Ric Bessin, Entomology
There may be considerable confusion regarding refuge requirements in 2010 for Bt corn. In the past in Kentucky all we need to understand was that the minimum refuge size needed to 20% of the total corn acreage. If there was a Bt toxin to control corn rootworm, then the refuge needed to be within the same field or immediately adjacent to the Bt field. Immediately adjacent to means that a fence, ditch, or road is all that separates the refuge from the Bt field. Bt corn that only had toxins to control corn borers and other Lepidoptera must have the refuge within ½ mile, but a ¼ is preferred.
This has become a bit more complicated with the approval of SmartStax corn. The minimum refuge size for SmartStax is different, it is only 5% of total corn acrage (in cotton producing areas it increases to 20%). Where the possible confusion lies is that the refuge size for all other Bt corn technologies stays the same, only the SmartStax will have the reduced refuge size of 5%. The table below outlines the refuge requirements for the various Bt technologies on the market, corn grown in Kentucky would use the corn belt minimum refuge sizes. The reason why there is a reduced refuge with SmartStax is that we use multiple independent toxins to control the key insect pests. This is a new strategy for resistance management that the other Bt technologies don’t have.
Order of details:
Product Name, Min. Refuge (Corn Belt), Min. Refuge (Cotton Areas), Proximity to Bt Field
YieldGard CB, 20%, 50%, Within 1/4 to 1/2 mile
YieldGard RW, 20%, 20%, Within or adjacent to
YieldGard Plus, 20%, 50%, Within or adjacent to
YieldGard VT, 20%, 20%, Within or adjacent to
YieldGard VT3, 20%, 50%, Within or adjacent to
YieldGard VT3 Pro, 20%, 20% Within or adjacent to
SmartStax, 5%, 20%, Within or adjacent to
Herculex I, 20%, 50%, Within 1/4 to 1/2 mile
Herculex RW, 20%, 20%, Within or adjacent to
Herculex Xtra, 20%, 50%, Within or adjacent to
Agrisure CB, 20%, 50%, Within 1/4 to 1/2 mile
Agrisure RW, 20%, 20%, Within or adjacent to
Agrisure CB/RW, 20%, 50%, Within or adjacent to
There are two other types of Bt corn that are still in the regulatory process with approvals pending. This includes AcreMax and Viptera. These again may have different refuge requirements, particularly the AcreMax.
While the reason for planting a refuge is to maintain a population of Bt- susceptible corn borers, growers should still manage those refuges to avoid serious losses. When using a 20 or 5 % (Smartstax only) refuge with Bt corn plantings, growers may consider spraying for corn borers if scouting indicates it is an economic problem.