It’s been easy for me to take for granted not having to count bollworms in cotton with Bt technology. UGA Entomologist Dr. Phillip Roberts discusses Bt traits at meetings, but don’t have to get in depth because of how effective the technology is for us. After our cotton field day yesterday, UGA Agronomist Dr. Jared Whitaker and I looked at plots for a while. It was a great learning experience for me as he was showing me to how to actually scout for bollworms and make seeing some damage.
Tobacco budworm and corn earworm make up the Heliothine complex. Though they are different insects, they appear similar in the egg and larval stage. Three generations of tobacco budworm infest cotton each year and two generations of corn earworm occur each year. ID is important since TBW are resistant to pyrethroid class of insecticides. But susceptibility of CEW to pyrethroids has declined in recent years.
We have Bollguard II, Widestrike, Twinlink, and Widestrike III technologies of Bt. The difference between technologies is how much they are expressed throughout the plant. Bt is not immune from economic damage from caterpillars and don’t have actually on regular bugs (Stink bugs & plant bugs). TBW are actually more susceptible to Bt than CEW (and other worms).
Dr. Whitaker showed me how to look for caterpillars. Since the flower has the least expression of Bt, if the moth lays an egg in the flower, it can hatch and feed. Once it feeds outside this, Bt should kill the caterpillar. We were seeing some larger bollworms and bollworms moving from one boll to another.
Since it takes the eggs three days to hatch, it’s best to look in pink flowers. Pull the petals back and look for a very tiny black-headed worm, OR you may see a black dot where the worm “hit” the edge of the boll. You can also look for a flared square. Here are some pictures of all of this we saw yesterday.