Probably a nutrient imbalance. Corn does not favor being in pots.

Well I'd certainly be actively treating for the thrips and fungus gnats. Fungus gnats especially can do a great deal of root damage but I can't say they are the cause of this. It looks much more like the common description of thrip damage common sign of a heavy thrips infestation is distorted leaves that turn brownish around the edges and cup upward.

Corn is very seldom grown in a GH or in containers over here so assuming you have done this successfully before, my first question would be what are you doing different this year that could have caused such a severe thrip infestation? Different/more fertilization? Different watering/humidity regimen? Or is there something else/new growing in the GH that could be the source?

Corn in the field/garden will usually outgrow thrip damage but can't say if that is true for in the GH given the different environment.

Dave

I am having a similar problem. I am in north Georgia, USA. I have seeds for a new variety bred for containers called 'On Deck'. They've had a poor germination rate for me, and so far all the sprouts on the first round developed yellowish brown leaf tips and then turned yellow near the base, seemed to grow thinner and fell over dead. Growing in a large container on south facing patio, in a compost based potting mix, using Garden-tone fertilizer. A couple sprouts have come up in my 2nd attempt. Any other ideas for improving this situation? All advice greatly appreciated :)

Corn is a super-heavy feeder. If it is going to spend much time at all in a pot it will have to be sizable.

Thank you for your replies. I don't really know how to navigate here, not too clever about "optional URLs"? "name of Link"? but hope the relevant folks will be able to read this.
I think pnbrown is correct about thrips being the problem in my case. I've started hardening off the plants now, a little early as it's still pretty chilly here (coldest spring in 34 years say the papers), hoping that breezy weather might disperse the thrips. Fingers crossed the plants will recover from the damage but I'm sowing another lot today for insurance, ready with Neem oil at the first sign of the bug. FYI, because our season is short and cool, I chit the seeds in a dark, warm closet in April, then grow them on hot trays in the greenhouse till they're around 8 " tall, then plant out usually mid-May -otherwise no corn in the summer. Unthinkable! However, last year something shredded all the ripe ears in one night. Problems, problems.

Sorry, I meant paygep had the likely answer. Pot size or feed isn't an issue at this stage of development, I would think.

I have never had much luck with sweet corn between it's very finicky growing habits (as compared to dent and flint cultivars) and animal pests eating the ears as they begin to ripen. Sweet-corn regions tend to have very good ground, ideal climate and extirpation of pests. No doubt though we will all continue to try.