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• Corn Insecticide Evaluations 2014
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Occasional & Non-Economic Corn Pests

Chinch bug

Blissus leucopterus leucopterus Say

Appearance and Life History

Nymphs (immatures) are small (1/16" or 1.6 mm long) have red bodies with a pale yellow band on the forward part of the abdomen. Adults (3/16" or 4.7 mm long) are black with obvious white forewings. They produce a foul odor when crushed. Adults overwinter in field debris.

Damage

They can be found in small grain fields in early spring. Under dry conditions later in the season, they may move to corn fields. Both adults and nymphs feed on and damage corn. The leaves on damaged plants may be rolled and discolored with damaged plants appearing purple in color. Severe infestation may cause stunting and plant death. Damage is rare unless the chinch bug population is excessive and dry conditions persist.

Sampling Method

Monitor corn field edges during drought periods, especially those adjoining mature or harvested small grain fields. Estimate the percent of plants infested with chinch bugs. Look for the chinch bugs behind leaf sheaths or at the bases of stalks.

Management Guidelines

Corn Insect Control Recommendations: E-series 219-W (PDF)

Treatment is usually recommended only if the plants are under stress, wilting is apparent, and a majority of the plants in an area are infested. Often, spot treatment may be possible to control a localized damaging population.

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

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Corn earworm

Helicoverpa zea Boddie

Appearance and Life History

The corn earworm moth has a wing span of approximately 1-1/2 inches (38 mm), is buff colored, and has irregular spots or markings on the wings ("wavy lines" near the tips of the hind wings). In addition, a dark "comma-shaped" marking is visible near the center of the forewing. Second generation moths typically lay their eggs on corn silks, with a strong preference for fresh, green silks. The eggs are laid individually and appear as tiny, milky-white spheres. On fresh silks, these tiny eggs are very difficult to see. Under optimal temperatures, the eggs will hatch in about 2 to 4 days. Hatched larvae move into the ear and feed on kernels. Mature larvae drop to the base of the plant and pupate in the soil. Larvae will occasionally be found in the whorls of corn feeding on leaf tissue. Severe damage gives the plant a ragged appearance. The larvae, 1/8 to 1-1/2 inches (3 to 38 mm), vary considerably in color from light green to tan, brown, pink, maroon, green, or nearly black, with light and dark stripes running lengthwise on their bodies. The underside of larvae is a lighter color. Head capsules are light brown.

Damage

Larvae are often found feeding within the ear on kernels. This feeding results in yield reductions and may provide an avenue for the introduction of disease organisms leading to ear rots. In seed corn production, feeding results in partially-eaten kernels, which must be removed during seed conditioning. Loose-husked genotypes may experience high losses due to this pest.

Sampling Method

Control of this pest in commercial yellow dent corn is not normally economical. Fields of corn of greater economic and food value (i.e., seed, sweet, and popcorn) should have moth monitoring programs initiated prior to and during silk emergence. Within approximately 1 hour of hatching, larvae will migrate from the silks to& the ear tips. Therefore,treatment decisions should be based on moth flights. Once larvae enter the ear, treatment is futile.

Management Guidelines

Corn Insect Control Recommendations: E-series 219-W (PDF)

For seed production fields, if 10 or more moths are captured in a pheromone trap for several consecutive nights, economic damage is possible. However, only fields silking and/or pollinating during this time are candidates for treatment.

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

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Corn root aphid

Anuraphis maidiradicis Forbes

Appearance and Life History

These subterranean aphids are blue-green to gray-green in color, spherical, soft bodied, and 1/16 inch (1.6 mm) long or less. Except for a few winged aphids that migrate to new locations in the summer, the corn root aphid remains in the soil throughout the year.

Damage

Aphids cluster on roots and suck plant juices. Infested plants wilt, then become yellow and eventually turn brown. Plants are often stunted but rarely killed outright. Corn root aphid infestations are normally not noticed unless plants are stressed from dry conditions.

Aphids are moved about in the soil by a 1/4 inch (6 mm) long brown ant, the cornfield ant, Lasius alienus (Foerster), which feed on the aphids' exudates or "honeydew."

Sampling Method

In a damaged area, dig-up wilted plants and inspect for aphids on the corn roots. Ant hills will often be seen at the base of infested corn plants.

Management Guidelines

Corn Insect Control Recommendations: E-series 219-W (PDF)

No rescue treatments are available. During favorable growing conditions, plants are able to out-grow damage. Tillage, which may disturb ant colonies, can reduce aphid numbers and stimulate root development.

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

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Crane Fly

Family Tipulidae

Appearance and Life History

The immature stage is a large, up to 3/4" (19 mm) long, brown to gray, legless maggot with finger-like projections on the last abdominal segment. The adult is a long-legged, skinny fly, which is often mis-identified as a "giant mosquito." The adults do not bite.

Damage

Crane fly maggots feed on decaying plant material in the soil. They do not injure corn. Because they are often found in the soil at the base of corn seedlings, they may be mistaken for cutworms.

Sampling Method

Sampling is not necessary for this non-economic insect.

