Corn Rootworm Beetle Counts to Assess the Risk of Economic Injury

Click on a tab below to see data collected each year for this study

 

Using 2020 Corn Rootworm Beetle Counts to Help Evaluate the Risk of an Infestation for 2021 

 

TRIAL OBJECTIVE

  • Monitoring of corn rootworm (CRW) beetle numbers in current corn and soybean fields can be used to help assess the potential risk of a CRW larval infestation reaching economic damage levels in corn fields during the next growing season. 

  • This information may help guide decisions regarding management strategies including corn product selection. 

  • The objective of this study was to measure adult CRW populations in corn and soybean fields in 2020 to assist in risk evaluation for 2021.

 

RESEARCH SITE DETAILS

Location 1440 fields     
Soil Type  Drained or well-drained  

Previous
Crop
Various    
Tillage
Type
Various  


 
Planting Date Various    
Harvest Date Various  

Potential Yield
 (bu/acre)
110-250    
Seeding Rate
(seeds/acre)
Various

 

 

  • One to four Pherocon® AM non-baited trapping sites were established at 1440 field locations across the corn-growing areas of IA, IL, IN, OH, MI, WI, MN, ND, SD, NE, KS, CO, and MO (Figure 1).

  • The trapping sites were installed in the interiors of corn and soybean fields that encompassed a variety of crop and management histories. Soybean fields were sampled in parts of the corn-growing area to assess the potential risk associated with the variant western CRW, which is known to lay eggs in soybean fields.

  • The Pherocon® AM traps were changed at 5- to 10-day intervals for 2-8 consecutive weeks through CRW adult emergence, mating, and egg laying phases (late July through late September).

  • Following each sampling interval, the counts of adult northern and western CRW beetles were recorded and used to calculate the average number of CRW beetles/trap/day by field.

  • At the end of the collective sampling period, the average capture value for each field was determined and the data were used in further analysis.

 

UNDERSTANDING THE RESULTS

Categories for CRW beetle counts are based on action thresholds (beetles/trap/day) suggested by Extension entomologists at the University of Illinois (UI) and Iowa State University (ISU) and provide the economic injury potential for the following season.1,2

  • Less than 2 beetles/trap/day indicates a relatively low risk of economic injury.
    • Greater than 1 beetle/trap/day suggests a low risk for economic injury but could indicate populations are increasing.
  • Greater than 2 beetles/trap/day indicate the probability for economic injury is likely if control measures are not used. 
  • Greater than 5 beetles/trap/day indicate that economic injury is very likely, and populations are expected to be very high the following year.

image Figure 1a. Corn field locations for corn rootworm trapping in 2020.
image Figure 1b. Soybean field locations for corn rootworm trapping in 2020.

(Data in this graph are the result of field trials conducted on 1440 field plots in 13 different states in 2020).

image Figure 2. Overall summary of average corn
image Table 1. Summary of field sampling and adult corn rootworm captures in 2020.

2020 CRW Beetle Survey Data

 
  • CRW populations were variable across the corn-growing area, which suggests that environment and management affect CRW pressure. 

  • 22% of corn fields had counts exceeding the economic threshold of 2 beetles/trap/day.

  • 8% of the corn fields were approaching threshold levels.

  • Corn followed by (fb) corn had higher average maximum daily counts than first-year corn (2.79 vs. 0.42 beetles/trap/day) (Table 1).

  • Of the corn fb corn fields, 33% exceeded the economic threshold while less than 3.9% of first-year corn fields exceeded the threshold (Figure 2).

  • Counts from soybean fields were low, with no adults being captured in 29% of the fields and fewer than 4.7% of the fields exceeding the threshold. 

  • Counts of 0 were recorded in 21% of corn fields sampled.

 

2020 Data Interpolation 

 
  • Point data were interpolated to estimate populations and relative risk at the landscape level.

  • To account for variations in sampling density and distribution, interpolations were based on average maximum values calculated within a systematic grid applied to the estimation area.

  • On a broad scale, CRW populations, and consequently 2021 risk potential, are possibly elevated in corn fields in central and southwest NE, northeast CO, northwestern KS, west, central, and east central IA, southwest WI, northern IL, central and southern MN, and southeastern ND (Figure 3).

