Delayed Soybean Planting: Prospects for Insect Injury

The stormy spring weather across much of the nation’s mid-section continues to cause planting delays. Planting estimates (USDA NASS, May 28, 2013) indicate that approximately 40% of Illinois soybean acres have been planted. Roughly 12% of the soybean crop has emerged across the state. These percentages are well below the five-year averages for Illinois by this date – 53% planted and 28% emerged. As overwintering bean leaf beetles break dormancy and begin to seek out soybean fields, those fields that are first to emerge will be most susceptible to early season feeding. Overwintering adults typically become active in April and initially may spend most of their time feeding within alfalfa or clover. As soybean plants become available in May and June, they become a preferred host. Fields most at risk this spring would include those that were planted first within an area and are now serving as a very attractive trap crop. These fields should be scouted for signs of defoliation. Fortunately, a rescue treatment for seedling soybeans is most often not justified because densities of 16 beetles per foot of row (early seedling stage) or 39 adults per foot of row at the V2+ stage of development are necessary for economic injury.

Seedling soybeans, May 31, 2013, Piatt County, Illinois.

Continuing delays in soybean planting could dim the prospects for soybean aphid establishment this season. Infestations of this insect pest have become less predictable and more sporadic the last several years in many areas of the Midwest. Soybean aphids first detected in North America (Wisconsin) in July of 2000, quickly spread to 10 North Central states by September of that same year. At the conclusion of the 2003 summer, they could be found in 21 states and three Canadian provinces. Entomologists have learned a great deal about this aphid species during the past 13 years and have developed some very sound economic thresholds that can be used in the effective management of this insect pest. Currently, alate (winged) viviparous (give birth to living young, nymphs) females are flying from their primary and overwintering host (common buckthorn) to their secondary host (soybean plants). These spring migrants may have more challenges this year locating soybean fields that are ready to receive them. It’s too early to offer any kind of firm predictions for soybean aphids this year. More moderate summer temperatures would work in favor of soybean aphids. For now, it appears they may have some establishment hurdles to clear this spring.

Management questions regarding soybean aphids and bean leaf beetles are often intertwined. A paper published in 2008 by some entomologists at Iowa State University provided some helpful insights regarding the use of insecticidal seed treatments and early-season rescue treatments in soybeans. They determined that neither of these approaches that targeted early-season bean leaf beetle densities had much value for overall soybean aphid management. For more information about this 3-year investigation, I encourage you to take a look at this useful journal article.

Johnson, K.D., M.E. O’Neal, J.D. Bradshaw, and M.E. Rice. 2008. Is preventative, concurrent management of the soybean aphid (Hemiptera: Aphididae) and bean leaf beetle (Coleoptera: Chrysomelidae) possible? Journal of Economic Entomology 101(3): 801-809.

Bean leaf beetle, Warren County, June 5 - Courtesy of Angie Peltier, Commercial Agriculture Educator, Northwestern Illinois Research and Education Center, Monmouth, Illinois.

Mike Gray


Western Corn Rootworm Injury in First-Year Corn: A Diminished Threat?

The economic impact of the variant western corn rootworm that evolved in the eastern Corn Belt continues to reverberate nearly twenty years later. The overall impact includes yield losses in first-year corn and the additional input costs of Bt seed and/or soil insecticides to rotated corn. In 1995, severe root injury and punishing yield losses occurred in first-year cornfields across east-central Illinois and northern Indiana. These were fields in which the annual rotation of corn and soybeans had rigidly taken place for decades. Producers had unwittingly selected for a rotation-resistant western corn rootworm in which females were laying at least a portion of their eggs in the soil of soybean fields. This behavior enhanced the survival of their progeny the following spring in first-year cornfields. In 2012, some University of Illinois researchers determined that the variant western corn rootworm could tolerate soybean foliage to a greater extent than the non-rotation resistant population. Based on their investigations, they discovered that the variant western corn rootworm had 3 to 4 times more of a key digestive enzyme (cathepsin L-like protease) enabling them to feed on soybean foliage for longer periods of time. Consequently, these western corn rootworms spent more time in soybean fields laying eggs. The reference for this very nice contribution to the entomological literature is provided.

Curzi, M.J., J.A. Zavala, J.L. Spencer, and M.J. Seufferheld. 2012. Abnormally high digestive enzyme activity and gene expression explain the contemporary evolution of a Diabrotica biotype able to feed on soybeans. Ecology and Evolution: DOI 10.1002/ece3.331.

