Drought conditions are beginning to settle into the central Cornbelt as rainfall in most of this region has been less than half normal levels in the last 30 days.

The Illinois Natural History Survey has recently reported that Yieldgard rootworm corn is more than 20 inches tall in field trials near Urbana, Illinois, versus conventional corn that is only ~12 inches tall, as root observations of the latter have shown significant rootworm damage and thus drought stress.

Rootworm infestation levels are high this year

University entomologists expect significant rootworm pressure this year, as all the conditions that favor high rootworm populations are in place. First, egg densities were high this spring from abundant egg-laying adult populations in 2005. The winter was mild and had limited adverse frost impacts on egg survival. Lastly the spring was not excessively wet, which can cause drowning of the larvae.

Yield benefits will drive trait penetration

If these drought conditions persist in the central Cornbelt, it will accelerate the penetration of rootworm-protected corn in 2007. We look for 10 million acres of Monsanto’s Yieldgard rootworm corn this year, up from 4 million acres in 2005, and more than 1 million acres of DuPont and Dow’s Herculex rootworm corn, following a limited launch in 2005, due to the significant yield benefits of rootworm-protected corn in 2005. In the most drought-affected areas of Illinois, growers that planted Monsanto’s Yieldgard rootworm corn last year had as much as a 35/bu/acre yield benefit (more than $75/acre) versus conventional corn.

Rotation no longer protects against rootworms in Illinois

Soybean roots are toxic to rootworm larvae and thus crop rotation between corn and soybeans was historically an effective way to control rootworms, but this pest management practice is no longer effective in Illinois. A variant of the northern corn rootworm, prevalent in northern Illinois and further north, has developed a prolonged diapause phase in which the eggs remain dormant for two winters, and thus hatch when rotated fields return to corn. The western corn rootworm, found in central Illinois and Iowa, has recently developed a behavior in which the adult beetles, which can fly, will lay eggs in soybean fields that are rotated into corn the following spring.

Yield benefits could increase with market penetration

Adult rootworm beetles feed on pollen, foliage, and corn silks, but are unaffected by the insecticidal proteins that kill the larvae. If adult beetle populations are high, it can lead to low pollination success even in rootworm protected corn, if the ear silks are consumed. We believe this encourages growers to plant rootworm-protected corn in all their fields, rather than just parcels, to reduce adult populations.