Tag: corn earworm

Scout Sorghum for Key Insect Pests

David Owens, Extension Entomology Specialist, University of Delaware | owensd@udel.edu
and Kelly Hamby, Extension Entomology Specialist, University of Maryland | kahamby@umd.edu

Although sorghum faces relatively few pests compared to our other grain crops, it is not a “plant and forget” crop. Sorghum is often grown on marginal ground, in areas with greater deer pressure, dryland fields, and as a rotational component for managing weed and disease pressure. Sorghum is generally a minor component of a farming operation, and as such is easy to overlook during the season, especially now as other pests are requiring more attention and corn is nearing harvest. However, there are two significant insect pests that need to be scouted for to avoid potential losses and both are active right now on Delmarva.

The first pest that has the greatest impact on sorghum is corn earworm (Figure 1), also known as sorghum headworm (among many other crop related common names). Heads that began pollinating within the last two weeks coincided with a significant increase in earworm activity, and last week, earworm spray thresholds were exceeded in some locations in Delaware. The best way to scout for earworm is to use a ‘beat bucket’ – traditionally a 2-5 gallon bucket, although a sweep net can serve in a pinch. Gently bend the head to fit inside the bucket and shake it against the sides of the bucket several times to dislodge worms. Do this for 10 heads in a location, and 5 locations per field. Keep notes on how many larvae are small (1/4 inch or less), mid-sized (1/4 – ½ inch) and large (>1/2 inch). Texas A&M has a useful sorghum threshold calculator that takes into account control costs, grain value, and heads per acre and calculates a threshold based on the number of medium and large larvae. If your field is over threshold, we have several good options for earworm. In a 2019 spray trial, the greatest worm reductions came from Carbaryl (1.5 qts), Lannate (1.1 pints), Besiege (8 fl oz), Prevathon (now Vantacor), and Baythroid XL (2.8 fl oz). Before treating sorghum for corn earworm or the next pest of interest, remember to read labels carefully; the label is the law.

Figure 1. Corn earworm adult.

The second pest of concern is the white sugarcane aphid (Figure 2). This is a relatively new pest, and should not be confused with yellow sugarcane aphid or corn leaf aphid, both of which are common but not damaging. Yellow sugarcane aphids are bright lemon yellow, larger, and have hairs. Corn leaf aphid is a darker green color and often present in the whorl before head emergence, but quickly disappears afterward. I think of it as a beneficial insect in sorghum because lady beetles and other natural enemies get established on corn leaf aphids early. White sugarcane aphid are small, pale white-yellow, and buildup large colonies under leaves. When it is present in a field, it is obvious. Aphids produce copious honeydew which attracts flies, bees, and butterflies. It can cause yield loss as late as soft dough, particularly in drought stressed fields. So far this year in Delaware, its populations have been spotty, slow to build, and our soils for the most part have adequate moisture. There are two thresholds: 40-150 aphids per leaf or 30% of plants with aphids and scattered areas of honeydew slicks present on the upper surface of a leaf just below the aphid colony. In 2019, we found our first sugarcane aphid on August 8. By September 11, the field averaged between 227 and 644 aphids per leaf! If you recall, September 2019 was oppressively hot and dry. In 2020, sugarcane aphids were detected at the end of July and several fields were treated. I am optimistic that they will not pose as much of a threat this year, but you need to be scouting. Pay attention to any fields that are pollinating or still have heads emerging (pretty much any field you would scout for corn earworm). If you deem a field needs treating, the only good options are Sivanto, Transform, and Sefina. Sivanto has a 2ee recommendation to use at 4 fl oz, although even lower rates will work very well. Lorsban and dimethoate annoy aphids for about a week before their population increases. Pyrethroids are completely ineffective. If sorghum is going to continue serving in your rotation, reach out to your agronomist – several varieties have some level of resistance or tolerance to aphids, and this far north, that may be all we need for late sorghum.

Figure 2. White sugarcane aphids.

