Western Corn Rootworm Adults Present in Some Central Illinois Fields

In spite of the very heavy precipitation and saturated soils in many fields across the state, some western corn rootworm adults have survived and have been sighted in several fields in central Illinois. Matt O’Whene, Research Associate with DuPont Pioneer, observed western corn rootworm adults in a cornfield located in Piatt County on June 24. The western corn rootworm in Matt’s photograph appears to be a male. Males typically emerge first followed by the emergence of females a few days later. By late next week, I expect sightings of western corn rootworm adults to become much more common. It remains to be seen how much root injury will occur this year, especially in areas of the state where resistance to some of the Cry proteins (Cry3Bb1 and mCry3A) has been confirmed. Plants may be more susceptible to lodging this season due to saturated soils, shallow root systems, and frequent storm activity accompanied by windy conditions. As plants become increasingly top heavy, I anticipate more calls related to lodged fields. Don’t automatically assume that lodged fields have root injury associated with rootworm feeding. The only way to confirm corn rootworm larval injury is to dig up plants, wash the soil from the root system, and evaluate the roots for feeding and pruning. We typically wait until mid-July to begin rating roots for injury in our product evaluation trials.

Male western corn rootworm adult, Piatt County, Illinois, June 24, 2015 (Courtesy of Matt O’Whene, Research Associate, DuPont Pioneer).


In addition to observations of western corn rootworm adults in Piatt County,  Preston Schrader, Monsanto Company, and Jeremy Lake, Technical Agronomist Asgrow/DeKalb found adults in Macoupin County on June 22. Preston Schrader also indicated adults had been sighted in Menard County. Bottom line — adult emergence is underway and in the coming weeks, it will be time to evaluate the performance of root-protection products (Bt hybrids and/or soil insecticides).

Mike Gray, Professor and Extension Entomologist

Corn Rootworm Emergence Just Around the Corner for East Central Illinois

Joe Spencer, an entomologist with the Illinois Natural History Survey, observed 2nd and 3rd instar corn rootworm larvae earlier today (June 23) in his research plots located north of Urbana, Illinois. He anticipates the emergence of adults from these plots by early next week. As we begin the 4th of July Holiday, I suspect initial sightings of western corn rootworm adults will begin to occur across central Illinois. Overall, I anticipate the statewide population of western corn rootworms to be reduced this season due to the heavy precipitation many areas have received throughout June leading to saturated soils at the time of larval hatch.

Corn rootworm larva in non-Bt plot north of Urbana, Illinois, June 23, 2015 (Courtesy of Joe Spencer Illinois Natural History Survey).

Corn rootworm larva in non-Bt plot north of Urbana, Illinois, June 23, 2015 (Courtesy of Joe Spencer Illinois Natural History Survey).


On June 11, 2015 I observed a few Japanese beetles in cornfields scattered across western and central Illinois counties. In recent years, densities of this pest have been most significant in northwestern Illinois. If you begin to observe western corn rootworm adults in your area of the state, please let me know and I will pass along your observations to readers of this Bulletin.

Mike Gray, Professor and Extension Entomologist


Armyworms Inflict Damage to Corn in Northeastern Illinois

On June 8, I received a report from Stephanie Porter, Burrus Sales Agronomist, concerning a severe infestation of armyworms in McHenry County. Significant damage had been inflicted to a field of no-till corn in which rye had been used as a cover crop. Throughout my career, the most common reports of damaging infestations of armyworms have occurred in corn when rye has been used as a cover crop. For more information on the biology, life cycle and management of this pest, please refer to the Department of Crop Sciences fact sheet regarding this insect.


No-till corn planted into a rye cover crop, McHenry County, June 8, 2015 (Courtesy of Stephanie Porter, Burrus Sales Agronomist).

No-till corn planted into a rye cover crop, McHenry County, Illinois, June 8, 2015 (Courtesy of Stephanie Porter, Burrus Sales Agronomist).


