Fight against Blight. Independent Blight Fungicide Trials Summary years 2003 to Report prepared by: Nick Bradshaw ADAS UK Ltd Ruairidh Bain SAC

Transcription

1 Fight against Blight Independent Blight Fungicide Trials Summary years 2003 to 2005 Report prepared by: Nick Bradshaw ADAS UK Ltd Ruairidh Bain SAC May 2006

2 Contents Introduction... 3 Methodology... 4 Early season fungicides (Protocol 1)... 5 Main season fungicide evaluation (Protocol 2)... 5 Results summary... 7 Early season fungicides (Protocol 1)... 7 Main season fungicide evaluation (Protocol 2) Discussion Early season fungicides (Protocol 1) Main season fungicide evaluation (Protocol 2) Conclusions Early season fungicides (Protocol 1) Main season fungicide evaluation (Protocol 2) Where do we go from here? British Potato Council

3 Introduction Fungicides will continue to be used routinely for blight control for the foreseeable future not least because of the enormous impact the disease can have on yield, tuber quality and storage potential. Whilst forecasting systems do have a place in blight control strategies, they are mostly used as a guide to spray frequency rather than as providing field specific advice. Maintaining short spray intervals in high-risk conditions is essential and in these situations the interval between fungicide applications can be just as important as product choice. The 2005 UK Pesticide Guide lists 15 different fungicide actives currently approved for blight control, down from 20 in These are available in 20 formulations or coformulations and are sold as approximately 61 proprietary blight fungicides. Blight fungicides cost from 5 to 25/ha/application and because of the nil tolerance for tuber blight set by retailers in the UK, fungicide use to control blight is a significant production cost. A number of new fungicides were approved for use in the UK shortly before and during the period of the project, i.e to These were C50, Consento, Electis, Epok, Option, Sonata, Ranman TP and Tanos. As a result of the reevaluation of registration data required for Annex 1 listing under EU legislation (Council Directive 91/414 EEC), the approval for a number of older blight fungicides has been revoked and these are no longer available to UK potato growers. This may be due to commercial considerations and the costs of providing new data packages, or the safety profile does not meet modern standards. The revocation of the fentin (tin) based products in particular was considered by some to be a major loss to the industry because they had an important role in the control of tuber blight. Independently generated data on product performance is extremely valuable and is of immediate value to GB potato growers. The British Potato Council is ideally placed to support such a programme of work to investigate the effectiveness and technical attributes of the new and some existing blight fungicides. This Grower Report describes what has been done in the three years of the current fungicide evaluation project in support of the ongoing Fight against Blight campaign. However, it is important to note that blight epidemics rarely behave consistently in trials because of the overriding effects of local weather conditions that vary greatly between locations and between seasons. Whilst the results should be of interest to the industry, such a relatively small data set should always be treated with some caution. In these trials the number of applications of some fungicide products sometimes contravened the label recommendation. This was planned to allow scientifically valid comparisons between different fungicide chemistry. Neither the BPC, ADAS nor SAC recommend the use of fungicides in such a way that contravenes label recommendations. The trials in this summary also included fungicide programmes devised by the fungicide manufacturers. The results of these programmes are not included in this report. For the full interim reports on this project, including all results, treatment dates and blight risk periods, please see or contact BPC publications ( ). British Potato Council

4 Methodology The BPC commissioned ADAS & SAC to carry out field trials in 2003, 2004 & 2005, located at ADAS Rosemaund and SAC Auchincruive. It should be noted at the outset that only two trials were carried out at each site in each year. To maximise the chances of a successful disease challenge, the unsprayed guard areas surrounding the trials were inoculated with the blight pathogen and its development was encouraged by overhead mist irrigation (see Fig. 1). The P. infestans isolates used were all recent isolates from the UK. Fig 1. Overhead misting in operation at ADAS Rosemaund At Rosemaund, the spray treatments were applied using an Oxford Precision Sprayer in 250 litres of water per hectare operating at 2.5 Bar through 110 flat fan nozzles. The spray booms were mounted on a Growmobile mechanised sprayer which allowed up to eight different treatments to be applied in one pass whilst maintaining a constant forward speed. (Fig. 2) Fig 2. Spray applications at ADAS Rosemaund (NB: When this sprayer is in use, operators wear full PPE) British Potato Council