September IPM Insect Scouting Tips

Emily Zobel, Senior Agriculture Agent Associate | ezobel@umd.edu
University of Maryland Extension, Dorchester County

Soybeans: Continue scouting for corn earworm, stink bugs, and soybean looper in double-crop fields. Defoliation thresholds at R5 are 15% and between 20 and 30% at R6. Corn earworm pheromone trapping information for Maryland can be found at https://extension.umd.edu/resource/corn-earworm-pheromone-trapping. NC State Extension has a good CEW threshold calculator can be used to help decide if it is worth treating: https://www.ces.ncsu.edu/wp-content/uploads/2017/08/CEW-calculator-v0.006.html. Stink bug thresholds are 5 bugs per 15 sweeps until the soybeans reach the R7 stage, after which treatment for stink bugs is not necessary.

As the month progresses and fields get closer to harvest, sample stems in any field with a history of Dectes stem borer issues. If the field has a large stem infestation, prioritize that field for as timely a harvest as possible to reduce loss due to lodging.

Sorghum: Sugarcane aphids have been found on the Eastern Shore. This week’s cooler weather should slow down their reproduction rate, but if we get some warm days in September, that might change. To scout, check the 50 plants in 4 different locations at least 25 feet into the field. If honeydew is present, check the upper and lower canopy of 15-20 plants for aphids. Treatment thresholds are when the field has an average of 50 and 125 aphids per leaf or 30% infested plants with localized areas with honeydew present. David Owen from UDel recommends using Sefina, Sivanto, and Transform for control. See Texas A&M “Scouting Sugarcane Aphids” handout for more information.

How bad is bad? Soybean defoliation and new tools for assessing it

Maria Cramer, Graduate Student | mec@umd.edu and Kelly Hamby, Extension Entomologist | kahamby@umd.edu
University of Maryland, Department of Entomology

As soybean plants mature, tolerance for defoliating pests drops from about 30-35% during the vegetative stages to closer to 15-20% during the reproductive stages (flowering and pod fill). Any defoliation can look worrying, but it is hard to accurately measure defoliation. Most people tend to overestimate damage in three ways: overestimating the leaf area lost, not taking the full plant canopy into consideration, and not sampling the field randomly. Luckily, there are some great new tools to help you measure accurately and train your eye. Accurate measurement is the key to avoiding unnecessary treatments, saving you money, time, and preserving beneficials.

What defoliates soybean?

  • Grasshoppers tend to be concentrated on the edge of the field, especially near grasses or small grain fields1, and can cause jagged holes in leaves and sometimes clip pods (Fig. 1a).
  • Japanese beetle is an introduced pest that aggregates in large groups and skeletonizes leaves (Fig. 1b).
  • Bean leaf beetle is a native pest that can cause damage to seedlings, defoliate, and occasionally feeds on pods, but generally is not a problem on large plants unless other defoliators are abundant (Fig. 1c).
  • Mexican bean beetle occurs late in the season and feeds on the underside of leaves, causing a lacy appearance (Fig. 1d ).

    Figure 1. a) Grasshopper, photo from Prairielands FS. b) Japanese beetle, photo from Prairielands FS. c) Bean leaf beetle (they can also be yellow or lack spots), photo by Wikimedia Commons. d) Mexican bean beetle, photo from University of Maryland Extension.

There are also caterpillars that can feed on soybean foliage.

  • Soybean looper is distinctly larger towards its tail-end, has two pairs of prolegs in the middle of its body, and moves in a “looping” fashion (curls its body into a hump while walking) (Fig. 2a).
  • Silver spotted skipper has thin stripes and a dark head-capsule, with a noticeable constriction (narrower) behind the head (Fig. 2b).
  • Green cloverworm looks similar to soybean looper and also moves in loops (notice hump forming in the image), but the two ends are the same size, and it has three pairs of prolegs in the middle of its body (gripping the stem in the image) (Fig. 2c).
  • Velvetbean caterpillar has four pairs of prolegs in the middle of their body and can also be identified by its violent thrashing when handled (Fig. 2d).

    Figure 2. a) Soybean looper, photo by NCSU extension. b) Silver-spotted skipper, photo by Josh Em. c) Green cloverworm, photo by Daren Mueller. d) Velvetbean caterpillar, photo by Clemson University.

These pests make up the defoliating insect complex in soybeans, although they do not necessarily all occur together. However, if you must treat for them, make sure your insecticide works against the complex that is in your field.

When is defoliation a problem?

