Statewide Corn and Soybean Survey Indicate Lower Insect Populations in 2019

The Illinois Statewide Corn and Soybean Insect Survey has been occurred in eight of the last nine years (2011, 2013–2019). These surveys have been conducted with the goal of estimating densities of common insect pests in corn and soybean cropping systems. In 2019, 40 counties representing all nine crop reporting districts were surveyed, with five corn and five soybean fields surveyed in each county.

 

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).

A common question during the growing season was, “How would insect populations respond to the severe cold events from the 2018/2019 winter following by the record breaking precipitation in the spring?” A very simple answer? Not well. For the most part, insect numbers were lower when compared with our 2018 survey.

 

While Japanese beetle populations were trending higher statewide in 2018, district averages declined everywhere with the exception of the East crop reporting district. High averages in both Iroquois and Livingston counties pulled the district average up. Growers in western and northwestern Illinois were happy to see lower numbers after extremely high Japanese beetles present in 2018 (Figure 1).

Figure 1. Average number of Japanese beetles per 100 sweeps (2019 Statewide Soybean Survey).

Included for the first time in the soybean survey, was the Dectes stem borer. While present in Illinois for many years, recently this pest, this insect pest has been garnering attention from soybean growers in southern Illinois for the past couple of years. Soybean sweeps did confirm higher numbers in the southern part of the state, particularly in the southeast, but was present at low levels in other districts as well (Figure 2).

Figure 2. Average number of Dectes Stem Borer per 100 sweeps (2019 Statewide Soybean Survey).

As expected with the very wet spring, western corn rootworms populations remained very low in 2019. In addition to sweep samples in soybeans (Figure 3), 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.  Despite lower statewide averages, there are local areas where populations were higher. This was especially evident in Iroquois and Livingston county soybean fields that were also contending with Japanese beetles. In corn, Christian, Sangamon and Greene counties each had a few fields with higher western corn rootworm numbers compared to others in those respective districts.

 

Figure 3. Average number of western corn rootworm per 100 sweeps (2019 Statewide Soybean Survey).

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, including Cooperative Agriculture Pest Survey Program interns Evan Cropek, Calli Robinson, Jacob Styan, Carson Robinson, Morgan Rothermel, and Mitch Clodfelter.

 

 

 

 

 

 

 

 


Japanese Beetle Management Guidelines

Japanese beetles (Fig. 1) have been arriving throughout Illinois over the last couple of weeks, and are becoming pretty conspicuous in some areas. Our crops are well behind their usual progress when Japanese beetle emergence occurs, which could impact scouting and management decision making. Several of my colleagues recently wrote an in-depth article on the history, distribution and management of this pest1; you can read the full open-access article here. Some notes on management follow by crop:

Japanese beetle adult

Fig. 1. A Japanese beetle adult hanging out on a corn leaf

Corn: Silk clipping is the primary concern with Japanese beetle infestations in corn. While the beetles will nibble on the leaves also, this does not amount to much. Many fields this season are likely to begin silking when Japanese beetles are at their peak, so scouting will be especially important. Silk clipping by Japanese beetles (as well as corn rootworms) can interfere with pollination. The effect of this feeding can be compounded by heat and drought stress2, which could be an issue in many fields this year given the late timing of pollination. Feeding tends to be concentrated on field edges, so thorough scouting within the field is necessary to determine if a treatment is justified. A rescue treatment with an insecticide is recommended if the following additions are observed:

  • Silks are being clipped to within ½ inch throughout the field
  • There are 3 or more beetles per ear (consider reducing this number if silk clipping is occuring under drought and heat-stress conditions)
  • Pollination is ongoing/less than 50% complete (especially during the first 5 days of silking).

Soybean: Control of Japanese beetles in soybean is rarely justified in Illinois, even though the damage is often conspicuous. Soybeans are fairly tolerant of defoliation in general. The only “wild card” this year is that, like corn, our soybeans are well behind their normal level of development when Japanese beetles (and other defoliators) become active. Making a rescue treatment decision for defoliators is a three-step process:

  • Determine the overall level of defoliation in the field. The recommended economic threshold is 30% defoliation prior to bloom, and 20% defoliation after bloom. Train your eye to accurately measure defoliation, and be careful not to over-estimate the extent of the damage (Fig. 2)
  • If a field is above the economic threshold, sample using a sweep net, shake sheet, or other sampling method to identify the insect responsible and verify that it is still present in the field. (Avoid “revenge” applications, which will not provide an economic return).
  • Choose an insecticide and rate that will provide effective control of the target insect. (Efficacy results from 2018 can be found in the 2018 Applied Research Results on Field Crop Pest and Disease Control report here. Results from trials conducted previously at the University of Illinois can be found in the “On Target” summaries of field crop insect management trials here.
Soybean defoliation levels

Fig. 2. Soybean leaves with differing levels of defoliation. Most observers tend to over-estimate the actual level of defoliation in the field

Most insecticides that control Japanese beetles have a relatively short period of residual control. This is no big deal in corn, as the critical period to protect silks is short anyway. In soybean, the short period of residual activity is another great reason to abide by the economic thresholds for defoliating insects; yield-reducing numbers of Japanese beetles in soybean are rare, and multiple applications for this insect are usually a wasted expense.