Management Guidelines

Corn Insect Control Recommendations: E-series 219-W (PDF)

No rescue treatments are available. During favorable growing conditions, plants are able to out-grow damage. Tillage, which may disturb ant colonies, can reduce aphid numbers and stimulate root development.

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

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Garden symphylan

Scutigerella immaculata Newport

Appearance and Life History

Symphylans are small, white, 1/4" (6 mm) long centipede-like animals with 12 pair of legs. The immatures look similar, but have fewer pairs of legs.

Damage

These root feeders may cause leaf rolling, stunting, and purpling of plants. Under heavy infestation, small plants may die. Damaging populations are often spotty in fields, but when present are usually found in heavily manured areas or soils with high organic matter. Symptoms may not be seen unless plants are under environmental stress.

Sampling Method

Dig up plants in areas showing damage symptoms and carefully sort through the soil for the quick-moving symphylans. Also, inspect roots for symphylan-caused damage. Positively identify and count the number of symphylans per plant.

Management Guidelines

Corn Insect Control Recommendations: E-series 219-W (PDF)

There is no known economic threshold or rescue treatment for symphylans. It is likely that populations of 50 to 100 symphylans per plant are needed before damage will be evident.

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

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Grape Colaspis

Colaspis brunnea Fabricius

Appearance and Life History

The adult is a yellowish-brown, elliptical beetle about 3/16 inch (4.7 mm) long with wing covers that are marked with longitudinal rows of ridges. The tiny (1/8 inch or 3 mm long), white grub is comma-shaped with a brown head. The white pupa may be found a few inches deep in the soil near damaged plants. There is one generation per year. It overwinters as a grub in the soil and emerges as an adult in late June to early July. Adults proceed to feed, mate, and lay eggs, which hatch in early fall.

Damage

The grubs are root feeders and may cause wilting and stunting of plants. Under a heavy infestation, small plants may die. Damage is usually noted in patches within a field. Damage is most likely to occur following clover or alfalfa, and occasionally where patches of smartweed existed the previous year.

Sampling Method

Dig up plants in 2 linear feet (0.6 m) of row in damaged areas of the field. Inspect for missing and/or damaged roots. Carefully sort through the soil and verify the presence of grape colaspis grubs and/or pupae.

Management Guidelines

Corn Insect Control Recommendations: E-series 219-W (PDF)

There is no known economic threshold or rescue treatment for grape colaspis. If necessary, replanting should be done after grubs have begun to pupate (refer to "Cutworms" in the soybean section for replanting information).

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

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Grass Thrips

Anaphothrips obscurus Müller

Appearance and Life History

Grass thrips are the most common species of thrips found in corn. They are orange or yellow, slender insects about 1/16 inch (1.6 mm) long. Adults have 2 pair of feather-like wings and are darker in color.

Damage

Both winged adults and immatures feed by penetrating leaf cells and sucking out their contents. Minute, longitudinal, whitish scars become so numerous that entire leaves look grayish and desiccated. Most feeding takes place behind leaf sheaths, in the whorl, or on the underside of lower leaves. Damage is usually noticed only under extended periods of hot, dry weather conditions when plants are moisture-stressed. Gusty winds during these periods will further desiccate plant tissue and compound thrips' injury.

Sampling Method

Thoroughly examine discolored plants for thrips and their damage. Estimate the extent of damage in the field.

Management Guidelines

Corn Insect Control Recommendations: E-series 219-W (PDF)

No management guidelines have been established for thrips in corn. Vigorously growing corn with adequate soil moisture can tolerate thrips damage. If dry conditions are expected to continue, plants are grayish in color and wilting, and thrips are present, then a treatment may be justified.

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

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Millipedes

Class Diplopoda

Appearance and Life History

Millipedes are brownish, hard-bodied, and worm-like with two pairs of legs per body segment. Most species found in agricultural fields will be 3/4 to 1-1/2 inches (19 to 38 mm) in length.

Damage

Millipedes typically feed as scavengers in high organic matter soils, feeding on dead or decaying plant materials. On rare occasions, they have been documented to feed on corn seeds or seedlings if soil conditions are extremely dry. The build up of populations in agricultural fields is attributed to reduced tillage, which increases soil surface residue and thus provides a suitable environment for their development.

Sampling Method

If soils are dry, corn emergence is spotty, and millipedes are abundant, refer to "Cutworms" in the corn section for scouting methodology.

Management Guidelines

Corn Insect Control Recommendations: E-series 219-W (PDF)

No management guidelines have been established for millipedes in corn. The likelihood for control is low.

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

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Southwestern corn borer

Diatraea grandiosella Dyar

Appearance and Life History

This pest, although not normally noted in the northern Midwest, is an economic threat in certain areas of this region.

Mature larvae, about 1 inch (26 mm) long and pale yellow with very faint spots, overwinter below the ground at the base of stalks where pupation will take place in the spring. Moths, white to yellowish-white with a wingspan of 1-1/4 inches (31 mm), lay single eggs or a mass of overlapping eggs usually on the upper surface of corn leaves. The creamy-white eggs change in color before hatching, developing three parallel rows of reddish-orange lines. Larvae, 1/8 to 1 inch (3 to 26 mm), are whitish-gray in color with a brown head and rows of obvious dark brown to black spots running the length of their bodies.