These insects become a problem when their defoliation exceeds treatment thresholds. Vegetative soybeans are tolerant of feeding, especially as they get larger, so until up to about two weeks prior to blooming this is around 30-35%.  From about two weeks prior to blooming until pods fill (R7-R8) the treatment threshold is 15-20% defoliation. If defoliation exceeds these numbers at these times, yields can start declining, especially in drought conditions2. Pests that feed on pods (including some caterpillar species), have different thresholds, so it can be important to identify specific pests during sampling.

Sampling

To accurately determine percent defoliation, a thorough assessment of the field is necessary. Because many defoliators tend to congregate in the field, this means sampling a minimum of ten plants in four locations and averaging the results is needed for an accurate assessment. Figure 3, from the University of Nebraska Extension, outlines how to properly sample. Although this is a lot of sampling, it is important to eliminate bias and avoid overestimating damage. Nebraska Extension also has a work sheet3 to plug in your measurements for an average.

Figure. 3 Sampling soybean defoliation. Infographic by Justin McMehan, University of Nebraska.

If you see caterpillar pests in your field, you may also want to use sweep net sampling4 to determine which pests and how much pressure is present. The threshold for velvetbean caterpillar is ≥10 in 10 sweeps, and for soybean looper it is ≥15 in 10 sweeps. Corn earworms (Fig. 4.) which feed on terminals, flower clusters, and pods and can also be sampled using sweep nets. A dynamic threshold calculator5 has been developed for corn earworm in soybeans.

Figure 4. Corn earworm (also known as podworm).

New technology

Some good news is that even though it is hard to visually gauge defoliation, there are new tools you can use to be more accurate. One is the Crop Protection Network’s Soybean Defoliation Training6. With this tool you can use a slider to see what different levels of defoliation look like on a leaf. You can also test your skills by taking a quiz where you estimate defoliation. This is a great way to train your eye before you go out to sample.

Alternatively, if you have a smartphone, you can use a new app called “Leafbyte” to accurately assess defoliation7,8. With this app, you take pictures of leaves on a white background and the app calculates the percentage of leaf removed (Fig. 5).

Figure 5. Leafbyte app calculates the amount of leaf area missing from a leaf photographed against a white background.

Treatments

For many of these pests, avoiding broad-spectrum insecticides early in the season is likely to keep their populations in check. However, if defoliation has exceeded treatment threshold, you have several options; remember that less mature insects are easier to control. For most of these pests, pyrethroid products (e.g., Baythroid®, Warrior II®, Hero®) are reasonably effective and provide residual control. Soybean looper is an exception, because it has evolved resistance to pyrethroids, carbamates, and organophosphates (and other modes of action in the lower coastal plain areas of North Carolina), so it will not be controlled if these insecticides are used for other pests. Indoxacarb (e.g., Steward®), methoxyfenozide (e.g., Intrepid®), chlorantraniliprole (e.g., Coragen®, Prevathon®), spinosyns (e.g., Radiant®, Blackhawk®), and methoxyfenozide/spinetoram mixtures (e.g., Intrepid Edge®) can be effective9,10. Large grasshoppers require a higher rate of pyrethroid insecticides, while grasshopper nymphs (those without fully formed wings, Fig. 6) can be controlled using the insect growth regulator diflubenzuron (Dimilin®)11. When using insecticides, always consult and follow the label.

Figure 6. a) Grasshopper nymphs range from having no wings to having wing pads like the one pictured, but these do not cover the abdomen. Photo by Lyle J. Buss. b) Adult grasshoppers have wings that cover their abdomen. Photo by John L. Capinera.

Additional resources:

