rober49

The small caterpillars enter the corn stalks right where the silks enter the ears-shucks after the corn has been pollinated. That means when the silks have begun to turn brown. Then they chomp away on the kernels and get bigger and fatter along with any remaining kernels!

If you use mineral oil (any cooking oil works as well to smother them) before then, the pollen is blocked by the oil on the silks and the ears won't be pollinated and therefore won't develop kernels. The small caterpillars invade the corn only when the kernels first begin to fill out. So the race is between you and the caterpillars to know when that is and you need to be wily! Just remember, that time is when the silk-tips begin to turn brown, not when the ears are ready to pick! :-)

You'd need to apply bt at the same time in the same place (right where the silks enter the ears) since it needs to get down inside the top of the ear to kill the caterpillars.

Bt kills them when they ingest it, oils smother them, and either one is recommended for control.

If you want to use oil to smother them, I've seen some people recommend buying a can of spray cooking oil, corn, vegetable, canola, etc., and just walk down the row when the ears are ready and squirt a small amount of the oil onto the silks where they enter the corn. If you want to use bt, you can dilute the recommended amount in water and put it in a spray bottle and do the same thing.

I've used a lot of BT and really couldn't tell if there was any control. Last year I sprayed BT from well before silking until harvest. It was sprayed on at a high rate about every other day. There were still ear worms everywhere. Sevin didn't work any better.

fruitnut

Did you spray the bt where the silks enter the ears? You must also spray it at the optimal time -- those two elements must be in place!

The following link describes the difficulty of controlling the corn earworm, at least in large agricultural plantings. The corn earworm is in the ear for 14-16 days, and once inside the ear and feeding, it's nearly impossible to control. The link suggests "pyrethroids" for commercial plantings as the most effective insecticide, "driven deep into the silks" by the spray.

Just a note about this sentence in the link: A preventive program against corn earworms may begin when 10% of the ears are silked.

When a water-based insecticide (bt or pyrethroids) is used instead of oil, a spraying program begun earlier will not interfere with the pollination process.

anney:

Every two days from before silk until nearly mature. And I sprayed it everywhere including into the silks. The ear worms can attack elsewhere than the silk. In fact the ones attacking lower on the ear are most damaging. I can live with the tip damage. But when the side of the ear is attacked things get real messy. This was on more than one planting, about five plantings last year for the BT. I also tried it other years with the same results. I even sprayed right at dusk so photodegredation would not be such an issue.

The worms weren't bad on the first planting. After that terrible.

These same worms also attack the leaf worrel (the small developing leaves) from emergence until silking. They do a lot of damage that way.

Later in the year last year I used a Triazide insecticide. It was by far the most effective. It may have been a pyrethroid, not 100% sure.

thanks y'all! i rarely use pesticides. i wonder if D.E. would help since i cannot find rotonone any more. i'm probably jinxing myself by saying this publicly but so far no squash borers, minimal squash bug infestation, & some bunny damage to the green beans. i only have a few ears starting on the corn . i'm getting my strategy started in advance. do thee corn worms over-winter in some form? i burned all the old stalks & put infested ears in the trash, not the compost.

FN

That link says that the middle of the stalks is the most important place to spray the plants overall, probably because that's where the majority of the ears develop.

I suspect that with small plantings, unless they've been a pest for years and now pupate to overwinter in the soil, they aren't as much a problem. I've grown corn and have been able to destroy most of them with corn oil spray. But I don't grow corn every year for several reasons. My neighbor usually grows a lot of it and gives us literally bushels of it. And the corn ear worms are also tomato fruitworms, so they'll infest tomatoes as well. And if I must buy it, summer corn is cheap in the farmers markets around here.

rober49

No, I don't think DE will do a thing to destroy corn earworms. It's usually intended for spreading on the ground to kill slugs -- their bodies are cut and macerated by it.

And yes, corn earworms will overwinter in the soil as pupae if you don't control them. I think burning the debris would do the trick!

rober:

The corn ear worms over winter in the south. Not exactly sure but maybe zone 7? They don't take long to show up here in SW Texas. But in the summer they migrate north. Where I grew up in northern Illinois they are almost unheard of. My family up there has grown sweetcorn every year since the 50s that I'm aware of and no ear worms.

Just checked my insecticide which is not the same as last year. What I'm trying now is Spectracide Once and Done. The active ingredient is gamma-cyhalothrin, a pyrethroid. Don't know how it is working this year. We have had so much rain lately from that hurricane that I can't be sure of anything.

in the 70's i had gardens & never had a problem with the worms. squash borers, occasional horn worms, & a few other passer-thrus but never the infestations like the last few years. last year i did not have a single uninfected ear of corn. i'm still trying not to use poisons