Over the past two weeks Louisiana has experienced a slow but steady corn earworm moth flight in cotton, which has lead to a slow but steady egg lay. Fortunately, this type of worm activity has not put the selection pressure on our Bt technology we experienced last year. This has also drastically reduced our insecticide oversprays as well. As of this week, Louisiana has more cotton that has not been sprayed for bollworms than cotton that has been sprayed.
Based on small plot research and Bt sentinel plot work from the Louisiana cotton growing areas, all of the technologies are performing better this year than last year. Results from our Bt technology tests indicate Bollgard 2 varieties are experiencing an average of 2.5% fruit injury, Bollgard 3 varieties are experiencing an average 3.0% fruit injury, both Widestrike and Widestrike 3 varieties are experiencing 4.0% fruit injury. TwinLink and TwinLink Plus are experiencing 5.0% and 3.0% fruit injury respectively. These numbers are also reflected in reports I am receiving from the field with only a few instances of rescue sprays needed for bollworm escapes in Bt cotton. Remember, the fruit injury threshold for Louisiana cotton is 6% with the presence of live worms.
Overall, this is good news for Louisiana cotton producers and signals that our Bt technology may still have some life left in it. Beware, this situation can change quickly and bollworm escapes can and will happen in all technologies. Scouting is key and under light pressure our Bt technology is appearing to hold but if pressure intensifies a rescue spray may be warranted. Keep in mind that bollworms are cryptic feeders, and worms that have established in squares and bolls may not be controlled by insecticides including the diamides. If you have any questions or comments, please feel free to contact your county agent or me.