Factsheet 11/09 Horticultural Bradbourne House Development East Malling Company Kent ME19 6DZ T: 01732 848383 Protected Crops F: 01732 848498 E: [email protected]

Impatiens downy mildew David Jones, (ex) Central Science Laboratory and Tim O’Neill, ADAS, updated by Martin McPherson STC, Wayne Brough ADAS and Phil Jennings, the Food and Environment Research Agency (Fera)

Downy mildew ( obducens) was found affecting for the first time in the UK in 2003. It remained absent or at low levels during 2004–2006 but re-appeared in 2007 and subsequently caused severe infection in UK crops, particularly in 2008. The disease has been reported previously from overseas on both wild and cultivated of Impatiens. This factsheet provides updated information about the disease, its biology and control.

Action points • Treat plants with an effective • Where possible sub-irrigate crops fungicide programme, taking note to minimise leaf wetness. • Purchase seed and cutting raised of what products were applied plant material from reputable pre-delivery and alternate • If overhead irrigation systems sources and request evidence of products with different modes of are used ensure water is any preventative cultural and action for resistance management applied early in the day and on fungicide treatments made to the purposes. days when the crop can dry plant material. out quickly. • Inspect plants on a regular basis • Prior to delivery of young plant for signs of downy mildew, if • Prior to dispatch apply a final material ensure a thorough confirmation is required, submit systemic fungicide to provide as nursery hygiene programme has plants for laboratory analysis. long a period of protection post- been undertaken and that any planting out as possible (taking self-seeded impatiens have been • Remove any infected plant into consideration the potential removed from inside and around material and place it in a covered risk of fungicide product deposits the glasshouses. skip or bin to go to land-fill. on leaves).

• Review the glasshouse environ- mental management regime to ensure good air circulation and ventilation.

• Apply an effective systemic fungicide for downy mildew control either pre-or post-sowing/post- rooting, preferably as a drench treatment to the module substrate.

• On delivery of plant material keep seed and cutting- raised plants separate and segregate cutting material from different sources.

• Where possible, keep other impatiens crops eg I. hawkeri (‘New Guinea’ types) and I. hybrida separate from I. walleriana cultivars to minimise disease pressure on these crops. 1 Sporulation on the lower leaf surface of impatiens identifies the problem as P. obducens Background and the UK that the disease has is apparently derived from also been found on ‘New Guinea’ I. balsamina, which originates from What is the disease impatiens; an ornamental hybrid the Indomalayan region. situation in the UK? derived from I. hawkeri. Yet, in There are so far no records of other situations ‘New Guinea’ types P. obducens on I. glandulifera syn. During spring 2003, downy growing alongside severely infec- I. roylei (Himalayan or Indian balsam) mildew was found for the first time ted I. walleriana have remained which has become very prevalent in the UK on Impatiens walleriana disease-free. In 2008, there was on river banks and wetlands since in Southern England and the also one UK report of the pathogen its original introduction to the UK pathogen responsible identified as affecting I. hybrida, which is claimed around 1839. Plasmopara obducens (Figure 1, to have some I. walleriana in its Although specific reports of the previous page). During the summer genetic background. pathogen have largely come from that year the disease was subse- the countries identified above, its quently found more widely on both distribution has been described as seed and cutting-raised impatiens Where did the disease worldwide. Certainly, in recent years in various locations around the originate? there have been similar outbreaks UK, including nurseries, garden of downy mildew on I. walleriana centres, civic floral displays and The exact origin of the disease has cultivars in other European countries, private gardens. Most of the not been determined, but it is most South Africa, Australia, Japan and outbreaks were first observed after likely to have gained entry to the UK the USA. This potentially implies a planting out. Severely affected via impatiens material imported from common dissemination route, or is an plants either died during establish- overseas. Whilst the disease was indication that P. obducens is more ment or pre-flowering outdoors not found in the UK until 2003, it has widespread in wild plants within the whereas those less affected lost been known to occur in several other genus Impatiens than has currently much of their ornamental value countries in Europe and elsewhere been reported. through partial or complete defo- for some time. It may therefore have liation. In some planting schemes been introduced earlier but remained the disease differentially affected undetected at low levels until cultivars and even flower colours environmental conditions were more within a series suggesting that conducive to its development. either only certain cultivars or series were originally affected or that differences in cultivar Where else has the disease susceptibility exist. been found and on which Following the initial disease hosts? outbreaks in the UK, Defra Plant Health Division introduced Plasmopara obducens was first emergency phytosanitary mea- described in Germany in 1877 on sures. Following the completion of Impatiens noli-tangere (touch- a Pest Risk Analysis (www.defra. me-not balsam), a wild species of gov.uk/planth/pra/pobducens. Impatiens native to many temperate pdf) and widespread industry countries in the northern hemisphere, consultation, a decision was taken including some parts of the UK. The to remove the emergency measures fungus was subsequently reported and allow the industry to manage on the same host in Bulgaria, the disease in a similar manner to Czech Republic, Denmark, Finland, other downy mildew pathogens on Lithuania, Romania and Russia. It is protected ornamentals. likely to be quite widespread on Between 2004 and 2006, I. noli-tangere throughout northern the disease remained absent or at and central Europe although, it has low levels in commercial crops not been reported on this wild host in reappearing at moderate levels in the UK. 2007. In 2008, due in part to In North America, P. obducens extremely favourable environmental was identified in the 1880s on conditions for the disease, infection native Impatiens species including was widespread in material planted I. capensis synonym I. biflora outdoors and was also found (orange jewelweed) and I. pallida within growing crops on nurseries (yellow jewelweed). The pathogen where plants had to be treated or has also been found in China and disposed of as appropriate. India primarily on I. balsamina There have been unsubstantiated (garden balsam). The popular reports from both the Netherlands impatiens bedding plant I. walleriana Symptoms unseen (latent) for anything from for the main veins (Figure 4). Usually a few days to several weeks depend- as symptoms develop leaves fall Usually, the first symptom of downy ing on the growing temperature. prematurely from the plant leaving a mildew infection on impatiens is Sporulation may not occur for several series of unattractive bare stems, in a pale green to slight yellow dis- days after initial symptom expression, some circumstances however leaf coloration on the upper leaf surface, only appearing under favourable fall can occur with minimal levels of often with a downward curling of conditions (generally following an associated sporulation making disease the leaf (Figure 2). A few days later extended period of leaf moisture identification difficult. Plants infected the same leaves can exhibit a white and high humidity). early are likely to be stunted and pro- ‘downy’ growth largely on the lower The white ‘downy’ growth may duce small, pale green or yellow leaves. leaf surface. Following infection be either sparse (Figure 3) or cover Flowering is usually reduced or absent P. obducens symptoms can remain the entire lower leaf surface except as a consequence of infection.

