Intense use of Bt hybrids is also anticipated for the 2012 growing season. "I have questioned the wisdom of applying such intense selection pressure on insect populations when many of the pest species are well below economic levels in most producers' fields," said Gray. Nonetheless, this pattern is not expected to change.
When Bt hybrids entered the market place in 1996 and for many years thereafter, the use of a 20 percent refuge was the standard protocol for the Corn Belt, based upon the use of Bt hybrids aimed primarily at the European corn borer, which express a high dosage level of Cry proteins. In 2003, Bt hybrids were commercialized for corn rootworms, and similar refuge requirements were implemented across the Midwest, even though the Bt hybrids targeted at corn rootworms were not high dose and the mating characteristics, along with dispersal patterns of adult corn rootworms, are different than those of corn borers.
Why were the refuge requirements similar for such distinctly different insects?
"Because of familiarity, convenience, and thus, the greater likelihood of implementation of the 20 percent structured refuge by producers rather than tailoring refuge requirements to the unique biological characteristics of corn rootworms," said Gray.
Today producers have more flexibility with respect to the type of refuge they implement. Although more than half of the producers at the 2012 Classics indicate they intend to use the 20 percent structured refuge this growing season, the seed blend (refuge-in-a-bag) strategy is gaining popularity as more pyramided Bt hybrids enter the marketplace.
At the 2012 Classics, producers were asked if they planted a refuge in 2011. On average, 83 percent of producers said they had established a refuge. The proper establishment of refuges will become increasingly important as more acres are planted to Bt hybrids, selection pressure increases, and the threat of the development of western corn rootworm resistance looms.
Approximately 37 percent of the producers who took part in the 2012 Classics will use a seed blend as their refuge and hedge against insect resistance development.
"From a convenience angle, it's easy to see why this approach will increase in popularity," said Gray. Of concern is the anticipated reduction in the volume of non-Bt seed produced by the seed industry as refuge requirements drop from 20 percent levels, which could make it more difficult for producers to purchase elite germplasm from non-Bt product lines. Access to non-Bt hybrids by producers is important if the industry wants to maintain an integrated approach to pest management across the Corn Belt.
Black cutworm moths abundant and on the move
Editor's note: High-resolution digital files are available to use with this story at http://www.aces.uiuc.edu/news/News_Photos/weeds
Professor of entomology and crop sciences Extension coordinator Mike Gray urges producers to look for early signs of leaf-feeding injury from black cutworm larvae. The migratory moths, which lay eggs on winter annual weeds in producers' fields, have been captured in pheromone traps throughout much of Illinois. Following hatch from the eggs, the larvae begin to feed on weeds, but they eventually have the potential to cut seedling corn plants.
Record-breaking warm temperatures in March persisted into early April, and as a consequence many fields across southern and central Illinois have been planted and are beginning to emerge. Corn in the one- to four-leaf stage of development is most susceptible to cutting by black cutworm larvae.
"Even if you planted a Bt hybrid, don't be lulled into complacency," said Gray. Under heavy infestations, control afforded by some Bt hybrids may be inadequate. University of Illinois Extension personnel Dale Baird (Lee County) and John Fulton (Logan, Menard, and Sangamon) reported captures of nine or more moths over a one- to two-day period on March 24 and March 30. Retired crop systems Extension educator Jim Morrison reported that 16 moths were caught on April 2, the earliest and most significant capture in many years.
Fields most at risk from black cutworm injury include those heavily infested with winter annual weeds. Favorite targets for egg-laying black cutworm moths include mouse-eared chickweed, bitter cress, shepherd's purse, yellow rocket, and pepper grass. More information about the biology, life history, and scouting procedures for the black cutworm is available at: http://extension.cropsci.illinois.edu/content/black-cutworm.
Gray encourages readers to visit the following North Central IPM PIPE website (http://apps.csi.iastate.edu/pipe/?c=entry) to view captures of black cutworm moths. According to Kelly Estes, State Survey Coordinator, Illinois Natural History Survey, trapping for other insect pests -- the European corn borer, corn earworm, western bean cutworm, and fall armyworm -- will also be reported on this site throughout the summer.