  • Corn rootworm populations are estimated to be relatively low in many parts of ND, SD, MN, IN, and central IL; however, localized hot spots can be found every year.

  • CRW beetle presence in soybean fields was found to be low in most of the areas that were sampled.

 
image Figure 3. Estimated corn rootworm risk in 2021 using interpolated 2020 corn rootworm data from all fields sampled.

Comparison of 2019 vs. 2020 CRW Beetle Data (Figures 4a and 4b).

 
  • Absolute comparisons between 2019 and 2020 populations should be made with limited confidence due to differences in sampling intensity and distribution. However, trends may still be reliably identified. 

  • Areas with large populations (i.e. “hot spots”) are generally consistent from year to year.

image Figure 4a. Estimated corn rootworm risk in 2020 using interpolated 2019 corn rootworm counts from corn fields sampled (based on 1123 fields).
image Figure 4b. Estimated corn rootworm risk in 2021 using interpolated 2020 corn rootworm counts from corn fields sampled (based on 1123 fields).

KEY LEARNINGS

  • Corn rootworm is a persistent and annual threat to yield and profit potential, making it a pest that cannot be ignored. University research has demonstrated that even a moderate level of CRW feeding can cause yield losses averaging 15% with losses of 45% or more being possible.3

  • In the absence of site-specific data, local/regional surveys may provide insight at the landscape level and can be used to make informed decisions regarding management and product selection decisions.

  • Beetle numbers and infestation geographies change. Continue to monitor present and historical data to gain information regarding CRW infestation potential. This information can be used to help prepare for the 2021 season and the selection of CRW Bacillus thuringiensis (B.t.)-protected corn products or soil-applied insecticides to protect your crop against the risk of CRW larvae damaging roots and reducing your yield potential.

 

 

 

 

 

Sources

1Western corn rootworm. Diabrotica virgifera virgifera LeConte. Extension & Outreach. Department of Crop Sciences. University of Illinois. http://extension.cropsciences.illinois.edu/fieldcrops/insects/western_corn_rootworm.

2Hodgson, E. and Gassmann, A. 2016. Guidelines for using sticky traps to assess corn rootworm activity. Integrated Crop Management. Iowa State University. https://crops.extension.iastate.edu/cropnews/2016/06/guidelines-usingsticky-traps-assess-corn-rootworm-activity.

3Tinsley, N.A., Estes, R.E., and Gray, M.E. 2012. Validation of a nested error component model to estimate damage caused by corn rootworm larvae. Journal of Applied Entomology.

 

 

1001_R1_20

 

Using 2019 Corn Rootworm Beetle Counts to Help Evaluate the Risk of an Infestation for 2020 

 

TRIAL OBJECTIVE

  • Monitoring of corn rootworm (CRW) beetle numbers in current corn and soybean fields can be used to help assess the potential risk of a CRW larval infestation reaching economic damage levels in corn fields during the next growing season. 

  • The objective of this study was to measure adult CRW populations in corn and soybean fields in 2019 to assist in risk evaluation for 2020. 

  • This information may help guide decisions regarding management strategies including corn product selection. 

 

RESEARCH SITE DETAILS

Location 1440 fields     
Soil Type  Drained or well-drained  

Previous
Crop
See Figure 1    
Tillage
Type
Various  


 
Planting Date Various    
Harvest Date Various  

Potential Yield
 (bu/acre)
110-250    
Seeding Rate
(seeds/acre)
Various

 

 

  • One to four Pherocon® AM non-baited trapping sites were established at 1442 field locations across the corn-growing areas of IA, IL, IN, OH, MI, WI, MN, ND, SD, NE, KS, CO, and MO (Figure 1).

  • The trapping sites were installed in the interiors of corn and soybean fields that encompassed a variety of crop and management histories. Soybean fields were sampled in parts of the corn-growing area to assess the potential risk associated with the variant western CRW, which is known to lay eggs in soybean fields.

  • The Pherocon® AM traps were refreshed at 5- to 10-day intervals for 2-8 consecutive weeks through CRW adult emergence, mating, and egg laying phases (late July through late September).

  • Following each sampling interval, the counts of adult northern and western CRW beetles were recorded and used to calculate the average number of CRW beetles/trap/day by field.