2 Early disease symptoms on impatiens – leaf paleness and curling

3 Diffuse, white, spores and spore-bearing structures of Plasmopara 4 A dense, white layer of spores and spore-bearing structures obducens on the lower surface of an impatiens leaf of Plasmopara obducens on the lower surface of an impatiens leaf Biology Spread and survival of impatiens downy mildew

Under conditions of high humidity, P. obducens produces spore- bearing structures that are visible as a white ‘downy’ growth on the underside of the leaves. The spores are spread from plant to plant by water splash and over longer distances on air currents. Leaf wetness caused by conden- sation on the leaf surface, rain and irrigation water is required for successful spore germination and infection. If the environmental conditions are unfavourable for spore germination and infection these spores soon die. However, once infection occurs the pathogen 5 Diffuse sporulation on impatiens flower bud can quickly colonise the plant internally, sometimes systemically. It is capable of invading all parts of its host (Figure 5) until the nutrient supply is exhausted and the plant dies. Just prior to the death of the host plant tissues, downy mildew pathogens often produce long- lived survival or over-wintering spores. These spores can survive in decaying host tissue and soil for many years, thus allowing carry- over as new infections from one season to the next. Such spores were found for the first time in infected impatiens stem tissues during 2008 (Figure 6). In India, over-wintering spores of P. obducens, as well as vegetative strands of the pathogen, 6 Microscopic image of resting spores of Plasmopara obducens inside the stem tissue of impatiens have been detected inside seed harvested from diseased I. balsamina plants. When sown, Pathways for the pathogen (orange balsam) and one or all of such infected seed was reported to enter impatiens these may be susceptible to the to have given rise to systemically production systems disease and capable of harbouring infected plants. The HDC funded the pathogen. However, evidence project PC 230, has shown that The pathogen is most likely to have to date, which includes the lack of many seed-lots were contami- been introduced into commercial records of P. obducens in the UK nated with the DNA of P. obducens, production systems in the UK and until 2003, suggests that it is unlikely yet when such seed-lots were elsewhere as symptomless infections that the outbreak originated from grown on under conditions on cuttings and/or possibly seed. wild species in the UK. conducive to downy mildew devel- Another potential possibility is that opment, no disease symptoms were the disease may have originated from expressed. The significance wild plants growing in close proximity Conditions that favour of the pathogen DNA in or on seed- to nurseries. There are a small disease development lots therefore remains unclear number of indigenous or introduced at the current time though perhaps Impatiens species that grow wild The optimum conditions for suggests the detected pathogen in the UK, including I. noli-tangere, germination and infection by is non-viable. I. glandulifera and I. capensis downy mildew are relatively cool temperatures (around 15°C) Moisture raises humidity levels humidity levels and surface and high humidity (around 95–100%), and permits the pathogen to moisture which encourages disease preferably with prolonged (greater sporulate, whilst prolonged periods development (Figure 7). A single than 5 hours) leaf surface moisture. of surface water on leaves allows diseased plant can potentially Disease outbreaks usually occur spore germination and infection. generate sufficient spores to infect after a period of wet weather or when In protected environments, over- hundreds of others in the confined crops are irrigated inappropriately. head irrigation systems create high space of a glasshouse.

