IT'S a murder mystery in a class of its own – "who dung it?"
• Liz Grace tends to her plot on the Midmar allotments by Blackford Hill Pic: Greg Macvean
As thousands attended Scotland's national gardening show yesterday, the real action was a few miles to the east, where allotment holders were mourning the loss of their potentially prize-winning vegetables.
Dreams of winning trophies at Ingliston – the nation's premier gardening event – were shattered for the allotment holders in south Edinburgh after manure spread on their produce is believed to have contained a pesticide.
The green-fingered enthusiasts at Midmar Allotment Association thought they were getting top-quality organic fertiliser when they bought bags of horse dung from a local stables. About 40 gardeners paid for a share of the manure, spending about 20 each.
However, after spreading it on their allotments in Morningside, vegetables began to shrivel and die. Potatoes, peas, beans, carrots and parsnips were among the carnage.
Experts believe the dung contained a pesticide, aminopyralid, used where animals graze to kill weeds such as ragwort, which is poisonous to horses.
However, it is not broken down when eaten by the animals, meaning the chemical remained in the droppings. It was then unknowingly spread on the Midmar allotments.
It is not known where the pesticide originated from – whether from Ravelrig Riding for the Disabled, where the manure was bought, or from a farm that provided hay to feed the horses. But the product is only permitted for use on agricultural grassland grazed by cattle or sheep – and not on land where the grass will be cut for hay or silage.
The incident has led to calls for tighter controls on the pesticide and a ban on manure containing the chemical from being sold to the public.
Liz Grace, chair of the Midmar Allotment Association, said: "It has caused a lot of dismay and upset for quite a lot of people.
"They try to be chemical- free and they are pretty upset.
"At first people thought it was the late frost but then it became clear that it was the plants that had been put in the ground where this manure had been spread that were affected. They thought they were going to improve their plants and then they ended up dead."
The pesticide will only break down very slowly once in soil, meaning the allotments at Midmar are likely to remain contaminated for about a year.
Grace has contacted the Scottish Allotments and Gardens Society so the problem can be highlighted to other gardeners.
Sally Foster, 46, from Morningside, who was victim to the chemical, said: "It's quite distressing. I'm upset and disturbed by it. We try to be organic and that's the disappointing thing for us. We put a lot of love and effort into the allotment."
Foster says awareness needs to be raised of the hazardous nature of the chemical. "Are the farmers who are putting it on their fields fully aware of what's happening further down the chain?"
Green MSP Robin Harper, who used to have an allotment at Midmar, thinks there needs to be tighter controls, such as labelling to show when fertiliser could contain the pesticide.
"There's no big health risk from it, but it's a worry in that the allotment holders could have their vegetable beds inoperable for at least a year," he said.
Aminopyralids are in products such as Forefront, marketed by Dow AgroSciences Ltd. Ian Rowland, of the Chemicals Regulation Directorate of the government's Health and Safety Executive, told the allotment holders that it was likely their vegetables had been attacked by aminopyralid.
"If the manure has been incorporated into the beds, there is little that can be done," he wrote. "Your choice is either to wait and see if the crops recover and produce some sort of harvest or to dispose of the crop now and leave the beds empty until autumn at the earliest."
He explained how the pesticide would end up remaining in the soil: "The aminopyralid is held in the remnants of the treated grass which, having passed through the livestock which produced the manure, form part of the manure. As these grass remnants decompose, they release aminopyralid, which then becomes available for take up by any plants growing in the soil."
He reassured the allotment holders that it "should not pose a risk to their health". He added: "Aminopyralid is an effective herbicide/weedkiller, but of low toxicity to mammals. We do, however, appreciate that not everyone will be happy to eat food produced in these circumstances and that they will prefer to dispose of any crops."
A spokeswoman at the Ravelrig riding school said the manure had been delivered to the allotment holders in "good faith" and was not responsible for the death of the vegetables.
"We have talked to other allotment holders who received this and they have told us there have been no problems. We think it is more likely to have been caused by frost."