1 Shanovich et al. 2019. Journal of Integrated Pest Management 10: 9

2 Steckel et al. 2013. Journal of Economic Entomology 106: 2048-2054

Author contact: Nick Seiter | nseiter@illinois.edu | 217.300.7199


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.


Increased Insect Densities Reflected in Annual Corn and Soybean Survey

 

Thirty-six counties representing the nine crop reporting districts were surveyed at the end of July/beginning of August as part of our annual statewide corn and soybean survey. The surveys were performed by sampling five corn and five soybean fields per county. For the past several years (2011, 2013–2017), surveys in corn and soybean fields 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.

Crop Reporting Districts

Figure 1. Illinois crop reporting districts surveyed during 2017 annual corn and soybean insect survey.

 

Western corn rootworm beetles were sampled in cornfields 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 1). Per plant averages are up compared to recent years, though looking at the big picture, these numbers are still considered low. The district average from the northeast (1.95 beetles per plant), was affected by a single field in LaSalle county that average 7 beetles per plant which leads to a very important point to consider with this survey. Fields are randomly selected. We have no knowledge of insect management strategies that are used – soil insecticides, transgenics, or foliar applications.

Table1

Within an adjacent soybean field, 50 or 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 2 and 3).

Table2

 

Table3

The number of western corn rootworm adults in soybean fields throughout the state was low as well. The greatest number of beetles in soybeans occurred in McLean County, 8.00 beetles per 100 sweeps. All other counties sampled had fewer than 5 beetles per 100 sweeps (range of 0 to 2.4 per 100 sweeps).

Japanese beetles continued to increase in number from 2016 in the western part of Illinois. Both Fulton and McDonough counties recorded over 200 beetles per 100 sweeps in several fields, with their county averages of 525 and 340 beetles per 100 interior sweeps, respectively. Undoubtedly some of the highest numbers I’ve seen in this survey.

Overall, grape colaspis numbers were higher in several districts. This follows earlier reports during the growing season of grape colaspis feeding in soybeans. Unfortunately, there is no direct correlation between grape colaspis presence in soybeans and potential for larval injury in corn the following year. Numbers continue to be variable for this insect, but were high in the east southeast counties and should bear watching in 2018.

Stink bug injury in soybeans continues to make news in the southern states. We saw little damage caused by stink bugs in this survey, though numbers were slightly higher than past years. We continue to monitor for potential spread of not only the southern species like red banded and redshouldered stink bugs, but also the spread of brown marmorated stink bug as it gets its foothold here in Illinois.

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, Ryan Pavolka, Emma Sementi, Jacob Styan and Hannah Hires as well as Department of Crop Science interns Lacie Butler, Kaela Miller, and Matt Mote.


A Mixed Bag of Insect Densities in 2016 Corn and Soybean Surveys

Once again, statewide surveys of insects in corn and soybean fields were conducted during the summer of 2016.  A total of 33 counties were surveyed this year. The surveys were performed during the first week of August by sampling five corn and five soybean fields per county. For the past several years (2011, 2013–2016), surveys in corn and soybean fields have been conducted with the goal of estimating densities of common insect pests. Densities are reported for the various USDA crop reporting districts of Illinois to highlight portions of the state where the risk of economic insect damage is greatest. 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.

Western corn rootworm beetles were sampled in cornfields 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. Much like 2015, the number of western corn rootworm adults in corn was very low throughout the state (Table 1).

Table 1  ∙  Mean number of western corn rootworm beetles per plant in corn by crop reporting district and year
District 2011 2013 2014 2015 2016
Northwest 0.26 0.33 0.05 0.02 0.02
Northeast 0.15 0.20 0.02 0.00 0.02
West 0.01 0.10 0.01 0.01 0.00
Central 0.35 0.37 0.74 0.02 0.05
East 0.31 0.81 0.51 0.01 0.01
West-southwest 0.01 0.20 0.06 0.00 0.01
East-southeast 0.02 0.01 0.00 0.00 0.00
Southwest 0.00 0.00 0.00 0.01 0.01
Southeast 0.00 0.03 0.01 0.00 0.02
Means were determined by counting the number of beetles on 20 consecutive plants for between 15 and 50 fields per district.

 

Within an adjacent soybean field, 50 or 100 sweeps were performed 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. Depending on the year, five or ten pairs of corn and soybean fields were sampled at random in each county visited. The number of western corn rootworm adults in soybean fields throughout the state was very low as well. The greatest number of beetles in soybeans occurred in McLean County, 8.00 beetles per 100 sweeps. All other counties sampled had fewer than 5 beetles per 100 sweeps (range of 0 to 2.4 per 100 sweeps.)

