Ah, I took a couple pictures a few days ago and forgot about them—here they are as well. I'll get a couple more of the curling behavior tonight.

Hi Daniel, thanks for the question.

Okra has not been very popular in the past, and there seems to be limited science-based information available.  Okra leaves seem to abscise (drop) from the bottom for no particular reason; however, it may have more to do with disease, pests, and abiotic problems.  Sometimes all the leaves drop. When plants drop their leaves, it usually means they are responding to stress issues.  If the plants aren't showing disease symptoms, look for pests (Japanese beetles, leaf footed bugs, stink bugs, leaf hoppers, spider mites, aphids, et al.) Abiotic symptoms, like water (too much, or too little), nutrients, cool damp weather, poor light, etc.).  Leaf drop is quite common and usually does not greatly impact harvest.  

The curling pods is most likely a pest problem, leaf footed bugs and stink bugs are the usual culprits.  These pods can be eaten. Neem and insecticidal soap can help.

Growing and Harvesting Okra: University of Illinois Extension

Okra - UC Master Gardener Program of Sonoma County (ucanr.edu)

Pests of Okra | NC State Extension Publications (ncsu.edu)

Okra | Diseases and Pests, Description, Uses, Propagation (psu.edu)

I hope this is helpful.

After a couple weeks, the two plants that were distressed previously have lost all their leaves. New leaves try to appear but dry up and fall off before they get to be more than an inch or two across. Now a third plant is showing the beginnings of similar symptoms, and I'd really like to save it if I can. Regarding the possible causes you mention:

There clearly are some kinds of insects eating holes in the leaves, but I wasn't concerned as it's not particularly severe, and indeed the NC State source you linked suggests it's not a problem unless the plant is severely defoliated. I will look more closely and see if I can identify the type the next chance I get.

Abiotic problems seem unlikely in general simply because the plants are right next to each other, so the conditions they're exposed to should be more or less the same, yet two are dead, one is distressed and the fourth is totally fine.

Water-wise, I'm 99% sure we've supplied enough water, and I'm aware of the possibility of overwatering and don't think that's the issue. I pulled one of the nearly-dead plants and took pictures of the roots, and honestly to my untrained eye they look pretty good? No sign of the rot that I would expect from severe overwatering anyway. What do you think?

Nutrients, we've never gotten our act together to fertilize mid-season, so they may be short of the ideal there, but again this would be the same for all four plants, and I would expect it to simply slow their growth (perhaps especially slow the growth of fruit?) rather than causing serious issues like this—right?

The weather hasn't been particularly cool or damp by our standards, though compared to a more southern climate, maybe a little? We had a couple weeks of regular rain with temperatures in the 60s and 70s at one point—is that enough to be a concern? But the thing is, the two plants that are dead now were already showing clear signs of trouble before this time period, and I wouldn't call it a particularly cool and wet summer overall.

Light is definitely not the issue, these plants are completely out in the open, with basically no shade except a treeline >100ft away—about as good as you're going to get short of an actual farm field.

I did some reading myself on okra diseases and pests, and still nothing jumps out at me as clearly the problem, but I have a few possibilities I'd like to hear your thoughts on:

Apparently the same pathogen that causes tomato blight can also infect okra. There are definitely sources of it nearby—lots of fellow gardeners growing tomatoes and having issues with blight. Looking at pictures though, it seems like this would likely cause serious rot and visible fungal mats near the base of the plant, which I don't see any sign of. There are these little white nodules just below the soil line—are they a concern?

Fusarium and Verticillium wilts seem plausible from the descriptions I've read, but again in pictures, it seems they tend to cause more visible, moist rot, more wilting of stems and leaf petioles, more browning of leaf edges (though some of that has occurred). Are the symptoms I'm seeing within the possible range, that I should be concerned about these diseases?

One source says a heavy aphid infestation may cause yellowed and/or distorted leaves, necrotic spots on leaves and/or stunted shoots. At a glance I don't see any aphids, so I doubt I have a "heavy" infestation, though again, I'll check as soon as I can. Would that at all match the symptoms I'm seeing?

Are there any nutritional deficiencies specifically that could cause this sort of reaction, like with calcium deficiency and blossom-end rot in tomatoes? I'm really grasping at straws here, it's hard to see something like that (a) having this dramatic of an effect, and (b) being so inconsistent between plants just a couple feet apart, but I thought I'd ask...

A few more photos. All of these were taken just now—the dead plant (the stem and root photos) is the same one that was distressed in earlier photos, the distressed plant now (the leaf photos) is one that previously was fine.

And one more.

Hi David,

Blight is a set of symptoms caused by various diseases.  Southern blight does affect tomatoes and okra.  Fungal mats may not always be present and may depend on the stage of the infection. Looking at the last picture of the root, the white dots near the soil line look like the fungus Sclerotium rolfsii the causal agent of Southern Blight. Fusarium and Verticillium are remote possibilities.  The aphids that usually attack okra are small and black and you would notice them. Nutrition can always be a factor if nothing more than how it affects the vulnerability of the plant.  It really isn't that unusual that plants in close proximity are affected differently.  Check out these links:

Southern blight, southern stem blight, white mold (apsnet.org)

Southern Blight | Texas Plant Disease Handbook (tamu.edu)