Growing food, for reasons I haven't quite got to the bottom of, is an intensely emotional process. The satisfaction I get from harvesting a good crop bears no relationship to any value that crop possesses. I take more pride in my fruit and vegetables than in any of the work I do. When the slugs mow down my seedlings, or my watering system fails, or blight knackers my tomatoes, it throws me into a depression which sometimes lasts for days.

It might be because gardening is about hope: you are always thinking months ahead. Even if every other aspect of your life seems to be in ineluctable decline, you have something to look forward to, something that makes you jump out of bed in the morning and run outside to see what's happening.

So think of those gardeners a few years ago whose plants thrived for a while, then suddenly stopped growing and curled up like arabesque scrollwork. At first, no one knew what was happening. But gradually the syndrome was linked to residues of a new, hormone-mimicking pesticide manufactured by our old friends Dow Chemical, which was first approved in this country in 2005. It's called aminopyralid.

It is used by farmers to kill broad-leaved weeds growing in fields of grass. It locks onto the cellulose in the plants, passes through the guts of the animals that eat them, and retains its potency in their manure, sometimes for two or three years or more. It is not believed to present a risk to human health.

The poisonings were a cruel cosmic joke. The people hit hardest by careless agri-business were the small producers and amateur gardeners trying to do the right thing, by using manure rather than chemical fertilisers. They had no idea there was trouble until it was too late, and, because of the remarkable persistence of the pesticide, no guarantee that the trouble would be confined to the year in which it was detected.

After a major fuss by gardeners, government approval for the chemical was suspended in 2008. Farmers were allowed to use it again after "a stringent stewardship programme" was introduced. They would be permitted to spray it only on fields which would be grazed directly by cattle and sheep, rather than on fields where silage or hay is grown.

All manure from animals kept in these pastures would have to stay on the farm. Horses could not be grazed on treated fields (because horse manure tends to be collected, rather than left on the grass). Farmers using the herbicide, according to Dow, "are required to confirm in writing that they have been instructed on product use, manure management issues and measures to reduce the risk of damage to flower-rich grassland". These rules, the company says, "should allay concerns amongst gardeners and allotment-holders over using manure."

Are your concerns allayed? They shouldn't be. It's back.

My friend and neighbour Ann Owen is a market gardener who, with her husband John, invested most of the money she had into her smallholding. After three years of back-breaking work they expected, in 2011, to make a profit for the first time. Until a few weeks ago, their crops were growing well. Then they started to curl up into fantastic shapes. Before long most of their vegetables either stopped growing or became unsaleable. They've had to dig out the beds they had spent so much time and energy layering up, skip the plants, the soil and the manure and refill the garden with expensive compost. If you cost both their expenses and their time, they have lost thousands.

"It's unreal," Ann says, "almost like watching ourselves on a movie in rewind, undoing all our previous work. And even though we are doing as much as we can to both repair and contain the damage, we know that this season might be a total loss."

They are as angry and upset as I know I would be.

So how had it happened? That's the problem – it seems almost impossible to find out. The manure they used came from a local stables, which had bought its hay from a merchant. Both the manure and the hay were fresh the hay was cut last year. Someone had failed to follow the "stringent stewardship programme", but who? Ann's attempts to trace the hay back to source have been fruitless. Worse still, despite claims by both the company and the regulators to have run an effective awareness-raising campaign, neither the merchant who sold the contaminated hay to the stables nor any of the three farmers he contacted as possible sources had ever heard of aminopyralid, or had any idea what Ann was talking about.

She took the case to the government's Chemicals Regulation Directorate (CRD), which is now investigating. Though Dow, which is doubtless making millions from this herbicide, has thrust it into the lives of people who wanted nothing to do with agro-industry, Ann has discovered that she has no hope of compensation. She says: "we have lost faith that there actually is any protection for hardworking people like us and our livelihoods."

I asked the CRD how many cases of aminopyralid poisoning it had investigated since the new rules were brought in, and was amazed to discover that Ann's was the only one. It told me that it receives "only a handful of inquiries per month." Of these, it says, the other cases are either less clear-cut than Ann's, or involve gardens which have bought manure from several sources, making it harder to trace the source. Ann's was the only case worth investigating.

I find that hard to believe, and I suspect there's another explanation. Ann is a well-informed and very determined person. It took her a while to work out what the problem was. None of the gardening books she consulted list aminopyralid poisoning, because it has arisen so recently. She then waded through several layers of ignorant and unconcerned officialdom before she discovered that the CRD was the right body to approach. Then she had to persuade the directorate that the hay and the manure post-dated the new rules, and that the poisoning should be investigated.

She has now discovered that a near-neighbour, who had obtained her manure from a different source, has also been struck by this curse, and has produced almost nothing in the past two years. She had blamed disease and poor weather. It was only when she saw Ann's plants and heard the explanation that she realised what had happened to her.

How many people have noticed a strange curling disease in their vegetables, but didn't link it to aminopyralids? How many others either had no idea who to turn to, or were fobbed off by the CRD when they got there?

Let's find out. If you've noticed similar effects to those you can see here, in John Mason's pictures of Ann's plants, or if you've complained to the CRD and got nowhere, please say so in the comment thread. We'll keep it open longer than usual in order to gather as wide a sample as we can. I will then take any cases to the directorate and find out what it intends to do.

If suspected cases of aminopyralid poisoning are still widespread, or if it becomes clear that the CRD has failed properly to investigate, I will use this space to call for sales to be suspended again, until the industry and the regulators get their act together. For now, I'm using it to call for compensation for people like Ann. If this chemical is to remain on sale in the UK, a minimum requirement should be that Dow pays for the damage done to people's livelihoods.

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