7 Extensive disease symptoms (including plant death) in a crop of pot grown impatiens

Management and Incoming vegetative cutting mat- crop inspections are very useful as erial from different sources should the first signs of the disease may control ideally be kept in temporary be detected before spread has isolation upon receipt and inspected occurred (Figure 8, overleaf). What should be done thoroughly for any possible signs to prevent the disease of downy mildew. If confirmation is Hygiene occurring? required submit plants for laboratory Any self-seeded impatiens plants analysis. Ensure batches of plants in or around glasshouses should Pathogen exclusion are labelled upon receipt and that be destroyed. Wild Impatiens The most effective form of control the labels remain with the crop species growing as weeds near to is to exclude the pathogen from throughout its life on the nursery glasshouses should be checked nursery production. This can only be to provide full traceability back to for downy mildew and destroyed if achieved if sources of propagating the supplier in the event of problems diseased. Where diseased plants are material (both seed and cuttings) with downy mildew. Seed-raised found on nurseries they should be are free of the pathogen, therefore and cutting-raised plants (including carefully placed into a plastic bag or sources of seed/stock material any wild impatiens species a covered bin and removed from the should be selected carefully. Supp- adjacent to nurseries), should be nursery to land-fill. Hard surfaces liers of young plants (both UK and checked regularly for signs of such as benching and standing overseas based) should undertake disease. However, it is important down areas should be regularly precautionary measures to ensure to appreciate that the disease swept, washed with water and then nursery-freedom from downy mildew can have a long latent period, treated with a suitable disinfectant and provide evidence of an effective especially under cooler environ- between crops eg Jet 5 and at the disease control programme. mental conditions. In contrast, end of the season eg Horticide, under ideal conditions for the as these are known to be effective Monitoring for disease pathogen, symptom expression, against the spores of related On delivery of plant material keep spore release and infection of sur- pathogens. Diseased plants and seed and cutting-raised plants rounding plants may occur very associated debris in floral displays separate and segregate cutting quickly in succession and before and gardens should be removed as material from different sources. being noticed. As such, regular soon as possible not left to decay in situ (Figure 9). The material should should be avoided as this can lead Fungicide treatments be discarded via land-fill facilities to the development of conden- Impatiens crops have not previously as the over-wintering spores of the sation on the crop. Drip or ebb and required much in the way of fungicide pathogen can survive in the soil for flood irrigation systems reduce applications but, given the recent several years to potentially re-infect the chances of moisture on plant increased prevalence and severity new plantings in the same location. surfaces thereby lowering of the disease consideration should Soil where poorly performing the risk of infection. Overhead irri- now be given to a routine preventative impatiens plants have been rotovated gation should only be used when the programme for downy mildew or dug-in may be contaminated with leaves are likely to dry quickly. control. Regular early treatments with over-wintering spores and extra care During dispatch, avoid trans- fungicides are advisable from the out- may be needed to protect plants porting wet plants long distances set to minimise any risk from potential from infection the following season. in poorly ventilated lorries as this seed-borne infection and introduction could encourage pathogen sporula- via vegetative cuttings. The use of Cultural practices tion and further plant infection. systemic products with good activity Good ventilation and air movement Don’t let crops of impatiens should be used where possible. in glasshouses should help become starved, especially towards Non-systemic protectant fungicides prevent the build-up of high humidity the point of marketing, as this are also important in a programme of levels and prolonged leaf surface could make the plants more prone sprays to reduce the risk of resistance wetness that favours disease to disease establishment. developing. Fungicides that have been development. Adequate levels of Any impatiens plants remaining used successfully to control downy plant spacing will also help to on nurseries at the end of the season mildew diseases of various crops and minimise humidity levels within the that are not specifically required are permitted on protected and out- crop canopy. Rapid drops in should be removed or destroyed as door ornamentals (at growers own risk) temperature within glasshouses a precautionary sanitation measure. are shown in Table 1.

