Project Title:Evaluation of chemical disinfectants for treating modular trays against club root
Report:Interim Report April 1998
Project No:FV 178 (ADAS XHAHE)
Project Leader:Dr J M Ll Davies
ADAS Terrington
Terrington St Clement
King's Lynn
Norfolk PE34 4PW
Location:ADAS Terrington
Project Co-ordinator:Mr R Bingham
Date Commenced:December 1995
Date to be Completed:May 1998
Keywords:Cabbage, GPG modular trays, disinfectant dips, steam heat jet wash, inoculum and club root ( Plasmodiophora brassicae).
Whilst reports issued under the auspices of the HDC are prepared from the best available information neither the authors or the HDC can accept any responsibility for inaccuracy or liability for loss, damage or injury from the application of any concept or procedure discussed.
1998 Horticultural Development Council
No part of this publication may be produced in any form or by any means without prior permission
from the HDC.
CONTENTS
Page No
PRACTICAL SECTION FOR GROWERS
Objectives and background3
Summary of results3
Action points for growers4
EXPERIMENTAL SECTION
Introduction5
Materials and methods5
Results7
Discussion9
Acknowledgements9
Appendix 10
PRACTICAL SECTION FOR GROWERS
Objectives and background
Club root disease, caused by the fungus Plasmodiophora brassicae, remains a problem affecting all members of the brassicae family. Currently, there is no fungicide commercially available in the UK for the control of club root, although farmers can control the disease to some degree using husbandry techniques in the field. One particular problem is the contamination of trays with club root in the field which, without treatment, may result in infection of subsequent module plants grown in them. This may lead to the introduction of club root into ‘clean’ fields.
The aim of the current work is to evaluate the efficacy of various disinfectant treatments compared with steam heat and power washing (‘jet wash’) treatments for the control of club root in brassicae crops raised in modular trays. The disinfectant treatments chosen were the most effective following preliminary disinfectant experiments at HRI Wellesbourne.
Summary of results
The effects of disinfectant treatments were evaluated on club root disease of cabbage grown in GPG 345 modular trays. The disinfectants Jet 5, Iodel and sodium hypochlorite and jet wash and steam heat treatments, all for 1 minute or 15 minutes, were evaluated on club root inoculated modular trays. They were compared with untreated inoculated trays. Clean untreated trays were also included as controls.
High levels of club root developed (98.9% plants affected) in the untreated inoculated trays. This was reduced to less than 10% by seven of the ten treatments. Iodel, Jet 5, sodium hypochlorite and steam heat all gave reductions at 1 minute treatment duration. The results with sodium hypochlorite appeared unusual in that the 15 minute treatment was less effective than the 1 minute treatment. The 15 minute jet wash treatment was effective, but the 1 minute treatment was ineffective. None of the treatments reduced the incidence of club root to zero. Occurrence of club root in uninoculated trays (4 - 38% plants affected) indicated a source of club root additional to that on trays. It is suggested that the compost was the most likely source although cross infection during plant production cannot be excluded.
Action points for growers
Practical and financial benefits from study
Earlier laboratory tests showed that Iodel, Jet 5 and sodium hypochlorite can be very effective in killing P. brassicae. The result of this trial showed that all of the treatments gave good control of club root on GPG 345 trays severely contaminated with P. brassicae at one 1 minute treatment except for jet wash.
Further work is needed to confirm these results as the degree of disinfectant efficacy in this practical test was not established owing to a low level of infection which occurred in the uninoculated trays (where infection should have been nil).
EXPERIMENTAL SECTION
Introduction
Club root is becoming an increasing problem in the propagation stage of the brassicae crop. Three disinfectant treatments produced promising results in laboratory experiments at HRI Wellesbourne and these were evaluated alongside jet wash and steam sterilising treatments, compared with an untreated inoculated control. An untreated uninoculated control was also included in the experiment.
Materials and methods
Site
The experiment was sited at ADAS Terrington, Terrington St Clement, King’s Lynn.
Design
The experiment was arranged as a two way factorial randomised block design plus three untreated controls. There were ten treatments and four replicates. Each plot consisted of one GPG 345 modular tray.
