Feedback sought on Pest Degree Day Calculator Upgrade

The Illinois Degree Day calculator has been available to Illinois producers since 2004. Hosted by the Illinois Climate Network (ICN), this pest management tool was developed to help aid producers in monitoring insect development throughout the growing season and aid in pest management decisions.

The calculator uses weather data from 19 network stations across Illinois to provide degree day accumulations and forecasts for 30 agricultural and invasive pests based on long-term averages. While this has been a great resource for many years, technology has changed, along with how information is disseminated.

Our main goal is to provide a calculator for priority pests for Illinois growers and deliver that information in way that is most useful and effective for them. In order to do that, we need your help. During February and March, we are collecting feedback from a short survey at https://go.illinois.edu/PDDSurvey. The information we collect will be used to design new tools to better communicate with growers.

The current plan is to have the new tools available by the end of 2020. During this time, the pest degree day calculator will remain available at the WARM website (https://www.isws.illinois.edu/warm/).


What effect will cold temperatures have on pests and pathogens?

Nathan Kleczewski Research assistant Professor and Extension Field Crop Pathologist

Nick Seiter- Research Assistant Professor and Extension Field Crop Entomologist

 

Many in the Illinois agricultural community are wondering what effects the recent extreme cold might have on pests and pathogens. While it would be nice if the cold temperatures we are experiencing could help to reduce our potential for pest damage, past experience tells us that the most serious pests we deal with are unlikely to be impacted much by these conditions.

Many of the pathogens and insect pests that commonly affect field crops in Illinois are well adapted to survive our winter conditions.  In many cases, pathogens produce recalcitrant survival structures (e.g. cysts in soybean cyst nematode, oospores in Phytophthora, sclerotia in white mold).  These structures allow the pathogen to survive extreme conditions including cold, drought, and flooding. Different species of insects overwinter in different life stages, including eggs (for example, western corn rootworm), larvae (Japanese beetles), pupae (corn earworm, though they do not survive the winter in most of Illinois), or adults (stink bugs). The overwintering stage has characteristics that help these insects to survive the winter, either by adjusting its physiology to better survive the cold, seeking out an overwintering site that protects it (such as soil, tree bark, or leaf litter), or both. The overwintering sites that insects find mean that they are not experiencing the same temperatures that we are when we venture outside. Wind chill has little effect for this reason (even though it has a major, unpleasant effect on us).

Extreme cold temperatures can impact some insects and plant pathogens, particularly those that may not overwinter as well (e.g. powdery mildew).  When cold weather pushes into the Southern regions of the country it can push certain diseases, such as rusts, further south, delaying disease onset in Illinois and other regions further north. The same is true of migratory insects, such as black cutworm and fall armyworm, which do not usually overwinter in Illinois; colder temperatures during winter often delay the arrival of these insects, and may ultimately lead to lower numbers. The opposite is also true – warmer than normal temperatures during the winter can allow these migratory insects to become a problem earlier in the season.

Although cold temperatures may not impact most of the diseases we encounter in Illinois field crops, fluctuation between conditions of cold and warm may have a negative impact on some diseases.  Dormancy by fungi can be broken by environmental conditions such as higher temperatures.  This is similar to what occurs in plants, where warm weather may result in trees flushing out buds and flowers.  Consequently, the wide swings in temperature that we have experienced during the 2018/19 winter may negatively impact some diseases. While some insects (such as stink bugs) can also break dormancy during brief warm periods, many of our most serious pests will stay “hunkered down” until the spring and avoid these fluctuations. Unfortunately, insects and plant diseases are unlikely to suffer as much from the recent cold as we have. The best way to reduce the impact of insects and pathogens on those cold days is to stay inside, grab a hot cup of coffee, and curl up to the latest UI Extension recommendations or UI applied research results guide.


Field Performance of Seed Treatments and Soil Insecticides for Corn Rootworm Control

Authors: Nick Seiter and Joe Spencer

Producers across east-central Illinois have enjoyed low western corn rootworm pressure for several years, due to a combination of saturating rains during rootworm egg hatch and widespread use of Bt corn hybrids. Following a low point in the rootworm population in 2015, statewide monitoring of corn and soybean fields has documented a slow western corn rootworm population rebound in some areas.  Recent low corn pest abundance (combined with lower commodity prices) provides an opportunity to become reacquainted with rootworm monitoring and non-Bt options for their management. While relying on soil insecticide or a seed treatment to protect corn roots may not fit into every growers’ operation every year, rotating among different rootworm management tactics should be considered a part of the best management practices for corn rootworms in the transgenic era. Rotating between different rootworm management tactics and Bt modes-of-action is necessary because western corn rootworm populations are evolving resistance to the Bt proteins expressed in Bt corn hybrids. In addition, monitoring adult populations in fields that will be planted to corn the following year will help to assess the need for control (whether a Bt trait or an insecticide).