8 Early symptoms of leaf yellowing and stunting on a crop of impatiens

9 Impatiens plants in a floral display showing signs of severe infection Table 1 Commercially-available fungicides with potential for the control of impatiens downy mildew and permitted for use on ornamental crops

Fungicide group and Active ingredient(s) Contact or systemic Protectant or curative Permitted on crops Approval status and comments Resistance risk products Protected Outdoors

Carbamate

Filex Propamocarb- Systemic Protectant Label approval for use on ornamentals Low to medium hydrochloride Flash

Pan PCH

Previcur N

Propeller

Proplant

Carbamate + phosphonate

Previcur Energy Propamocarb- Systemic Protectant and curative SOLA approval 2667/08 Low to medium hydrochloride + fosetyl-aluminium

Carboxylic acid amide

Paraat Dimethomorph Systemic Protectant and curative Continuation of LTAEU from SOLAs Low to medium 1751/06 and 2777/07

Revus Mandipropamid Systemic Protectant and curative SOLA approval 2867/08 Low to medium

Carboxylic acid amide + dithiocarbamate

Invader Dimethomorph + Contact and systemic Protectant and curative Continuation of LTAEU from potatoes Low to medium mancozeb and various outdoor vegetable crops

Valbon Benthiavalicarb- Contact and systemic Protectant SOLA approval 0240/07 Low to medium isopropyl + mancozeb

Table 1 continued… Table 1 continued…

Fungicide group and Active ingredient(s) Contact or systemic Protectant or curative Permitted on crops Approval status and comments Resistance risk products Protected Outdoors

Cyanocetamide + dithiocarbamate

Curzate M WG Cymoxanil + mancozeb Contact and systemic Protectant Continuation of LTAEU from potatoes Low to medium

Dinitroaniline

Shirlan Fluazinam Contact Protectant Continuation of LTAEU from SOLAs Low 2168/03 and 0597/08 Tizca

Dithiocarbamate

Karamate Dry Flo Mancozeb Contact Protectant Label approval for use on ornamentals Low Newtec

Thianosan DG Thiram Contact Protectant Label approval for use on ornamentals Low

Triptam

Microbial disrupter (biological)

Serenade ASO Bacillus subtilis Contact Protectant SOLA approval 0246/09 Low

Multi-site contact (inorganic)

Croptex Fungex Cupric ammonium Contact Protectant Label approval for use on ornamentals Low carbonate

Phenylamide

Fongarid Gold Metalaxyl-M Systemic Protectant and curative Label approval for use on ornamentals High

Subdue

Phenylamide + dithiocarbamate

Fubol Gold WG Metalaxyl-M + Contact and systemic Protectant and curative Continuation of LTAEU from Medium mancozeb protected lettuce (SOLA 2142/03)

Phenylamide + phthalonitrile

Folio Gold Metalaxyl-M + Contact and systemic Protectant and curative Continuation of LTAEU from various Medium chlorothalonil outdoor vegetable crops

Phosphonate

Aliette 80 WG Fosetyl-aluminium Systemic Protectant and curative Provisional approval Low

Fosal

Route one Fosetyl 80

Standon Fullstop

Phthalonitrile

Bravo 500 Chlorothalonil Contact Protectant Label approval for use on ornamentals Low

Repulse (and equivalent products)

Strobilurin

Amistar Azoxystrobin Systemic Protectant SOLA approval 0443/09 High (translaminar) Beem WG Kresoxim-methyl Label approval for use on ornamentals

Kresoxy 50 WG

Stroby WG

Galileo Picoxystrobin SOLA approval 2855/08

Vivid Pyraclostrobin Protectant and curative SOLA approval 2884/08

Swift SC Trifloxystrobin Protectant SOLA approval 2882/08 Fungicide group and Active ingredient(s) Contact or systemic Protectant or curative Permitted on crops Approval status and comments Resistance risk products Protected Outdoors

Cyanocetamide + dithiocarbamate

Curzate M WG Cymoxanil + mancozeb Contact and systemic Protectant Continuation of LTAEU from potatoes Low to medium

