ALERT: Fall Armyworms May Reach Damaging Levels in Pastures Across Southern Illinois

Doug Johnson, University of Kentucky Extension Entomologist, has received reports of large densities of fall armyworms in pastures from central Kentucky to the Mississippi River. These infestations follow some large flights of these moths as reported recently by Professor Johnson. The fall armyworm is a tropical insect and the moths migrate to northern states during the late summer and early months of fall. Gulf Coast storms may increase the late summer flights northward. As female moths find grassy or pastured areas, they begin to lay eggs on grass blades. The life cycle (egg to adult) is temperature dependent and takes about 30 to 50 days to complete. Partially grown larvae overwinter in Gulf Coast states. Larvae currently feeding within pastures across southern Illinois counties will not survive hard frosts and the ensuing winter. However, their current feeding can still lead to significant damage to newly-seeded hayfields, pastures, wheat, and double-cropped soybeans. Double-cropped soybeans, if less than R6 stage (full seed) are most at risk when fields are adjacent to severely damaged pastures, especially the rows closest to pastured areas. Injury to plants typically occurs during the morning, late afternoon, or early evening hours. Densities of 5 to 7 larvae per square foot may cause economic damage to stands. Larvae that are 0.75 inches or less in length are easier to control. Those that are 1.25 to 1.5 inches long are the most damaging. Producers are encouraged to scout their pastures, double-cropped soybeans, and newly seeded hay or wheat fields. If fall armyworms are found in damaging levels, producers should consider a rescue treatment paying careful attention to harvest and grazing restrictions for the insecticide that is chosen for use.

Mike Gray


Destructive diseases of soybean – sudden death syndrome and white mold – observed in the state

Signs and symptoms of a few soybean diseases have begun to show up in the last few weeks in some areas of the state.  Two of these diseases, sudden death syndrome (SDS) and Sclerotinia stem rot (a.k.a. white mold) certainly are going to cause economic losses in some growers’ fields this year.

Symptoms of SDS that currently are being observed are interveinal chlorosis and necrosis of the leaves (veins remain green while the tissues between the veins turn yellow and then brown).  These symptoms look exactly like the foliar symptoms caused by a different disease, brown stem rot.  Brown stem rot, however, will cause internal browning of the pith in soybean stems, while SDS does not affect soybean stems.  On SDS-affected plants, the leaves will fall off eventually, while the petioles will remain attached to the stems and branches.  In some cases, a bluish-white mass of spores of the SDS fungus (Fusarium virguliforme) may be observed on the roots.  Although the foliar symptoms of SDS are now being observed, infection by the SDS fungus occurred during the seedling stage, not long after planting.  The symptoms that are now being observed are the effect of toxins that the SDS pathogen produces that are phytotoxic.  Cool and wet weather after planting and the recent rainfall received in parts of the state were favorable for infection and disease development, and are the reasons why SDS incidence is high in some areas this year.  The primary method of managing SDS is to choose the most resistant soybean varieties available.  Some evidence has shown that high soybean cyst nematode (SCN) egg populations may also increase the likelihood of severe SDS; therefore, managing SCN populations through resistant varieties and crop rotation may also reduce the risk of SDS.  Unfortunately, there currently are no fungicide products registered that are effective in managing SDS, but an experimental fungicide seed treatment known as “ILeVO” that is currently making its way through the EPA registration process has shown efficacy against SDS in University of Illinois field trials.

Symptoms of sudden death syndrome of soybean (Photo by C. Bradley).

 

A bluish-white mass of spores of the SDS fungus (Fusarium virguliforme) on a soybean root (Photo by C. Bradley).

