Border Carnations. Final Trials Report. Trials Office The Royal Horticultural Society Garden, Wisley, Woking, Surrey, GU23 6QB

Transcription

1 Border Carnations Final Trials Report Trials Office The Royal Horticultural Society Garden, Wisley, Woking, Surrey, GU23 6QB

2 RHS Trial of Border Carnations Objectives The objectives of the trial were: To evaluate the best garden cultivars and propose the very best for the Award of Garden Merit. To demonstrate the various garden uses of the genus Dianthus. Judging The Border Carnation and Pinks Trials Assessment Panel assessed the trial on 29 th June and 20 th July in 2011 for the AGM. They used a scoring system out of 25 points, based on the following criteria: Plant growth (max 5 points) Floriferousness (max 5 points) Flower size/form/colour (max 5 points) Colour (max 5 points) Scent (max 5 points) Trial assessment on 29 th June 2011 The Trials Assessment Panel also visited the trial on 31 st August 2011 to inspect and score the late season foliage. Although a few plants in the trials of Border Carnations and Garden Pinks died, the Dianthus trials generally survived the harsh, wet winter of well. All of the Dianthus trials performed very well in the summer of The Border Carnations were performing well when the trials were assessed on 7 th March 2012, so members were surprised to see that the trials of Garden Pinks and Dwarf and Miniature Pinks looked so poor. At the next meeting, on 24 th April 2012, the trials of Garden Pinks and Dwarf and Miniature Pinks were suffering badly from disease, and looked so poor that those two trials were reluctantly terminated early. Although some of the Border Carnations had died and a few had some dead foliage, most of them were looking good so it was decided that this trial should be continued. Final Report for Trial No Border Carnations

3 Left: Border Carnations (left hand row) on 26 th April Below: Dianthus trials on 26 th April The Miniature and Dwarf Pinks (back row) as well as the Garden Pinks (middle row) seemed to be in poorer health than the Border Carnations (front row). On 13 th June 2012 the Border Carnations were showing significant symptoms of disease and the decision was taken to terminate the trial early. Entries There were 17 entries in this trial, of which 3 already hold the AGM. Entries were submitted as plants raised from cuttings or layers. Cultivation The site was prepared and entries were planted in autumn 2010 in blocks of four plants per entry, at 45cm apart. When the soil was tested in March 2011, the ph of this site was 7.5. This was considered a little high but the use of sulphate based fertilisers should help reduce this, therefore no other action was required. The following top dressings were applied on 13 th April 2011 after soil analysis: Ammonium sulphate for nitrogen at a rate of 48g/m 2 Sulphate of potash for potassium at 130g/m 2 Superphosphate for phosphorus at 180g/m 2 Kieserite for magnesium at 80g/m 2 The plants were watered only when required in very hot, dry weather. After the entries finished flowering, they were deadheaded. Pest and Disease The plants were sprayed against aphids as necessary. They were also sprayed with the fungicide Systhane (active ingredient myclobutanil) on 1 st September 2011 for mildew and rust. Final Report for Trial No Border Carnations

4 As a number of plants in the pinks trials had previously been tested by the Pathology department, individual plants in the trial of Border Carnations were not tested. The following pathogens were found in the trials of Miniature and Dwarf Pinks and Garden Pinks which were alongside the Border Carnations: Phytophthora cactorum - stem rot Pythium species (including Pythium intermedium and Pythium ultimum var. ultimum) - root / stem rot Fusarium species wilt / general rot It was thought that these pathogens had spread across the site and also affected the Border Carnations. Unfortunately no treatment is available for these diseases, so the affected plants were removed and destroyed. The following is part of a report compiled by the Pathology Department on all 3 of the Dianthus trials (Dwarf and Miniature Pinks, Garden Pinks, and Border Carnations): Both Pythium species identified are known pathogens. Pythium ultimum var. ultimum is one of the most common Pythium species in soil. It can become a severe parasite on many plants and causes damping-off and foot rots. P. intermedium was originally isolated from dead plant material and is a typical soil inhabitant. It is recorded as pathogenic on some plants. Phytophthora cactorum is also a ubiquitous pathogen and has been recorded in the Wild Garden at Wisley previously. Both Pythium sp. and Phytophthora sp. cause blackening and rotting of the roots and stems. Die-back and eventually death of the plants often follows. There are several species of Fusarium that infect Dianthus including Fusarium oxysporum f.sp. dianthi which is specific to Dianthus. Fusarium oxysporum f.sp. dianthi causes abnormal growth and stunting of the young shoots. The leaves become yellowed and withering gradually follows. These symptoms slowly spread upwards and often on one side of the plant. Following an initial one-sided development in the main stem, the entire plant eventually wilts. The stems become softened and easily crushed and before the death of the plant brown striping or zonation is obvious in the stem, with diseased tissue easily distinguished from healthy tissue. In hot and humid environmental conditions, white mycelium is present including many macroconidia and sometimes pink to orange coloured sporodochia. There are two main sources of inoculum, soil and infected cuttings (possibly from symptomless stock). In the rooting substrate, the fungus sporulates and surrounding cuttings are then infected. Cuttings may carry the fungus only in the substrate, or possibly in the roots as well. Depending on the inoculum level and temperature the incubation period can vary between one month and several months. The optimum temperature is o C and in the field a latent period of several months is noted with decreasing winter temperatures. The fungus survives in soil (probably as chlamydospores) for at least 14 years and to a depth of 80cm. Fusarium avenaceum and F. culmorum are also known to infect Dianthus. To my knowledge these species of Fusarium do not cause discolouration of the vascular tissue. Some of the plants showed brown/red staining inside the stems whereas others did not, yet the presence of Fusarium spp. was confirmed. I suspect that more than one species of Fusarium was infecting the plants in the trial. To further complicate matters I noted that Pythium spp. also caused pink/red staining of the vascular tissue. Final Report for Trial No Border Carnations