In 2018, we conducted a series of field trials to evaluate control options for corn rootworm. These trials were planted following a 2017 “trap crop” of late planted corn and pumpkins to artificially increase rootworm populations in the field. Root masses (5 per plot) were removed during the early reproductive stages (R1-R3), cleaned using pressure washers, and rated for corn rootworm damage using the 0-3 Node-Injury Scale developed by researchers at Iowa State (Oleson et al. 2005). The rootworm population at this location consisted almost entirely of western corn rootworm, and previous bioassay data indicated a high level of resistance to the “Cry3” Bt traits within the population. Note that additional information and data for these trials (as well as additional insect and disease management trials) are available in the recently published “Applied Research Results on Field Crop Pest and Disease Control,” available at the following link: http://cropdisease.cropsciences.illinois.edu/wp-content/uploads/2018/12/Pestpathogenappliedresearchbook2018.pdf. In addition, readers are encouraged to consult “on Target” for summaries of applied research trials conducted by University of Illinois personnel from 2004-2014: http://ipm.illinois.edu/ontarget/.

Seed Treatments. Seed treatments are nearly ubiquitous on seed corn planted across the Corn Belt.  In our trials, the seed treatments Poncho Votivo and Poncho Votivo 2.0 offered significant root protection from corn rootworm larvae compared to an untreated control (Table 1).  For many years, some corn hybrids have been marketed with seed treatments at what has been described as the ‘rootworm rate’.  These data indicate that at modest larval pressure (ca. 1.9 on the 0-3 Node Injury Score scale), these seed treatments provide some root protection; however, based on previous studies these treatments should not be relied upon alone for control under heavy rootworm pressure. Note that all hybrids used in this trial expressed Cry3Bb1 for root protection. The relatively high root pruning observed in the untreated plots illustrates that resistance to the “Cry3” proteins is an issue at this site.

Soil-Applied Insecticides.  We tested soil-applied insecticides with a non-Bt hybrid for rootworm control, and all insecticide materials tested in 2018 reduced injury from corn rootworm larval feeding compared with the untreated control. This trial was conducted under relatively low larval pressure (1.07 on the 0-3 node-injury scale in the untreated plots), and no distinctions among the different insecticides could be made.

Before commercialization of Bt corn hybrids, a soil-applied insecticide was one of the only options available to growers anticipating economic rootworm injury in continuous or rotated corn.  Over the years, soil-applied insecticides were regularly evaluated in University of Illinois Insect Management Trials (see previously linked “on Target” reports). They typically provided significant reductions in corn rootworm larval damage to corn roots compared to untreated controls.  Oftentimes, soil-applied insecticides provided root protection equivalent to, or approaching that provided by single trait Bt corn hybrids with similar yield results (see 2013 “on Target” report). Ultimately, Bt corn’s season-long root protection that was as good as or better than a soil-applied insecticide, reduced pesticide exposure, and simplified planting operations were powerful motivations that drove adoption of Bt corn. However, use of a granular or liquid soil-applied insecticide on a non-rootworm Bt corn hybrid remains a viable tactic to protect corn roots without the use of a Bt corn hybrid. If you are interested in using one of these products and have not done so in a while, now is a good time to verify that your application equipment is in good shape. Rotating corn hybrids that incorporate Bt traits with non-Bt corn treated with a soil-applied insecticide should be considered as a strategy to slow resistance evolution, especially in areas that are currently experiencing only moderate corn rootworm pressure.

Oleson, J. D., Y. Park, T. M. Nowatzki, and J. J. Tollefson. 2005. Node-injury scale to evaluate root injury by corn rootworms (Coleoptera: Chrysomelidae). Journal of Economic Entomology 98: 1-8.

 

Table 1. Mean (± standard error) node-injury ratings of corn rootworm larval feeding injury on corn hybrids expressing the Bt trait Cry3Bb1 treated with Poncho Votivo, Poncho Votivo 2.0, or Untreated at Urbana, IL in 2018.

Treatment

Node-injury ratings

10 July (R1)

Untreated 1.83 ± 0.18 aa
Poncho Votivo 0.57 ± 0.06 b
Poncho Votivo 2.0 0.55 ± 0.10 b

a Means followed by the same letter within a column are not different based on the Fisher method of least significant difference (α = 0.05)

 

Table 2. Mean (± standard error) node-injury ratings of corn rootworm larval feeding injury on non-Bt corn treated with granular and liquid insecticides at planting at Urbana, IL in 2018.

