic importance.
Life History – Asparagus beetles overwinter as adults in sheltered sites, particularly under bark or in stems of old plants. Common asparagus beetles appear slightly earlier in spring than the spotted species. The beetles feed as soon as they emerge and several days later egg laying begins. Eggs hatch 3 to 8 days later depending on temperature. For 10 to 14 days, larvae feed and develop through four instars. Fully grown larvae crawl to the ground and dig chambers in the soil. Within the chambers, they spin silken cocoons and pupate for 5 to 10 days. Soon afterwards a new generation of beetles emerges.
This 3- to 4-week cycle is typical in the summer. In fall or early spring, 8 weeks may pass from the egg to the adult stage. As many as five generations per year occur in North Carolina.
Many beneficial insects feed on or parasitize the various life stages of asparagus beetles. Ladybird beetles, other predaceous beetles, soldier bugs, and certain small wasps, flies, and dragonflies reduce asparagus beetle populations. These beneficial insects often do not give sufficient control.
In small gardens, larvae can be knocked from plants onto the soil. The larvae usually are unable to reclimb the plants and die on the hot soil. In the case of the spotted asparagus beetle, gathering and burning asparagus berries helps lower and prevent further infestations.
Should populations of this pest become a problem, chemical controls are available. For up-to-date recommendations, consult the current North Carolina Agricultural Chemicals Manual.
Asparagus miner, Ophiomyia simplex (Loew), Agromyzidae, DIPTERA
Adult – The shiny black, slightly humpbacked asparagus miner fly is 2.5 to 3.5 mm long.
Egg – Inserted beneath the epidermis of an asparagus stalk, the egg is rarely seen. White at first, the 0.5 by 0.2-mm egg later assumes the color of asparagus tissues.
Larva – When newly hatched, the miner is pure white and about 0.4 mm long. The mature third instar has black rasping mouthparts and may be as long as 5 mm.
Puparium – The puparium is the shed skin of the last larval instar within which the pupa develops. Dark brown, flattened, and up to 4 mm long, the puparium has many hooks which attach it firmly to the plant.
Distribution – The asparagus miner has been reported to occur from southeastern Canada into Tennessee and North Carolina. It is also found in California, Hawaii, Europe, and Great Britain.
Host Plants – Asparagus and celery are the only known food plants of this insect.
Damage – Asparagus miners tunnel just below the surface of spears, usually near the base of plants. These insects were formerly believed to girdle plants causing yellowing of foliage and premature death. These symptoms are now attributed to the disease-causing fungus Fusarium. It has not yet been determined whether heavy miner infestations predispose plants to this disease. Miners cause some tissue breakdown (brown streaks) which may render spears unsalable, but they do not interfere with water or nutrient uptake and probably do not reduce yields. Seedlings and plants in newly set beds are most likely to become infested.
Life History – Biological studies on this insect have not been undertaken in North Carolina or other southern limits of its range. In New York, pupae within puparia overwinter in spears left in the field or 2.5 to 15 cm below the soil surface. Flies emerge the latter half of May and mate. One to two days later, oviposition begins. The flies live only 4 or 5 days and, therefore, produce only one batch of eggs. Eggs may be thrust into plant stems or deposited in the soil. After incubating 12 to 17 days, eggs hatch.
Larvae feed beneath the epidermis of the stem and develop through three instars in 2 to 3 weeks. Before pupating they usually mine toward the base of the plant. Pupation lasts 17 to 21 days and new adults usually emerge in July. The life cycle is then repeated except for the fact that the next generation of pupae overwinters. Only two generations are produced each year in New York.
Several wasps (Dacnusa rondani, Dacnusa bathyzona, Sphegigaster spp., and Pleurotropis epigonus) parasitize asparagus miner pupae and thereby help reduce populations. Cultural practices such as pulling and destroying spears at the end of the season or in early spring also do much to eliminate the overwintering stage of this pest. Chemical control of the asparagus miner is rarely necessary.
Beet armyworm, Spodoptera exigua (Hubner), Noctuidae, LEPIDOPTERA
Adult – The beet armyworm moth has a wingspan of 25 to 32 mm. Its forewings are mottled gray or brown with a pale spot near the center of each wing. Its hind wings are white with dark veins and have a fringe-like border.
Egg – The white to pink, ribbed egg is roughly spherical in shape and slightly peaked on top. Scales and hairs from the moth give the egg cluster a gray, fuzzy appearance.
Larva – This green or black caterpillar has a dark head, five pairs of prolegs, and sometimes three lightly colored stripes running the length of the body (Figure B). On the second segment behind the head, there is a small black spot on each side of the body. This spot usually becomes visible to the field observer when the caterpillar reaches 7 to 8 mm long; however, the spot may be difficult to see on a dark caterpillar. About 1 mm long when newly emerged, a larva may be 25 to 30 mm long when fully grown.
Pupa – About 15 to 20 mm long, the pupa is light brown with dark brown margins along the abdominal segments.
Distribution – Native to the Orient and introduced into this country around 1875, the beet armyworm is now common throughout the southern and western United States. It occurs northward into Montana.