As mentioned previously, the economic impact of this unique adaptation continues to be sobering in the eastern Corn Belt. Prior to the evolution of the variant western corn rootworm, crop rotation was considered to be a sound pest management strategy to limit root injury and yield loss caused by this insect pest. Since the mid-1990s, producers who felt they were at risk to first-year corn rootworm damage began to use planting-time soil insecticides on rotated corn ground. Western corn rootworms began to move across the Corn Belt in the 1950s and 1960s and continuous corn was the primary sink for soil insecticides delivered during planting. After 1995, concern over potential injury to rotated corn was most common in the northern two-thirds of Illinois and northern Indiana. In 2003, Bt hybrids that offered corn rootworm protection were commercialized. Producers quickly transitioned away from soil insecticides as their primary corn rootworm control tactic. However, many of these producers who were using soil insecticides on rotated and non-rotated corn ground continued to use Bt corn rootworm hybrids across all their corn acres regardless of crop history. Recently, it has become increasingly common to use both a planting-time soil insecticide and a Bt corn rootworm hybrid in some areas of the eastern Corn Belt even though crop rotation has been practiced.

A journal article was published recently (February 2013) by Mike Dunbar and Aaron Gassmann, entomologists at Iowa State University, that clearly pointed out the viability of crop rotation as a corn rootworm management strategy for northern and western corn rootworms in eastern Iowa. They indicated rotation resistant western corn rootworms were present in eastern Iowa at very low levels. By comparing their data with previous surveys, they reported no measurable expansion of this behavior in the last 5 years. They concluded their paper by recommending that growers scout, familiarize themselves with economic thresholds, and consider crop rotation as a viable corn rootworm management strategy in eastern Iowa. Based upon their findings, it would seem reasonable to suggest that producers in eastern Iowa could potentially save on their input costs for corn rootworms in rotated corn. The citation for this research is provided.

Dunbar, M.W., and A.J. Gassmann. 2013. Abundance and distribution of western and northern corn rootworm (Diabrotica spp.) and prevalence of rotation resistance in eastern Iowa. Journal of Economic Entomology 106(1): 168-180. DOI: http://dx.doi.org/10.1603/EC11291

What do the densities of western corn rootworm adults look like in Illinois soybean fields? In 2011 (late July and early August), we conducted a statewide (47 counties) survey of both corn and soybean fields for various insect pests. In each county, five soybean and five cornfields were selected randomly and sampled. In each soybean field, 100 sweeps were taken with a sweep net. In corn, 20 consecutive plants were examined for western corn rootworm adults. In both corn and soybean fields, western corn rootworm densities were exceedingly low. With one exception (Ford County, 25 western corn rootworm adults per 100 sweeps), on average, fewer than 10 western corn rootworm adults were recovered after 100 sweeps per field in all 47 counties. Historically, 10 adults captured per 100 sweeps was considered the benchmark that indicated the presence of variant western corn rootworm adults in a soybean field. For the vast majority of Illinois soybean fields sampled in 2011, this threshold was not even approached. In fact, it was exceeded only once (Ford County) and nearly reached in Vermilion County (9.4). In 28 counties, no western corn rootworm adults were found in soybean fields that we sampled. It’s worth noting, that Ford County still has the greatest density of variant western corn rootworms. Many will recall that Ford County was the epicenter of the outbreak that erupted in 1995.

Western corn rootworm densities (per 100 sweeps) in Illinois soybean fields, 2011.

Our data collected in 2011, look far different from survey results of western corn rootworm densities in soybeans collected approximately 1 decade ago (2002 and 2003). State surveys (2002 and 2003) conducted by Dr. Joe Spencer, an entomologist with the Illinois Natural History Survey, revealed densities of western corn rootworm adults that commonly went well beyond the 10 per 100 sweep threshold mentioned previously. Western corn rootworm densities such as those observed 10 years ago in soybean fields, would likely justify the use of a planting-time soil insecticide or a corn rootworm Bt hybrid on first-year corn. Can the same argument be made today even at the higher commodity prices? Unfortunately, most producers are no longer scouting for western corn rootworms in soybean fields (or cornfields) and assume the input costs will be worth the investment. In many instances, this may not be a wise decision with these very low western corn rootworm densities observed in Illinois soybean fields in recent years.

Western corn rootworm densities (per 100 sweeps) of soybean fields, 2002 and 2003, Courtesy of Dr. Joe Spencer, Illinois Natural History Survey.

