No. 15 Article 1/July 7, 2006

Corn Rootworm Larval Damage "The Worst I Have Ever Seen" Reported in Some Fields

Shortly after the article "Still Too Early to Assess Western Corn Rootworm Impact" (the Bulletin, issue no. 14, June 30, 2006) was posted to the Web, I received some reports of severe rootworm larval damage. Apparently my comment about our not receiving many reports of severe rootworm larval damage in 2006 sparked some responses. In fact, the phrase in the title of this article are attributed not to me but to a couple of people who reported damage. I have seen a lot of severe rootworm larval damage during my 30 years of observing the insect. However, when others indicate that damage is "the worst I have ever seen," we take notice, especially hearing that from people who are observing damage caused by the variant western corn rootworm for the first time.

First, a report from an area where the western corn rootworm has been entrenched for quite some timeright here in east-central Illinois, near the area we lovingly refer to as the "epicenter." Jim Goss with AG Farm Management in Urbana sent me some photos of severe rootworm larval damage in a field of corn planted after soybean just east of Piper City in Ford County. The damaged roots were from a non-Bt rootworm corn refuge that had not been treated with a soil insecticide. With damage so severe in the nontreated refuge, we will be interested in observing how much larval damage, if any, occurs on the Bt rootworm hybrid planted in the same field.


A range of corn rootworm larval damage to four plants, corn planted after soybean, Ford County, July 3, 2006 (photo courtesy of Jim Goss, AG Farm Management).


Severe corn rootworm larval damage, corn planted after soybean, Ford County, July 3, 2006 (photo courtesy of Jim Goss, AG Farm Management).

As some readers may remember, two fields very near Piper City were the first two in Illinois in which entomologists from the University of Illinois first observed significant western corn rootworm larval damage in corn planted after soybean. Although we had no idea what we were observing then (1987), we now know that we witnessed the early establishment of the variant western corn rootworm that lays eggs in soybean (as well as in other crops). Apparently the pest is still hard at work in this area of the state.

Now for some information from farther south. Based on a couple of reports received during the past week, the variant western corn rootworm is beginning to establish along the I-70 corridor. As I indicated in the aforementioned article in the Bulletin (issue no. 14, June 30, 2006), we received a couple of unconfirmed reports of severe rootworm larval damage in corn planted after soybean in southern counties. Well, we now have confirmation. Ryan Hasty, seed agronomist with Effingham-Clay Service Company, sent us photographs of severe damage in a field of corn planted after soybean just west of Effingham. The field had not been treated with a soil-applied insecticide at planting time. Ryan reported finding 20 to 30 rootworms per root system on some of the plants dug from the field. The damage is so severe that some of the corn plants have died.


Severe corn rootworm larval damage, corn planted after soybean, Effingham County, June 29, 2006 (photo courtesy of Ryan Hasty, Effingham-Clay Service Company).


Dead corn plants resulting from severe corn rootworm larval damage, corn planted after soybean, Effingham County, June 29, 2006 (photo courtesy of Ryan Hasty, Effingham-Clay Service Company).

I also received photos of severe rootworm damage from Kurt Maertens, technology development rep for Monsanto, taken in a field of corn planted after soybean near Donnellson on the Montgomery/Bond county line. The severe damage had first been noted by Rex Gray, M & M Service Company in Butler, two weeks before the photos were taken. The field, planted on April 24, had not been treated with a soil- or seed-applied insecticide. The most severe root damage (ranging from 2 to 2.5 on the 0-to-3 node injury scale) was observed on about 2 plants out of every 10 examined. The damage ranged from 1 to 1.5 on the 0-to-3 node injury scale on the other 8 plants.


Range of corn rootworm larval damage, corn planted after soybean, Montgomery/Bond counties, June 29, 2006 (photo courtesy of Kurt Maertens, Monsanto Company).


Severe corn rootworm larval damage, corn planted after soybean, Montgomery/Bond counties, June 29, 2006 (photo courtesy of Kurt Maertens, Monsanto Company).

The recent reports of severe corn rootworm larval damage are certainly in line with the large numbers of western corn rootworm adults being observed in cornfields at this time (refer to "Tassel High by the Fourth of July: Prepare for Silk Clipping by Western Corn Rootworms" by Mike Gray in this issue of the Bulletin). As the days and weeks roll by, we'll get a better idea of the statewide impact of western corn rootworms (variant and otherwise) in 2006. For now, it seems that the variant western corn rootworm is beginning to establish in some new areas, and it continues to remind us of its potential for crop damage in areas where it has been established for some time. As always, we will report preliminary information from our own assessments of rootworm larval damage as soon as they are available. In the meantime, please continue to keep us informed about rootworms in your area of the state.--Kevin Steffey

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