 

White mold can be observed in fields located in the northern half of Illinois this year.  The appearance of this disease also is weather-related.  Areas in the northern half of the state, that were cooler and wetter than normal after soybean plants began to flower, are the areas that are affected the most severely.  Unfortunately, once white mold signs and symptoms are detected in the field, fungicide applications generally will be futile, as the damage has already been done.  Management of white mold was discussed in an earlier article of the Bulletin this year (http://bulletin.ipm.illinois.edu/?p=2412).  Growers with severe levels of white mold may encounter some discounts at the elevator this year for high levels of foreign matter.  Some sclerotia (dark survival structures produced by the white mold fungus – Sclerotinia sclerotiorum) that are formed on plants may similar in size to the seed, and will make their way to the hopper and eventually the elevator, where discounts may be received.

 

Soybean plants dying prematurely because of white mold in a field in Champaign County (Photo by K. Ames).

 

White mycelia of the white mold fungus (Sclerotinia sclerotiorum) on a soybean plant (Photo by C. Bradley).


Preliminary Corn Rootworm Injury Evaluation Results from Illinois’ Trials, 2014

In late July, the annual University of Illinois root “digs” and corn rootworm product evaluation trials were completed. Each experiment was established on plots that had been planted to a trap crop (late-planted corn interplanted with pumpkins) in 2013. The results for three of these studies are presented in the following bar graphs. The charts are arranged with the soil insecticide only treatments appearing in light blue, Bt hybrid only products shaded in orange, Bt hybrids combined with soil insecticides represented by the darker blue color, and the untreated checks shaded in dark gray. Treatment bars that share the same letter do not differ statistically (P=0.05).

Most rootworm protection products at the Northern Illinois Agronomy Research Center (DeKalb), were able to keep root injury below 0.5 (1/2 node pruned). Products that resulted in root injury that exceeded this level included: Capture LFR (0.83), Agrisure Viptera 3111 (0.69), Genuity VT Triple Pro (0.92), and Genuity VT Triple Pro RIB Complete (0.9). These treatments were not statistically different from two of the untreated checks. The Agrisure Viptera 3111 treatment expresses the mCry3A rootworm protein along with some other proteins (Cry1Ab, Vip3A) designed to provide lepidopteran control. The Genuity VT Triple Pro and Genuity VT Triple Pro RIB Complete treatments express the Cry3Bb1 rootworm protein as well as some other Bt proteins (Cry1A.105, Cry2Ab2) for lepidopteran pests.  With respect to the checks, three were treated with insecticidal seed treatments: NK N69Z-GT – Cruiser 500; DeKalb DKC63-35RIB – Poncho 500, and Mycogen 2K591 – Cruiser 250. Seed for the TA617-18 check does not have any insecticidal treatment.

Overall pressure in the DeKalb trial was good with approximately two nodes of roots pruned in two of the check treatments. Under this level of injury, the root protection afforded by Bt hybrids expressing only the Cry3Bb1 protein was not stellar. With the exception of Capture LFR, the soil insecticide (only) treatments offered very good levels of root protection. Overall, the combined use of a planting-time soil insecticide and a Bt hybrid did not statistically improve root protection over that of a soil insecticide used alone.

 

Figure 1. Node-injury ratings for root protection products, Northern Illinois Agronomy Research Center, Shabbona, IL. Planting date - May 8; Root dig date - July 28. Node injury scores - 1 = one node of roots pruned to within 1.5 inches of the stalk (or soil line if roots originate from above ground nodes); 2 = two complete nodes pruned; and 3 = three or more complete nodes pruned. Means for RIB treatments may or may not include ratings for refuge root systems.

 

The past few seasons, corn rootworm injury at the Monmouth location has been low and difficult for us to effectively evaluate product performance. In 2014, root injury in one of our checks (NK N69Z-GT, treated with Cruiser 500) exceeded two nodes (2.18) of roots destroyed. The other check (DeKalb DKC63-35RIB, treated with Poncho 500) had less root injury (1.34). Most of the root protection treatments in Monmouth keep root injury below 0.5 (1/2 node pruned). However, root pruning in several treatments exceeded 1.0 (one node pruned) and included: Capture LFR (1.23), Agrisure Viptera 3111 (1.8), Genuity VT Triple Pro (1.83), Genuity VT Triple Pro RIB Complete (1.07), and Capture LFR + Genuity VT Triple Pro (1.02). Root protection afforded by Agrisure Viptera 3111 and Genuity VT Triple Pro was not statistically different from the untreated check (NK N69Z-GT) and use of both treatments resulted in nearly 2 nodes of roots destroyed. Resistance to the Cry3Bb1 protein has been confirmed in several northwestern Illinois counties and cross resistance with this protein to the mCry3A protein has been confirmed in Iowa. Although not confirmed, it seems possible that the resistant western corn rootworm strain may have affected the performance of these treatments within this trial.