  1. Boethel DJ. Integrated management of soybean insects. Soybeans Improv Prod Uses. 2004;(16):853-881. doi:10.2134/agronmonogr16.3ed.c17
  2. Klubertanz TH, Pedigo LP, Carlson RE. Reliability of yield models of defoliated soybean based on leaf area index versus leaf area removed. J Econ Entomol. 1996;89(3):751-756. doi:10.1093/jee/89.3.751
  3. Soybean defoliation worksheet: https://cropwatch.unl.edu/2016/soybean-defoliation-worksheet
  4. Sweep-net sampling: https://www.youtube.com/watch?v=QiokQqLFD5U&t=1s
  5. Podworm dynamic calculator: https://www.ces.ncsu.edu/wp-content/uploads/2017/08/CEW-calculator-v0.006.html
  6. Defoliation estimation training: https://severity.cropprotectionnetwork.org/crop/soybeans/soybean-insect-defoliation-training
  7. Getman-Pickering ZL, Campbell A, Aflitto N, Grele A, Davis JK, Ugine TA. LeafByte: A mobile application that measures leaf area and herbivory quickly and accurately. Methods Ecol Evol. 2020;11(2):215-221. doi:10.1111/2041-210X.13340
  8. Leafbyte app: https://zoegp.science/leafbyte
  9. Cook DR, Crow W, Gore J, Threet M. Performance of selected insecticides against soybean looper in soybean, 2020. Arthropod Manag Tests. 2021;46(1):2021. doi:10.1093/amt/tsab020
  10. Reisig D. Soybean looper thresholds and insecticide recommendation. NC State Extension.
  11. Royer TA, Giles KL, Jeffcoat MD, Griffin J. Evaluation of Dimilin insecticide for control of a mixed-species grasshoppers using an RAAT application, 2000. Arthropod Manag Tests. 2001;26(1):10-11. doi:10.1093/amt/26.1.g54

Corn Earworm Trap Captures Up, and New Web Page for Updates

Alan Leslie, Agriculture Agent | aleslie@umd.edu
University of Maryland Extension, Charles County

Figure 1. Corn earworm moths in a pheromone trap at the Central Maryland Research and Education Center in Beltsville.

A few hot spots where corn earworm (also known as tomato fruitworm, soybean podworm, and sorghum headworm) activity is starting to rise have been identified in central Maryland. The relatively mild 2020-2021 winter allowed adult moths to overwinter in Maryland, and some parts of the state experienced a higher than normal first flight in early June. Now that we are heading towards the end of summer, the next generation of moths are emerging as adults and have begun flight. Some areas continue to capture few moths and are experiencing low pressure, while others have been experiencing moderate pressure that has increased to heavy pressure (Fig. 1). See Figure 2 for pressure at select sites in Maryland. Monitoring pressure using on-farm traps provides the most accurate information for making management decisions. We recommend using two pheromone traps and replacing the lures frequently, especially during periods of hot weather. For weekly updates on pheromone trap captures across the state and information on how to scout for and manage corn earworm in vegetable and grain crops, visit the new webpage: https://extension.umd.edu/resource/corn-earworm-pheromone-trapping.

Figure 2. Weekly captures of corn earworm moths using pheromone traps at select sites across the state. Dashed line represents the cutoff for what is considered heavy moth pressure.

Corn Earworm Pressure Varying Regionally—Make Sure to Scout

Kelly Hamby1, Maria Cramer1, Galen Dively1, Sarah Hirsh2, Andrew Kness2   Alan Leslie2, Kelly Nichols2, Emily Zobel2, and David Owens3
1University of Maryland, Department of Entomology | 2University of Maryland Extension
3University of Delaware Extension

 

A few hot spots where corn earworm (also known as tomato fruitworm, soybean podworm, and sorghum headworm) activity is starting to rise have been identified in central Maryland and Delaware. The warm 2019-2020 winter allowed for overwintering in our area, and some parts of the state experienced a higher than normal first flight in early June. The warm weather through June and July made for speedy development and earlier activity for the second summer generation. Because corn earworm has developed resistance to most Bt hybrids, significantly more adult moths are emerging compared to levels a decade ago. Some areas continue to capture few moths and are experiencing low pressure, while others have been experiencing moderate pressure that may continue to increase towards heavy pressure (>65 moths captured per 5 days). Captures for select sites in Maryland and Delaware are pictured below, and values within the gray box indicate low pressure (<7 for weekly captures, and <5 for four to five day captures).

corn earworm on corn ear
Corn earworm larva feeding damage to corn

Although corn earworm prefer fresh corn silks for egg laying, they will lay eggs on wilted and brown silks if the plants remain green and unstressed. As corn matures further over the next several weeks, corn earworm activity will shift to other host plants including soybeans and vegetables. See last summer’s articles for scouting and management recommendations in vegetables as well as sorghum and soybeans.

