There was an explanation of this this summer in IFVN talking about earworm. Below is a cut and paste of the section explaining it.

Tom

What about Bt sweet corn varieties?
•From a grower's perspective, there are three different categories of Bt sweet corn varieties on the market or soon to come to market. (1) The Attribute series sweet corns produce one kind of Bt toxin. It is very effective against European corn borer and corn earworms. The "problem" is that only 3 of 4 kernels on ears in Attribute series Bt sweet corn fields produce the toxin (a result of the heterozygous nature of the genetics of the variety and random recombination in the offspring ��" the kernel). Additionally, the Bt toxin in the Attribute series is not very effective against black cutworm or western bean cutworm (or rootworms or sap beetles). (2) The Seminis "Performance" series of Bt sweet corn varieties produces two toxins that kill Lepidopteran larvae; they also have genes for corn rootworm larval resistance and resistance to Roundup. The second Bt toxin in these varieties provides much greater resistance to black cutworm, fall armyworm, and western bean cutworm (as well as European corn borer and corn earworm). However, only 3 of 4 kernels on ears in Performance series Bt sweet corn fields produce the toxin (again, a result of the heterozygous nature of the genetics of the variety and the fact that the genes for the two toxins are linked and so they move together in the random recombination of genes in the offspring ��" the kernel). (3) A new "Attribute II" series of sweet corn varieties is under development by Syngenta. Varieties that will be available for sale in 2014 are not the ones that most fresh-market growers in Illinois will plant. In the Attribute II series, genes code the production of two very different toxins that kill Lepidopteran larvae (cutworms, armyworms, European corn borer, and corn earworm). These genes are not linked, and as a result, 15 of 16 kernels on ears in Attribute II series Bt sweet corn fields produce one or both toxins.
•Do Bt sweet corn varieties still need to be treated with insecticides? Yes. Although the Attribute II series will suffer less damage when untreated than existing Bt varieties, this technology will not be available in 2014 in varieties that most Illinois producers grow. The original Attribute series and the Performance series varieties must be treated when corn earworm moth flights are heavy or if western bean cutworm is present. The jury is still out on the characteristics of a reduced spray program that would adequately protect these varieties. In varieties with long silk channels, early sprays might be skipped (because larvae would ingest Bt toxins as they feed on silks while moving toward kernels). Bt concentrations decline somewhat in silks after pollination, and as ears elongate and kernels have less cover, sprays may be more necessary. The point for now is simple ... do be prepared to use insecticides on Bt sweet corn if it must be worm-free for your markets.

Here is a link that might be useful: IFVN V20N6 (July 7, 2014)

Thank you.

Mine is Attribute, and not Performance or Attribute II.

I feel like I got hoodwinked by Monsanto into spending $200 to save $12 in spray. I know I'm complaining, but I wanted to share the experience here so other growers can learn from my mistake - don't buy Attribute corn and expect it to not have worms.

I wish I could put a gif of Nelson from Simpsons saying 'Ha ha!!!'

lol. Now I have to buy the Attribute II to see if it works. It reminds me of the I-phone and how they keep coming out with new ones.

what is the expected yield of a $200 sack of seed?

You could do about an acre, maybe slightly less. It would take 50lb of Nitrogen, costing about $100. Yield could be a thousand dozen ears at $4 per ear. But after bug damage, eating a lot, and giving a bit away, I'd be more than happy netting $2,000 an acre. Of course all of this is in a year with agreeable weather.

$4 an ear!?

Attribute is a Syngenta product, why are you mad at Monsanto?

That's $4 a dozen. And my mistake, I was thinking Seminis instead of Syngenta.