Notice: Using Internet Explorer may cause some issues with loading dynamic content such as Cash Bids. Please use a modern browser such as Edge, Firefox, or Chrome.

Dynamic Weather Icon for Today's Forecast
Weather N/A

Corn Rootworm Update and Scouting

06/03/2019
Corn Rootworm Update and Scouting
  • Corn rootworms (CRW) are one of the most important insect pests of corn in the Midwest with the potential to cause significant yield losses and increase lodging.
  • As of May 31st, 2019 depending on where you are across the Midwest we are a day or two or a week or two away from corn rootworm peak egg hatch.
  • The wet conditions across the territory that have delayed corn planting have us wondering about the damage potential and survival of corn rootworms.
  • Even though low CRW populations have been observed in recent years, scouting is key to prevent, correct and predict the potential for CRW damage.

Corn rootworms (CRW) are one of the most important insect pests of corn in the Midwest with the potential to cause significant yield losses and increase lodging. A compilation of field research trials suggests that around 15% yield reduction can occur for each nodal root consumed by CRW larvae (Tinsley et al. 2013). Female CRW beetles lay eggs in the soil in late summer, those eggs overwinter and resume development the following spring. CRW development is driven by soil temperatures and it’s measured in degree days. Peak CRW egg hatch occurs between 684 and 767 accumulated degree days (52°F base soil temperature). As of May 31st, 2019 depending on where you are across the Midwest we are a day or two or a week or two away from corn rootworm peak egg hatch. 

In typical years, scouting should start about two weeks after peak hatch but can also be done later in the season to evaluate the extent of root damage. Although in general the potential for corn rootworm damage in late plantings may be low, all corn fields should be scouted. To evaluate the number of larvae present, carefully dig and remove a 7” x 7” cube of soil around the base of one plant in at least ten locations of the field. Place and crumble the soil over a dark background and examine for CRW larvae. Alternatively you can immerse the sample in a bucket of water and if CRW larvae are present, they will float to the surface. Finding an average of two or more larvae per plant using the soil crumbling method or eight or more using the float method may indicate the potential for economic damage. To determine the severity of root damage, evaluate root injury around mid-late July. Dig one plant in each of ten randomly selected areas and wash the roots to remove the soil. Using the Iowa State node injury scale, rate the roots from 0-3 where 0 = no damage and 3 = three or more nodes have been eaten. Scout high risk fields first. These include fields planted with hybrids without CRW Bt traits, fields with a history of CRW Bt trait failures, fields on continuous corn and fields with high CRW beetle counts the previous year. 

This season, questions are coming up about corn rootworm damage potential in late planted corn and wet planting conditions. If planting occurs days after egg hatch, mortality of corn rootworm larvae due to starvation will be significant. A 1989 study by Terry Branson, found that corn rootworm larvae have about 3 days to find roots before their survival is severely impacted. However even when they starve for only one day, 45% reduction in larval survival can occur. Nonetheless, late planted fields may have more issues with silk clipping by corn rootworm adults as fresh pollen and silks in these fields may attract more beetles. In terms of wet weather, saturated soil conditions that happen or persist around the egg hatch timing or before the larvae have found a root to feed on can reduce corn rootworm survival. However, if wet weather is prevalent before egg hatch but conditions are good enough for the soil to dry by the time egg hatch happens, corn rootworm survival should not be affected much at all. Likewise, if wet conditions are prevalent after the larvae have found corn roots and have started feeding, corn rootworm development should not be affected (Gray, 2009).

Even though low CRW populations have been observed in recent years, a few hot spots have been consistently identified across surveyed areas. Scouting is key to prevent, correct and predict the potential for CRW damage. Keeping field records across years will help evaluate the performance of our current CRW management program and adjust our CRW control strategies. 

References: 

Branson, T. 1989. Survival of Starved Neonate Larvae of Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae). Journal of Kansas Entomological Society. 62(4): 521-523

Gray, M. 2009. IPM bulletin Illinois. http://bulletin.ipm.illinois.edu/print.php?id=1126

Tinsley, N.A., R.E. Estes, M.E. Gray. 2013. Validation of a nested error component model to estimate damage caused by corn rootworm larvae. Journal of Applied Entomology. 137(3):161-169

Related Articles

Jun 24, 2016

During 2015 we observed several fields of corn following soybean with isolated areas of corn v10a.jpgthat had root lodged. Upon investigation, rootworm feeding was evident on the roots and there was an abundance of corn rootworm beetles present in those areas. These incidents were not trait failures since the hybrids were simply double stacked glyphosate and corn borer resistant.

Apr 15, 2015

Corn root worm resistance to the Bt trait Cry3Bb1 has been confirmed by researchers in the four Midwestern US states of Illinois, Iowa, Minnesota, and Nebraska. Resistance has also been documented for the mCry3A Bt event, and now cross-resistance has been documented for both traits.

Jun 9, 2017

Both adult and larval forms of corn rootworm can cause significant crop damage. Larvae feed on corn root hairs and roots, and develop through three instars phases before pupating into adult beetles. Larvae rob the plant of valuable water and nutrient flow and put the corn under yield-reducing physiological stress.

Related Videos

Sep 8, 2021

Tips from the field with Matt Aberle.

Nov 17, 2019

Exciting new FS InVISION corn products in the 100 and 105 day maturity range.

Nov 5, 2019

Exciting new products int he 100 and 105 day maturity range from FS InVISION.

We have revised our Privacy Policy and Terms of Use.

Please read both of these documents as the changes affect your legal rights. By continuing you agree to these updates.

We have revised our Privacy Policy and Terms of Use.

Please read both of these documents as the changes affect your legal rights. By continuing you agree to these updates.