Treatment

Node-injury ratings

10 July (R1)

Untreated 1.07 ± 0.12 aa
Capture 3RIVE 3D (16 oz/a) 0.37 ± 0.07 b
Force CS (9.9 oz/a) 0.22 ± 0.05 b
Aztec 4.67G (52.3 oz/a) 0.25 ± 0.06 b
Ampex EZb (12 oz/a) 0.15 ± 0.02 b
Poncho 1.25 mg ai/seed 0.19 ± 0.03 b
Poncho 0.5 mg ai/seed 0.31 ± 0.07 b
Ampex EZb (8 oz/a) 0.13 ± 0.01 b

a Means followed by the same letter within a column are not different based on the Fisher method of least significant difference (α = 0.05)  b Note that Ampex EZ is not labeled for use in corn at the time of this publication

Contact:

Nick Seiter nseiter@illinois.edu, University of Illinois Department of Crop Sciences

Joe Spencer spencer1@illinois.edu, University of Illinois Natural History Survey


Despite local Bt resistance, growers still have options

The development of resistance to Bt Cry toxins by the western corn rootworm is a growing concern, highlighted by the recent confirmation of field-evolved resistance to Cry34/35Ab1 in Iowa (https://www.agriculture.com/crops/corn/why-managing-corn-rootworm-just-became-more-complicated). Across the Corn Belt there are western corn rootworm populations with resistance to multiple Bt Cry toxins expressed in Bt corn. In Illinois, Bt resistance can be found in western corn rootworms from both continuous and first-year cornfields; rotation-resistant populations are vulnerable to Bt resistance. Since the first report of western corn rootworm Bt resistance in 2011, resistance to each of the Bt toxins expressed in Bt corn hybrids (i.e. Cry3Bb1, mCry3A, eCry3.1Ab and Cry34/35Ab1) has been documented at multiple Corn Belt locations (Gassmann et al. 2016: https://doi.org/10.1093/jee/tow110, Zukoff et al. 2016: https://doi.org/10.1093/jee/tow073). Repeated use of the same Bt trait(s) in the same continuous (or rotated) fields imposed strong selection for rootworm resistance to those traits. This problem is not limited to rootworms; Tabashnik and Carrière (2017) have recently documented examples of increasing Bt resistance around the globe (https://doi.org/10.1038/nbt.3974).

The introduction of corn hybrids that expressed two different Bt toxins was an important innovation in Bt technology that offered a way to slow the development of resistance and manage rootworms already resistant to a Bt trait. Because these “pyramided” Bt corn hybrids expressed Bt proteins with two different modes of action, a larva feeding on a pyramid’s roots must have resistance to both Bt proteins to survive.  Thus, pyramided hybrids provided a “second line of defense” against western corn rootworms in areas where some Bt resistance may already be present.

Cross-resistance among the structurally similar “Cry3” family of Bt Cry proteins (Cry3Bb1, mCry3A, and eCry3.1Ab) has further complicated rootworm management (Gassmann et al. 2014: https://doi.org/10.1073/pnas.1317179111). With cross-resistance, rootworms with resistance to one Cry3 toxin were also resistant to the other two. This significantly reduces grower options, as despite the availability of many different commercial Bt corn hybrids, there are functionally only two different Bt modes of action with activity against western corn rootworm beetles. Choosing an effective hybrid requires information about which traits work well against the rootworm populations in a particular field or area and information about which Bt Cry toxins are expressed in different Bt corn hybrids. Information about the Bt traits expressed in commercial Bt corn hybrids can be found in the “Handy Bt Trait Table” (https://www.texasinsects.org/bt-corn-trait-table.html).

Though western corn rootworm Bt resistance is increasing across the Corn Belt, field efficacy trials and bioassays reveal that some susceptibility to one or more proteins remains in most populations.  Furthermore, a recent publication from University of Nebraska (Reinders et al. 2018: https://doi.org/10.1371/journal.pone.0208266), showed that the level of resistance to a particular Bt protein(s) could vary from field-to-field even within a portion of a county. In east central Illinois, we have conducted a series of experiments to examine the susceptibility of local western corn rootworm populations to Bt traits.

Measuring local patterns of Bt susceptibility.

Local western corn rootworm populations have been periodically assessed for their susceptibility to the Cry toxins expressed in Bt corn hybrids.  Last spring, a variety of single trait-, pyramided- and non-Bt corn hybrids were planted for a Bt efficacy trial at the UI Agricultural and Biological Engineering (ABE) Farm in Urbana, Illinois.  Laboratory Bt resistance bioassays were also conducted using the offspring (larvae) of rootworm populations collected from the ABE farm during 2017.

Local field efficacy of Bt traits.  Bt corn hybrids expressing three of the four Bt toxins commercially available for corn rootworm management (Cry3Bb1, mCry3A, and Cry34/35Ab1; eCry3.1Ab Duracade®, a Cry3 toxin, was not tested) were evaluated as single trait hybrids and in pyramided hybrids with one other Bt protein (i.e. Cry34/35Ab1 + Cry3Bb1 proteins and Cry34/35Ab1 + mCry3A) (Table 1).

