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Bt Traits’ Values
Sandy Steckel, research technician for Dr. Scott Stewart, IPM specialist at the University of Tennessee discusses newer Bt corn traits and some late season insect management in university field corn plots.
Photo by John LaRose, Jr.
Reduced Refuges May Be Big Benefit Of Newer Bt Traits
BETTY VALLE GEGG-NAEGER
MidAmerica Farmer Grower
MILAN, TENN.
Some of the newer Bt corn traits were discussed recently by Sandy Steckel, research technician for Dr. Scott Stewart, IPM specialist at the University of Tennessee. She also discussed some late season insect management in university field corn plots.
“We’ve been examining some of the newer Bt traits in several university trials and we’re comparing them with the older technologies,” Steckel said. “One thing they have similar is they all provide excellent control of the tunneling caterpillar pests. We really have great control of corn borers with both the older and newer Bt traits.”
The difference in them is that the newer traits have some activity or improved activity is evident against corn earworm. Some of the newer Bt traits are providing effective protection of kernels from some ear feeding pests.
“Probably the biggest impact that these newer Bt stacked traits will have for Tennessee corn producers is it allows us to reduce the mandated refuge requirements of the non-Bt corn,” she said. “Some of these multiple stacked traits allow us to go to a 20 percent non-Bt corn refuge in some corn and cotton counties, and some of these traits will allow us to go as low as a 5 percent refuge in corn counties. That includes the refuge in a bag or RIB options where the commercial seed companies actually blend the 5 percent non-Bt seed with the 95 percent Bt seed in the unit of corn for sale to Tennessee producers. Corn growers are really fortunate there, and that’s about the biggest benefit that we see from the newer technology.”
Studies also have been done on some late season pests. A test at Jackson on southwestern corn borer infestations over two years showed that southwestern corn borer infestations in non-Bt corn in the earlier vegetative stages had much more dramatic impact on yield compared with a later infestation timing at the R2 blister stage. So regardless of the number of larvae infested, infestation timing had the most impact on yield.
“We also presented some information that Dr. Fred Musser and colleagues of Mississippi State University put together that compared scouting methods and pheromone trap catches,” Steckel said. “They established a new southwestern corn borer threshold which will be adopted here. Treatment is warranted prior to tasseling when 5 percent or more of plants are found with SWCB egg masses or live larvae or 7-10 days after pheromone traps catch an average of 50 or more moths on a 7-day catch. Beginning at tasseling (VT) and through the milk stage (R3), treat when 10 percent or more plants are found with egg masses or live larvae or 7-10 days after pheromone traps catch an average of 100 or more moths on a 7-day catch. These studies indicate that the threshold can be relaxed a bit as infestation timing is delayed.
Corn earworm data was also presented. The data shows the newer Bt traits are definitely protecting corn from kernel damage; however, over multiple university trials, this has not always translated into an increased yield.
“That made us very curious as to why,” she related. “So Dr. Stewart established some studies where we simulated corn earworm damage and we reviewed some of the results from that trial. In certain environments, when we injured corn at the blister or milk stage, the remaining undamaged kernels were able to get bigger and larger and compensate for the loss of those injured kernels.”
The newer Bt technologies coming on the market to replace the older do provide more kernel protection from corn earworm.
“However this will not necessarily translate into increased yield for the farmers,” she added. “The biggest benefit in Tennessee, we believe, for the new Bt technologies is that we will be allowed to reduce our refuges of non-Bt corn. Also, it may improve grain quality and prevent micotoxins from entering the ear because earworm will not be able to establish a pathway for those pathogens to enter the ear, but this is not a silver bullet for us. There are also considerations from an insect resistance management standpoint.
“Many entomologists believe that the multiple stacked Bt traits could actually help us delay resistance development in the corn borers, but for corn earworm we really just do not know. Corn earworm is the same animal as cotton bollworm. Many Bt varieties incorporate the same proteins that are seen in corn. There are some questions about whether we should put these multiple stacked traits out over millions of acres of corn, thereby putting more selection pressure for the development of resistance in corn earworm. This could potentially have serious implications for our Tennessee cotton acres should resistance develop,” she summed. ∆
BETTY VALLE GEGG-NAEGER: Senior Staff Writer, MidAmerica Farmer Grower
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