5 At Auchincruive fungicides were applied in 200 litres of water per ha using a tractormounted, modified AZO compressed air sprayer operating at 3 Bar, to give a medium/fine spray quality. The nozzles used were Lurmark F All trials were carried out on small plots of the variety King Edward. Blight fungicide programmes invariably contain several different products, not only because of cost but also because the properties of different fungicide active ingredients make them more suited to certain crop growth stages. Some fungicides also have restrictions on their use as part of a resistance management strategy. To make comparisons of all possible combinations would be prohibitively expensive therefore the work reported here concentrated on two protocols: Early season fungicides (Protocol 1) This was an evaluation of fungicides applied very early in the development of the crop, i.e. from 100% emergence. This is before the traditional start of the spray programmes which is usually either at rosette stage or when haulm growth is meeting along the rows. A frequently asked question is what fungicide should be used to start the programme? There was little available information on product comparisons at this early growth stage, despite many products being targeted at this growth stage. Two new fungicides, Sonata and Tanos, were compared with three established fungicides often used at the start of programmes, Dithane NT, Invader and Shirlan (Fig. 3). Untreated Dithane for 4 sprays From 100% emergence Shirlan for 4 sprays From 100% emergence Tanos for 4 sprays From 100% emergence Sonata for 4 sprays From 100% emergence Mancozeb through to trial end Invader for 4 sprays From 100% emergence In 2005 three applications of the different fungicides were made, starting at 100% emergence. Fig 3. Products applied early in the spray programme and their effect on blight control (Protocol 1) Main season fungicide evaluation (Protocol 2) The performance of fungicides applied from the end of rapid canopy growth was compared because most of the new fungicides are recommended for this growth phase of the crop. In addition, this would allow their effectiveness in controlling tuber blight to be evaluated. The new fungicides Electis, Ranman TP and Sonata, were compared with the established products, Curzate M, Invader and Shirlan. These fungicides were applied from the fourth spray in the programme until haulm British Potato Council

6 desiccation. Label restrictions on the number of permitted applications were overridden in the trials to allow a robust and scientific evaluation of their efficacy against foliar and tuber blight (Fig. 4). Shirlan until desiccation Curzate until desiccation Tattoo from haulm meeting along the rows, for 3 sprays Invader until desiccation Ranman TP until desiccation Electis until desiccation Sonata until desiccation Fig 4. Products applied in the main season and their control of blight (Protocol 2) British Potato Council

7 Results summary Early season fungicides (Protocol 1) In 2003 and 2004 and at both sites there was a clear benefit from applying fungicides at an early stage of crop development (Fig. 5). This was the case in both severe and less severe blight epidemics. There was no untreated in the 2005 trials therefore these results are not included. 100 % Untreated Mean of Fungicides 20 0 Rosemaund 13 Aug 2003 Auchincruive 22 Sept 2003 Rosemaund 12 Aug 2004 Auchincruive 1 Sept 2004 Fig. 5 Early fungicide treatment and % foliar blight (Protocol 1) The benefit of early fungicide use remained evident for several weeks at Rosemaund in 2003 and treatment effects were recorded well after they had been applied (Fig. 6). Even where disease pressure was low during the period that the fungicides were applied but high afterwards, there was a clear benefit from the early use of fungicides for the control of foliar blight. This suggests that fungicides were suppressing blight inoculum well before visible symptoms became evident. Differences in fungicide performance were recorded in the Rosemaund trial in 2003 (Fig. 6) and to a much lesser extent in a much more severe epidemic at Auchincruive in 2004 (Fig. 7). British Potato Council

8 Foliar blight progress Rosemaund 2003 Foliar blight progress Auchincruive % foliar blight Dithane DG NT* Dithane DG NT Shirlan Tanos Sonata Invader % foliar blight Dithane DG NT* Dithane DG NT Shirlan Tanos Sonata Invader May 8 Jun 18 Jun 28 Jun 8 Jul 18 Jul 28 Jul 7 Aug 17 Aug 0 14 Jun 4 Jul 24 Jul 13 Aug 2 Sep 22 Sep T r e a t m e n t s D i t h a n e o v e r s p r a y s T r e a t m e n t s D i t h a n e o v e r s p r a y s Fig 6. Early application of potato blight fungicides (Protocol 1) Rosemaund 2003 Fig 7. Early application of potato blight fungicides (Protocol 1) Auchincruive 2004 British Potato Council