 

Table 1. Hybrid number and corn rootworm Bt trait(s) expressed in single- and pyramided Bt corn hybrids evaluated for node injury in 2018 ABE Farm Bt field efficacy trials.

aStandard commercial seed treatments were present on all hybrids. CRW: corn rootworm.

 

Local rootworm pressure has been low for several years. To assure significant western corn rootworm pressure for the efficacy trial, in 2017, the site was late-planted with corn and pumpkins to attract egg-laying adults. The 2018 trial was planted on May 2nd in a 6 x 6 grid of 8r x 9m plots. On July 18th, five roots were dug from each plot and evaluated for rootworm larval feeding injury using the Iowa State University 0-3 Node-Injury Scale (NIS)(Oleson et al. 2005: https://doi.org/10.1093/jee/98.1.1).

Western corn rootworm larval pressure in the trial was only modest leading to a pattern of variable results. The roots of non-CRW Bt hybrids sustained nearly two full nodes of injury (NIS = 1.987 ± 0.335; mean ± SE) (Table 2) which was greater than injury to all of the Bt corn hybrids, except the Cry3Bb1 single trait hybrid. The injury to roots of the mCry3A-expressing single-trait hybrid was not significantly different from injury to the Cry3Bb1- or the Cry34/35Ab1-expressing single trait hybrids.  The lowest NIS (=best root protection) occurred on the two pyramided hybrids, though this was not significantly different from the NIS for the single trait Cry34/35Ab1-expressing hybrid.

While a significant contribution of Cry34/35Ab1 to better root protection is evident from these data, the level of root protection provided by Cry3 traits (i.e. Cry3Bb1- and mCry3A-expressing single trait hybrids) compared to unprotected roots (i.e. non-CRW Bt) would be unacceptable in a commercial setting. Unsatisfactory Cry3 toxin performance is hardly surprising, given Cry3 cross-resistance, prior local evidence of reduced Cry3 Bt toxin efficacy, and current bioassay data (below). In single trait hybirds, Cry3 traits are unlikely to meet root protection expectations.

 

Table 2. Node Injury Scores (NIS) for Bt corn hybrids from the field efficacy trial. There were n=5 roots evaluated per replicate and n=6 replicates per each of the six corn hybrids; n=180 total roots evaluated.

aAll hybrids also expressed Lepidopteran-specific Bt traits. b Data were Log10 (NIS + 0.5) transformed before ANOVA and comparison of Least Squares Means with Tukey HSD using JMP Pro 13; untransformed means are shown. NIS scores sharing the same letter are not significantly different at alpha <0.05.

 

The importance of the Cry34/35Ab1 Bt toxin can be highlighted by pooling the NIS data according to whether the Cry34/35Ab1 Bt toxin was or was not expressed in a Bt hybrid (regardless of Cry3Bb1 or mCry3A expression) (Table 3).  After a re-analysis, the pooled Cry34/35Ab1 (+) hybrids are found to experience significantly less root injury than the two Cry34/35Ab1 (-) hybrids or the non-Bt control.

 

Table 3. Node Injury Scores (NIS) for the field efficacy trial from Table 2, data were pooled according to Bt-corn hybrid Cry34/35Ab1 protein expression category. Five roots were evaluated per replicate and n=6 replicates per each of the six corn hybrids; n=180 total roots.

aData were Log10 (NIS + 0.5) transformed before ANOVA and comparison of Least Squares Means with Tukey HSD using JMP Pro 13; untransformed means are shown.

 

Western corn rootworm Bt resistance bioassays. Single-plant Bt resistance bioassays compared the survival of larvae from a suspected-Bt resistant population and a Bt-susceptible population from a USDA laboratory colony (Brookings, SD). Larval survival was measured using corn hybrids expressing single Bt toxins (Cry3Bb1, mCry3A, or Cry34/35Ab1) and their respective non-Bt near-isoline hybrids. The suspected-Bt resistant rootworm larvae were the offspring of adults collected from the ABE field during 2017. Because, these larvae were the siblings of those attacking the plants in the field efficacy trial, we expected similar results.

Corn hybrids were obtained from the respective trait licensees and greenhouse-grown singly in 1-liter cups. When plants reached the V5-V6 stage, they were each inoculated with n=10 newly-emerged larvae. Twelve cups were inoculated for each of the six treatments, for a total of n=72 cups per rootworm population. Inoculated cups incubated for 17d at 25°C before transfer to Berlese funnels to recover surviving larvae. The bioassay was replicated twice.

 

 Table 4. Mean proportion larval survival for western corn rootworm on the roots of Bt- and non-Bt isoline hybrids in single-plant Bt-resistance bioassays.

aANOVA was performed on Log10(proportion survival + 0.5) transformed data. Untransformed data are depicted; JMP Pro 13 (2013 SAS Institute) was used to perform analyses. Means sharing the same letter within a trait family do not differ significantly (P<0.05) based on least-squares means (Tukey HSD).

