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Extension > Agriculture > Crops > Corn Production > Pest management > Black cutworm

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Black cutworm

Agrostis ipsilon Hufnagel (Lepidoptera: Noctuidae)

Ken Ostlie, Extension Entomologist and Bruce Potter, Extension Educator IPM

Distribution

gray moth with dagger shape on wings

Photo: Mark Dreiling, Bugwood.org

Figure 1. Black cutworm moth. Note color pattern and dagger marking.

The black cutworm is widely distributed in the temperate regions of the world. It cannot survive winters in Minnesota or other latitudes with freezing winter temperatures. In these areas, annual infestations are produced by migrant moths each spring.

Host range

Black cutworm adults feed on plant nectar. In addition to corn, the larvae feed on a wide range of broadleaf and grass crops and weeds.

Description and life cycle

Adult

The adult black cutworm is a moderate size moth with a wingspan of about 1-1/2 inches (Figure 1). The forewing is dark brown to back with the outside 1/3 markedly lighter. Markings on the forewing are for the most part indistinct. There is a distinct small black dagger shaped mark that extends outward from a faint kidney shaped (reniform) spot at the light to dark boundary of the forewing. The scales of the hindwings are pale gray to darker gray near the veins and edge.

Eggs

Eggs produced by spring migrant moths are often laid before crops are planted. The female moth can lay 1000 eggs or more, singly or in small groups of up to 30 on grasses, weeds and crop debris. Eggs hatch in 5 -10 days depending on temperature. Each female can lay 1000 eggs or more. Females seek out low-lying and weedy areas to lay eggs. While not winter hardy, the eggs can tolerate colder temperatures than other life stages.

Larva

gray larvae with dark brown head

Photo: John Capinera, University of Florida, Bugwood.org

Figure 2. Black cutworm larvae. Note head capsule, true and prolegs and tubercles near back.

bumps on larvae skin

Adam Sisson, Iowa State University, Bugwood.org

Figure 3. Magnified view of larva skin with tubercles.

Black cutworm larvae are gray to nearly black in color with a light dorsal band and a ventral surface lighter in color (Figure 2). The distinct head is dark brown. The larvae have three pairs of true legs and 5 sets of fleshy, abdominal prolegs. Overall, the larva has a greasy appearance; earning the common name "greasy cutworm" in some parts of the world. Under magnification, the skin of larger larvae has a granular appearance (Figure 3). Black cutworm larvae can be distinguished from the more common dingy cutworm and several other species attacking corn by the unequal sized and dark bumps (tubercles) on upper edges of each body segment. On the black cutworm, the front tubercle is obviously smaller than the rear. On the dingy cutworm these tubercles are nearly equal in size.

As they grow, cutworm larvae molt and pass through several larval stages or instars. There are 6 to 9 larval instars with 7 instars most common. The number of larval instars is influenced by diet, with poorer diet leading to prolonged development and more instars. Full grown larvae are about 2 inches long.

Larval development from egg hatch to pupa takes approximately 28 to 35 days depending on temperature.

Pupa

brownish-orange pupa in soil

Photo: Merle Shepard, Gerald R. Carner, and P.A.C Ooi, Insects and their Natural Enemies Associated with Vegetables and Soybean in Southeast Asia, Bugwood.org

Figure 4. Black cutworm pupa.

The mature larva burrows into the soil and creates an earthen cell to pupate. The naked pupae are orange-brown becoming dark brown as they age and are approximately 3/4 inches in length (Figure 4). The pupal stage lasts 12-15 days. It is believed that the environmental conditions encountered by the pupae determine if the resulting moths remain in the area, migrate south in the spring or north in the fall.

The entire life cycle from egg to adult takes 35 – 60 days. Multiple generations are produced until migration is triggered by weather conditions.

Crop damage

The larva is the damaging stage and damages plant tissue by feeding with chewing mouthparts. The potential for feeding black cutworm larvae to kill plants, thereby reducing stand, and potentially yield, makes large infestations of black cutworm a serious threat to corn and other crops.

Larvae are active mainly at night. Small larvae feed on leaves creating irregular holes and can cut small weed seedlings.

corn seedling cut off at base near larva

Photo: W.M. Hantsbarger, Bugwood.org

Figure 5. Black cutworm damage to a young corn plant.

