I'm not a member of the whole organic movement. I go out of my way to avoid buying organic produce (and not just because I'm cheap), believe wholeheartedly in the benefits of GMOs, and have very little fear of nebulously defined 'chemicals'. Pesticides, herbicides, and synthetic fertilizers are all tools and while they shouldn't be the first resort ("If all you have is glyphosate, everything looks like a weed") they are quite effective at specific tasks. In general I'm more than fine with conventional agriculture practices, if not necessarily the business models.
There's a class of herbicides known as picolinic acids that mimic the plant hormone auxin. When sprayed on plants it disrupts the natural growth patterns and causes severe malformations that eventually lead to the death of the plant. It's particularly valued because it rarely affects monocots (grasses and grains) while heavily damaging dicots (weeds and everything else). This means you can spray it over entire wheat, corn, and rice fields (those three crops represent about 2/3 of all calories consumed by humans) without fear of it destroying your crop. The class as a whole has been around since the 1940s (it was used during the Vietnam War as Agent White, the inferior-performing (and dioxin free!) alternative to Agent Orange) but as is the nature of the chemical business, it has been expanded over time by new chemicals to improve performance and counteract resistances.
These newer versions are known as picloram, clopyralid, and aminopyralid and are sold under dozens of trade names including Grazon, Reclaim, and Forefront. They're used in pastures to kill various undesirable plants for such as clover, nightshades, and thistle. They're especially suited for this use because they're not easily absorbed or digested by livestock. However, clover is a legume like beans and peas, nightshades include peppers and tomatoes, and thistles are related to sunflowers, lettuce, and artichokes. So basically they're also really good at killing most vegetable crops. Which is fine as long as you're not a farmer growing tomatoes right next your neighbor's pasture when they spray for weeds. However, the newer members of this class are also extremely persistent in the environment. While most herbicides decay relatively rapidly over the course of 2 to 3 months, picloram et al. remain active in soil and dead vegetation for 2 to 3 years.
This is the whole point. By lingering in the soil long-term it ensures that farmers only need to spray once a year or more and the fact that it is not digested by animals means it's safe for them to consume. It's so safe that farmers often spray fodder with it after harvest so that the plant dies and dries out faster.
So we have a persistent chemical, that's not digested, and used widely on livestock feed. Once that feed meets its logical conclusion the waste is usually composted and resold as fertilizer, still containing the herbicide. Which is how it ended up in my garden.
My tomatoes, which are particularly sensitive, have contorted themselves into corkscrews and will likely be stunted with reduced harvest at best. The beans I'd planted underneath them are also germinating extremely poorly and have similar (though far less severe) distortions. My options are essentially to dig out and replace all the contaminated soil and plants, plant unaffected crops (corn), or to give up and let it lie fallow for a year or more.
The worst part is that this has happened before: in the early 2000s, compost contaminated with clopyralid caused crop losses in Washington, leading to several states banning its use outright and producer Dow Chemical deregistering it for use on lawns. Now the same thing is happening with the latest iteration, aminopyralid. I would strongly advise any and all gardeners to avoid using composted manure for the forseeable future as even the smallest amount of contamination (2 to 5 ppb) can damage tomatoes and other sensitive plants. I'm an unironic believer in the 60s-style idealism of science paving the way for a better future, but damn if this isn't a pain in the ass.