Why are the densities of variant western corn rootworm adults so low in Illinois and Iowa soybean fields in recent years? I have stated previously that I believe three key factors are involved: 1) excessively wet springs and saturated soils (2012 being an exception) over many successive years leading to significant larval mortality during the spring hatch, 2) continued significant use of Bt corn rootworm hybrids in first-year corn and continuous corn production systems, and 3) popular broadcast applications of tank-mix treatments (fungicide/insecticide) to corn and soybean fields across a large swath of the Corn Belt. With increasing concern over emerging western corn rootworm resistance to the Cry3Bb1 protein expressed in some Bt hybrids, the use of crop rotation, along with a non-Bt hybrid in first-year corn would seem to make increasing sense. This would reduce the selection pressure on various Cry proteins targeted at corn rootworms. Ultimately, in order for management decisions to be optimized, they should be made on a field by field basis and rely upon scouting inputs the previous season and knowledge of rootworm densities and economic thresholds.

Is the variant western corn rootworm threat diminished as compared with the threat it posed 10 to 15 years ago? Recent data would suggest this to be the case. We should not expect this reduced threat to be permanent. Instead, producers are encouraged to scout soybeans for western corn rootworm adults and to make more informed management decisions regarding this insect pest in first-year cornfields. By more carefully targeting inputs (Bt hybrids, soil insecticides), their longevity can be enhanced.

Mike Gray


Mark Your Calendars for the 2013 AGMasters Conference

The 2013 AGMasters Conference will be held at the i Hotel and Conference Center in Champaign, IL on December 2 and 3. The conference will begin with a morning general program followed with 1 1/2 days of specialized sessions. Participants will be able to pick and choose the sessions of most interest to them. These sessions are designed to encourage interaction between instructors and students and cover a broad range of topics including crop production challenges, soil fertility, water resource management, entomology, plant pathology, weed science, and introductory statistics. Each session is taught twice and is limited to 40 students (per session). Registration for the most popular topics is very competitive. The overall conference is limited to the first 160 registrants. The conference will be pieced together over the summer and registration information will become available by early fall. For now, please add these dates to your calendar and look for more conference information to follow in this Bulletin. Conference co-chairs include Dennis Bowman, Carl Bradley, Aaron Hager, Sandy Osterbur and me, all members of the Crop Sciences Department. As the growing season unfolds, please contact any of us with your suggestions for the 2013 program. We welcome your input.

Mike Gray


Brown Marmorated Stink Bugs Breaking Winter Dormancy

On May 9, Robert Bellm, University of Illinois Extension Commercial Agriculture Educator, Brownstown Research and Education Center, found a brown marmorated stink bug (BMSB) in Madison County, Illinois (Figures 1 and 2). As we move further into spring, more reports of these sightings will begin to surface across the state. BMSB adults are now beginning to break their winter dormancy and move outside of their shelters (sheds, barns, homes, or other protected sites).

Figure 1. Brown marmorated stink bug, dorsal surface, courtesy of Robert Bellm.

 

Figure 2. Brown marmorated stink bug, ventral surface, courtesy of Robert Bellm.

This stink bug species was first confirmed in Illinois during 2010 in Cook County. Kelly Estes, Cooperative Agricultural Pest Survey Coordinator for Illinois, indicates that the BMSB has been confirmed in nine counties across the state (Figure 3). As the year unfolds, please send any specimens that you collect to Kelly at the following address: Illinois Natural History Survey, 1816 S. Oak Street, Champaign, IL 61820. Kelly will also look at photographs if they are sent to her email address: kcook8@illinois.edu. The BMSB feeds on many types of fruits and vegetables. In addition, corn and soybeans are susceptible to injury. Later this summer, we intend to conduct a statewide survey for this insect in corn and soybean fields. At this point, it’s too early to tell if this stink bug species will cause significant problems in 2013.

