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Bt technology, insecticides evaluated for rootworm control

Agriculture.com Staff 09/06/2006 @ 10:46am

How do current Bt technology and insecticide options stack up against rootworm larvae?

To answer this question, trials were conducted in 2006 at the Ohio Agricultural Research and Development Center's Western Agricultural Research Station near South Charleston, Ohio.

The evaluation trials were planted in an area that was planted to corn in late May and early June 2005. In late July 2006, plants were randomly dug from each of the treatments, the soil washed from the root systems and the roots evaluated for rootworm injury using the 0-3 Node Injury Scale.

When using the 0-3 scale, 0.00 means no damage to the root system, 1.00 equals one node (or the equivalent of one node) removed from the root system, 2.00 means two nodes or the equivalent removed from the root system and 3.00 represents three nodes or the equivalent removed from the root system.

One trial had 10 insecticides (including granules, liquids and seed treatments) and a YieldGard Rootworm hybrid (Dekalb DKC61-68) that were evaluated for their ability to control rootworm larvae. The insecticides were applied to Dekalb DKC61-72, an isoline of Dekalb DKC61-68. Rootworm injury was very heavy in this trial with the untreated averaging 1.81 on the 0 to 3 scale.

All of the treatments in the YGRW trial had significantly less rootworm injury as compared to the untreated check. Click here for full information about this trial. Counts of lodged plants and yields will be made from this trial later this fall.

Another trial was conducted to evaluate Herculex rootworm technology. In this trial, two Herculex hybrids containing the Bt-rootworm trait Mycogen 2G777 (HxRW) and Mycogen 2P788 (HxXTRA) were compared to a hybrid without this trait, Mycogen 2784, for their ability to control rootworm larvae. Insecticides were not evaluated in this trial. Rootworm injury was also very heavy in this trial with the untreated averaging 1.89 on the 0 to 3 scale.

The two Herculex hybrids had significantly less rootworm larval injury as compared to the untreated check. Click here for complete information on this trial. The number of lodged plants also will be counted later in this trial.

In a third evaluation, effects of seeding rate and early season defoliation on the performance of hybrids with and without Bt rootworm resistance were investigated. Three Bt rootworm resistant hybrids (two Yieldgard hybrids and one Herculex hybrid) and their conventional isolines (non-rootworm resistant hybrid counterparts) were planted at four seeding rates targeting populations of 24,000, 30,000, 36,000, and 42,000 plants per acre. Plants were defoliated at the 4- to 5-leaf collar stage (V4-V5).

The Herculex and YieldGard hybrids exhibited significantly less rootworm larval injury than the conventional isolines. On the 0 to 3 scale, rootworm injury for the three Bt rootworm hybrids ranged from 0.07 to 0.55, versus 1.01 to 1.81 in the conventional isolines.

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