 

Survival of larvae from the suspected-resistant, Urbana population on Cry3Bb1- and mCry3A-expressing corn was significantly higher than the Bt-susceptible population. The Urbana population survived as well on the Cry3 hybrids as they did on the non-Bt isoline hybrids indicating that they were resistant and had little if any susceptibility to either of the Cry3 proteins. In contrast, survival of larvae from the same population on Cry34/35Ab1-expressing corn was low and did not differ from that of Bt-susceptible WCR populations indicating that the Urbana field population was susceptible to the Cry34/35Ab1 toxin.

Results from field efficacy trials and Bt-resistance bioassays suggest that the Urbana, Illinois western corn rootworm population is susceptible to the Cry34/35Ab1 toxin, but resistant, or nearly so, to the Cry3 toxins (i.e. Cry3Bb1 and mCry3A).  Based on these data, growers anticipating economic populations of western corn rootworm should select Bt corn hybrids (pyramided hybrids) that express the Cry34/35Ab1 toxin. Whenever possible, rotating to soybean (a recommended Best Management Practice or BMP) should also be a first choice when an economic population is anticipated. The Urbana population’s minimal susceptibility (only in the field efficacy trial) to Cry3 toxins was too low to prevent significant injury to single trait hybrids and did not add to the efficacy of the Cry34/35Ab1 toxin expressed in pyramided corn hybrids.

Conclusions. Local populations of western corn rootworm in east central Illinois are still mostly susceptible to Cry34/35Ab1, despite the recent confirmation of resistance to this toxin in Iowa. The efficacy of pyramided hybrids in our area is largely dependent on this toxin, as local populations are mostly resistant to the “Cry3” toxins.  Western corn rootworm abundance monitoring is the first step when initiating an integrated pest management approach to corn rootworm. Rotating with a non-Bt alternative (e.g. non-host soybeans, a seed treatment or liquid/granular soil-applied insecticide) rather than using a Bt hybrid in every field every year helps to preserve the efficacy of Bt traits. When a Bt hybrid is used, planting pyramided Bt corn hybrids that express Cry34/35Ab1 is also an appropriate response. Finally, when field-specific monitoring indicates that rootworm populations will be below economically damaging levels in continuous or rotated cornfields, forgoing rootworm control helps to prevent needless selection of Bt-resistant individuals.  Using pest monitoring to guide selection of the appropriate management techniques fosters long-term strategies that are justified by data and responsive to field-specific pest threats.

Given evidence for field-evolved resistance to Cry3 and/or Cry34/35Ab1 traits elsewhere in the Corn Belt, it is important to protect local Bt trait efficacy by adopting IPM-based approaches. Remember that local adoption of BMPs can help mitigate resistance in problem fields. When the next generation of rootworm protection products reach the market, the new RNAi-based mode of action is slated to be pyramided with existing Cry3Bb1 and Cry34/35Ab1 Bt traits in a product called “SmartStax®Pro”. Careful stewardship of current Bt traits is in the best interest of growers. Not only does it preserve the remaining management options, but it will help to prolong and reinforce the efficacy of new products.

Joe Spencer and Nick Seiter

 

Links to helpful scientific literature:

Gassmann, A.J., J.L. Petzold-Maxwell, R.S. Keweshan, and M.W. Dunbar. 2011. Field-evolved resistance to Bt maize by western corn rootworm. PLOS ONE 6:e22629.  https://doi.org/10.1371/journal.pone.0022629

Gassmann, A.J., J.L. Petzold-Maxwell, E.H. Clifton, M.W. Dunbar, A.M. Hoffmann, D.A. Ingber, and R.S. Keweshan. 2014. Field-evolved resistance by western corn rootworm to multiple Bacillus thuringiensis toxins in transgenic maize. PNAS, 111 (14):5141-5146. https://doi.org/10.1073/pnas.1317179111

Gassmann, A.J., R.B. Shrestha, S.R.K. Jakka, M.W. Dunbar, E.H. Clifton, A.R. Paolino, D.A. Ingber, B.W. French, K.E. Masloski, J.W. Dounda, and C.R. St. Clair. 2016. Evidence of Resistance to Cry34/35Ab1 corn by western corn rootworm (Coleoptera: Chrysomelidae): root injury in the field and larval survival in plant-based bioassays. J. Economic Entomology, 109(4): 1872–1880. https://doi.org/10.1093/jee/tow110

Oleson, J.D., Y.L. Park, T.M. Nowatzki, and J.J. Tollefson. 2005. Node-injury scale to evaluate root injury by corn rootworms (Coleoptera: Chrysomelidae). J. Economic Entomology, 98:1–8. https://doi.org/10.1093/jee/98.1.1