 

Figure 2. Node-injury ratings for root protection products, Northwestern Illinois Agricultural Research and Demonstration Center, Monmouth, IL. Planting date - May 7; Root dig date - July 14. Node injury scores - 1 = one node of roots pruned to within 1.5 inches of the stalk (or soil line if roots originate from above ground nodes); 2 = two complete nodes pruned; and 3 = three or more complete nodes pruned. Means for RIB treatments may or may not include ratings for refuge root systems.

 

As compared with the DeKalb and Monmouth experiments, the overall root injury in the Urbana study was lower with the four checks ranging from approximately 1 to nearly 1.5 nodes of roots pruned. Even with this moderate pressure, root injury in the Capture LFR (0.78) and Genuity VT Triple PRO RIB Complete (0.96) treatments approached one node of roots pruned and were statistically similar to several of the untreated checks. Root injury in the other treatments was generally below 0.5 (1/2 node pruned).

 

Figure 3. Node-injury ratings for root protection products, Agricultural and Biological Engineering Farm, Urbana, IL. Planting date - May 12; Root dig date - July 23. Node injury scores - 1 = one node of roots pruned to within 1.5 inches of the stalk (or soil line if roots originate from above ground nodes); 2 = two complete nodes pruned; and 3 = three or more complete nodes pruned. Means for RIB treatments may or may not include ratings for refuge root systems.

Root ratings were not presented for the Orr Agricultural Research and Demonstration Center located near Perry Illinois due to the low overall injury in the untreated checks (0.29 to 0.76). Each of these experiments, including the Orr site, will be harvested later this fall. A final report of the root injury ratings and yields will be published in the on Target Report. This report also includes product performance summaries for previous years going back to 2004.

I offer my thanks to Ron Estes (Principal Research Specialist in Agriculture, Department of Crop Sciences) and Nick Tinsley (Postdoctoral Research Associate, Department of Crop Sciences) for their important leadership in all aspects of this research.

 

Agricultural and Biological Engineering Farm, Urbana, IL, July 2014.

Mike Gray, Ron Estes, and Nick Tinsley


Rotation Resistant and Rotation Susceptible Western Corn Rootworms React Similarly to Bt Corn

A journal article published recently (July 2014) confirms that rotation resistant and rotation susceptible western corn rootworms are affected by Bt root tissue in a similar fashion. The citation for this article is provided below.

Tinsley, N.A., J.L. Spencer, R.E. Estes, J.R. Prasifka, P.M. Schrader, B.W. French, and M.E. Gray. 2014. Larval mortality and development for rotation-resistant and rotation-susceptible populations of western corn rootworm on Bt corn. Journal of Applied Entomology. doi: 10.1111/jen.12149

Based upon some earlier research, investigators hypothesized that rotation resistant western corn rootworm larvae were able to inflict more injury on Bt root systems than rotation susceptible larvae. In this recent paper the scientists made the following observations refuting this hypothesis: “Rotation-resistant and rotation-susceptible larvae had statistically similar mean levels of mortality and head capsule widths when exposed to both single-toxin (Cry3Bb1 or Cry34/35Ab1) and pyramided (Cry3Bb1+Cry34/34Ab1) Bt corn, suggesting that these two populations do not differ with respect to survival or development when exposed to Bt corn.”

