Britain and the PNW- How do Gardeners’ Questions Differ?
No surprise – British gardeners have many of the same concerns as do gardeners in the Pacific Northwest. I recently took a look at the questions most commonly asked of the Royal Horticultural Society, and the similarity to those asked of MGs at clinics and on the Plant Information Line is striking.
The RHS reported that the fifteen most commonly asked general questions were: pruning clematis, clematis wilt, camellias failing to flower, pruning hydrangeas, pruning roses, magnolias, sooty mold, amending soil, fertilizer use, mulching, ivy, groundelder, bindweed, Japanese knotweed, and safe chemical use.
Other frequently asked general questions related to 'plants for difficult places', apple canker and scab, bacterial canker, box blight, cornus anthracnose, damping off, hellebore leaf spot, weed and moss control in lawns, trees for small gardens, raspberry blight, potato and tomato blights, peach leaf curl, rabbits and moles, replant diseases, Japanese maples and pesticide residues in manure.
The 'top ten' pest-related questions saw slugs and snails knocked out of their usual top spot by questions about viburnum beetles; the rest of the top ten was filled out by questions on cushion scale, chafer grubs (which surprised me), harlequin ladybirds, vine weevils, lily beetles, horse chestnut scale, glasshouse red spider mites and ants.
Something that did surprise me, however, was that the following statement was prominently placed on the main page of the RHS advice website www.rhs.org.uk/Gardening/Help-advice:
“Garden chemicals or pesticides such as insecticides, fungicides and weed-killers, are perfectly safe, providing they are used in exactly the way described on the container or packaging.”
The RHS is well-known for advocating IPM-based approaches, actively supports and researches organic gardening, and promotes reduced pesticide use. This lead me to wonder what might be different in the UK gardening environment that would lead the RHS to post a separate, endorsement-like statement of garden chemicals on the main page of their advice site – perhaps there is widespread, entrenched misuse of certain chemicals or perhaps there are certain weeds or pests which are aggressively destroying sensitive plants or ecosystems.
Because the climate and growing conditions in the PNW are similar to many parts of Britain, the RHS is one of the sources I look to when I receive questions on the Plant Info Line from PNW gardeners – although their noted expertise and similarities in the questions they respond to supports my continued use of them as a resource, their statement about pesticide use is a reminder to me that there are differences between our respective gardening cultures that we need to take into account.
Many Gardeners Fertilize Unnecessarily
The RHS advises that composts are highly beneficial to gardens, but recommend fertilizers not be added to gardens unless a distinct nutrient deficiency is shown through unhealthy growth and soil testing. If soil is shown to be deficient in a single nutrient, an organic fertilizer supplying only that specific nutrient should be added. Where there are chronic soil imbalances, they recommend finding plants which grow well in the existing soil. Fruit and vegetables are an exception to the ‘No Need for Supplementary Fertilizer’ rule and yields can be increased by a yearly addition of organic fertilizer and compost tailored to the specific needs of the vegetable or fruit.
Pesticide Residues in Commercial Composts
Unlike the PNW, the RHS reports that they have received many calls about aminopyralid herbicide contamination of commercial compost. A limited number of problems have also been reported in Western Washington and periodically in the interior of BC, but, by diligently assessing their manure sources, Canadian commercial compost operators have ensured the problems are infrequent here.
All herbicides which are registered for home use are broken down by microbial action, light, heat, water and air during composting, but aminopyralid which is available for farmers and registered operators, does not break down during composting. Aminopyralid is an unusual pesticide, not only does it not break down in composting, it does not break down in a foraging animal’s digestion so is eliminated in animal manure. This has led to large scale problems. In Britain when aminopyralid was sprayed on fields where animals graze then the contaminated manure was used in commercial composts. Vegetable crops have been lost on farms and in community and home gardens when commercially- or farm-composted manure containing aminopyralid has been applied. Sadly, even organic farmers have had problems because organic regulations in BC and other areas allow organic farmers to use manure and compost sourced off their farms to fertilize their fields.
Aminopyralid was registered for use in Canada in 2006. Yvonne Herbison, Regional Pesticide Officer, generously provided MGs with information on the contamination problem in BC. The broadleaf herbicide is only available for use by commercial operators, including farmers, and certified government staff who use it to spray principally for the control of aggressively spreading, invasive weeds in rangeland. It is used much more in the BC interior than on the coast because knapweed and Canada Thistle are more of a problem there. Because of this, problems with aminopyralid residues have been seen periodically in composts and manures in the Interior but not on the Coast. She recommended the excellent BC Organic Grower article ‘Hazardous Composts & Soils Contaminated with Persistent Herbicides’ for an overview of the BC problem.
Contamination of commercial composts can be avoided if commercial operators know and monitor the source of their manure. Although there are a few Canadian commercial compost operators who treat composting as a waste-management operation (and who appear to have little knowledge of, or concern for, the environmental impact of their products), the majority are run by operators with a strong commitment to producing an ecologically-beneficial product. Those who believe in soil health and the contribution that compost makes to garden health know who supplies their raw materials, visit their suppliers’ farms to develop personal relationships with these suppliers, and vigilantly watch the quality of their finished products. Good commercial compost operators candidly admit the risk of contamination of their products, and, knowing that they cannot test for every contaminant, they run growing tests with their products to monitor plant vigour. Company websites and product labels indicate which category a producer falls into.
The problems that occurred in the UK led to the suspension of aminopyralid’s sale. When aminopyralid sales resumed, Dow added usage warning advising farmers to take steps to ensure that their manures, sprayed grasses, hay and silage do not leave the farm and are not used in a manner where they could enter compost operations. With farmers’ and commercial composters’ awareness, future contamination-risk is minimized.
Because proper composting breaks down the majority of pesticides except for a few like the commercially-available aminopyralid and picloram, it has only rarely been found in commercial composts. Gardeners can help ensure they purchase uncontaminated compost by diligently reading labels and checking websites to determine whether a producer has made a commitment to produce an environmentally-beneficial product.
Author: Jane Sherrott, MG, Vancouver Chapter