Armyworm defoliation in no-till cornfield following a rye cover crop, McHenry County, June 8, 2015 (Courtesy of Stephanie Porter, Burrus Sales Agronomist).

Armyworm defoliation in no-till cornfield following a rye cover crop, McHenry County, Illinois, June 8, 2015 (Courtesy of Stephanie Porter, Burrus Sales Agronomist).


Armyworms in no-till cornfield following a rye cover crop, McHenry County, Illinois, June 8, 2015 (Courtesy of Stephanie Porter, Burrus Sales Agronomist).

Armyworms in no-till cornfield following a rye cover crop, McHenry County, Illinois, June 8, 2015 (Courtesy of Stephanie Porter, Burrus Sales Agronomist).

According to the Entomological Society of America (ESA) Handbook of Corn Insects page 50

“Armyworm larvae may feed only on leaf margins, or they may strip the plants, leaving only the stalks and leaf midribs. A corn plant recovers from this injury when feeding activity is moderate, as long as the growing point of the plant has not been injured. However, entire cornfields can be defoliated when an armyworm infestation is heavy and feeding damage is severe.”

I offer my thanks to Stephanie Porter for sharing this information and photographs.

Mike Gray, Professor and Extension Entomologist

Western Corn Rootworm Hatch Update: Typical Timeline this Season

The annual western corn rootworm hatch appears to be similar this spring to the two most recent growing seasons. Thanks to Larry Bledsoe and his entomology colleagues at Purdue University, we have compiled a list of hatch dates over the past 20 years! Beginning on May 21 (and at 3-day intervals), Larry examined the root tissue of untreated corn plants for first instar larvae. On June 4 in Tippecanoe County, Indiana he found his first corn rootworm larva and estimated that hatch occurred the day before. As readers of this Bulletin know, saturated soils at the time of hatch can inflict significant mortality on corn rootworms. It remains to be seen how the heavy precipitation on June 7 across much of central and northern Illinois will affect larval survival.

Dates of Western Corn Rootworm Larval Hatch – Based upon Purdue University, Department of Entomology estimates.

  • 1996–June 12
  • 1997–June 13
  • 1998–late May (no precise date reported)
  • 1999–June 1
  • 2000–May 22
  • 2001–May 16
  • 2002–May 31
  • 2003–May 29
  • 2004–May 28
  • 2005–May 31
  • 2006–May 29
  • 2007–May 18
  • 2008–June 4
  • 2009–June 1
  • 2010–June 3 (second instars observed)
  • 2011–June 6
  • 2012–May 4–6 – Earliest observation of hatch by Larry Bledsoe in 35 years!
  • 2013 – June 4
  • 2014 – June 2
  • 2015 – June 3

As we move into late June, I anticipate the first sightings of western corn rootworm adults will begin to occur. Please share those observations with me and I will pass this information along to the readers of this Bulletin.

Mike Gray, Professor and Extension Entomologist

Black Cutworm Damage Reported in Northern Illinois

In a recent Bulletin article, I shared an observation of black cutworm damage in southern Illinois. Just recently (May 20), James Kennedy, Advanced Crop Care, Inc., found black cutworms were at work in northern Illinois as well. He found three fields that were infested with cutworms (4th instar) with cutting of plants in the 1-3% range. The fields were located in northern Kane County and McHenry County. James indicated that rescue treatments would be applied in the near future to these infested fields. The take home message — cornfields throughout Illinois (top to bottom) are potentially susceptible to black cutworm damage. As we near the Memorial Holiday weekend, it would be worthwhile to devote some effort to scouting fields for signs of leaf feeding and cutting.

I offer my thanks to James Kennedy for sharing his observations.