Whether you are concerned about the rotation-resistant or rotation-susceptible population of western corn rootworm, now is the time to evaluate the root protection afforded by your Bt hybrid or planting-time soil insecticide. Signs of potential problems include lodging. However, it’s necessary to dig up lodged plants and wash the soil away from root systems to confirm larval feeding. Previous research has shown that one node of roots destroyed can equate to a 15% yield loss in some years. It’s definitely well worth your time to accurately assess the value of your corn rootworm protection tool.

Mike Gray


A Quiet Season on the Insect Front Continues in the Midst of Rootworm “Digs”

From a field crop entomology perspective, this summer remains exceptionally quiet across most areas of Illinois. Japanese beetle and soybean aphid densities have remained very low, seemingly near absent in many fields. With 82% of the corn silking process completed statewide by July 20 and  soil moisture plentiful in most areas, the threat of insects negatively affecting the pollination process have largely diminished. We intend to conduct some insect surveys in corn and soybean fields across the state as we move through early August. Similar to recent seasons, I suspect the overall densities of most pests will remain below economic levels.

Last week, we began our annual corn rootworm “digs” headed up by Ron Estes (Principal Research Specialist, Department of Crop Sciences)  and Nick Tinsley (Postdoctoral Research Associate, Department of Crop Sciences). Overall root injury in our checks at the Northwest Research and Education Center located near Monmouth was greater than in previous years. Thus far, injury in our checks across various trials located near Urbana has been impressive as well. So, in spite of significant precipitation throughout much of June and early July, it appears that larvae were able to hatch successfully and establish on root systems quite well. As in previous years, once we complete the root evaluations from our trials, we will publish the preliminary results in this Bulletin.

Mike Gray


2014 Field Day August 7 at Dixon Springs Ag Center

The 2014 Dixon Springs Agronomy and Horticulture Field Day presented by the University of Illinois, Department of Crop Sciences will be held on Thursday, August 7 at the Dixon Springs Ag Center.  The research center is located on IL Route 145, near Glendale, IL, 25 miles south of Harrisburg and 25 miles north of Paducah, KY.

Tours will start at 9:00 AM with the final bus leaving at 9:30. A lunch to follow will be provided by sponsors and UI Extension.

The following presenters will speak about current conditions and management challenges in field crop and horticulture production.

  • Carl Bradley: Fungicide Resistance
  • Angie Peltier: Corn Nematodes, The Hidden Menace in Your Fields
  • Jake Vossenkemper: Nitrogen on Soybeans
  • Rachel Cook: Tillage is Recreational, Fertilizer is Essential: A 44 Year Study
  • Jeff Kindhart: High Tunnels, Hydroponics and Mushrooms

For more information contact John Pike at 618-695-2441 or by email at jpike@illinois.edu


Brownstown Agronomy Research Center Field Day – August 6

The 2014 Brownstown Agronomy Research Center Field Day, presented by the University Of Illinois Department Of Crop Sciences, will be held on Wednesday, August 6. Extension researchers and specialists will address issues pertinent to the current growing season. The tour will start at 8 a.m. and will last about two and a half hours. It will be followed by lunch provided by U of I Extension.

Shaded tour wagons will take participants to each stop. These topics will be addressed:

  • N Fertilizer for Soybean:  Where’s the Yield? – Jake Vossenkemper, U of I
  • Tillage is Recreational, Fertilizer is Essential – Dr. Rachel Cook, SIU
  • Field Crop Diseases & Fungicide Treatments – Dr. Carl Bradley, U of I
  • Corn Nematodes:  the Hidden Menace in Your Fields – Dr. Angie Peltier, U of I
  • Factors Contributing to a Healthy Soil – Troy Fehrenbacher, NRCS

The 208-acre Brownstown Agronomy Research Center has been conducting crop research on the claypan soils of southern Illinois since 1937. More than 30 research and demonstration projects are conducted at the Center every year. Visitors are always welcome.

The research center is located south of Brownstown on IL Route 185, approximately 4 miles east of the IL Route 40 / 185 junction.