Damage

First generation: Newly-hatched larvae feed on the leaves in the corn whorl, typically producing a "shot hole" (random) damage pattern. As the larvae grow, they may be found tunneled into the midrib of leaves. Eventually the larvae drop onto leaf axils and bore into the stalk, leaving behind their sawdust-like excrement called frass. While leaf feeding may not lead to serious yield losses, they occasionally bore into the growing point which can result in a "dead heart" and complete yield loss.

Second generation: Young larvae feed on leaf tissue and pollen in the leaf axils or behind the leaf sheaths usually in the corn ear zone. Older larvae then bore somewhere into the lower two-thirds of the plant. They proceed to tunnel down through the center of the stalk thus greatly weakening the plant. In addition, the overwintering larvae increase plant lodging due to girdling of the bases of stalks.

Sampling Method

Examine 20 plants in each of 5 representative areas per field. Note the percentage of plants with feeding injury. Pull leaf whorls from 1 injured plant in each of the 5 areas sampled per field; unroll each whorl and note the average number of live larvae per plant

Management Guidelines

Corn Insect Control Recommendations: E-series 219-W (PDF)

Early planting, when possible, is generally the most efficient and economical method of preventing plant damage and yield losses. The primary reason for early planting is to reduce the establishment by second generation borers.

Insecticides can be used for first generation infestations, but timing is critical for control. Larvae can only be effectively controlled while they are feeding within the whorl. Once borers enter the stalks, they cannot be controlled. Treatments should be applied at or just before 35% of the plant whorls show fresh feeding damage and live larvae are present.

Controls aimed at the second generation are less effective and not economical. Transgenic corn producing the insecticidal protein derived from Bacillus thuringiensis (Bt) provides protection that persists through the late season to include second generation larval feeding. Where this pest has become a yearly problem and late planting is probable, planting Bt corn may be a viable management tactic (resistance management protocols should be followed.

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

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Webworms

Several species

Appearance and Life History

Webworms vary in color from cream to dark gray and have many prominent black spots and bristly hairs. The larvae measure up to 1 inch (25 mm) in length and are often found in silk-lined tunnels near the base of damaged plants. Pupation occurs late in May in silken cocoons. Adult female moths lay eggs on grasses in June, which marks the beginning of the next generation.

Damage

Feeding damage ranges from ragged, torn leaves to whole plants, cut off at or below ground level. Damage is most common in corn following sod.

Sampling Method

Check 20 consecutive plants in 5 different locations in a field for leaf feeding and/or plant cutting. Confirm the presence of webworms by carefully digging near the base of a damaged plant.

Management Guidelines

Corn Insect Control Recommendations: E-series 219-W (PDF)

No management guidelines have been established for sod webworms in corn. The black cutworm management guidelines for corn may be appropriate in certain situations.

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

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Wooly bear caterpillars

Several species

Appearance and Life History

The adults, known as tiger moths, can commonly be seen in the spring and mid-summer at night. These moths, with a 1-1/2 to 2 inch (38 to 50 mm) wing span, have snow-white, yellowish, or white and black-spotted wings with abdomens that are white to yellow. White to yellow spherical eggs are laid in clusters on leaves. The white, yellow or brown "woolly" or furry worms range in length from 1/4 to 2 inches (6 to 50 mm). Mature larvae leave the plant, seek a protective place, and pupate inside a thin silken cocoon which is covered with the hairs from their bodies. There are two generations per year, with only the second or mid season larval population posing a potential economic threat to soybean.

Damage

Woolly bear caterpillars are foliage feeders. Generally, their presence and damage is not noticed until late in the season.

Sampling Method

Determine defoliation levels in each of 5 areas of the field. Inspect the larvae for a commonly occurring fungal disease. If infected, they will appear "frozen" and may appear water soaked or covered with cottony-like substance.

Management Guidelines

Corn Insect Control Recommendations: E-series 219-W (PDF)

Should damage become apparent in areas or whole fields, treatment may be necessary if 25% or more defoliation is noted during pod fill stages. Before treating, however, look for diseased larvae. When larval numbers reach high levels, naturally occurring fungal pathogens often control the woollybear population.

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

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Yellowstriped armyworm

Spodoptera ornithogalli Guenée

Appearance and Life History

This caterpillar is identified by the bright yellow stripe on each side of its dark, velvety body. It has a wide variety of hosts.

Damage

The larvae are general defoliators.

Sampling Method

Sampling for this occasional invader of soybean should not be necessary because economic damage is rare.

Management Guidelines

Corn Insect Control Recommendations: E-series 219-W (PDF)

It is unlikely that numbers of yellowstriped armyworm and their damage will reach economic levels. Consider their damage additive to that of other defoliators and refer to "Green Cloverworm" management guidelines for soybean.

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