Mike Gray, Professor and Extension Entomologist


Plant Clinic Screening Waterhemp for Herbicide Resistance this Season

New testing for 2015: U of I Plant Clinic is offering molecular screening of waterhemp populations for resistance to glyphosate and PPO inhibitor herbicides this growing season. Protocols developed by University of Illinois Weed Scientist Dr. Pat Tranel, supported by Illinois Soybean Association and Pioneer, are now being offered through the Plant Clinic. The fee for the molecular testing is $50 per tested field. This includes both tests.
Herbicide-resistant waterhemp populations continue to expand into more areas of Illinois each season. Waterhemp has evolved resistance to herbicides encompassing more mechanisms of action than any other Illinois weed species. Not every individual waterhemp plant is resistant to one or more herbicides, but the majority of field-level waterhemp populations contain one or more types of herbicide resistance. Perhaps even more unnerving is the occurrence of multiple herbicide resistances within individual plants and/or fields. Don’t know if you have resistance or an application failure? Let us test it to get an answer for you.
To submit waterhemp weed samples:
After applying herbicide, select five waterhemp survivors in the field. Remove the top two inches from each plant (containing young, newly emerged, healthy leaves), and seal it in a sandwich-sized zip-top plastic bag. Use a separate bag for each plant. Do not place damp paper towels in bags. Place the bags in an envelope and send by overnight delivery to University of Illinois Plant Clinic. Ideally, samples should be sent the same day they are collected, but if necessary, they can be stored for a day or two in a refrigerator (but do not freeze). Do not send samples on a Friday or Saturday.
Submit the sample with the sample form; download form at this Plant Clinic website link:

Completely fill out the form for each field (1 field=5 plants=1 sample).
Additional Information: Please include herbicide use history, herbicides and rates applied this season, comments on observed weed control, and any other relevant information.

Need some Pigweed/Amaranth/Waterhemp ID practice? : See this recent article from Dr. Aaron Hager http://bulletin.ipm.illinois.edu/?p=3168

Waterhemp plant.

Waterhemp. University of Illinois Plant Clinic photo.

Question 1: I have Marestail, giant ragweed, etc. that I think is resistant to glyphosate. Will the Plant Clinic test it?
Answer 1: No, at this time our testing protocols are specific for Waterhemp.

Question 2: Do you test for all mechanisms for resistance to glyphosate and PPO inhibitors?
Answer 2: No, the protocol used for testing resistance to glyphosate looks for the amplification of the EPSPS gene. Dr. Tranel’s research indicates that this mechanism represents about 80% of glyphosate resistant waterhemp populations in Illinois. The PPO resistance protocol tests for a specific mutation in the PPX gene.
Question 3: Does ‘sensitive’ mean it’s not resistant to the herbicide(s)?
Answer 3: No, a test result of “sensitive” to glyphosate does not rule out the possibility that the plant actually is resistant, but by a resistance mechanism that is different than for what we are testing.

Suzanne Bissonnette

Cutworm Activity Reported in Southern Illinois: Scouting Fields Closely Recommended

John Pike, University of Illinois Crop Sciences Research Agronomist, Dixon Springs Agricultural Center, observed some cutting of corn plants today (May 18) in some plots that had volunteer ryegrass prior to burndown (Figure 1). John indicated that overall moth flight has been low at this location; however, as his observations illustrate, it is still worthwhile to scout fields closely for cutting activity. Please refer to some previously published Bulletin articles for additional information on this topic.

Figure 1. Black cutworm injury to corn, Dixon Spring Agricultural Center, May 18, 2015.

Figure 1. Black cutworm injury to corn, Dixon Springs Agricultural Center, May 18, 2015, Photograph taken by John Pike.

Please consider sharing other reports of black cutworm activity and I will pass along the information to readers of this Bulletin.