  • At the end of the collective sampling period, the maximum capture value for each field was determined and the data were used in further analysis.

 

UNDERSTANDING THE RESULTS

 

Categories for CRW beetle counts are based on action thresholds (beetles/trap/day) suggested by Extension entomologists at the University of Illinois and Iowa State University (ISU) and provide the economic damage potential for the following season.1,2

  • Less than 2 beetles/trap/day indicate a relatively low risk of economic damage.
    • Greater than 1 beetle/trap/day suggests a low risk for economic damage but could indicate populations are increasing.
  • Greater than 2 beetles/trap/day indicate the probability for economic damage is likely if control measures are not used.

  • Greater than 5 beetles indicate that economic damage is very likely and populations are expected to be very high the following year.

 
Field sampling

2019 CRW Beetle Survey Data

 

  • CRW populations were variable across the corn-growing area, which suggests that environment and management are factors in determining CRW pressure. 

  • 11.2% of corn fields had counts exceeding the economic threshold of 2 beetles/trap/day.

  • 6% of the corn fields were approaching threshold levels. 

  • Corn followed by (fb) corn had higher average maximum daily counts than first-year corn (1.57 vs. 0.33 beetles/trap/day) (Table 1).

  • 18% of continuous corn fields exceeded the economic threshold while less than 3% of first-year corn fields exceeded the threshold (Figure 2).

  • Counts from soybean fields were low where no adults were captured in 36% of the fields and just less than 2% of the fields exceeded the threshold. 

  • Counts of 0 were recorded in 35% of corn. 

 

2019 Data Interpolation 

 

  • Point data were interpolated to estimate populations and relative risk at the landscape level.

  • To account for variations in sampling density and distribution, interpolations were based on average maximum values calculated within a systematic grid applied to the estimation area.

  • On a broad scale, CRW populations, and consequently 2020 risk potential, are potentially elevated in corn fields in central and southwest NE, northeast CO, northwestern KS, northwest, central, and east central IA, southwest WI, northern IL, southcentral and central MN, and southeastern ND (Figure 3). 

  • Corn rootworm populations are estimated to be relatively low in many parts of ND, SD, MN, IN, and central IL; however, localized hot spots can be found every year.

  • CRW beetle presence in soybean fields was found to be above the threshold in a small area in north central IL and southern WI.

 

Comparison of 2018 vs. 2019 CRW Beetle Data (Figure 3a and b).

 

  • Absolute comparisons between 2018 and 2019 populations should be made with limited confidence due to differences in sampling intensity and distribution. However, trends may still be reliably identified.  

  • Areas with large populations (i.e. “hot spots”) are generally consistent from year to year.

KEY LEARNINGS

 

  • Corn rootworm is a persistent threat to yield and profit potential, making it a pest that cannot be ignored. University research has demonstrated that even a moderate level of CRW feeding can cause yield losses averaging 15% with losses of 45% or more being possible.3

  • In the absence of site-specific data, local/regional surveys may provide insight at the landscape level and can be used to make informed decisions regarding management and product selection decisions.

  • Beetle numbers and infestation geographies change. Continue to monitor present and historical data to gain information regarding CRW infestation potential. Use this information to help prepare for the 2020 season by selecting CRW Bacillus thuringiensis (B.t.)-protected corn products or soil-applied insecticides to help protect your crop against the risk of CRW larvae damaging roots and reducing your yield potential.

 

 

 

 

 

 

Sources

1Western corn rootworm. Diabrotica virgifera virgifera LeConte. Extension & Outreach. Department of Crop Sciences. University of Illinois. http://extension.cropsciences.illinois.edu/fieldcrops/insects/western_corn_rootworm.

2Hodgson, E. and Gassmann, A. 2016. Guidelines for using sticky traps to assess corn rootworm activity. Integrated Crop Management. Iowa State University. https://crops.extension.iastate.edu/cropnews/2016/06/guidelines-usingsticky-traps-assess-corn-rootworm-activity.

3Tinsley, N.A., Estes, R.E., and Gray, M.E. 2012. Validation of a nested error component model to estimate damage caused by corn rootworm larvae. Journal of Applied Entomology.

 

 

1001_R1

 

 

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