Corn disease update and farewell

Last week, I visited all of the University of Illinois corn variety trials in the northern half of the state.  Gray leaf spot and northern leaf blight were beginning to appear in most of the locations, but were the most obvious at the trial located near Perry, IL (Pike County).

DSCN0119

“Young” lesions of northern leaf blight beginning to develop on a corn leaf.

DSCN0128

Gray leaf spot lesions developing on a corn leaf.

With the amount of rainfall received in the past few weeks, it is not surprising that these diseases were beginning to appear.  Since hybrids differ in their level of susceptibility to these diseases, not all hybrids in the trials had symptoms.  If the rainy conditions continue, then a foliar fungicide application sometime between tassel emergence and silking may need to be considered on hybrids that are the most susceptible.  Some general guidelines that may help make a foliar fungicide application decision follow:

  • On susceptible to moderately-susceptible hybrids:  consider a foliar fungicide if disease is present on the third leaf below the ear or higher on 50% of the plants prior to tasseling.
  • On intermediate hybrids:  consider a foliar fungicide if the field has a history of disease, if the previous crop was corn with at least 35% of the ground covered with residue, if disease is present on the third leaf below the ear or higher on 50% of the plants prior to tasseling, and if warm and humid weather has persisted.
  • On moderately-resistant to resistant hybrids:  foliar fungicides generally are not recommended, but scouting is important to confirm that diseases are not present.

The presence of diseases does make a difference in how profitable a fungicide application may or may not be.  From trials conducted at the University of Illinois from 2008 to 2014 at many environments (45 total environments) in Illinois, the results indicate that the overall yield response to foliar fungicides was 5.3 bushels/acre (see chart below).  However, this yield response was 9.5 bushels per acre when disease developed to affect at least 10% of the leaf area in untreated controls (in 17 of the environments).  In situations with low disease severity (disease developed to less than 10% of the leaf area in untreated controls), the average yield response was only 2.8 bushels per acre (in 28 of the environments).  Obviously, the marketing price of corn and the fungicide and application costs will determine if fungicide applications were profitable.  The chart below shows the profitability of fungicide applications under different yield response goals (3, 5, 8, and 11 bushels per acre).  The bottom line is that it takes a higher yield response to be profitable when corn marketing prices are lower.

Corn fung results 2014

Results from University of Illinois corn fungicide trials conducted from 2008 to 2014. All applications were made at tassel emergence (VT).

On a final note, my last day at the University of Illinois is today (June 30).  I will be moving to a similar position at the University of Kentucky, and will be based out of the Princeton Research and Education Center in the western part of Kentucky.  I want to thank the University of Illinois for my opportunities here and thank many of you for your support and interest.  There are no current plans to replace my position as Extension Plant Pathologist at the University of Illinois.  If you have field crop disease questions, the following contacts may be useful:

University of Illinois Plant Clinic

1102 S. Goodwin Ave.

Urbana, IL 61801

Tel: 217-333-0519

Email: plantclinic@illinois.edu

 

Commercial Agriculture Extension Educators:

Robert Bellm

Brownstown Agronomy Research Center

1588 IL 185

Brownstown, IL 62418

Tel: 618-427-3349

Email: rcbellm@illinois.edu

 

Dennis Bowman

Crop Sciences Research and Education Center

1102 S. Goodwin Ave.

Urbana, IL 61801

Tel: 217-244-0851

Email: ndbowman@illinois.edu

 

Russ Higgins

Northern Illinois Agronomy Research Center

14509 University Road

Shabbona, IL 60550

Tel: 815-824-2029

Email: rahiggin@illinois.edu

 

Angie Peltier

1000 North Main Street

PO Box 227

Monmouth, IL 61462

Tel: 309-734-5161

Email: apeltier@illinois.edu


Stink Bugs Observed in Soybean Fields of Southwestern Illinois

Byron Hendrix, Agronomist with Terayne AG Specialties, Venedy, IL, observed green and brown stink bugs in soybean fields in Washington County on June 25. The field in which stink bugs were observed was planted in early May. Management of stink bugs in vegetative stage soybeans is not typically necessary. As plants enter the reproductive stages of development and pods begin to fill, rescue treatments may be warranted. Growers should consider a rescue treatment when adult bugs or large nymphs reach densities of 1 per foot of row when pods are filling. As soybean fields begin to flower, they can become very attractive to stink bugs.

Adult green stink bug, Washington County, Illinois, June 25, 2015 (Courtesy of Byron Hendrix, Agronomist, Terayne AG Specialties, Venedy, Illinois).

Adult green stink bug, Washington County, Illinois, June 25, 2015 (Courtesy of Byron Hendrix, Agronomist, Terayne AG Specialties, Venedy, Illinois).

 

The holes in the soybean leaves (above photograph) appear to be the work of insect defoliators (e.g. bean leaf beetles). Stink bugs have piercing and sucking mouthparts which they use to remove fluids from plants. Stink bugs may feed on stems, leaves, blossoms, and seeds of soybean plants. They prefer the newest growth and developing seeds. As the season progresses, producers should continue to monitor soybean fields for this insect pest.

Mike Gray, Professor and Extension Entomologist


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:

http://web.extension.illinois.edu/plantclinic/downloads/WaterhempForm.pdf
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.

FAQ’s:
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