Podworm outbreaks have historically occurred in growing seasons where the corn crop was drought and heat stressed, with corn senescing earlier than normal. However, narrow row spacing in soybeans makes the plants less attractive to female moths and increases the likelihood that fungal pathogens will infect the larvae. Therefore, it is important to scout bean fields, especially paying attention to those fields with a more open canopy in areas where the nearby maturing corn is no longer attractive to earworm moths. North Carolina State University has produced a helpful economic threshold calculator for podworm in soybean: https://www.ces.ncsu.edu/wp-content/uploads/2017/08/CEW-calculator-v0.006.html

graph of maryland cew trap countsgraph of Delaware cew trap counts

Acknowledgements: Corn earworm trapping efforts in were supported by the Crop Protection and Pest Management Program [grant numbers 2017-70006-27171 and 2017-70006-27286] from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

 

Special Alert: Growers Need to Scout for Soybean Podworms and Sorghum Headworms

Kelly Hamby1, Galen Dively1, David Owens2, Ben Beale3, Peter Coffey3, Andrew Kness3, Alan Leslie3, Erika Taylor3, Kelly Nichols3, Matthew Morris3, and Emily Zobel3

1University of Maryland Department of Entomology
2University of Delaware Extension Entomology
3University of Maryland Extension

Moth flight activity for the corn earworm, also known as the soybean podworm and one species of sorghum headworm, has increased during the past week. Pest pressure varies across the state and Delmarva region. The early surge in activity is attributed to the record temperatures during June and July, which have accelerated larval development and shortened the generation time of this insect. Corn earworm has already caused significant damage to ears of sweet corn and early planted field corn. Note that Bt hybrids expressing single or multiple Cry proteins no longer control earworms due to the development of resistance; only hybrids expressing the Vip3a Bt protein provide good ear protection. These hybrids represent a relatively small portion of the planted acreage. Thus, significantly more adult moths are now recruited in corn compared to levels a decade ago.

Corn earworms are strongly attracted to and prefer fresh corn silks for egg laying. Outbreaks in other crops often follow a midsummer drought, which causes the corn to ripen earlier and become less attractive to the moths. As early planted corn fields dry down, moths will move into other vegetable and grain crops.

Podworms in Soybeans:

Corn earworm feeding on soybean pod. Image: Clemson University
Corn earworm feeding on soybean pod.
Image: Clemson University

In soybeans, female corn earworm moths prefer to lay eggs in open-canopied, late-blooming fields, and are most attracted to soybeans for egg laying from flowering to early pod-set. Drought conditions also delay soybean maturity and prevent normal canopy growth, so peak moth activity is more likely to coincide with blooming of open-canopied fields. In irrigated fields, activity may be greater along pivot tracks and dry corners. Corn earworm larvae can damage flowers; however, because soybeans produce more flowers than needed, flowering sprays are rarely necessary. Podworms cause the most damage when large larvae are feeding on full seed pods with large seeds (see information from NCSU).

What to do? Scout bean fields, paying special attention to those fields with a more open canopy in areas where the nearby maturing corn is no longer attractive to earworm moths.

Sampling should start during mid-August and be repeated at least weekly in each field until a spray decision is made or the pods reach full maturity. Most fields are planted as narrow-row beans, so a 15-inch sweep net is the most practical way to sample for earworms. Walk along the rows, swinging the sweep net so that the opening passes through the foliage. The net is turned 180 degrees after each sweep as you advance with each step to swing the net through the foliage in the opposite direction. Each stroke is counted as one sweep. A series of 25 sweeps should be taken at each of 5 sites in every 40 acres.

Treatment is recommended when counts exceed 3 medium to large podworms per 25 sweeps in narrow row fields, or 5 podworms per 25 sweeps in wide row fields (20 inches or greater). The timing strategy is to wait until most of the larvae are 3/8 inch or more in length, and then treat when pod damage is first evident. This allows for most egg laying and hatching to occur before treatment and reduces the chances of a second spray being needed later. These static thresholds are based on long-term averages for control costs and soybean prices. North Carolina State extension has developed a dynamic online threshold calculator for corn earworm in soybeans that takes into account the sampling method (uses a 15 sweep rather than a 25 sweep sample), row spacing, cost for control, and the value of soybeans, which can be found at:

https://www.ces.ncsu.edu/wp-content/uploads/2017/08/CEW-calculator-v0.006.html

Since the 2008 season, numerous reports of control failures with pyrethroids (Group 3A) used for earworm control have been reported from the Mid-Atlantic region and states to our south. This insect has developed moderate to high levels of resistance to this class of insecticides, so growers need to consider other modes of action. If a pyrethroid (e.g., Brigade, Warrior, Mustang Maxx, Hero, Baythroid, Tombstone) is used, the highest labeled rate timed for small to medium, rather than large worms, is recommended. Alternative classes such as diamides (Group 28; e.g., Coragen, Prevathon), oxadiazines (Group 22A; e.g., Steward) and spinosyns (Group 5; e.g., Blackhawk, Radiant) will be most effective. These materials are also generally softer on beneficial insects which prey upon other late season soybean pests, such as soybean looper and stink bug. ALWAYS read and follow instruction on the pesticide label; the information presented here does not substitute for label instructions.

Headworms in Sorghum:

Corn earworm female in sorghum. Image: John C. French Sr
Corn earworm female in sorghum. Image: John C. French Sr

Headworms (corn earworm, fall armyworm, and sorghum webworm) are caterpillar pests that infest grain heads. Flowering or heading sorghum is attractive to corn earworm females for egg laying, and headworm issues have been reported in Southern Maryland this year. Headworms feed on the flowers and developing kernels and large larvae can cause significant yield loss.

What to do? Scout sorghum fields from the end of flowering until hard dough.

Sample heads by bending them into a clean white 5 gallon bucket and beating them to dislodge the headworms. Sample 10 heads per location and sample multiple locations per field. If most larvae are small (up to ¼ inch) sample the field again in 3 to 4 days.

Thresholds vary by the size and species of larvae and sorghum value. In general, 2 corn earworm larvae per head would warrant treatment, and Texas A&M has developed a dynamic online threshold calculator that incorporates cost of control, grain value, anticipated yield (heads/acre), and larval size, which can be found at:

https://agrilife.org/extensionento/sorghum-headworm-calculator/

As mentioned above, pyrethroids (Group 3A) offer poor to moderate control of corn earworm in the Mid-Atlantic, and will not control heavy infestations or large worms. If a pyrethroid (e.g., Brigade, Warrior, Mustang Maxx) is used, the highest labeled rate is recommended. Alternative classes such as diamides (Group 28; e.g., Prevathon), spinosyns (Group 5; e.g., Blackhawk, Tracer), or carbamates (Group 1A; e.g., Sevin, Lannate) will be most effective. Selective insecticides that are less damaging to beneficials are recommended, such as Prevathon (most recommended) or Blackhawk. ALWAYS read and follow instruction on the pesticide label; the information presented here does not substitute for label instructions.

While scouting for headworms, growers are encouraged to look for sugarcane aphid in sorghum as well. Virginia Tech reported the first confirmed identification of white sugarcane aphid in Amelia County on August 1st. For more information on sugarcane aphid see Agronomy News Volume 8 Issue 1. If sugarcane aphids are also present, we strongly advise using selective insecticides to preserve the natural enemies that slow sugar cane aphid population growth.

Further Resources:

North Carolina State Podworm Factsheet:

https://soybeans.ces.ncsu.edu/corn-earworm/

University of Delaware Weekly Crop Update:

https://sites.udel.edu/weeklycropupdate/

University of Delaware Insect Management:

http://extension.udel.edu/ag/insect-management/field-vegetables-fruit/

Virginia Tech Pest Management Field Crops Guide:

https://www.pubs.ext.vt.edu/456/456-016/456-016.html (Sorghum Headworm Section)

Sorghum Checkoff Headworm Guide:

https://www.sorghumcheckoff.com/newsroom/2016/03/28/headworms/

Sugarcane aphid found in VA sorghum – 2019:

https://blogs.ext.vt.edu/ag-pest-advisory/sugarcane-aphid-found-in-va-sorghum-2019/

Agronomy News Sugarcane Aphid Article:

https://extension.umd.edu/sites/extension.umd.edu/files/_docs/AgronomyNewsApril2017.pdf

Guess the Pest! Week #22 Answer: Helicoverpa zea, Corn Earworm

Guess The Pest Logo

 

 

 

 

 

Bill Cissel, Extension Agent – Integrated Pest Management, University of Delaware; bcissel@udel.edu

Congratulations to Amanda Heilman for correctly identifying the insect as an adult corn earworm and for being selected to be entered into the end of season raffle for $100 not once but five times. Everyone else who guessed correctly will also have their name entered into the raffle. Click on the Guess the Pest logo to participate in this week’s Guess the Pest challenge!

