Using 2021 Corn Rootworm Beetle Counts to Assess the Risk of Economic Injury in 2022

• The objective of this study was to measure corn rootworm (CRW) beetle populations in corn and soybean fields in 2021 to assist in risk evaluation for 2022.  

• The monitoring of CRW beetle numbers in current corn and soybean fields can be used to help assess the potential risk of CRW larval infestations reaching economic damage levels in the following corn crop.

• The data may help guide CRW larval management decisions, including corn product selection, for the next corn crop.

   

• One to four Pherocon® AM non-baited trapping sites were established at 1291 field locations in corn and soybean fields across the corn-growing areas of CO, IA, IL, IN, KS, MI, MN, MO, NE, ND, OH, SD, and WI (Figure 1).

• The trapping sites were installed in the interiors of corn and soybean fields that encompassed a variety of crop and management histories (Figures 2 and 3). 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 to 8 consecutive weeks through CRW adult emergence, mating, and egg laying phases (late July through late September).

• Following each sampling interval, counts for northern and western CRW beetles were recorded and used to calculate the average number of CRW beetles/trap/day by field (Figure 4).

• 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.

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 and provide the economic injury potential for the following season.^1,2

• Less than 2 beetles/trap/day indicate 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 measues 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. 

Figure 4. Overall summary of average corn rootworm beetles captured per trap per day in corn and soybean fields in 13 states (2021).^1,2

Table 1. Summary of field sampling and corn rootworm beetle captures in 2021.

2021 Corn Rootworm Beetle Survey Data

• Populations for CRW were variable across the corn-growing area, which suggests that environment and management affect CRW pressure (Figure 5, right).

• 38% of the corn fields had counts exceeding the economic threshold of 2 beetles/trap/day (up from 22% in 2020).

• 52% of the continuous corn fields sampled were above the economic threshold (up from 33% in 2020).

• 17% of the first-year corn fields were above the economic threshold (up from 4% in 2020). This is a dramatic change from the previous year.

2021 Data Interpolation

• Point data 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 2022 risk potential, are possibly elevated in corn fields in west, central, and east central IA, southern MN, southwest, and southern WI, and northwestern IL (Figure 5, right).

• In comparison to 2021 CRW forecast (Figure 5, left), the risk for 2022 (Figure 5, right) appears to be greater over a broader area. 

• Larval populations are estimated to be relatively low in many parts of ND, SD, MN, NE, KS, MO, IL, IN, MI, and OH; however, localized hot spots can be found every year (Figure 5, right).

• Adult CRW presence in soybean fields was found to be low in most sampled areas; however, there were some hot spots in northwestern IL (Figure 6).

• Corn root injury from CRW larvae 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 larval feeding can cause yield losses averaging 15% with losses of 45% or more being possible.³

• In the absence of site-specific data, local and regional CRW beetle 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 larval potential. This information can be used to help prepare for the 2022 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 yield potential.

Source

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

²Hodgson, E. and Gassmann, A. J. 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-using-sticky-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. Department of Crop Sciences, University of Illinois, Urbana, IL. Journal of Applied Entomology.

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

• 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.

• 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.

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.

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.

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.

• 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.

• 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.

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.