Mike Gray, Professor and Extension Entomologist

Projected Cutting Dates for Black Cutworms: Don’t Forget to Scout

Kelly Estes, Illinois Agricultural Pest Survey Coordinator, works with a network of volunteers across the state to monitor flights of key insect pests, including the black cutworm. Significant flights (nine or more moths trapped over 2-day period) of black cutworm moths occurred in Ford County (April 30), Mercer County (May 2), Lee County (May 4), Whiteside County (May 5), and Henry (May 10). By using these dates as a biofix and projecting heat unit accumulations we estimate that cutting of corn seedlings could begin to occur in fields on the following dates: Ford County (May 24), Mercer County (May 25), Lee County (May 31), Whiteside County (June 1), and Henry (June 3). Rather than wait until cutting begins to take place, producers are encouraged to look for early signs of leaf feeding as a potential indicator of cutting that may ensue. As stated in a previous Bulletin article, don’t assume that all Bt hybrids offer the same level of cutworm protection. Plants in the 1- to 4-leaf stage are most susceptible to cutting. Cutting of plants earlier than these projected cutting dates is possible — localized intense flights may have occurred and were not picked up by our volunteers. For more information on the biology, life cycle, and scouting procedures I encourage you to review our Department of Crop Sciences black cutworm fact sheet.

Mike Gray, Professor and Extension Entomologist

US EPA’s Proposal to Prevent Western Corn Rootworm Resistance: Does IPM Implementation Have a Realistic Chance?

On January 28, 2015, the United States Environmental Protection Agency (US EPA)  published a “proposed framework to prevent corn rootworm resistance.” Public comments were sought across an original 45-day period that was extended 30 days beyond the original March 16, 2015 deadline. Within the proposal, the United State EPA acknowledges that corn rootworms have already developed resistance to “Bt corn” in some areas of Iowa and Illinois. US EPA has characterized some states within the Corn Belt as in the “red zone” and these include Iowa, Illinois, Nebraska, western Indiana, southwestern Wisconsin, southern Minnesota, and eastern South Dakota. The so-called “red zone” states are described by the US EPA as follows: “where corn rootworm infestations are common and the use of Bt corn is high, …” The Agency’s proposal also adds that producers may be part of the “red zone” if the following circumstances are met: 1) “corn-on-corn for multiple years”, 2) “heavy use of Bt corn”, 3) “regular corn rootworm infestations”, and 4) “spotty compliance with current refuge requirements.” As part of the US EPA’s proposed framework they offer the following proposal: “In areas at risk for corn rootworm resistance, to require crop rotation, use of corn varieties containing more than one Bt protein, or other integrated pest management (IPM) strategies and stewardship for corn rootworm.” Additionally, the US EPA proposes the following: “70% of corn acres in the “red zone” should take part in IPM efforts and that 50% of corn acres in non-“red zone” areas should participate in IPM efforts.” From my perspective, isn’t this setting the bar a bit low? Why not propose that some form of IPM be put in place on 100% of corn acres regardless of zone characterization?

In reaction to this US EPA proposal, not surprisingly, numerous comments have been received and published including a letter that I signed along with 14 other entomologists from 12 prominent institutions. I encourage you to review these comments from many individuals and organizations. As you will see, there are many different perspectives and opinions taken on this controversial proposal. Among the many concerns raised by the proposal are those that involve the use of a planting-time soil insecticide with Bt hybrids. Let me be clear — planting-time soil insecticides should be considered an important arrow in the IPM quiver targeted at the corn rootworm complex.However, the addition of a planting-time soil insecticide along with a corn rootworm Bt hybrid is not a good resistance management strategy. The authors of two recently published journal articles have confirmed that use of a planting-time soil insecticide with a rootworm Bt hybrid delays emergence and increases the chances of non-random mating (promotes assortative mating); thereby, hastening the onset of resistance to Bt proteins. The citations for these journal articles are provided below:

Petzold-Maxwell, J.L. et al. 2013. Effect of Bt maize and soil insecticides on yield, injury, and rootworm survival: implications for resistance management. Journal of Economic Entomology 106(5): 1941-1951.