Dinitroaniline

Shirlan Fluazinam Contact Protectant Continuation of LTAEU from SOLAs Low 2168/03 and 0597/08 Tizca

Dithiocarbamate

Karamate Dry Flo Mancozeb Contact Protectant Label approval for use on ornamentals Low Newtec

Thianosan DG Thiram Contact Protectant Label approval for use on ornamentals Low

Triptam

Microbial disrupter (biological)

Serenade ASO Bacillus subtilis Contact Protectant SOLA approval 0246/09 Low

Multi-site contact (inorganic)

Croptex Fungex Cupric ammonium Contact Protectant Label approval for use on ornamentals Low carbonate

Phenylamide

Fongarid Gold Metalaxyl-M Systemic Protectant and curative Label approval for use on ornamentals High

Subdue

Phenylamide + dithiocarbamate

Fubol Gold WG Metalaxyl-M + Contact and systemic Protectant and curative Continuation of LTAEU from Medium mancozeb protected lettuce (SOLA 2142/03)

Phenylamide + phthalonitrile

Folio Gold Metalaxyl-M + Contact and systemic Protectant and curative Continuation of LTAEU from various Medium chlorothalonil outdoor vegetable crops

Phosphonate

Aliette 80 WG Fosetyl-aluminium Systemic Protectant and curative Provisional approval Low

Fosal

Route one Fosetyl 80

Standon Fullstop

Phthalonitrile

Bravo 500 Chlorothalonil Contact Protectant Label approval for use on ornamentals Low

Repulse (and equivalent products)

Strobilurin

Amistar Azoxystrobin Systemic Protectant SOLA approval 0443/09 High (translaminar) Beem WG Kresoxim-methyl Label approval for use on ornamentals

Kresoxy 50 WG

Stroby WG

Galileo Picoxystrobin SOLA approval 2855/08

Vivid Pyraclostrobin Protectant and curative SOLA approval 2884/08

Swift SC Trifloxystrobin Protectant SOLA approval 2882/08

Table 1 Notes – A pot entially wider choice of fungicides are a v ailable for use out doors.

• Alw a ys read the label or specific off -label appro v al. • Use pesticides safely. • Check with suppliers for full details of an y side effects on biological control agents. Fungicide selection Curative activity is not possible to check all impatiens species or cultivars being grown, This new downy mildew disease on The systemic fungicides listed in growers should test treat a small impatiens should be treated in much Table 1 (previous page) and Table 2 number of plants before large batches the same way as downy mildews that are likely to have good to mod- are treated. are managed on other bedding erate curative action against downy plant crops. Early application of a mildew of impatiens grown under systemic fungicide eg metalaxyl-M protection include those containing Resistance management (Subdue) is advisable to protect the following active ingredients: both seed crops from potential Downy mildew pathogens worldwide seed-borne infection and vegetative • fosetyl-aluminium (eg Aliette are recognised as being prone to cutting crops from latent systemic 80 WG; Standon Fullstop etc) resistance development, especially infections. Regular (every 7–14 days) with some of the site-specific use of alternative protectant pro- • metalaxyl-M (eg Subdue, systemic fungicides eg metalaxyl-M. ducts eg dithiocarbamate (Karamate Folio Gold; Fubol Gold WG etc) Therefore, fungicides should be used Dry Flo Newtec) or strobilurin in a planned resistance management (Amistar) will help to minimise any • propamocarb hydrochloride strategy to reduce the chances of resistance risk in the pathogen (eg Filex, Proplant etc). the development of resistance. Some population (see Table 2). Prior to commercial products are formulated dispatch a further application with a protectant, such as mancozeb, of an effective systemic fungicide Crop safety as well as a curative fungicide, as is advisable to give a further a mechanism to reduce the risk of 10–14 days protection from Some of the fungicides listed in Table 1 selecting resistant strains. the disease once the plants leave (previous page) and Table 2 have It is not known if populations the nursery, but potential risks of been tested on a limited basis for their of P. obducens found on impatiens fungicide product deposits on safety to impatiens as part of the have developed resistance to any foliage should be taken into con- HDC funded project PC 230 and few of the fungicides listed in Table 1 sideration at this stage. problems were found. However, as it (previous page) and Table 2. In order

Table 2 Example fungicide spray programme for impatiens crops from propagation stage onwards*

Crop stage Pre or post-sowing/ Post-emergence and Pre-transplanting Post-transplanting post-rooting growing on