Guess the Pest Week #22 Answer: Helicoverpa zea, commonly known as corn earworm

The moth in the photograph is an adult Helicoverpa zea, commonly referred to as a corn earworm. The adult moth is a nectar feeder and not considered a pest. However, corn earworm larvae are considered by some to be the most economically important crop pest in North America. They are highly polyphagous meaning they feed on many different species of plants. Corn, especially sweet corn, is a preferred host plant. However, they also attack soybean, sorghum, snap bean, tomato, and cotton to name a few. Larvae prefer to feed on reproductive plant structures including blossoms, buds, and fruits. It is because of this large host range, and the fact that Helicoverpa zealarvae are so destructive that they are known by several other common names including tomato fruitworm, cotton bollworm, and podworm.

For the latest trap counts for corn earworm in your region, visit mdmothmap.com.

Should I Be Worried About Mega-Pests?

Peter Coffey, Agriculture Agent Associate
University of Maryland Extension, Carroll County
plcoffey@umd.edu

If you’re a farmer in the United States then you’re acquainted with the corn earworm, Helicoverpa zea. Maybe you know it as cotton bollworm, tomato fruitworm, sorghum headworm, soybean podworm, or maybe you remember when scientists used to call it Heliothis zea. To keep things from getting confusing we’ll just call it H. zea. No matter what you call it, it’s the same tan colored moth with caterpillars we all remember picking out of the tip of an ear of sweet corn as a kid. As you can guess from the variety of names, H. zea feeds on a lot of different crops. It’s actually been documented to eat over 100 different plants, usually the reproductive part of the plant (the fruit/grain/bean part).

Adult corn earworm
Figure 1. Adult Helicoverpa zea moth. Image: Peter Coffey, University of Maryland.

While H. zea is a devastating pest throughout North and South America, it has a bigger badder older brother. In Europe, Africa, Asia, and Australia they also call this moth the cotton bollworm, but it’s a different species, Helicoverpa armigera (we’ll call it H. armigera). In fact, H. armigera is the parent species to our H. zea. Scientists estimate that about 1.5 million years ago some H. armigera moths made their way over to the Americas, and over time they evolved enough that does we consider them to be a different species, H. zea. To put it another way, if dogs evolved from wolves, then H. zea is a bulldog, and H. armigera is the wolf. This is important because H. armigera as the older original species is more genetically diverse, which is probably why it’s better at evolving pesticide resistance.

In recent years, increasing global trade has increased the occurrence of introductions of invasive pests worldwide, and H. armigera has been one of the species that people are the most worried about. It has been caught at the borders several times in North America, but unfortunately in 2013 it was confirmed to be established in Brazil. Additionally, scientists have known for a while that H. armigera and H. zea could mate and create viable hybrids in the laboratory, and just this winter a paper was published documenting the first wild hybrids discovered in Brazil.

Hybrid moths are concerning, because even though H. armigera is the more genetically diverse species, H. zea has spent the last 1.5 million years developing its own unique set of genes. This means that the hybrids combine the genetic diversity of both species. If you’re wondering why genetic diversity is important, remember that when a population lacks genetic diversity we call it inbred, so you could think of hybrids as the opposite of inbred. Scientists worry that these hybrids could attack an even wider range of crops, and that they could evolve pesticide resistance even faster. There’s no reason to think that individual caterpillars would be more damaging, both species are cannibals, which is why you rarely see more than one worm in an ear of corn.

So what does this mean for you? It means that sometime in the future, if these hybrids make it here, pesticide resistance may become even more of a concern than it already is. For now, if you’re spraying corn remember to rotate your chemical families. You can also check out what the corn earworm population is doing at www.mdmothmap.com, or call your local extension office and ask.