While feeding near or below the soil surface, 4th instar and larger larvae can cut off corn plants (Figure 5), sometimes dragging the cut plants below ground. Plants cut above the shoot apical meristem (growing point) usually recover.

Dry soil conditions can encourage cutting below ground, at or below the growing point. Late-planted or corn delayed by cold weather conditions can be cut off by waiting cutworms before the corn emerges.

Although too large for even late instar larvae to cut off, corn plants larger than 5 collars can be killed by late instar larvae tunneling into the meristem. Most of the plant biomass is consumed by the last two larval instars.

Natural enemies

A range of Dipteran and Hymenopteran and nematode parasites have been isolated from black cutworm larvae. Cutworms can also be infected by viral and bacterial disease. Bird, mammal and insect predators (ground beetles) also impact cutworm larval populations. Birds and bats and motor vehicles prey on adults.

Management

Yield-limiting black cutworm infestations are relatively rare in Minnesota and when they do occur, require several factors to coincide:

  1. A large number of moths produced in the overwintering areas
  2. The proper weather systems, at the right time, to aid moth migration into the state
  3. Attractive and suitable sites for egg laying that will be planted are planted to susceptible crops (e.g. late emerging corn)
  4. Conditions favorable for black cutworm egg and larva survival

Although infestations can be devastating, the rarity of black cutworm problems indicates that insurance management tactics for black cutworm seldom pay.

Black cutworm migration

Two or more generations of the black cutworm occur in Minnesota. Typically, only the first generation larvae, produced by migrant moths, are damaging to corn.

The migration habits of the black cutworm have been documented on several continents. North American black cutworm moths use prevailing winds help them move north in the spring and south in the fall. In central United States, black cutworm moths migrate northward from over-wintering areas near the Gulf of Mexico, Texas and northern Mexico when appropriate weather systems occur.

U.S. map showing observed precipitation levels

Source: National Weather Service Advanced Hydrological Prediction Service

Figure 6. Nocturnal low-level jets are often associated with precipitation and thunderstorms as they draw warm moist air from the Gulf.

Black cutworm moths can move short distances north on their own but they take advantage of a much more efficient transport method to move long distances quickly. In spring, moths can make it from South Texas to Minnesota within 2 days. How do they do it? The moths hitch a ride on nocturnal low-level jet streams. These efficient transport systems are a common feature of the Great Plains in spring and summer and used not only by the black cutworm but other migrant Lepidoptera, aphids, leafhoppers and even rust spores. In North America, these low-level jets are powered by high elevation in the west and warm moist air in the Gulf of Mexico. Cool, dry, low pressure in the western plains interacts with moist high pressure systems in the eastern plains to create strong southerly flows that are especially strong at night (Figure 6).

Each winter, black cutworms are presumed to overwinter only as far north as topsoil remains unfrozen. Emigrating moths fly upward from the overwintering areas at dusk. If weather systems cooperate, they are whisked off by surface winds and rising air in advance of thunderstorms into the lower-level jet stream. These winds are strongest at night, moving at 30 to 80 miles per hour, and can occur from about 330 – 3000 feet in altitude. The flight is mostly passive with moths carried along until they decided to "drop out," encounter cold air, or rain out in thunderstorms. These migrating moths arrive in the north in excellent shape.

The ideal weather pattern for spring migration into Minnesota involves a HIGH pressure center to our east with a strong LOW pressure center approaching from the west. This pattern produces strong, persistent southerly winds that can bring black cutworm moths northward.

Two ingredients are necessary for black cutworm moths to arrive in Minnesota. First, the air parcels reaching Minnesota must have passed through the overwintering areas when migrating adults are present. Second, the track of the LOW pressure center is critical, if the LOW tracks too far south, migration is cut off south of Minnesota. If the LOW tracks through Minnesota or northern Iowa we have the potential for moths to drop out or precipitate out in Minnesota. These weather systems may stall with the frontal boundary cutting across Minnesota. In that case, if you’re south and east of the front, watch out! Several LOWS may ripple across the moist air pumping northward and compound the moth deposition in Minnesota. Moths often drop out on the edges of heavy rainfall.

Radar studies in the 1980s found most evening migrating insects move at an altitude of 1700 feet or so. Wind trajectories can be used to estimate where a significant immigration event (8 or moths / 2 consecutive nights) might have originated. Migration south in the late summer and fall is assisted by southerly flows associated with cold fronts.