5 As the plants were either dead or almost dead when I received them I was unable to look for the important characteristic of one-sided wilting which is characteristic of Fusarium oxysporum f.sp. dianthi infection. If required I am happy to look at further samples and culture from it so that a definite answer can be given. Summary and recommendations Disease occurs when the level of inoculum reaches a threshold and the conditions such as water and temperature are optimum for pathogen development and of course a susceptible host is present. Anything that encourages optimal conditions for the pathogen should of course be avoided if possible. The particularly cold temperatures in December 2010 will have helped to reduce pathogen inoculum levels. Most of the Dianthus performed well throughout 2011 but the mild conditions late into autumn/winter 2011 could have allowed inoculum levels to build up. This will then have caused the dramatic decline of the plants in late December 2011/ early Jan I haven t come across any negative information regarding landscape fabrics but they do tend to allow an even soil temperature. This could mean that the soil may not freeze for long which would allow inoculum levels to accumulate. The mild temperatures in late 2011 would have exacerbated the problem further. Pythium sp., Phytophthora sp. and Fusarium sp. are all soil-borne. They are all difficult to treat and hard to remove from the soil once present. You should therefore site future Dianthus trials in a new area which has not grown Dianthus previously for at least 14 years. If possible take cuttings only from healthy greenhouse-grown plants and avoid wounding plants during weeding and cultivation. Irrigation systems and fabric should be fully sterilised or replaced to ensure that crosscontamination does not occur. Drainage should certainly be improved if necessary as wet conditions are necessary for Phytophthora sp. and Pythium sp. infections. Soil water flow allows transmission of Fusarium oxysporum f.sp. dianthi locally as well as splash droplets. Avoidance of compaction around the plants will improve drainage and therefore reduce disease development. Plants Receiving AGMs During Trial There were no recommendations for the Award of Garden Merit following assessment of this trial. Final Report for Trial No Border Carnations

6 Trial Index and Senders Details Number Cultivar Award Sender 1 'Anne S. Moore' J Linnell 2 'Lord Nuffield' J Linnell 3 'Pink Nuffield' J Linnell 4 'White Champagne' J Linnell 5 'Chesswood Lidgett Yellow' P Booker 6 'Chesswood Wycoller' P Booker 7 'Chesswood Margaret Alison' AGM (H4) 2009 P Booker 8 'Chesswood Phil Dalby' P Booker 9 'Grace's Scarlet Clove' P Booker 10 'Emjay' P Booker 11 'Hazel Ruth' AGM (H4) 1994 P Booker 12 'Spinfield Joy' AGM (H4) 2004 P Booker 13 'Mike Briggs' P Booker 14 'Braeside Crimson' P Booker 15 Seedling B9/120 P Booker 16 Seedling B9/129 P Booker 17 Seedling B9/131 P Booker Sender Details Mr J. Linnell, Linfield, Duncote, Towcester, Northants, NN12 8AH Mr P.J. Booker, 15 Kings Road, Barnetby Le Wold, North Lincolnshire, DN38 6HF Source: Horticultural Trials and Relations, RHS Garden Wisley, Woking, Surrey GU23 6QB trials@rhs.org.uk More information about RHS Trials and other colour illustrated reports can be found on the RHS Website: Final Report for Trial No Border Carnations