For more information, contact Robert Bellm (618-427-3349); rcbellm@illinois.edu
Visit us on the web at http://web.extension.illinois.edu/barc/


2014 Field Day July 16 at Orr Ag Center, Perry

The 2014 Orr Agricultural Center Field Day presented by the Department of Crop Sciences at the University of Illinois will be held on Wednesday, July 16 at the Orr Center, which is located roughly halfway between Jacksonville and Quincy on Route 104, four miles west of the junction of Illinois Routes 104 and 107.

The first tour group will start out at 9:00 AM, with the second and third groups leaving the headquarters at about 9:20 and 9:40. The tour will take about two hours, and will be followed by lunch provided by UI Extension.

The following presenters will speak about current conditions and management challenges in crop production and protection.

  • Dennis Bowman, UI: Unmanned Aerial Vehicles: Sky High Scouting
  • Emerson Nafziger, UI: N Fertilizer for Soybean – Where’s the Yield?
  • Mike Gray, UI: Update on Western Corn Rootworm Resistance to Bt: Are Soil Insecticides + Bt Necessary?
  • Mark Bernards, WIU: Stewardship of Dicamba and 2,4-D Resistant Soybeans
  • Robert Bellm, UI:  Managing the Threat of Palmer Amaranth

For more information call Mike Vose at 217 236-4911 or by email at mvose@illinois.edu


Assessing the risk of white mold (Sclerotinia stem rot) of soybean in 2014

White mold of soybean (a.k.a. Sclerotinia stem rot), caused by the fungus Sclerotinia sclerotiorum, is a disease that can occur in the northern half of the state in cool, wet years.  The most recent, widespread white mold epidemic in Illinois occurred during the 2009 season, where several fields in the northern half of the state were affected.  In some of the northern-most areas of Illinois, white mold can be considered a more consistent problem.

The white mold fungus overwinters in the soil as, small, black, and dense structures known as sclerotia.  These sclerotia germinate and form mushroom-like structures known as apothecia when soil remains moist for several consecutive days and soil temperatures are at 60 degrees F or below.  These apothecia generally will not form until the soil is shaded from sunlight due to soybean canopy closure.  Spores of the white mold fungus are shot out of the apothecia and land on senescing flower petals, where infections first occur on the soybean plants.  The white mold fungus becomes inactive when temperatures within the soybean canopy are above approximately 82 degrees, so infection and disease development may cease or slow down during periods of hot (above 82 degrees) and dry weather.

Apothecia of the white mold fungus germinating from a sclerotium. Image courtesy J. Venette, North Dakota State University.

 

Soybean plant with symptoms and signs of white mold (a.k.a. Sclerotinia stem rot). Image by C. Bradley.

 

So, what does the risk of white mold look like for 2014?  This is not an easy question to answer.  In general, rainfall has been consistent in the northern portion of the state, which would favor white mold, but recent temperatures in the 80s and 90s have not been favorable.  However, the short-term weather forecast shows cooler temperatures (60s and 70s).  If a cool and wet trend continues throughout soybean flowering, then the risk of white mold will be elevated.

In University of Illinois research trials, some fungicide products have shown efficacy against white mold.  Foliar fungicides will not provide complete control of the disease, but may reduce disease.  The results of University of Illinois trials conducted in 2009, 2010, and 2013 are shown in Tables 1-3.  Note that some of the more popular, frequently marketed fungicides are not listed in the tables since many do not have white mold on their label because of no to poor efficacy.  In these trials, the primary targeted growth stage to apply foliar fungicides was at R1 (beginning flower).  In some cases, R1 may occur before canopy closure.  If this is the case, then an application at canopy closure (rather than R1) might be more effective in protecting against white mold.  Also note that some treatments in these research trials were applied twice during the season.

 

Table 1. Results of soybean foliar fungicide research trials focused on white mold conducted in 2009 at the University of Illinois Northern Agronomy Research Center (DeKalb County).