Figure 3

For additional information about how to identify the BMSB and manage this insect, I encourage you to look at the following web resources provide by Penn State University and Rutgers University. Because infestations have been severe in the Mid-Atlantic states, considerable information about this insect pest has been generated.

http://ento.psu.edu/extension/factsheets/brown-marmorated-stink-bug

http://njaes.rutgers.edu/stinkbug/identify.asp

http://njaes.rutgers.edu/stinkbug/control.asp

Mike Gray


Plant Diagnostic Clinic Ready for the 2013 Season

2013 Season at the University of Illinois Plant Clinic

After the extra early season last year, now we are in the midst of an extra late one. Samples have been slowly appearing this spring here at the Clinic in our 38th year of operation.  The unusually cool wet weather has kept many out of the field and landscapes.  The University of Illinois Plant Clinic began year-round operation in the fall of 2011, when we moved from our facility on St. Mary’s Road to our new location in Jonathan Baldwin Turner Hall on the south end of the Urbana campus.    With the new phone system at the U of I we actually have voice mail too.  During the winter our hours are reduced, but, we resumed regular business hours, 8am-12pm and 1pm-4:30pm on Monday April 29th, 2013.

 

One of the Diagnostic labs at the University of Illinois Plant Clinic

Plant Clinic services include plant and insect identification, diagnosis of disease, insect, weed and chemical injury (chemical injury on field crops only), nematode assays, and help with nutrient related problems, as well as recommendations involving these diagnoses. Microscopic examinations, laboratory culturing, virus assays, and nematode assays are some of the techniques used in the clinic. Many samples can be diagnosed within a day or two. Should culturing be necessary, isolates may not be ready to make a final reading for as much as two weeks. Nematode processing also requires about 1-2 weeks depending on the procedure. We send your final diagnoses and invoices to you through both the US mail and email.  If you provide your email address on the sample form you will get your information earlier.

Please refer to our website http://web.extension.illinois.edu/plantclinic/ for additional details on sampling, sample forms, fees and services offered. If you have questions about what, where, or how to sample call us at 217-333-0519 during operational hours.  Whenever submitting a sample, provide as much information as possible on the pattern of injury in the planting, the pattern on individual affected plants, and details describing how symptoms have changed over time to cause you concern.

Our fees vary depending on the procedure necessary.  General diagnosis including culturing is $15, ELISA and immunostrip testing is $25, Nematode analysis for SCN or PWN is $20, Specialty Nematode testing (such as corn) is $40.  Please include payment with the sample for diagnosis to be initiated. Checks should be made payable to the University of Illinois or to the Plant Clinic. Companies can setup an account, call and we will accommodate you. Call if uncertain of which test is needed or how to send a sample.

Preparing media for diagnostic culturing

 

 

Sending a sample thru US mail or Overnight delivery service address packages to:

University of Illinois Plant Clinic
1102 S. Goodwin, S-417 Turner Hall
Urbana, IL 61801

 

 

 

Map to the University of Illinois Plant Clinic S-417 Turner Hall, 1102 S. Goodwin, Urbana IL 61801

Drop off a sample:

You can also drop off a sample at S-417 Turner Hall. Park in the metered lot F 28 on the east side of Turner or at the ACES library metered lot on the west side of Turner. Come in the South door. Take the elevator located in the SE corner of the building.  Turn left when exiting the elevator; we are located along the SE corridor of the 4th floor.  Please use the green drop box located just outside S-417 if we are temporarily out of the office.

Social Media:

We have a lot of ways to keep you up to date on what is happening at the Plant Clinic and about other plant and pest issues.  Follow the U of I Plant Clinic on Facebook, http://www.facebook.com/UofIPlantClinic or, follow U of I Plant Clinic’s Stephanie Porter on Twitter: http://twitter.com/skporter or,  check out our Illini Plant and Pest podcasts http://web.extension.illinois.edu/podcasts/plantandpest/ or,  follow the U of I Plant Clinic on Blogger http://universityofillinoisplantclinic.blogspot.com

Regards, Suzanne Bissonnette


The Trapping Line: April 23

Black cutworm trap

Black cutworm pheromone sticky trap

UPDATE(4/25): Additional volunteers needed. Kelly Estes, Coordinator of the Illinois Cooperative Agricultural Pest Survey suggests anyone interested in monitoring traps contact her at:  kcook8@illinois.edu or 217-333-1005.

Currently, black cutworm moth pheromone traps are active in the University of Illinois insect monitoring program.  Traps for other species will be brought online as the season progresses. Extension Educators and volunteers monitor the traps and report the results through the North Central IPM PIPE system, hosted by Iowa State University. We will keep you updated about the trapping network here in the Bulletin.

Here is the current list of black cutworm moth captures:

April
County 11 12 15* 16 17 18 19 22* 23
Lee 1 0 0 1 0 0
Grundy 0 2 5 6
Champaign 1 1
Logan 1 2 4
Menard 0
Macon 3 1 0
Macoupin 1 0 0 1
Fayette 0 0 1 0 0 0 2
Madison 0 0 0 0 0 2
Edwards 0

 

The full website and current map can be found here.