Husbandry
Cultivar:Cabbage, cv. Golden acre
Compost:Proprietary Ericaceous
Sowing date: 28 August 1997
Fungicide:Tolclofos-methyl (as Basilex) 10 September 1997 to control Rhizoctonia solani
Insecticide:Cypermethrin (as Cyperkill) 3 October 1997 to control caterpillars
Final assessment date: 12 November 1997
The experiment was located in a polytunnel at ADAS Terrington. Treatments were carried out immediately prior to sowing. The GPG 345 modular trays were arranged in the polytunnel on wooden laths over black polythene. Adjacent trays were touching. The bases of the trays were in contact with wooden laths but not with the black polythene floor covering. The plants were raised as per standard plant propagation practise being regularly watered and fed as necessary.
Treatments
1.Untreated plus the centre 100 cells inoculated with a slurry suspension of club root spores mixed with soil (‘inoculated’)
2.As 1) plus a tray dip in Jet 5 at 8% product for 15 minutes
3.As 1) plus a tray dip in Jet 5 at 8% product for 1 minute
4.As 1) plus a tray dip in Iodel FD at 6% product for 15 minutes
5.As 1) plus a tray dip in Iodel FD at 6% product for 1 minute
6.As 1) plus a tray dip in sodium hypochlorite at 20 % product (12% chlorine w/v B.D.H.) for 15 minutes
7.As 1) plus a tray dip in sodium hypochlorite at 20 % product (12% chlorine w/v B.D.H.) for 1 minute
8.As 1) plus a Genri 4107 Classic ‘jet wash’ (approx. 60C) for 15 minutes
9.As 1) plus a Gerni 4107 Classic ‘jet wash’ (approx. 60C) for 1 minute
10.As 1) plus steam heat for 15 minutes (mean temp. of 98C)
11.As 1) plus steam heat for 1 minutes (mean temp. of 97C)
Plus an untreated clean modular tray, as a control, but not included in the analysis.
Plus an untreated infected modular tray, as a control, having previously grown an infected crop with club root in propagation, but not included in the analysis.
Preparation of club root plus soil infested trays (Treatment 1)
Inoculum of P. brassicae was prepared by macerating two large club root galled broccoli roots in 0.5l of distilled water in a Kenwood blender, then mixed with 250g of low pH soil (pH 4.5) into a slurry and applied to the central 100 cells of each tray to excess (approximately 250 ml per tray). The trays were kept at 7 C for four days to ensure a slow drying of inoculum.
Assessments
At 100% emergence in the untreated trays, plant counts were recorded in the centre 100 plants in all plots. This assessment was repeated after one week. There was no phytotoxicity present. The experiment was monitored for the presence of club root in the untreated trays and first incidence of the disease was noted. It continued to be monitored and once a high proportion of the plants showed symptoms, in some of the treated trays as well as the untreated, the final disease assessment was made. Each of the central 100 module plants was removed and examined for root galling characteristic of club root. A sample of roots showing galling was examined microscopically to confirm the disease.
Statistical analysis
Data were subjected to analysis of variance. Standard errors of differences between means (SED) are quoted when probability P is<0.05. NS = not significant, P>0.05.
Results
Establishment and plant vigour
Table 1. Effect of tray treatment on plant emergence.
Disinfectant / % plants emerged 9 September 1997Treatment time
1 minute / 15 minutes
Untreated inoculated / 77.5 / - / -
Jet 5 / - / 72.0 / 84.9
Iodel / - / 87.5 / 74.2
Sodium hypochlorite / - / 77.0 / 71.2
Jet Wash / - / 81.7 / 83.7
Steam heat / - / 83.5 / 82.0
Significance / NS
By 12 days after sowing, there was over 70% seedling establishment in all trays, with no significant differences between treatments. No differences in plant vigour were observed.
Club root incidence
The experiment was monitored for the presence of club root and the disease was first recorded on 15 October in the untreated trays. The trays were inspected again on 29 October when club root was found in some of the treated trays as well as the untreated. A destructive assessment of all plots was made on 12 November when every plant from the centre 100 cells was inspected and presence or absence of club root was recorded.