What makes a field high risk for black cutworm damage?

Field topography, tillage and crop rotation

The overwintering cutworm species lay eggs based on soil type and previous year’s vegetation.

Photo: Bruce Potter, University of Minnesota

Figure 7. Good early-spring cutworm egg-laying. Unworked soybean residue with lambsquarters growth in a low-lying protion of the field.

Black cutworm moths arriving in Minnesota seek out areas with crop debris, sheltered areas and low spots in the field to lay eggs. Early season weed growth is very attractive to the moths. Areas with dense populations of winter annual (e.g. shepherdspurse, Capsella bursa-pastoris L.) and early-spring emerging (e.g. lambsquarters, Chenopodium album L.) broadleaf weeds in fields are often infested. Similarly, overwintering cover crops might attract egg-laying moths. Black cutworm damage associated with winter rye has been observed in Minnesota and Iowa (Figure 7).

bar graph

Figure 8. Influence of tillage and previous crop on the percentage of corn plants cut by black cutworm. Waseca, MN. K. Ostlie, 1985.

Egg-laying black cutworm moths are less attracted to fields after spring tillage. Unworked fields, or fields with reduced tillage where more crop debris is on the surface, attract more egg laying moths. The higher risk of black cutworm attack associated crop residues and tillage can be seen in tillage plots at the Southern Research and Outreach Center in Waseca, MN during 1985 (Figure 8) and 1986 and the Southwest Research and Outreach Center near Lamberton, MN during 2001 (Table 1).

Table 1. Black cutworm damage to corn as affected by soybean tillage (crop residue and weed growth at two locations. Source: K. Ostlie and Bruce Potter

  Corn plants cut (%)
Tillage system Waseca1 Lamberton2
Fall MB plow/spring fld. cult. 5.0
Fall chisel plow/spring fld. cult. 10.1 1.4
Spring field cultivator 3.0
Ridge till 14.7 7.9
No-till 10.2 1.0
Fall strip till 4.0
Spring strip till 9.2
1Waseca, MN, 1986.
2Lamberton, MN, 2001

Predicting black cutworm development and damage using pheromone traps and degree-days

Tracking moth flights

white trap hanging in tree

Photo: Travis Vollmer, University of Minnesota

Figure 9. Pheromone trap and black cutworm lure in early spring.

moths in sticky trap

Photo: Bruce Potter, University of Minnesota

Figure 10. Significant black cutworm moth pheromone trap capture.

Like most other moths, black cutworms are attracted to light. Black light traps capture both male and female moths throughout the flight but captures are not predictive of moth density. In addition to lights, male moths are attracted to a chemical sex lure (sex pheromone) released by females. Pheromone traps use a synthetic version of this sex pheromone and for a short period after they arrive unmated migrant males are attracted to the traps (Figures 9 & 10). These captures can be used to estimate moth population density and predict the potential for crop damage.

Degree-days and black cutworm growth and development

Since insects are cold blooded, their activities, including how quickly they grow, depends on the temperature of their environment. The effect of temperature on growth is known as temperature dependent development. An organism grows and develops faster if it is exposed to cumulative heat. Similar to predicting corn growth with degree day accumulations (a.k.a. growing degree, heat units, growing degree days), we can use degree-days to predict what stage the cutworm eggs, larvae or pupae will be at.

There are several ways to calculate degree-days for insect development but for crops and black cutworm, the simple model works fine. First, you need to know the maximum and minimum daily temperatures. Secondly, you also need to know the minimum temperature (lower development threshold or base temperature) at which cutworm growth occurs. Conveniently, we can use a 50° F lower developmental threshold for both corn and black cutworms.

Technically, limited larval development can occur whenever temperature for part of the day exceeds the developmental threshold, development ceases at an upper temperature threshold (e.g. 86°F for corn), individual life stages can have different threshold temperatures and temperature dependent development rates, temperatures where the eggs and larvae are located are slightly different than air temperatures, and some black cutworms go through fewer or extra larval stages (instars). Fortunately, for our purposes, these subtleties can be ignored.

