YIELD IS STILL KING

High yields and KnockOut (Bt) built-in European corn borer (ECB) control are two of the main reasons your farmer customers will want to plant Ciba Seeds Maximizer corn hybrids this coming spring.

Part of your job is going to be helping them keep those high yields coming year after year. Actually, it probably won't be as hard as it may sound.

Farmers will plant Maximizer hybrids for much more than an innovative insecticide delivery system. If yields aren't high, insect control doesn't mean much. One of the reasons Maximizer hybrids tend to deliver high yields (in addition to their overall quality) is that they provide effective corn borer control.

The hybrids will need to continue offering effective ECB control in order to maintain their yield advantage. That's where resistance management comes in.

RESISTANCE MANAGEMENT IN CORN

There are two primary weapons in the Bt corn resistance MANAGEMENT arsenal: The high-dose strategy and the refugia concept. Together, they work to mitigate the natural tendency you'd expect in any population exposed to a specific stress: to adapt to it by selecting for tolerance or resistance.

The high-dose strategy is designed to keep from exposing target pests to repeated sub-lethal doses of Bt endotoxin (laboratory studies suggest this may hasten the onset of tolerance in other pest population). The LC99 dose, the concentration of an insecticide required to kill 99 percent of the target pest population exposed to it, is established during product testing. Maximizer hybrids with KnockOut Bt protection express 33 times the LC99 level of Bt endotoxin during the peak of the growing season. This "overkill" capacity minimizes the chance that ECB individuals will survive exposure.

"Refugia" refers to the concept of growing some non-BT plants to provide food and habitat (a refuge, as it were) for the target pests. THe population in the refuge would not select for resistance because there's no pressure to do so. This helps mitigate the onset of resistance by maintaining a high percentage of susceptible biotypes in the breeding population.

The two concepts work together this way: The high-dose strategy ensures that few or no resistant biotypes survive to mate and produce offspring, while the refugia strategy ensures that any resistant individuals are vastly outnumbered by susceptible individuals.

MANAGEMENT BY MARKET FORCE

Ciba Seeds is committed to the principle of resistance MANAGEMENT. Still, they're not making specific recommendations as to the ratio of Bt to non-Bt corn, or the minimum percentage required to provide adequate refuge. This is primarily due to the wide range of estimates (anywhere from 5% to 50% of corn acreage) made by various authorities in the field. These percentages are derived from computer models. Filed research is needed to test these concepts. Your customers are probably already providing adequate refuge simply in the way that they grow corn.

A Cibo-conducted market study showed that corn producers typically plant five varieties from two or three seed companies on a given farm. This gives them a wide range of genetic diversity in the crop, which helps manage production risk. The practical effect in the case of Maximizer is that not all those varieties will be Bt corn. FOr that reason, at least for the first few seasons of Maximizer availability, specific refuge recommendations shouldn't be necessary.

For all its innovation, Bt corn is only attractive to the farmer to the degree that it outperforms (outyields and/or outprofits) other available variety options. The potential for ECB damage is highest during the mid-whorl (10-leaf) stage and the pretassel stage.

IT ALL COMES BACK TO YIELD

Infestation during these periods can cause 5% to 7% or even more yield losses, which is quite significant in what may be an emerging era of $5 corn.

Maximizer varieties produce KnockOut build-in corn borer protection as long as the plant is green. The crop is protected during these critical periodss. Insects ingest only a tiny amount of plant material before taking a lethal dose of Bt endotoxin and ceasing to feed. This helps give Bt corn varieties like Maximizer, their yield-boosting advantage. Proper stewardship with you and your customers will ensure that these varieties will maintain that advantage for a long time to come.