Fungicide treatment Apply a high volume Apply protectant Apply a high volume Apply alternate spray/drench of a sprays of a spray/drench of sprays of metalaxyl-M systemic product, for dithiocarbamate a systemic product, + mancozeb example: fungicide for example: (eg Fubol Gold WG) (eg Karamate Dry with strobilurin 1 metalaxyl-M Flo Newtec) at 1 metalaxyl-M (eg Amistar) every (eg Subdue). 7–14 day intervals. (eg Subdue). 7–14 days. Adjust Adjust spray timings spray timings 2 propamocarb depending upon 2 propamocarb depending upon hydrochloride weather conditions, hydrochloride weather conditions. (eg Filex). extending the interval (eg Filex). Ensure final spray if the weather is prior to dispatch 3 fosetyl-aluminium not conducive to 3 fosetyl-aluminium to maintain protection (eg Aliette 80 WG). downy mildew. (eg Aliette 80 WG). from downy mildew.

4 A mixture of 2. + 3. 4 A mixture of 2. + 3. (eg Previcur (eg Previcur Energy). Energy).

Ensure a different product is used to that at sowing/ rooting.

*Note this spray programme is for example purposes only, the listed products have not been tested on all the available impatiens species and cultivars, so small numbers of plants should be test treated first before wider scale applications are made. to minimise the risk of selecting against fungi related to downy mildew are being gradually phased out resistant strains of the pathogen, eg Pythium and Phytophthora and and replaced (in some cases) it is recommended that: therefore control could also be with specific off-label approvals expected. As the pathogen target is (SOLAs). A number of active • Fungicide products from dif- not a statutory condition of use, substances have already been ferent active ingredient groups such products can be used on evaluated and SOLAs issued where are alternated. impatiens at growers’ own risk, but possible. For these active sub- it is important to emphasise that crop stances the LTAEU cease to apply • Strobilurins should not com- safety on a range of cultivars should on 1 June 2009. For all other active prise more than 50% of be assured first. substances the LTAEU continue until the total applications of fungicide Specific off-label approvals: such time that the product comes per season. Some fungicides may be used on up for re-registration. For more ornamental crops, including impatiens, information on the changes to the • Label recommendations should be via specific off-label approvals LTAEU see: www.pesticides.gov. followed carefully, especially advice (SOLAs). It is important to recognise uk/approvals.asp?id=2634. on application rates. that these uses are not supported It is also important to remember by manufacturers and therefore are, that the location of the crop to be • Fungicides should not be relied in all cases, at the growers’ own risk. treated is relevant in relation to on alone for disease control; Crop safety must therefore be checked pesticide availability. For crops monitoring, cultural and hygiene in advance especially when using the grown under protection there is a measures detailed in this factsheet product for the first time on a specific more limited range of products should also be followed. ornamental crop or new cultivar. that can be used due to the require- Use by extrapolation: For ments for operator and worker Permitted products many years growers of ornamental safety. Crops grown under protection On-label approvals: There are no crops have been able to use also tend to be more sensitive to fungicides with a specific on-label many pesticides approved on other pesticide application and the risk approval for the control of impatiens arable and horticultural crops of phytotoxicity can be higher. It is downy mildew. However, several at their own risk via the Long Term important therefore to test treat a fungicides are available that do have Arrangements for Extension few plants of different cultivars approved uses on ornamentals. of Use (LTAEU). Due to changes prior to large-scale use of a parti- Some of these have known activity in EU pesticide legislation the LTAEU cular product on the nursery.

Further information Good horticultural practice for the prevention and control HDC funded project PC 230 of impatiens downy mildew ‘Detection and control of downy (Plasmopara obducens). mildews on ornamentals’.

Acknowledgements updated in 2009 with assistance permission of Martin McPherson, from various members of the British STC, Ryan Goodwin and Connall This Factsheet was originally Protected Ornamentals Association, Oosterbroek of the South African produced (in 2004) by David Jones, especially the Technical Committee Bedding Plant Growers Association CSL and Tim O’Neill, ADAS in Chairman Mike Smith. (SABPGA), Ball Horticultural Company consultation with various industry Photographs of symptoms are and the Food and Environment representatives. It has since been reproduced here with the kind Research Agency (Fera). Additional information:

Whilst publications issued under the auspices © 2009 of the HDC are prepared from the best Agriculture and Horticulture Development Board. available information, neither the authors or No part of this publication may be reproduced in the HDC can accept any responsibility for any form or by any means without prior permis- inaccuracy or liability for loss, damage or injury sion of the Horticultural Development Company. from the application of any concept or April 2009 procedure discussed. Design and production: HDR Visual Communication