A daily degree day accumulation = ((Maximum temperature + minimum temperature) / 2) - developmental threshold temperature

For an example of calculating degree-day accumulations: The daily high was 70°F and the daily low was 48°F. The degree-day accumulation would be:

((70+48) / 2) – 50 = 9

Daily degree-day accumulations are summed over the time period of interest.

To know when to start the degree day accumulations we need a "biofix." That biofix is a significant moth capture (8 or more moths over a consecutive 2-night period) and is where the black cutworm pheromone trapping network comes in.

The black cutworm life cycle, from egg to moth, takes 1-1/2 months or more. The simple degree-day model for development predicts when larvae large enough to cut plants after 300 hundred degree-days from a moth flight have been accumulated. Only cutworm larvae 4th instar or larger can cut corn plants. We can use degree-days to predict when larvae will be large enough to cause visible damage, begin to cut corn and cease feeding.

Scouting corn crops for black cutworms should start before 300 degree-days after a significant catch accumulate. This will, of course, happen sooner if warm and later if cool, but is about three weeks in a typical Minnesota spring.

Table 2. Temperature dependent development and feeding damage of the black cutworm.

Cumulative degree-days (base 50°F) Stage Activity
0 (biofix) Significant moth capture Egg-laying
90 Egg hatch
91-311 1st - 3rd instar Leaf feeding
312-364 4th instar Cutting begins
365-430 5th instar Cutting
431-640 6th-7th-instar Cutting slows
641-989 Pupa No feeding

Scouting for black cutworm

corn seedling with holes in leaves

Photo: Bruce Potter, University of Minnesota

Figure 11. Early (2nd) instar black cutworm and its leaf feeding on 1-leaf corn.

Scouting for cutworms is easily combined with stand evaluations and scouting weeds for herbicide selection and application timing.

The first sign of black cutworm damage is leaf feeding on emerged corn or weeds. Sometimes, larvae will cut weeds before they move to corn. Partially cut plants will wilt.

Be wary when lambsquarters and ragweed patches begin to disappear without the aid of an herbicide and herbicide applications may cause cutworms to switch from feeding on weeds to corn.

gray larva curled up next to cut corn seedling

Photo: Bruce Potter, University of Minnesota

Figure 12. A 4th instar black cutworm and corn plant cut at soil.

The leaf feeding and missing or cut plants caused by cutworms are not hard to see but it is useful to find a few of the larvae that caused the damage to determine size and species. This can be frustrating so why bother? Knowing the size of cutworm larvae will help determine the potential for future damage (Figures 11 & 12).

Knowing which species is present is important to understand the extent of the threat. Black cutworms are more damaging to corn than some other species. Dingy cutworms are a more common species in Minnesota that feeds at or above the soil surface. As a result, it does not cut corn below the growing point.

Cutworms are nocturnal. During the day, they hide under soil clods, crop residue and loose soil, typically at the boundary between dry and moist soil. Cutworms will likely be deeper when soils are dry. Carefully look under pieces of residue and soil clods close to cut or injured plants. If you don’t find a cutworm near the base of an injured plant, look near a couple plants on either side in the row. Using a possum-like defense strategy, most cutworm species roll into a semicircle and remain motionless when disturbed. Unfortunately for us and other predators, most cutworm species, including black cutworms, are more or less soil colored.

Finding cutworms in high residue, cloddy or muddy conditions is especially difficult. With leaf feeding you are looking for very small larvae. Move to another area with injured plants if unsuccessful. Looking at this optimistically, you only need to find a few to make your treatment decision. Do not confuse headless, legless cranefly larvae with cutworms. All cutworm species have a distinct head capsule and 3 pairs of true legs near the front with fleshy abdominal prolegs at the back.

Do stand counts in areas of the field with damage and note the percentage of plants with leaf feeding and those cut. To help with your decision, you can flag areas of row within the field and return the next day to determine if damage is ongoing.

Cutworms infestations in small corn (3 leaf or less) require more aggressive management than large corn. Don't give up on scouting too early. Late-instar black cutworms can kill up to 6 collar corn by burrowing into the growing point.

Economic thresholds: When to treat a problem

Cutworms reduce yield by decreasing final stand or plant population. The generic economic threshold for black cutworm in corn is 2 to 3 percent of the plants cut or wilted when the larvae are less than 3/4 inch long. The threshold increases to 5% cut plants when larvae are larger. However, with high corn prices, these thresholds could be lowered to 1% wilted or cut and small larvae and 2 -3% wilted or cut for large larvae.