Reinders J.D., B.D. Hitt, W.W. Stroup, B.W. French, and L.J. Meinke. 2018. Spatial variation in western corn rootworm (Coleoptera: Chrysomelidae) susceptibility to Cry3 toxins in Nebraska. PLoS ONE 13(11): e0208266. https://doi.org/10.1371/journal.pone.0208266

Tabashnik, B. and Y. Carriere. 2017. Surge in insect resistance to transgenic crops and prospects for sustainability. Nature Biotechnology. 35(10):926-935. https://doi.org/10.1038/nbt.3974

Zukoff, S.N., K.R. Ostlie, B. Potter, L.N. Meihls, A.L. Zukoff, L.French, M.R. Ellersieck, B.W. Wade French, and B.E. Hibbard. 2016. Multiple assays indicate varying levels of cross resistance in Cry3Bb1-selected field populations of the western corn rootworm to mCry3A, eCry3.1Ab, and Cry34/35Ab1. J. Economic Entomology, 109(3):1387-1398. https://doi.org/10.1093/jee/tow073


Dectes Stem Borer and Lodged Soybeans

Many soybean growers have had problems with lodging at harvest this year. The primary culprit for this (as for many of our woes this fall) was the extended period of unfavorable weather that we have suffered. However, in parts of southern Illinois damage by the dectes stem borer contributed to this problem.

The adult dectes stem borer (Figure 1) is a “long-horned” beetle that can often be found in soybean and on other plants. The adult female chews a hole into the surface of the plant (usually at the petiole), and lays her eggs in the pith. This often results in individual petioles wilting or falling completely off of the plant, which is usually the first sign of an infestation. Upon hatching, the larva (Figure 2) tunnels throughout the stem and feeds on the pith. As the plant nears maturity, the larva moves into the base of the stem where it will spend the winter. As awful as the bored-out stem of a soybean plant looks after being attacked by dectes stem borer (Figure 3), economic losses only occur if this damage leads to lodging. When preparing to overwinter, larvae will often girdle the base of the stem, causing the plant to break off and leading to harvest difficulties and reduced yield (Figure 4). This insect has one generation per year, with the adults usually emerging from soybean residue beginning in late June in Illinois to start the cycle again.

Adult dectes stem borer

Figure 1. An adult dectes stem borer at rest.

 

Larva of the dectes stem borer

Figure 2. A larva of the dectes stem borer removed from a soybean stem

Dectes stem borer larva in soybean stem

Figure 3. Damage to the inside of a soybean stem caused by a dectes stem borer larva

Soybean lodging caused by dectes stem borer

Figure 4. Lodged soybeans due to dectes stem borer feeding (Photo: Eric Alinger, Dupont Pioneer)

Insecticides are generally not recommended for control because the larvae are protected within the stem and the adults lay eggs over a long period of time in the summer (approximately mid-July through August in Illinois). While there appear to be some differences in varietal susceptibility, these differences are not well documented, and to my knowledge no soybean varieties have been characterized as resistant to dectes stem borer. However, there are some cultural management options available to producers:

  • Monitoring. While there is no economic threshold established, finding adults at higher than average numbers will be the first indication of a problem. Note wilting or broken-off petioles, and split soybean stems toward the end of the season to gauge the level of infestation. In addition, examine soybean stems in lodged areas to determine if dectes stem borer was part of the problem. If you have never done so before and you are in southern Illinois, the results might surprise you.
  • Timely harvest. Obviously, we would harvest on time every year in every field if we could. However, if you note fields that are infested with dectes stem borer, put those fields as early as possible on the priority list to reduce the potential for lodging.
  • Soybean stubble. Destroying or burying soybean stubble in the fall reduces dectes numbers locally, but the adults readily move from their overwintering sites to surrounding fields. Areas with a lot of no-till production are likely to have more issues with dectes stem borer.
  • Alternate hosts. Dectes stem borers feed on several other host plants, including sunflowers and giant ragweed. Areas with high populations of these plants could have higher populations of dectes stem borers as well. (As if you needed another reason to kill giant ragweed).

Contact:

Nick Seiter nseiter@illinois.edu (217) 300-7199

Research Assistant Professor, Field Crop Entomology

University of Illinois Department of Crop Sciences


And the Survey Says…

Figure 1. What pests were most prevalent in Illinois corn and soybeans in 2018? The survey says…

 

For those that attended Agronomy Day this past August, the title and above graphic may look familiar. As field and research season winds down, we’re able to finish collecting and summarizing data. One of our biggest summer projects is the annual corn and soybean survey. While some of that information was shared at Agronomy Day, the complete results are summarized below.

As a recap, this survey has been carried out across the state for several years (2011, 2013–2018). In 2018, 40 counties representing all nine crop reporting districts were surveyed, with five corn and five soybean fields surveyed in each county. These surveys have been conducted with the goal of estimating densities of common insect pests. The estimates provided in this article should not be considered a substitute for scouting individual fields and making informed pest management decisions—even areas of the state that appear to be at low risk could have contained fields with high densities of a given insect pest.