Frank, D.L. et al. 2015. Effect of seed blends and soil-insecticide on western and northern corn rootworm emergence from mCry3A + eCry3.1Ab Bt maize. Journal of Economic Entomology DOI: 10.1093/jee/tov081

Planting-time soil insecticides will remain an important tool targeted at the secondary insect complex when present at economically threatening levels. They also represent an important option when used with non-Bt hybrids in fields with corn rootworm infestations. When a planting-time soil insecticide is used with a pyramided Bt rootworm hybrid for the sole purpose of rootworm protection, it’s hard to find any convincing argument that this is a good IPM or resistance management (IRM) approach.

Resistance by many pests, including corn rootworms, has occurred when we have used the same arrow over and over again and failed to integrate management tactics. Since 2003, the year in which Bt rootworm hybrids were commercialized, growers have increasingly failed to integrate tactics and have relied upon a narrow set of Bt rootworm proteins expressed at low levels within a refuge system designed for high-dose events targeted at European corn borers. We should not have been surprised when reports of western corn rootworm resistance to Bt corn began to occur in Iowa soon followed by Illinois. Finally, while I am supportive of crop rotation as a viable pest management tactic for corn rootworms in many areas of the Corn Belt, growers in east central and northeastern counties of Illinois recognize that a segment of the western corn rootworm population in those areas is now resistant to two Bt proteins (Cry3Bb1 and mCry3A) as well as crop rotation. Rotation, even in those Illinois counties, remains a good strategy; however, other tactics will need to be more fully integrated into a long-term corn rootworm management program.

Mike Gray, Professor and Extension Entomologist

Black Cutworm Moth Captures Common in Several Midwestern States

Impressive flights of black cutworm and armyworm moths have been reported by Doug Johnson an Extension Entomologist at the University of Kentucky . Entomologists at Purdue University also have received reports that black cutworm moth captures are now common in many areas of Indiana. Kelly Estes, Agricultural Pest Survey Coordinator with the Illinois Natural History Survey, has established a network of trapping cooperators across Illinois. Although no intense flights (nine or more moths caught over a 2-day period) of black cutworm moths have been reported by these cooperators, captures of this species have been common the past two weeks in the following counties: Champaign, Fayette, Logan, Lee, Macon, Macoupin, and Madison. This distribution of captures suggests that black cutworm moth flights have likely taken place throughout Illinois and growers are encouraged to remain vigilant for early signs of leaf feeding when corn seedlings begin to emerge. Today (April 21) strong winds from the south are undoubtedly bringing many black cutworm moths into Illinois and fields like the one featured in the photograph below will be prime targets for egg laying by this species.

Champaign County field considered a prime target for black cutworm moth egg laying, April 21, 2015.


For more complete information about the biology, life cycle, and management of black cutworms and armyworms, fact sheets are available from the Department of Crop Sciences, UIUC. Provided below is a brief overview of some key life cycle and management facts concerning black cutworms.

  • Black cutworm moths are strong migratory insects with northward flights commonly observed from Gulf States into the Midwest from March through May.
  • Moths are attracted to fields heavily infested with weeds such as chickweed, shepherd’s purse, peppergrass, and yellow rocket.
  • Late tillage and planting tends to increase the susceptibility of fields to black cutworm infestations.
  • Cutting of corn plants begins when larvae reach the 4th instar — with a single cutworm cutting an average of 3 to 4 plants during its larval development.
  • Cutting tends to occur most often during nights or on dark overcast days.
  • Fields at greatest risk to cutting and economic damage are in the 1-to-4 leaf stage of plant development.
  • An early warning sign of potential economic damage includes small pinhole feeding injury in leaves (caused by the first 3 instars).
  • A nominal threshold of 3% cutting of plants has traditionally been used as a point at which growers should consider a rescue treatment.
  • Not all Bt hybrids offer adequate protection against black cutworm damage. Growers should consult the Handy Bt trait table prepared by Dr. Chris DiFonzo at Michigan State University to determine the level of protection provided by their chosen Bt hybrid.

As the season progresses, if you learn of significant black cutworm infestations, please let me know and I will share this information with the readers of this Bulletin.

Mike Gray, Extension Entomologist