Remember to take into consideration corn populations in individual fields and adjust threshold numbers accordingly. For example, if the current plant population is at or near yield limiting levels, you can afford to lose fewer plants than in a field with a higher emerged population. The role of corn plant stands in determining yields can be found in Table 3.

Table 3. Corn yield response to plant population (Morris, Lamberton, and Waseca, 2009-2011). Source: Manage corn planting decisions to optimize yield and economic return

Final corn stand (plants/acre) Expected yield (%)
44,000 100
41,000 100
38,000 100
35,000 100
32,000 100
29,000 99
26,000 96
23,000 92
20,000 87
17,000 81
Source: Manage corn planting decisions to optimize yield and economic return

The reason the black cutworm economic threshold varies by larval size is based in larval feeding. Cutworms must shed their skins (molt) in order to grow. The stage between molts is called a larval instar. Cutworms will begin to cut corn at the 4th instar (∼1/2 inch long). The smaller larvae tend to cut corn at or near the soil surface while larger larvae tend to feed below ground. The larvae are full grown and cease feeding between 1-1/2 and 2 inches long. While larger larvae will cut or tunnel into larger plants, they have less time left to feed and as a result have the potential to cut fewer plants. Table 4 gives approximate sizes in length and width of the head for black cutworm larvae.

Table 4. Black cutworm body and head capule sizes by instar stage.

Instar Body length (mm) Head capsule width (mm)
1 1-2 0.3
2 3-6 0.5
3 7-9 0.6-0.8
4 12-25 1.1-1.5
5 25-37 1.8-2.4
6 30-35 2.5-3.3
7 31-50 3.6-4.3

There are more detailed dynamic black cutworm thresholds available. They use stand, crop stage, projected damage and crop price. However, caution is advised when dynamic thresholds generate lower thresholds below those described above. Yield loss, actual or measurable, does not begin with the first missing corn plant. With higher grain prices and a good planted and emerged stand, you could easily be treating cutworm populations that would not reduce stand enough to actually hurt yields.

The rescue insecticide calculator (Table 5) is adapted from a University of Illinois publication and is an example of a dynamic threshold that is used in several management guides. Modern corn yields and prices could indicate treatment at a very low percentage cut plants using this worksheet, perhaps leading to over-reactive treatment decisions. However, the yield loss factors are still useful when combined with yield loss by stand reduction charts.

Table 5. Yield loss factors and equations (see below) to calculate the profitability of a rescue insecticide treatment for black cutworm. Source: http://extension.cropsciences.illinois.edu/fieldcrops/insects/black_cutworm/

  Yield loss factor for calculating corn yield loss
  Number of corn leaves when moisture is NOT limiting Number of corn leaves when moisture IS limiting
Avg. cutworm instar 1 2 3 4 5 1 2 3 4 5
3 2.4 1.8 0.8 0.7 0.7 1.6 1.2 0.4 0.4 0.2
5 1.2 1.8 0.6 0.3 0.3 0.8 0.9 0.3 0.2 0.2
6 0.7 0.2 0.1 0.1 0.1 0.5 0.2 0.1 0.0 0.0

Equations

PROJECTED BU/A YIELD LOSS= _______YIELD LOSS FACTOR X _______% PLANTS CUT (DECIMAL) X _______EXPECTED YIELD (BU/A)

PROJECTED $ LOSS/A = _______BU/A LOSS X $_______(PRICE/BU)

PREVENTABLE LOSS/A = $_______PROJECTED LOSS/A X _______% CONTROL*
*(95% CONTROL WITH ADEQUATE MOISTURE, 80% CONTROL WITH LIMITED MOISTURE

$ RETURN (+/-) FOR INSECTICIDE TREATMENT = $_______ PREVENTABLE LOSS/A - $_______ CONTROL COST/A

BT hybrids, seed applied and at-plant insecticides

Bt hybrids containing the Cry1F protein (Herculex /HX1) or Vip3a protein (Viptera), alone or in stacks, are labeled as controlling black cutworm. While they reduce risk, they might still be damaged under heavy cutworm pressure. An at-plant insecticide is probably not that helpful for cutworms when added on these hybrids. Remember, the Cry34/35 Ab1 (Herculex RW protein) is not the same as the Cry1F above-ground protein.