Figure 2. Average number of Japanese beetles per 100 sweeps.

As I’ve talked with growers throughout the summer, in their opinion, the top insect pest of 2018 is the Japanese beetle. And both the survey results and I agree.

Within the soybean fields surveyed, 100 sweeps were performed on both the exterior of the field (outer 2 rows) and interior (at least 12 rows beyond the field edge) using a 38-cm diameter sweep net. The insects collected in sweep samples were identified and counted to provide an estimate of the number of insects per 100 sweeps (Tables 1 and 2).

Japanese beetle populations were higher statewide compared to 2017. Western Illinois saw record numbers last year and populations stayed high in 2018. The highest Japanese beetle populations remained in western Illinois, but numbers increased dramatically in the northwest as well (from 54 beetles per 100 sweeps to 175).

Table 1. Average number of insects per 100 sweeps on the edge of the field.

 

Table 2. Average number of insects per 100 sweeps on the interior of the field.

Western corn rootworms are always a concern, but populations have been very low in recent years. In addition to sweep samples in soybeans, cornfields were sampled for western corn rootworm by counting the number of beetles on 20 consecutive plants beyond the end rows of a given field—a beetle per plant average was calculated for each field. A mild winter followed by favorable conditions at egg hatch and adult emergence helped the small populations from 2016 gain some traction in 2017 (Table 3). However, per plant averages were lower in all districts again in 2018. Populations were variable. Many fields had low to nonexistent populations, but there were fields with higher numbers. It is important to remember, fields are randomly selected. We have no knowledge of insect management strategies that are used – soil insecticides, transgenics, or foliar applications.

Table 3 Mean number of western corn rootworm beetles per plant in corn by crop reporting district and year.

As we’ve seen repeatedly, grape colaspis populations are highly variable. Despite having reports of sporadic larval injury in the spring, adult populations were lower in 2018 compared to last year. We did see more stinkbugs as well as green cloverworms and soybean loopers statewide. While the majority of the stink bugs are green and brown, we did not pick up any of the southern species like red banded and redshouldered stink bugs in the survey. Brown marmorated stink bug was found for the first time in soybean field sweeps in several counties, though.

 

Funding for survey activities was provided by the USDA National Institute of Food and Agriculture. This survey would not be possible without the hard work and contributions of many people. I would like to thank Illinois Cooperative Agriculture Pest Survey Program interns Evan Cropek, Hannah Hires, Calli Robinson, and Cale Sementi as well as Department of Crop Science intern Matt Mote.


Soybean Gall Midge: New Pest of Soybean in Nearby States

Producers in Nebraska, Iowa, and South Dakota have been dealing with gall midges in soybean. This is a fly in the family Cecidomyiidae, which is the same family as the Hessian fly, sorghum midge, and several other agricultural pests. We have not confirmed any infestations of this insect in Illinois at this time; the closest confirmed, damaging infestations that I know of are in western Iowa. However, because so little is known about the biology of this insect, producers should learn to identify it in case it does show up in Illinois. The following links to material produced by my colleagues in Iowa and Nebraska contain information on the identification and distribution of this insect pest; if you find any potential infestations within Illinois, please let me know at the contact information below. Happy scouting!

https://crops.extension.iastate.edu/cropnews/2018/07/new-soybean-pest-iowa-soybean-gall-midge

https://cropwatch.unl.edu/2018/orange-gall-midge-soybeans

 

Author:

Nick Seiter nseiter@illinois.edu (217) 300-7199

Research Assistant Professor, Field Crop Entomology


Ewing Demonstration Center Celebrates 50 years of Continuous No-till Research at Agronomy Field Day on July 26

The University of Illinois Extension will host the Ewing Demonstration Center Agronomy Field Day on Thursday, July 26, 2018 at 9 a.m.  Every growing season presents challenges to production, and this year is no exception!  We are happy to host this summer field day to share with local growers current, ongoing agronomy research in southern Illinois, including cover crop trials on corn and soybeans, nitrogen management in corn, weed management in soybean, and our continuous no-till field, now in its 50th year of continuous no-till production.

We are highlighting our 50th year of continuous no-till production in our field day this year.  This no-till trial area was established in 1969 by George McKibben, the “Father of No-Till”, long-time agronomist and researcher at the Dixon Springs Ag Center in southern Illinois.  This plot has been cropped utilizing no-till production of corn and soybeans ever since.  The “zero-till” system as it was first called, was researched to “save the soil” that was lost over the many years of intensive tillage required to raise grain crops on the sloping hills of southern Illinois with the planting equipment available at the time.

