by Evelyn Parker
Members who listen to Gardeners Question Time will have picked up on the query recently raised about hormone weedkiller residue in farmyard manure affecting some particular plants.
The culprit is thought to be aminopyralid, a hormone-type herbicide which is used on pastures to control weeds. Manure from animals fed on treated pastures contains chemical residues sufficient to damage susceptible crops. Gardeners buying this manure to apply to vegetable crops are coming across abnormal growth, particularly on tomatoes, potatoes and legumes. Symptoms of damage are distorted foliage, cupping of leaves and fern-like foliage. There are no known remedies once damage has occurred, and there is no assurance that affected produce will be safe to eat.
The RHS Horticultural Advisory Service commented that this kind of problem was fairly unusual, and mostly attributed to accidents and carelessness, but instances have risen this year and farmyard manure has been frequently implicated. They recommend that gardeners should seek assurances from their suppliers of manure. Pippa Greenwood, who is a plant pathologist, warned that ground affected by the contaminated manure should not be used for up to two years.
We ourselves came across a similar problem in 1999, and the substance implicated was not FYM but Progrow, the soil improver produced by Hampshire County Council using composted material collected from household collections and stuff taken to the tip. I should add that we have used this product many times and this was the only occasion when we had problems with it.
What I noticed first was that my little tomato plants, which looked fine until I planted them out in the polytunnel, were looking strange, with foliage more like fern than tomato. The young broad bean plants also looked odd – they were putting up leaves which were pointed rather than rounded. I wasn’t until May when I planted out my runners and they became stunted that we twigged the common factor was where we had spread Progrow. We took a closer look and realised that it was one particular batch of Progrow that was implicated.
We summoned the Admin Department, and a man came out and duly tutted over our exhibits, which were looking pretty weird by then. I was able to show him enough normal produce to convince him that it wasn’t me that was weird. He left with samples of compost and affected plants.
By now it was late June, and the broad beans were huge and fruiting abundantly – but the tips of the beans were pointed not rounded. I was marketing my produce at the time – as certified organic – and was in a quandary as to whether the beans were safe to sell or not. The crop was the heaviest ever, so with a heavy heart I watched them grow too old to sell. Meanwhile the tomatoes in the polytunnel had grown to about 7 feet high and were smothered in blossom like a yellow waterfall, literally several hundred flowers on each plant. The runners were on their third planting, and each time the ones planted in the Progrow treated bed grew stunted, while the rest grew normally.
Eventually the results of the plant assay came through:
“Samples of affected plants were examined at the (ADAS) Plant Clinic…The major symptoms were confirmed to be due to the presence of low levels of hormone herbicides which had come through the composting process. They re likely to have originated from herbicides used on grass and present in the grass clippings, but usually dilution with other green waste would make it extremely unlikely that significant levels would be present in the end product. It is possible, however, that there was contamination of one particular load of feedstock to the composting process, e.g. by accidental disposal/spillage of herbicide into a batch of grass clippings”.
How did they do the assay?
“Growing tests were carried out at ADAS Wolverhampton, using tomato plants as the indicator species, as they tend to show up phytotoxicity problems well. Both (samples) showed the same earlier symptoms of leaf distortion, confirming the presence of hormone weedkiller residues”
In fact what they did was put the dodgy compost samples into small pots, and a control pot of another standard type compost, and planted tomato seedlings into each, and the difference was evident within a few days.
So, if you want to establish whether FYM or municipal compost which you have acquired is safe or not, the thing to do is germinate a few tomato seeds in trusted compost on a windowsill, and transplant the seedlings into a pot of questionable and another of trusted compost, and within a couple of weeks they will either be different or similar. Meanwhile, you have the headache of storing your purchase, but from my experience that is a lesser headache than spreading contaminated stuff.
Have any other readers had interesting experience with bought-in composts and manures? Our experience, together with the Gardeners Question Time findings, leave me with many questions, not least, is it not time the offending chemicals were clearly identified and banned?
by Evelyn Parker
