Suhas
Vyavhare, Extension Cotton Entomologist, Texas A&M AgriLife Extension
Service
Variety selection is the most important decision
made during the year. Selecting Bt vs non-Bt or the kind of insect trait
package is an important consideration in selecting cotton varieties.
Bt
cotton is genetically altered to produce certain proteins which are toxic to
specific groups of insects. For example, currently available Bt traits in
cotton specifically target worm pests such as cotton bollworm, tobacco budworm,
and beet armyworm. On the other hand, conventional, or non-Bt cotton does not
produce such insecticidal proteins and as a result it is more vulnerable to
worm damage.
Since the introduction of Bt cotton into US
agriculture in 1996, the technology has transformed from a single-gene trait to
multi-gene trait packages. The 1st generation Bt cotton had only a
single Bt gene. The second generation Bt technologies, such as Bollgard 2,
TwinLink, and WideStrike produce two Bt toxins. While the most recent 3rd
generation Bt is a three-gene trait—Phytogen brand varieties with WideStrike 3 have
already been in the market for the last couple of seasons. Recently, Monsanto
(Deltapine brand) and Bayer CropScience (FiberMax and Stoneville brands) announced
the availability of some of their varieties with Bollgard 3 and TwinLink Plus technologies,
respectively.
Bt Technologies
|
Proteins expressed
|
Second generation
|
|
Bollgard 2
|
Cry1Ac + Cry2Ab
|
WideStrike
|
Cry1Ac + Cry1F
|
TwinLink
|
Cry1Ab + Cry2Ae
|
Third generation
|
|
WideStrike 3
|
Cry1F + Cry1Ac + Vip3A
|
Bollgard 3
|
Cry1Ac + Cry2Ab + Vip3A
|
TwinLink Plus
|
Cry1Ab + Cry2Ae +
Vip3Aa19
|
Over the years, Bt technologies have been fairly
effective controlling worms in cotton. The second generation Bt was more
effective than the first one, and the third generation technology is more
effective than the second generation due to the addition of toxin(s). Newer
traits usually come with additional costs, so if you don’t need these traits,
varieties with older trait packages are still competitive in yield and quality.
Some farmers may choose to go with non-Bt cotton to
avoid paying tech fees. With non-Bt cotton, field scouting becomes even more
important to stay on top of the game. In 2016, worm pressure on the Texas High
Plains was so low that many of our non-Bt cotton fields got away without
spraying for worms. This doesn’t mean we will have a similar situation in 2017---we
may face higher worm pressure—therefore, there is higher risk associated with
the non-Bt crop compared to Bt. However, with a good scouting program in place and
timely insecticide applications, non-Bt cotton can perform well.
Finally, insect trait is an important consideration in
selecting varieties but it should not take priority over agronomic
characteristics such as yield, maturity, and fiber quality. I have seen some of
the non-Bt cotton varieties performing as well as Bt cotton and sometimes even
better (especially on the Texas High Plains where worm pressure is usually
light). Therefore, it’s not the transgenic insect trait but the inherent yield
potential of a variety which should come first in the decision making.