Table 2  ∙  Mean number of various insect pests per 100 sweeps in soybean by crop reporting district and year

District

Year Bean leafbeetles Japanesebeetles Western cornrootworm beetles Grasshoppers Greencloverworms Soybeanloopers

Stink bugs

Northwest 2011 0.0 31.7 0.3 0.2 0.2 0.0 0.2
2013 0.3 28.3 1.0 0.4 0.0 0.0 0.1
2014 0.3 14.5 1.0 0.7 0.9 0.2 0.5
2015 1.1 13.4 0.0 1.6 1.9 0.1 0.5
2016 1.1 21.8 0 3.2 2.0 0.0 0.8
Northeast 2011 1.4 13.0 0.3 0.1 0.1 0.0 0.1
2013 0.5 13.8 10.0 0.5 0.2 0.1 0.0
2014 0.2 18.3 3.0 0.3 0.6 0.1 0.6
2015 0.7 12.9 0.1 1.7 2.3 0.0 0.6
2016 8.3 1.3 0.0 5.9 2.9 0.0 0.0
West 2011 0.7 9.5 0.1 0.6 0.7 0.0 0.2
2013 1.0 5.0 0.4 0.3 0.3 0.0 0.2
2014 11.7 2.1 0.2 1.2 0.4 0.2 1.5
2015 1.6 17.5 0.0 2.8 1.3 0.1 0.5
2016 0.9 89.4 0.7 1.5 6.6 1.4 0.2
Central 2011 3.3 24.1 0.9 0.5 0.1 0.0 0.1
2013 0.5 0.9 6.4 0.3 0.4 0.1 0.2
2014 2.4 0.7 18.9 0.6 2.6 0.3 0.7
2015 5.8 2.7 0.2 4.0 0.5 0.0 0.7
2016 16.8 2.0 5.2 4.0 10.0 0.0 0.0
East 2011 17.0 5.3 7.0 1.1 5.4 0.0 0.3
2013 1.4 2.2 9.8 1.0 1.4 0.0 0.1
2014 1.9 0.4 10.2 0.7 3.0 0.0 0.7
2015 5.5 2.0 0.1 3.8 2.3 0.0 0.8
2016 13.4 0.8 0.13 2.3 11.3 0 0.0
West-southwest 2011 1.4 7.0 0.0 1.3 6.1 0.0 0.5
2013 1.3 2.4 1.5 0.5 1.4 0.0 0.1
2014 1.8 7.3 0.4 0.4 0.9 0.3 1.9
2015 5.4 22.2 0.0 5.8 1.5 0.1 1.7
2016 4.0 10.5 0.3 5.2 12.8 0 0.6
East-southeast 2011 4.1 2.0 0.4 1.3 23.8 0.0 0.1
2013 1.1 0.5 0.1 0.4 1.6 0.0 0.0
2014 1.7 0.4 0.0 0.5 2.7 0.0 0.7
2015 0.9 2.7 0.0 1.7 3.4 0.5 2.1
2016 0.8 2.0 0.0 2.2 7.0 0.0 0.1
Southwest 2011 2.6 2.7 0.0 1.0 4.4 0.0 0.4
2013 1.2 0.4 0.1 0.3 3.4 0.0 0.2
2014 8.4 0.2 0.0 0.6 6.1 0.1 1.3
2015 0.8 2.1 0.0 1.1 2.7 0.0 0.3
2016 1.2 12.0 0.0 4.0 13.2 0.0 0.1
Southeast 2011 1.9 2.5 0.0 0.9 9.7 0.0 0.3
2013 0.5 0.5 1.5 0.1 2.4 0.2 0.3
2014 2.4 0.8 0.1 0.4 2.2 0.2 1.2
2015 0.2 2.5 0.0 1.1 3.3 0.1 0.3
2016 1.9 7.7 0.53 1.1 6.1 0 0.6
Means were determined by counting the number of insects in a 50- or 100-sweep sample for between 15 and 50 fields per district. The stink bug species reported here are the green stink bug and the brown stink bug.

 

Increased densities of some of the defoliating insect species were observed in several districts. Samples were screened for bean leaf beetles, Japanese beetles, grasshoppers, green cloverworm, soybean loopers, and stink bugs. As with many years, Japanese beetles “hot spots” were observed around the state. The western part of the state yielded the most impressive numbers (89.4 per 100 sweep average), with 240 per 100 sweeps and 108 per 100 sweeps recorded in Pike and Warren counties, respectively.  Interestingly, we had higher numbers across the board for green cloverworm in 2016. A few counties had noticeable bean leaf beetles in the samples (Central – 16.8 bean leaf beetles per 100 sweeps and East 13.4 bean leaf beetles per 100 sweeps). No brown marmorated stink bugs were detected in any of the soybean or cornfields that were sampled, though this species has been confirmed in many Illinois counties (Figure 1).

BMSB August 2016

Funding for survey activities was provided by the USDA National Institute of Food and Agriculture and the Illinois Soybean Association. 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, Colleen Musson, Ryan Pavolka, Emma Sementi, and Jacob Styan as well as Department of Crop Science interns Lacie Butler and Sarah Luce.