High rates of neonicitinoid seed treatments (e.g. Poncho, Cruiser, Gaucho) are very effective on many seed and seedling insects and they can provide some protection against black cutworm. They may not always provide satisfactory cutworm control.

Large numbers of late-instar cutworms moving from weeds to take a bite of corn can overwhelm seed treatments and Bt in corn tissues.

Some folks have been adding a soil insecticide to Bt-RW corn in areas with Bt-resistant rootworm populations. That is an entirely separate issue than cutworm management.

Soil applied at-plant insecticides can provide control of cutworm larvae. However, they are not recommended as insurance applications for two reasons. At planting, it is difficult to predict which individual fields will have economically damaging cutworm infestations. Secondly, post-emerge insecticide rescue treatments work very well.

T-band applications for granular insecticides, if so labeled, are sometimes more effective on cutworm than in-furrow applications. However, the banded insecticides are not necessarily more effective on corn rootworm. Always read the pesticide labels and use the appropriate rates. Incorporate the insecticide bands as indicated on the label. Windy planting conditions reduces the accuracy of banded applications when not incorporated. Later blowing of loose dry soils can also reduce efficacy of non-incorporated bands.

Cutworms are controlled well with rescue insecticide applications and many post plant insecticide products provide effective control of black cutworms. Spot treatments can be effective when combined with careful scouting. Make sure you still have cutworms present if you make a decision to treat. In springs when the top several inches of soil are dry, black cutworms tend to remain lower in the soil profile and insecticides are less effective. In dry conditions, a rotary hoe or row cultivation can help improve insecticide efficacy by incorporating insecticides and encouraging cutworm movement.

Be cautious of potential interactions between organophosphate insecticides (Counter 20G is one example) and some corn herbicides. Scouting and rescue insecticides applications are best defense against yield loss from black cutworms.

Cultural control

Maintaining good early- season weed control and reduce the attractiveness of fields to egg-laying females.

Tillage after eggs have been laid will have minimal effect on egg and larval survival.

Other cutworm species in Minnesota corn

Black cutworms are not the only cutworm species than can injure crops in Minnesota. As corn (and other row crops) germinate and begin to emerge they can be attacked by several species of cutworms. Table 6 lists some of the species that might be found in Minnesota corn fields. Most species can overwinter in Minnesota as eggs or larvae. Black and variegated cutworms cannot winter here and migrate into the state each spring.

While we can project cutting dates for the black cutworm, corn should be scouted for other cutworm species as soon as it emerges. Because cutworms that overwinter, particularly those that winter as larvae, begin development before migrant black cutworms arrive, they are ready to feed on corn early. Often, the first corn leaf feeding observed in the spring is from overwintered dingy cutworm larvae.

Certain species prefer particular habitats (Table 6). For example, sandhill cutworms are found in sandy soils and several species tend to be problems in crops planted into sod. Dingy cutworms are often abundant when corn is planted after alfalfa or fields that were weedy the previous year.

Species identification is important to determine damage potential. Small larvae of all species feed on weeds and leaves and cannot cut corn. Dingy, redbacked, and variegated cutworms are primarily leaf feeders feeding at or above the soil surface. Consequently, they don’t usually cut corn below the soil line and growing point and the plant recovers. However, unlike the climbing cutworms, the larvae of some cutworm species (e.g. glassy, sandhill, darksided, claybacked and black) tend to feed below ground at or below the growing point. This potential for their feeding to kill corn plants makes black cutworm a threat. When larger larvae tunnel into the growing point, corn as large as 5 or 6 leaves can be killed. Fortunately, damaging black cutworm populations are infrequently encountered.

With a bit of practice, the two species are easily distinguished by the size of paired black bumps (tubercles) on the upper edges of each segment. These tubercles are unequal in size on the black cutworm. Other Minnesota insects that cause damage that might be confused with cutworm include the hop vine borer and common stalk borer.

Table 6. Some cutworm species that can be found in Minnesota corn.

