To grow, or not to grow: that is the impatiens question.
In the wake of a season where impatiens downy mildew devastated bedding plants in gardens across the country, the ornamentals supply chain is asking itself what it is going to do with this £40 million chunk of the industry in 2012.
The question of disease risk management next season was discussed in detail by researchers, growers, retailers and gardener representatives at the end of October during an HDC/BPOA/HTA Impatiens Downy Mildew seminar. The HDC has spent around £200K on research into this devastating fungal disease of impatiens – the bedding staple more commonly known by gardeners as busy lizzies.
If you are a gardener, click here for advice about what you can do to combat this disease
If you are a grower, retailer or landscaper, click here to find out what you can do to combat this disease
More than 95% of the UK impatiens crop is raised from seed, but seed-borne infections of this disease have so far not been detected. The risk of infection comes with vegetative cuttings, which are used to propagate around 3-4% of the UK crop. Research and the rapid and extensive damage on UK nurseries this season have shown this diseases’ devastating ability to spread by sporulation, from cutting-raised material to cross-contaminate seed-raised material.
On one UK nursery alone, cross-contamination from sporulating cutting raised material caused widespread infection and 300,000 production units were dumped this season, filling a staggering 33 skips.
This infection process has been further complicated by the discovery of oospores – hardy resting spores that can overwinter in soils, potentially meaning the disease cycle cannot be broken from one season to the next, and raising the possibility that contaminated planting areas are sustaining infections.
Chemical control of the disease is being made increasingly difficult, as the limited range of fungicides available to professional growers is being compromised by the emergence of resistance to one of the key actives – metalaxyl-M. In any case, the propensity of this disease to spread, given the right environmental conditions, means post-infection sprays at best can only suppress the disease. Control is only possible with protectant fungicide programmes – provided effective products are available.
For the gardener, there is little that can be done to control the disease bar keeping foliage as dry as possible to try and prevent sporulation, which leads to the rapid defoliation on outdoor impatiens.
So given the constraints, the question raised for growers is whether or not they can produce impatiens that are essentially fit for purpose. Many in the industry think they can, and the first step in ensuring a ‘clean start’ is to abandon cutting raised material and only propagate from seed. This approach is supported by some of the propagators who have committed to not delivering cutting raised material into the UK market, and to keeping cutting and seed raised material separate in their European logistics network.
A question mark would still remain though over how well those clean impatiens plants would fair once sold and planted in contaminated garden soil, where they are potentially bombarded with air laden with fungal spores.
Some in the industry were advocating a more severe approach – stopping growing impatiens all together and looking at alternative crops, at least until mildew-resistant impatiens have been bred, or the chemical controls are available to enable effective control.
A straw poll at the seminar found that growers were around 2:1 in favour of still growing impatiens in 2012, and that no growers were going to use cutting raised material.
If impatiens do continue to be sold, clear communication with consumers will be vital – the industry needs to make sure the buying public are fully aware of the risks. The retailers at the seminar summed up everyone’s key concern – the potential damage to consumer confidence.
Ultimately customers buy things that work, and in the case of impatiens this has been a low-cost product that works. And garden retailers are increasingly re-enforcing this behaviour by offering no quibble guarantees across their whole range of products.
Can we as an industry still grow and sell impatiens that work for gardeners? The answer remains far from clear.
HDC funded work on this disease that you may find useful includes
A good practice guide to manage the disease (Good Horticultural Practice for the Prevention and Control of Impatiens Downy Mildew), and
A Factsheet (11/09 Impatiens downy mildew)
The HDC also has two ongoing research projects - PC 230 Detection and control of downy mildew on ornamentals and PC 230a Control of downy mildew an economically important foliar disease on impatiens.
For further detail on suitable cultural and chemical control programmes contact your local horticultural adviser or consultant. To obtain copies of all the information listed go to the HDC website or contact Kirsty Nichols on 0247 647 8677.
Thank you to Tim O’Neill of ADAS who provided the carousel banner image and Martin McPherson of STC who provided the image above.
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