Host Plants – The beet armyworm infests many weeds, trees, grasses, legumes, truck crops, and field crops. In various states, it is of economic concern upon asparagus, cotton, corn, soybean, tobacco, alfalfa, table and sugar beets, pepper, tomato, potato, onion, pea, sunflower, and citrus. In addition, plantain, lambsquarters and redroot pigweed are wild hosts which are attractive to beet armyworms.
Damage – Early instar beet armyworms most frequently damage the young terminal growth. Profuse silk webbing may give infested plants a shiny appearance. Later instars do not feed gregariously and the production of webbing is discontinued.
Life History – In warm areas, such as Florida and California, the beet armyworm moths may be found year-round. In less tropical areas, these insects can survive the winter as pupae in the upper 6 cm of the soil. The extent of the overwintering distribution, however, has not been adequately studied. This insect is not believed to overwinter as far north as Kentucky or North Carolina. Vegetable crops in North Carolina apparently become infested by migrating moths. In spring, soon after mating, fertilized females begin laying eggs in clusters of about 80. Each female can deposit approximately 600 eggs over a 3- to 7-day period. Moths die 4 to 10 days after emerging from pupae.
Eggs hatch in 2 to 3 days. The newly emerged larvae spin loose webs around themselves, feed gregariously on the remains of the egg mass, and then attack plant foliage. They eventually scatter to different parts of the plant. After feeding 1 to 3 weeks, larvae (fifth instars) pupate within loose cocoons composed of soil particles, leaf fragments and trash. About 1 week later moths emerge. The entire life cycle requires 4 to 5 weeks. Several generations occur each year.
The beet armyworm has few effective parasites, diseases, or predators to lower its population. Effective chemicals for beet armyworm control are available to the commercial vegetable producer or licensed applicator. Most chemicals cleared for home garden use will not control this pest adequately. For up-to-date recommendations, consult the current North Carolina Agricultural Chemicals Manual.
Black cutworm, Agrotis ipsilon (Hufnagel), Noctuidae, LEPIDOPTERA
Spotted cutworm, Amathes c-nigrum (Linnaeus), Noctuidae, LEPIDOPTERA
Variegated cutworm, Peridroma saucia (Hubner), Noctuidae, LEPIDOPTERA
Adult – Black and variegated cutworm moths have wingspans of 38 to 51 mm. The forewings of black cutworm moths are dark with three black dashes and a white splotch near the tip of each wing. Forewings of variegated cutworm moths are basically yellowish or light brown with pale mottled designs. Spotted cutworm moths have brown forewings, often tinged red or purple, with a pinkish trianglular spot on the anterior margin and a moon-shaped spot near the center of each wing. The wingspan is only 30 to 40 mm. The hind wings of all three species are pale gray or off white with dark veins.
Egg – White at first, the round eggs have a diameter of 0.5 to 0.7 mm and may become slightly tinted before hatching.
Larva – Black cutworms are greasy-looking, gray to black caterpillars up to 46 mm long (Figure Y). As long as 38 mm when fully grown, spotted cutworms have a pale brown or gray body with black wedge-shaped spots on each segment of the posterior half of the body. The spots increase in size toward the tip of the abdomen. About 50 mm long when mature, variegated cutworms are pale brown with a distinct yellow dot on each segment down the center of the back.
Pupa – Cutworm pupae are bout 20 mm in length and dark brown or mahogany in color.
Distribution – Cutworms are cosmopolitan in their distribution and are common throughout most areas of Canada and the United States. The spotted cutworm, common in northern, central, and Gulf states, has a scattered distribution from North Carolina to Florida.
Host Plants – As general feeders, most cutworms attack a wide range of plants. Some common vegetable hosts include asparagus, bean, cabbage and other crucifers, carrot, celery, corn, lettuce, pea, pepper, potato, rhubarb, and tomato.
Damage – Young cutworms climb plants and feed on spears and ferns of asparagus. The mature cutworm, however, are sluggish, nocturnal, and soil burrowing. They typically sever plant stems during the night and hide in soil near the base of plants during the day.
Life History – Cutworms overwinter as larvae or pupae, depending on the species. In early spring, overwintering larvae of some species become active, feed, and complete their development. In other cases, moths emerge from overwintering pupae and lay eggs on host plants or other vegetation. Therefore, depending on the species, damaging cutworms found in spring may be overwintered larvae or new generation cutworms. Cutworms develop through five to eight larval instars (again depending upon the species).
Pupation occurs in the soil and lasts about 2 weeks for nonoverwintering pupae. Moths emerge and deposit 55 to several hundred eggs on host plants. The number of annual generations depends on latitude. Generally, there are two generations per year in Canada, four generations per year in North Carolina, and five to six generations per year in Florida. The spotted cutworm, however, produces only two generations per year throughout the United States.
In small gardens, barriers around plants can prevent serious cutworm damage. By encircling individual plants with cardboard or metal "collars" pressed 2 to 3 cm (1 in) into the soil, gardeners put up "fences" the cutworms cannot cross. Such a method, however, is not practical for large acreages. Should cutworms become a problem, consult your Extension center for the latest recommendations.
Publication date: Jan. 1, 2003
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