I don't see any other signs of insects at all out there (I don't think it's pill bugs; it's almost like there are invisible flea beetles, but I don't know), and it's pretty dry. However, I took a horseradish leaf in the house for experimental purposes, a couple days ago or so, and there are little things developing on it, which might be mini cocoons, eggs, or something. Here's a picture, but they're so small in the picture that they just look like slivers in it (there are two you can see):
I think it's cabbage worms, or a similar caterpillar (the eggs look like that). Horseradish is in the cabbage family, anyhow, and the leaves taste like strong cabbage.
I don't know where they're hiding, though, and I didn't know they liked potatoes (the link has a picture of potato damage). I do find cabbage loopers on the ground in patches of lambsquarter (which is related to epazote), though.
Ah. There are serrations (though not pointed ones), but they were a lot more obvious before it got eaten. See the upper left leaf, on the right side? The first three lobes at the top are examples of its serrations (although the parts between got eaten a little, and other serrations it had didn't look exactly like those). Here's a picture of some epazote with a similar style. The leaves in my picture are those of an immature plant, though; those aren't always as heavily serrated as more mature ones in many kinds of plants.
The color is different than others I see, though.
Anyway, remind me and I can post another picture when it's older.
I think it's cabbage worms, or a similar caterpillar (the eggs look like that).
Cabbage worm don't crawl off and hide during the day. If you had cabbage worms, you would be able to fine them. The damage is too large for microscopic creatures. I think it is from something large like pill bugs or crickets. Several pests could be involved.
All our problems would be solved if only we would change our ways.
You may be right about the pill bugs. I came out in the morning when I've seen pill bugs feeding on pepper foliage before in a previous year (granted they came out little later, when the sun was a bit higher; maybe 7 or 8 AM), and although I found none on or near the horseradish or epazote, there were a few eating the potato leaves (maybe they call them potato bugs for a reason).
However, I disagree about caterpillars not hiding or going somewhere dark to sleep (whether or not they hide or sleep in the day particularly; they don't hang out on plants or in plain sight 24/7; even on cabbage, the ones I've observed hide tight inside the heads—I've never actually seen them come out, nor seen them feeding in the day to make the holes they make outside of the heads, but I've seen plenty in the heads when we've grown cabbage in previous years—but there are no heads here for shelter with horseradish; so, they'd probably go somewhere else like they do for peppers and such). However, caterpillars usually poop a lot, and I don't see any of that (so, I'm curious to see whatever comes out of those eggs).
Moths are nocturnal, as I understand it, and the cabbage worms we get look like cabbage loopers, which turn into moths, and we do get moths that look like that. I'm not sure if they're nocturnal at the caterpillar stage (but I don't know why they wouldn't be). Butterflies are another story, though. Some cabbage worms do turn into butterflies. We have the white butterflies that look much like those that come from cabbage worms (so we probably have the potential for both of those kinds).
I found more leafhoppers, another gnat, an aphid, and a spider, but that's about it on the horseradish, other than all the eggs (there are plenty of those on some leaves). Sometimes, I see things that look just like the eggs except that they're suspended by thread-like things.
pepperhead212 , So far so good. Well, I see a little new nibbling, but it should be growing fast enough.
tom , I found a caterpillar in the soil not far from the horseradish when I was transplanting a few onions, but I'm not sure that it was a cabbage worm, nor am I sure it's what ate holes in the horseradish. I know it's not the ideal time to transplant onions, but we needed to move them.