Treatment Rate/A Incidence (%) 

8-11-09

Incidence (%) 

9-14-09

Yield (bu/A)
Untreated check - 75 95 24
Topsin 4.5 L 20 fl oz 43 96 24
Proline 3 fl oz 38 95 24
Domark 5 fl oz 68 98 23
Cobra herbicide 12.5 fl oz 15 51 42
Omega 1 pt 23 80 34
Endura (2x)* 8 oz 38 86 39
Aproach (2x)* 8 fl oz 35 80 40
LSD 0.05** 33 15 8

*All treatments were applied at the R1 growth stage (July 20, 2009).  Treatments followed by “(2x)” were applied again 9 days later.

**Least significant difference (alpha level = 0.05).  Treatment values that differ by this number can be considered significantly differ from one another.

 

Table 2. Results of soybean foliar fungicide research trials focused on white mold conducted in 2010 at the University of Illinois Northern Agronomy Research Center (DeKalb County).  Funded in part by the Illinois Soybean Association.

Treatment Rate/A Incidence (%) 

8-11-09

Incidence (%) 

9-14-09

Yield (bu/A)
Untreated check - 18 95 62
Topsin 4.5 L 20 fl oz 9 83 61
Proline 3 fl oz 10 89 66
Domark 5 fl oz 7 76 63
Cobra herbicide 6 fl oz 6 86 56
Omega 1 pt 2 70 58
Endura 8 oz 4 79 69
Aproach (2x)* 8 fl oz 11 79 66
LSD 0.05** 11 NS 8

*All treatments were applied at the R1 growth stage (July 10, 2010).  Treatments followed by “(2x)” were applied again 7 days later.

**Least significant difference (alpha level = 0.05).  Treatment values that differ by this number can be considered significantly differ from one another.  “NS” indicates that no treatments were significantly different from each other.

 

Table 3. Results of soybean foliar fungicide research trials focused on white mold conducted in 2013 at the University of Illinois Northern Agronomy Research Center (DeKalb County). Treatments were applied at the R1 growth stage unless indicated otherwise.

Treatment Rate/A Incidence (%) 

9-19-13

Yield (bu/A)
Untreated check - 33 53
Incognito 4.5F 20 fl oz 20 68
Incognito 4.5F + Orius 3.6F* 20 fl oz + 4 fl oz 0 62
Proline + Stratego YLD** 3 fl oz + 4.65 fl oz 3 58
Domark 5 fl oz 3 62
Cobra herbicide 6 fl oz 25 52
Endura 8 oz 3 64
Aproach 8 fl oz 13 61
Fortix 5 fl oz 15 56
LSD 0.05*** 22 7

*Incognito was applied alone at the R1 growth stage and was followed by Orius applied alone at R3.

**Proline was applied alone at the R1 growth stage, and was followed by Stratego YLD applied alone at R3.

***Least significant difference (alpha level = 0.05).  Treatment values that differ by this number can be considered significantly differ from one another.  “NS” indicates that no treatments were significantly different from each other.

Overall, the highest level of white mold control will be achieved when several management practices are integrated (i.e. choosing the most-resistant varieties, utilizing recommended seeding rates, applying a foliar fungicide, and applying a biocontrol product).  For more information about white mold and management of this disease, go to http://www.soybeanresearchinfo.com/pdf_docs/WhiteMold_NCSRP.pdf, where a 7-page publication on white mold (developed in 2011) can be downloaded.


Remember the European Corn Borer?

The European corn borer, once regarded as a major and consistent insect pest, is now only rarely observed in most commercial cornfields across the Corn Belt. William “Bill” Luckmann, longtime retired and well known entomologist, once mentioned that he had only observed two cornfields “totally destroyed” by insects — “once by chinch bugs and once by European corn borers.”

Gray, M.E. & W.H. Luckmann. 1994. Integrating the cropping system for corn insect pest management. Chapter 12, pages 507-541 in Introduction to Insect Pest Management. R.L. Metcalf & W.H. Luckmann [eds.], John Wiley & Sons, Inc., NY (ISBN 0-471-58957-8).

