They're a pain. Some suggested adding mineral oil to the silks, last year, when I was growing mine. It requires one to be early and persistent. Others have recommended getting an early start with an early producing to avoid the barrage of bugs that thrive in mid summer and beyond.

I have also used liquid spinosad, but I was unable to determine if it was effective on the corn borer. I'm inclined to think it helped.

Applying any type of food grade oil will work , but it is tricky to get the timing right. If you apply it too early the silk will not get pollinated correctly. And if you apply it too late the worm is already in the ear.

Appling oil is for smothering the larva before it gets in the ear. Once it is in the ear, the oil does not smother it as some folks think.

I grew corn, but already have harvested both the early and mid-season varieties, and never got around to planting the late variety because by the time I should have been planting it, my garden was underwater.

This year I have had both the corn *earworms, which enter through the silks and eat at the top of the ear, working their way down, and the European corn borers, which tunnel right through the side of the ear and can be found anywhere within the ear. They were a minor issue on the early corn (which I deliberately plant as early as possible in order to harvest it before they show up) but a bigger issue on the mid-season corn.

What works best for me is to spray the entire plant with a caterpillar killer type pesticide containing Bt 'kurstaki' as the active ingredient. It was raining practically every day so I didn't do that this year. When you have the European corn borers, if the ears have been sprayed with Bt, they generally bore their way through the husk anyway, but die shortly thereafter. Bt takes a couple of days to kill them, but they usually stop feeding shortly after ingesting it. When I harvest the ears and process them for fresh eating or for freezing, I just cut out the damaged parts of the ears and salvage the rest.

I agree with Robert on the timing of a food-grade mineral oil. It can be very tricky to wait late enough that you are not interfering with pollination and yet do it early enough to kill them. Some people mix some Bt with the mineral oil in the hope it will be more effective than oil alone. I have no idea if it is. The mineral oil applied to the corn silks works only on the corn earworms that enter through the silks, and has no effect whatsoever on the European corn borers. It isn't 100% effective either, but just seems to be hit or miss. Maybe it smothers the first ones that come through and not enough remains for the next round of young earworms. In order for it to be consistently effective, you have to reapply often---maybe once every three days.

My non-organic gardening friends often spray their ears with liquid Sevin or something similar, but I don't want to eat something that has been sprayed with it, so I just use the Bt when needed (some years it isn't needed at all). This probably has been the worst corn earworm/European corn borer year since 2011, which was also a pretty bad pest year overall.

You might be successful spraying liquid spinosad, but it is a broad-spectrum organic pesticide that has the capacity to kill all your beneficial insects, so I never use it. I just think that it does too much widespread damage to beneficial insects I rely on to keep my pest population limited.

Finally, there are some kinds of parasitic wasps that attack caterpillars of all kinds. I have seen a lot of them in my garden this year, and have found cabbage loopers with their larvae all over bodies. I appreciate the parasitic wasps, and spinosad or any other broad-spectrum pesticide, whether organic or synthetic in nature, would kill the wasps, so I just accept a certain level of corn earworm/European corn borer damage is likely to occur. You can buy and release the parasitic wasps, but they are most effective if released early in the season before the caterpillars show up in large numbers. Once you're seeing corn earworms or European corn borers on your plants, it is pretty much too late to order and release the parasitic wasps. Looking back, I should have expected this to be a horrific caterpillar year (and it is) because the parasitic wasps were showing up really, really early, almost before there were any caterpillars around. I wonder how the wasps knew it would be (in their eyes) a great caterpillar year before a gardener like me was even seeing the caterpillars out there in the garden?

*Corn earworms also are tomato fruitworms, so if you are seeing a lot of corn earworms, you might need to be spraying your tomato plants with a Bt-type caterpillar killer to protect your tomato harvest.