Herbicide problems

A cousin in the UK contacted me recently concerning a major problem that UK organic gardeners and farmers are experiencing. I would like to draw your attention to it because a similar problem could occur here.
The cause of the problem is a hormone-based herbicide (weed killer) Aminopyralid, which is an ingredient in several brands of herbicides produced by Dow Agrosciences. Aminopyralid has become popular because it is only effective against broad-leaf weeds and does not kill grasses. However, the herbicide binds to woody tissue in grasses and remains active in the grass, hay and silage fed to animals. The herbicide survives passage through mammalian digestive systems and remains active in manure produced by animals that consume contaminated feed.
Consequently, the herbicide affects a range of vegetable crops planted where contaminated manures have been added to beds, or where contaminated hay or straw is used as mulch. As soil bacteria begin to decompose the mulch or manure, the herbicide is released into the soil and absorbed by roots of broad-leafed plants.
Symptoms of affected crops are dying seedlings or curled leaves and gross deformity of plants and produce. Susceptible crops include peas, beans and other legumes, carrots and parsnips, potatoes and tomatoes, and lettuce and similar crops. The affected beds remain unusable until soil bacteria have completely broken down the herbicide. As you can imagine, there are a lot of angry gardeners in England and Wales where this problem is endemic, and there are calls to for this product to be banned.
The best Dow Agrosciences can offer is: the levels of amylopyralid in crops “are unlikely to cause a problem to human health”, although the Dow website says: “As a general rule, we suggest damaged produce (however this is caused) should not be consumed.”
Originally the Royal Horticultural Society (RHS) advised allotment gardeners that contaminated soil would not be usable for two years. However, more recent information indicates that it can be used as soon as soil bacteria break down the herbicide, so the faster you can get them to do this, the better. Aerobic bacteria that break down organic matter faster than anaerobic bacteria require moisture, air and nitrogen for fast consumption. They work faster in a soil pH that is close to neutral. If soil is acidic, raise soil pH to close to neutral (6.5-7) by watering in agricultural lime. Start with a generous handful per square metre, and mix it through the topsoil. This will also aerate the soil to provide air for the bacteria. Don’t use hydrated or slaked lime (builder’s lime) as this will lose nitrogen from the soil, and the bacteria will work more slowly when soil is low in nitrogen. Check soil pH every six weeks because manures produce hydrogen ions as they break down (making soil more acidic), and turn the topsoil regularly to maintain good aeration. Keep soil just damp. If uncontaminated mulch can be sourced, it can be applied to the bed surface to maintain consistent moisture content and keep soil warmer through the colder months, especially if mulch is applied in the middle of the day when the soil is warmest.

Other herbicide problems
Other herbicides, including glyphosate, increase the risk of soil diseases by damaging the good fungi in soils that keep soil diseases under control. Recent research published by the United States Department of Agriculture (USDA), found that herbicide-resistant GM crops are causing an increase in “Fusarium” diseases, and predicted that there would be an epidemic of soil diseases and a food crisis, before long. Food crops from plants badly affected by fusarium diseases can also contain the disease fungi, causing a range of health problems, or death, as happened in Mexico some years ago when tortillas made from affected corn were eaten.
Herbicides cause more problems than they solve but many people would rather believe the advertising hype put out by chemical companies because weedkillers look as though they will save the gardener some work. (See post ‘Wilting diseases’ in the Pest-free Gardening category.)

3 thoughts on “Herbicide problems

  1. Why are these products even available? To anyone, let alone the domestic market. And why so many of them?
    I have a “neighbour from hell” living next door, who has previously poisoned a bamboo hedge with glyphosate. In the last two months my front garden bed and footpath has started dying, including mature trees! No evidence of who or what has done this, however. It is too easy to do the damage unnoticed.
    The regrowth of Hippeastrums, Agapanthuses, aloes, geraniums, heliconias, rhoeos, Cuban thyme is still dying off, poinciana tree dropping leaves and producing stunted versions that brown off and drop, has repeated the cycle several times in an attempt to survive. 6 and 4 metre foxtail palms with fronds browned/ chlorotic. Macadamia on the footpath has patches of brown on leaves, which then drop, the new growth small and shows curling and then dies. Golden penda with chlorosis of leaves and leaf drop. A mature dracaena’s leaves rotted on the tree, really stinky. Had to remove all leaves, the regrowth is showing toxicity. Would you like some photos?

    It is beyond me, Fiona. It sounds as though your neighbour is exceeding the recommended dosage rate for it to spread to your property. A few photos might help other readers to recognise herbicide damage, but no larger than 1 MB, please, as they clog up my In box.

  2. The problem is here. Our daughter came to me concerned about the distorted leaves (cupped, thin and twisted) on her tomatoes and bean plants in two new wicking beds. We know of another garden where the same problem has occurred. In both cases bought soil mixes were used to fill the beds. My daughter has a five-way mix purchased from a supplier in the western suburbs of Melbourne. The other garden was installed by a landscaper; we don’t know the supplier of his soil mix but it also was brought in. We were unaware of the seriousness of the problem at first so we started replacing sections of the wicking bed soil to the depth of about 20 cm with home-made compost and potting mix and planted fresh plants including lettuces. We also installed an in-ground worm farm. It was too big a job to replace all the soil so we left some crops undisturbed but pruned the tomatoes. The beans did not recover but some of the tomatoes did. My question is can the plants not affected be safely eaten? Cucumbers, chives, an eggplant oregano and thyme show no sign of broad-leaf herbicide poisoning- they are not showing any leaf distortion. I am surprised the cucumbers are as yet unaffected but they were planted between beans so perhaps the proximity to bean plants has some influence.
    It depends which herbicide was used. If it was one of the pyridine group the herbicide is active until broken down by soil micro-organisms, and if the plants look completely healthy, the crops should be fairly safe. I would definitely complain to your soil supplier and landscaper as pyridine herbicide product labels state that treated crops are not to be used for hay, silage or animal bedding, and manures are not to be spread on land used for growing susceptible crops. They should have checked that these products had not been used on the materials they purchased.

    You may find more information on this problem here: Manure and mulch warning update

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