In 1939, European corn borers were first reported in Illinois and by 1942 the pest could be found in all counties within the state. The circular below attests to the economic importance of this insect and offers management advice for producers in 1943.

 

University of Illinois 1942 Circular (539) on the European Corn Borer

 

University of Illinois 1942 Circular (539) on the European Corn Borer

 

Since the introduction of Bt hybrids in 1996, the use of transgenic corn has risen sharply. According to the USDA Economic Research Service, Bt hybrids were planted on 76% of the US corn acres in 2013. In 2013, transgenic corn hybrids (includes Bt hybrids, stacked hybrids [Bt and herbicide tolerant], and herbicide tolerant only) were used on 90% of corn acres. The widespread use of highly effective Bt hybrids on lepidopterous insect pests such as the European corn borer has had a significant areawide population suppression effect on this once prominent species. In evening drives around the state of Illinois the past few years, the first or second flights of European corn borers have been barely noticeable. Many will recall what these spring and summer evening drives did to our windshields. Depending on the accumulation of heat units, the first flight of European corn borers generally lasts from mid-May through mid-June. Moths emerge from corn residue and seek out areas of dense vegetation found in ditch banks, fence rows, and grass waterways. Females emit a sex pheromone in these “action sites”  very late in the evening that attracts males and mating ensues. Females depart action sites after sundown and begin laying egg masses in nearby cornfields — typically two egg masses per night for upwards of 10 days. Action sites near cornfields are ideal for the largest aggregation of moths as described by Dr. Tom Sappington in an Environmental Entomology (2005) journal article.

From June 13 to 26, a Department of Crop Sciences research team led by Ron Estes, Principal Research Specialist in Agriculture, and Nicholas Tinsley, Postdoctoral Research Associate, conducted surveys of action sites in the following 12 counties: Champaign (June 13, 5 action sites), Clinton (June 24, 3 action sites), Douglas (June 13, 5 action sites), Fayette (June 24, 4 action sites), Jefferson (June 24, 3 action sites), Kankakee (June 26, 5 action sites), Kendall (June 26, 5 action sites), Knox (June 17, 5 action sites), McLean (June 17, 5 action sites), Pike (June 18, 3 action sites), Sangamon (June 18, 3 action sites), and Whiteside (June 25, 5 action sites). Within each action site, 100 sweeps were taken. Very few moths (9 total) were collected: Champaign County – 1 moth, Douglas County – 3 moths (one in each of 3 sites), Kankakee County – 1 moth, Kendall County – 1 moth, Knox County – 1 moth, McLean County – 1 moth, and Sangamon County – 1 moth. In all, 51 action sites (100 sweeps/site) were sampled across 12 counties resulting in 5,100 sweeps that yielded 9 moths, or 0.0018 moths per sweep.

Based upon these results, I believe the following questions are worthy of consideration.

  • Are too few survivors emerging from Bt fields to sustain the continuing efficacy of Bt hybrids against European corn borers? So far, no field-selected Bt resistant strains of European corn borers have been documented.
  • Will the smaller (5%) seed-blend refuges result in even fewer European corn borer survivors in the landscape and further increase the selection pressure for resistance development? Recall that structured 20% refuges were the norm for Bt corn hybrids for many years. In addition, the structured refuge was a preferred resistance management approach along with the use of high-dose Bt hybrids for European corn borers. Early on, concern over larval movement from plant to plant by European corn borer larvae resulted in scientists favoring a structured refuge versus a seed blend for this insect pest.
  • Is the added cost of Bt hybrids worth the investment for this insect pest in light of very low densities of the European corn borer and the less than favorable current and projected commodity prices?
  • If the use of Bt hybrids declined, would producers have sufficient time to scout large commercial cornfields, utilize economic thresholds, and apply rescue treatments as needed?

Time will tell if this once very significant insect pest will return as a consistent threat.

Mike Gray