In honor of this milestone, we will have the original “zero-till planter” on display.  This planter was modified and built in the early 1960s at the Dixon Springs Ag Center and used there and also at the Ewing Demonstration Center and other research sites.  The demonstrated success of this zero-till planter and production system was one of the inspirations that led companies like Allis-Chalmers and John Deere to start engineering and producing no-till planting equipment.  Also, joining us for the field day will be Donnie Morris, retired farm mechanic and engineer who built this planter, along with other retired Extension advisors and educators that worked at the Ewing Demonstration Center over the years.

 

The topics to be discussed at Field Day include:

 

Looking Back at 50 Years of Continuous No-till

  • Current and Retired Staff, University of Illinois

Insect Management in Corn and Soybean

  • Nick Seiter, Research Assistant Professor, University of Illinois

What We Have Learned After 48 Years of Continuous No-till

  • Ron Krausz, Manager SIU Belleville Research Center
  • Sarah Dintelmann, Undergraduate Assistant ,Weed Science, SIU

Managing Cover Crops in Corn and Soybean

  • Nathan Johanning, Extension Educator, University of Illinois

Intro to Corn Genetics:  Why is Sweet Corn Sweet?

  • Talon Becker, Extension Educator, University of Illinois

 

Please join us for Agronomy Field Day to help celebrate this milestone in crop production!  The field day is free and open to anyone interested, and lunch will be provided.  Certified Crop Advisor CEUs will also be offered (Soil & Water – 2.0; IPM – 0.5, Crop Management – 0.5).  The Ewing Demonstration Center is about 20 minutes south of Mt. Vernon located at 16132 N. Ewing Rd; Ewing, IL 62836, on the north edge of the village of Ewing, north of the Ewing Grade School on north Ewing Road.  Watch for signs.

To help us provide adequate lunch and materials, please RSVP to the University of Illinois Extension Office in Franklin County at 618-439-3178 by Tuesday, July 24.  For additional information on the field day, contact Marc Lamczyk at the Franklin County office or lamczyk@illinois.edu.


Western Corn Rootworm: Adult Sampling and Economic Thresholds

Authors: Nick Seiter, Joe Spencer, and Kelly Estes

Based on degree day accumulations, western corn rootworm egg hatch should be underway in much of Illinois (roughly south of Peoria as of May 29; you can view your specific location using the degree day calculator here: https://www.isws.illinois.edu/warm/pestdata/sqlchoose1.asp). We are probably just over a month away from seeing the emergence of the first adult beetles. With low rootworm populations for the last several years, there has been a renewed interest in adult sampling. The only way to determine if larval densities will be high enough to justify a control action in a specific cornfield next spring is to monitor adults in the field this summer. Doing this correctly will require some preparation to obtain the correct materials. Now is a good time to review your monitoring procedures for western corn rootworm adults.

The most common monitoring tool for western corn rootworm adults is a 5.5 × 9-in yellow card trap coated in sticky material (e.g., Pherocon® AM No-Bait trap, Trécé, Inc., Adair, OK). The yellow color attracts the beetles, and when they land on the sticky substance they become trapped (Fig. 1). We recommend placing 12 of these traps uniformly throughout each field that you are monitoring beginning in late July. If the field you are monitoring is planted to corn this season (i.e., continuous corn), simply place each trap on a corn plant just above an ear. If you are monitoring a soybean field this season that will be rotated to corn next year, you will need to place each trap on a stake so that it will sit just above the soybean canopy. PVC pipes (½” diameter) are a relatively cheap and easy material that you can use to make these stakes, but wooden, metal, or plastic stakes also work.  Use poles that are long enough to allow trap height to be raised as the soybean crop grows taller.  Replace each trap once a week for 3-4 weeks, count all western corn rootworm adults stuck to the trap upon collection, and determine the average number of adults collected per trap per day.

 

Yellow sticky card trap

Figure 1. Yellow sticky card trap used to monitor western corn rootworm adults.

 

We recommend using the economic thresholds recently updated by our colleagues at Iowa State University [1] to determine if a control action is needed in corn the following spring (Table 1). If the beetle numbers you see on your traps are above these thresholds, a corn hybrid with Bt traits targeting corn rootworm or a soil insecticide is justified in that field when corn is planted the following spring. While monitoring for western corn rootworm takes some effort, it is the only way to get field-specific information on the economic need for a control tactic the following year.

Table 1. Economic thresholds for western corn rootworm in continuous or rotated corn.

Sticky Trap Location Economic Threshold
Corn (continuous corn) 2 beetles per trap per day
Soybean (rotated corn) 1.5 beetles per trap per day

 

1.             Dunbar MW, Gassmann AJ. Abundance and Distribution of Western and Northern Corn Rootworm (Diabrotica spp.) and Prevalence of Rotation Resistance in Eastern Iowa. Journal of Economic Entomology. 2013;106(1):168-80.