Species Eggs laid in # Generations Overwinters as Likely habitat
Black Spring-summer 3 Adults migrate Late-tilled fields, early weeds
Bronzed Fall 1 Eggs/larvae After sod
Claybacked Fall 1 Larvae After sod
Darksided Summer 1 Eggs After weedy crop
Dingy Summer-fall 1 Larvae After sod, alfalfa, weedy fields
Glassy Summer-fall 1 Larvae After sod
Redbacked Fall 1 Eggs After weedy crop
Sandhill Summer-fall 1 Larvae Sandy soils
Variegated Spring-summer 2 Adults migrate In and after alfalfa, weeds
larva with stripes down back

Photo: Whitney Cranshaw, Colorado State University, Bugwood.org

Figure 13. Bronzed cutworm. Note the distinct striping.

grayish-green larvae on leaf

Photo: John Capinera, University of Florida, Bugwood.org

Figure 14. Dingy cutworm. One of the most common MN cutworms. Note similar sized tubercles and diagonal slashes along top edge of body segments.

brown larva with tan stripes.

Photo: James Kalisch, University of Nebraska, Bugwood.org

Figure 15. Claybacked cutworm. Distinct light band along the back tubercles as black cutworm.

larva on leaf

Photo: Joseph Berger, Bugwood.org

Figure 16. Glassy cutworm. Note the squat, pale translucent body without any distinctive markings.

dark-colored larva on leaf

Photo: Frank Peairs, Colorado State University, Bugwood.org

Figure 17. Darksided cutworm. Note the white lateral strip above the legs and dark spots on the head.

light-colored larva

Photo: James Kalisch, University of Nebraska, Bugwood.org

Figure 18. Sandhill cutworm. Note pale color and faint stripes with internal organs visible through skin.

Photo: Bruce Potter, University of Minnesota

Figure 19. Variegated cutworm. Note the yellow diamonds along back and orange stripe along side. Color ranges from olive to black.

mass of gray larvae

Photo: Ed Lehman

Figure 20. Crane fly larvae. Not a cutworm or a pest. Not the lack of head capsules, legs and the head area tapered to a point.

curled-up larva

Photo: Bruce Potter, University of Minnesota

Figure 21. Black cutworm. Note the defensive C-shape. Find the larva's head, the true legs and prolegs. Examine the tubercles, the small black bumps on each segment near the cutworm's back. The unequal size, with the rear tubercle much larger is characteristic of black cutworms. The overall appearance is a black and “greasy.”

What about other crops?

Broadleaf crops have their growing points above ground at emergence. This means a cut plant can be killed and even climbing cutworm species can be a threat. Since yield loss from cutworms is related to stand loss, crops that are less able to compensate for stand loss are at greater risk.

While black cutworm larvae will cut soybeans, they are seldom a yield limiting problem in this crop. Soybeans are seeded at a much higher plant density and can compensate (up to a point) for reduced stand much better than corn.

Sugarbeets are at risk because of yield and quality sensitivity to beet stand. In addition, they are planted early and often with an oats cover which may encourage black cutworm egg laying. Cutworms move to beet seedlings as oats and weeds are killed by herbicides.

Selected references

Anon. http://extension.cropsciences.illinois.edu/fieldcrops/insects/black_cutworm/. University of Illinois, College of Agricultural, Consumer and Environmental Sciences, Extension & Outreach Publication. Accessed 4/27/17.

Archer, T. L. and G. L. Musick 1977. Cutting potential of the black cutworm on field corn. J. Econ. Entom. 70: 745-747.

Archer, T. L., G.L Musick and R. L. Murray. 1980. Influence of temperature and moisture on black cutworm (Lepidoptera: Noctuidae) development and reproduction. Can. Entomol. 112: 665-673.

Beck, S.D. 1988. Cold Acclimation of Agrotis ipsilon (Lepidoptera: Nocturidae). Ann. Entomol. Soc. Am. 81: 964-968.

Busching, M. K. and F. T. Turpin. 1976. Oviposition preferences of black cutworm moths among various crop plants, weeds, and plant debris. J. Econ. Entomol. 69: 587-590.

Busching, M. K. and F. T. Turpin. 1977. Survival and development of black cutworm (Agrotis ipsilon) larvae on various species of crop plants and weeds. Environ. Entomol. 6: 63-65.

Campinera, J. L., D. Pelissier, G. S. Menout and N. D. Epsky. 1988. Control of black cutworm with entomogenous nematodes (Nematoda: Steinernematidae, Heterorhabditidae). J. Invert. Pathol. 52:427-435.

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