The first date to expect damage is calculated based on growing degree day accumulations after the first intense flight, nine or more moths in a 2-day period.


Pyramided Bt Cotton and Factors Leading to Potential Compromised Longevity: Cautionary Findings for Bt Corn and Western Corn Rootworm?

In late March 2013, an article was published in the Proceedings of the National Academy of Sciences (PNAS) titled “Potential shortfall of pyramided transgenic cotton for insect resistance management.” The authors of the paper were as follows: Thierry Brévault, Shannon Heuberger, Min Zhang, Christa Ellers-Kirk, Xinzhi Ni, Luke Masson, Xianchiun Li, Bruce E. Tabashnik, and Yves Carrière. The scientists pointed out in their introduction that the first generation of Bt cotton plants, those expressing the Cry1Ac protein, were first used by US producers beginning in 1996. During that same year, corn producers began to grow Bt corn hybrids for European corn protection across many Corn Belt states. From 2003 to 2011, the authors of the PNAS paper indicated that the use of cotton plants expressing a single Cry protein were gradually phased out as producers began to use more pyramided products (either Cry1Ac + Cry2Ab or Cry1Ac + Cry1F). The scientists who wrote this PNAS article outlined several assumptions that explained the justification and increased use of pyramided cotton plants: 1) assumed – evolution of field resistance could be delayed by using more pyramided Bt cotton products, 2) assumed – insects that were resistant to one Cry protein would be killed by the other Cry protein expressed in plant tissue (redundant killing), 3) assumed – recessive resistance and only insects that had two resistant genes (homozygous for resistance) for each Cry protein (toxin) would survive on pyramided cotton plants, and 4) assumed – insects that are resistant to both Cry proteins are very rare within the overall population (assumed that target insect population has not been exposed to either Cry protein). Central to the effectiveness and long term durability of pyramided Bt plants is the concept of redundant killing. Redundant killing can be potentially compromised according to the authors of the PNAS article by the following factors: 1) some susceptible insects survive even though exposed to the Cry proteins, 2) as plants mature, Cry protein concentrations may decline, potentially increasing the number of survivors, 3) if an insect population has an inherently reduced susceptibility to a given Cry protein, exposure to reduced Cry protein levels as plants age may increase overall survivorship of the target insect pest, and 4) if cross resistance exists between Cry proteins being expressed in Bt plants.

The investigators reported that a Helicoverpa zea (cotton bollworm) strain that had been selected for resistance to the Cry1Ac protein had increased survivorship on pyramided cotton plants. They also concluded that cross resistance occurred between the Cry1A and Cry2A proteins. By using these data, they ran some simulation models and determined that the use of pyramided Bt plants – designed to substantially delay resistance development – could be compromised for Helicoverpa zea. They further pointed out that in order to prolong the usefulness of pyramided Bt plants to control Helicoverpa zea, large refuges may be needed as part of an IPM program that integrates several management strategies.

As we move forward into the 2013 growing season, it is increasingly clear that more corn producers will rely upon pyramided Bt hybrids for corn rootworm control. Have some of the assumptions regarding redundant killing already been violated with respect to the western corn rootworm and the use of pyramided Bt hybrids? Unlike the use of high dose events for many lepidopteran pests, Bt hybrids for corn rootworms are generally recognized as low dose – there are survivors and occasionally severe pruning in some high pressure fields. The following passage in the PNAS paper is worthy of reflection: “Previous experimental evidence on the pyramid strategy comes primarily from a model system with diamondback moth and noncommercial Bt broccoli plants producing Cry1Ac and Cry1C. Although most of the optimal conditions for pyramids apply to this model system, they may not apply for some other pest-Bt crop combinations, particularly when pests have inherently low susceptibility to one or more of the toxins in the pyramid.” We also know that root protection generally declines with some corn rootworm Bt hybrids as the season progresses. Consequently, a late-hatch and prolonged feed period can result in more severe root damage. Thus far, there has been no confirmation of western corn rootworm cross resistance between Cry3Bb1 and Cry34/35Ab1. That’s good news. However, as new rootworm Bt proteins (e.g., eCry3.1Ab) enter the market place and are expressed in pyramid combinations, potential cross resistance will need to be continuously evaluated.