High numbers of club root affected plants were recorded in the untreated, inoculated treatment and also from the inoculated ‘jet wash’ 1 minute treatment and, inexplicably, sodium hypochorite for 15 minutes. Lower numbers of club root affected plants were recorded in all the other treatments. The fact that none of the treatments reduced the incidence of club root to zero may be explained by the low level of club root which appeared to originate from a source other than the trays.
Table 2. Effect of tray disinfection on the incidence of club root in modular trays of cabbage plants -12-13 November 1997
Disinfectant / % plants affected with club rootTreatment time
1 minute / 15 minutes
Untreated inoculated / 98.9 / - / -
Jet 5 / - / 14.6 / 9.0
Iodel / - / 5.6 / 7.1
Sodium hypochlorite / - / 5.8 / 31.1
Jet Wash / - / 89.7 / 4.3
Steam heat / - / 4.1 / 8.4
Significance / ***
SED / 8.01
Five trays, one from each of the following treatments, (see appendix I) had no club root affected plants. All plants in these trays were assessed in addition to the central 100 plants:
Iodel FD for 1 minute
Sodium hypochlorite for 1 minute
‘jet wash’ for 15 minutes’
Steam heat for 15 minutes.
Untreated ‘infected’ tray
All other trays had club root affected plants ranging from 1 to 100%
Discussion
Although the tray inoculation technique proved very successful and high numbers of club root affected plants (98.9%) were recorded in all the inoculated controls, unfortunately, club root also developed (19.9% affected plants) in the untreated uninoculated ‘clean’ trays and in the trays which had previously grown an infected crop (8% affected plants). These results were not as expected and it was therefore thought that an additional, external source of club root, was present throughout the experiment. Affected compost was considered as the most likely source. Due to the need for a low pH to give the optimum conditions for club root infection and development, the compost used was one produced for growing ericaceous plants. It would not normally be used for propagating brassicae. Further tests on this compost need to be carried out. Alternatively, it is possible that uninoculated trays inadvertently became contaminated during plant production, perhaps by watersplash or water films running between inoculated and uninoculated trays, although measures were taken to minimise cross infection between trays.
ACKNOWLEDGEMENTS
Financial support from the HDC is gratefully acknowledged . Thanks are due to Dr T M O’Neill of ADAS Arthur Rickwood and Dr J Walsh and colleagues at HRI Wellesbourne.
Appendix 1. Effect of tray disinfection on the incidence of club root in modular trays of cabbage plants -12-13 November 1997.
Treatment / % plants infected with club rootBlock 1 / Block 2 / Block 3 / Block 4 / Mean
1.Untreated, inoculated / 98.8 / 100.0 / 98.5 / 98.4 / 98.9
2.As 1, plus Jet 5 for 15 minutes. / 2.6 / 16.5 / 9.2 / 7.5 / 8.9
3.As 1, plus Jet 5 for 1 minute. / 5.6 / 31.0 / 15.6 / 6.3 / 14.6
4.As 1, plus Iodel FD for 15 minutes. / 5.7 / 14.5 / 3.7 / 4.5 / 7.1
5.As 1, plus Iodel FD for 1 minute. / 5.3 / 0.0 / 16.0 / 1.1 / 5.6
6.As 1, plus sodium hypochlorite for 15 minutes. / 11.4 / 75.0 / 11.7 / 26.2 / 31.1
7.As 1, plus sodium hypochlorite for 1 minute. / 8.5 / 0.0 / 5.6 / 9.1 / 5.8
8.As 1, plus ‘jet wash’ for 15 minutes. / 1.5 / 0.0 / 14.6 / 1.1 / 4.3
9.As 1, plus ‘jet wash’ for 1 minute. / 72.8 / 90.8 / 95.2 / 100.0 / 89.7
10.As 3 plus steam heat for 15 minutes. / 12.5 / 0.0 / 8.8 / 12.3 / 8.4
11.As 3 plus steam heat for 1 minute. / 9.2 / 3.8 / 2.3 / 1.1 / 4.1
Untreated, clean trays. / 3.8 / 37.9 / 27.0 / 11.1 / 19.9
Untreated ‘infected’ trays / 2.5 / 22,6 / 0.0 / 6.9 / 8.0
1998 Horticultural Development Council
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