Ohio State University researchers previously discussed the concern with resistance developing in the western corn rootworm to one of the Bt proteins and what this means, if anything, for Ohio growers. A few additional comments should be made when considering Bt transgenic hybrids because a few new choices have come on the market.
There are two new hybrids from Syngenta, Agrisure 3220 and Agrisure 3122. Agrisure 3220 was released earlier this year and is in our table of current Bt corn products (as of April 2011) on our Web site. Agrisure 3220 is a stacked hybrid with Cry1Ab, Cry1F, and Vip3A Bt proteins providing resistance to many of the various lepidopteran (above-ground) pests, including the western bean cutworm. This product does not offer control of rootworms. Only a five percent structured refuge is required (this product is NOT refuge-in-a-bag). The second, newer product is Agrisure 3122, which contains the Cry1Ab, mCry3A, Cry1F, and Cry34/35Ab1 Bt proteins offering control of both the above-ground lepidopteran pests along with corn rootworms. This product will be marketed as Agrisure 3122 Refuge Renew trait stack requiring only a five percent structured refuge. We would mention that Syngenta has submitted a five percent blended refuge-in-a-bag version of Agrisure 3122 for EPA approval.
The second group of options comes from Pioneer, who previously had released Optimum AcreMax 1 and Optimum AcreMax RW, the latter being a refuge-in-a-bag product for rootworm. They have recently released two new products, Optimum AcreMax, containing Cry1F and Cry1Ab for lepidopteran or above-ground insect control, and Optimum AcreMax Xtra which includes those same two proteins as well as Cry34/35Ab1 for control of corn rootworms. Both Optimum AcreMax and AcreMax Xtra are integrated refuge products, meaning refuge-in-a-bag; no separate refuge is required. A major difference that growers should be aware of is that while Optimum AcreMax has a 5 percent integrated refuge, Optimum AcreMax Xtra has a 10 percent integrated refuge because of the addition of the genes for rootworm control. However, because the refuges are in the bag, no differences in planting will be evident; you open the bag and plant!