9 In four of the six trials the control of foliar blight was the same for the different fungicides in spite of the presence of a large number of limited inoculum sources close to the trial plots. For two of the trials there were significant differences between products in foliar blight control, i.e. at Rosemaund in 2003 and Auchincruive in 2004 (Figs. 6 & 7 respectively). In these two trials the epidemics were severe. At Rosemaund in 2003 the occurrence of a Smith Period on 7 to 9 July coupled with very intense misting from 12 to 23 July stimulated blight activity at the site and tested the fungicides fully in spite of short spray intervals (Table 1). At Auchincruive in 2004 differences between treatments were small but some were significant. This was because in spite of an average spray interval of nearly 10 days, the severe blight risk conditions occurred 2 weeks after the final spray. Table 1 The timing of the presence of inoculum and blight high-risk periods in relation to the application of the early sprays Trial Dates of Early sprays with interval (days) Date of first Inoculation Smith Periods within 7 days of the end of the early sprays Smith Periods 7 days or more after the end of the early sprays Date when foliar blight reached 1% in untreated Rose d June 20 June (9) 26 June (6) 3 July (7) Average June 7-9 July July 7-8 August 10 to 17 July Auch July 15 July (7) 26 July (11) 3 August (8) Average July July July 6-7 August 11 to 19 August Rose d June 25 June (6) 5 July (10) 12 July (7) Average June 4-5 August 9-10 August 27 July to 4 August Auch June 28 June (12) 6 July (8) 15 July (9) Average June 26 July to mid- Sept. (9 Periods) 9 to 16 August Rose d June 18 June (8) 26 June (8) Average June June July 9-11 Sept. No untreated but 8 to 15 August in adjacent trials Auch June 5 July (7) 12 July (7) Average June None None No untreated but 8 to 17 August in adjacent trials British Potato Council

10 In three of the trials tuber blight control was assessed. Tuber blight incidences were surprisingly high for some fungicide treatments considering the small amount of foliar blight recorded (Fig. 8 and Table 2). In 2003 and 2005, in which foliar blight levels were low and similar for treatments, there were significant differences in tuber blight incidence between treatments whereas in 2004 differences were not significant. Under the limited epidemic conditions of 2003 at Auchincruive a significant reduction in tuber blight infection was recorded following the use of Shirlan or Sonata. The period of protection between fungicide application and tuber infection was c. 60 days. This result was not repeated in the severe epidemic of 2004 in which tuber protection was overwhelmed by very high numbers of zoospores (data not presented). In 2005 the foliar blight epidemic was limited, as in 2003, but the early applications of Shirlan or Sonata did not result in significantly better control of tuber blight. Foliar blight severity in the 2003 and 2005 trials was probably much nearer to the typical amounts of disease found in blighted commercial crops. In 2005, two applications of Epok (metalaxyl-m plus fluazinam) resulted in an incidence of tuber blight significantly lower than all other treatments except one. This result was repeated with the Fubol Gold (metalaxyl-m plus mancozeb) treatment, sponsored by Syngenta, for which the incidence of tuber blight was 0.2%. In this experiment, the effect of the phenylamide products was long lasting. The second and final applications of Epok and Fubol Gold were made on 8 July. No visible symptoms of foliar blight were observed until 6 weeks later on 19 August. The development of the tuber blight epidemic was monitored in another trial in the same field. No tuber blight was detected until 21 September, i.e. c. 11 weeks after the final application of metalaxyl-based products. Although there were no significant differences in foliar blight between fungicides, Epok and Fubol Gold gave the best control of foliar blight. The effectiveness of the two phenylamide-based products was achieved in a trial inoculated with both sensitive and insensitive P. infestans. In fact the insensitive isolate established well after inoculation on 29 June whereas the sensitive isolate did not and needed to be re-inoculated on 15 July. The insensitive isolate had been subcultured on metalaxyl to select for insensitive sporangia. British Potato Council

11 Table 2. Foliar blight and pre-storage tuber blight incidence Auchincruive 2003 (Protocol 1) First 4 treatments % foliar blight* (22 Sept) % tubers infected (by weight) Untreated Dithane NT Shirlan Tanos Sonata Invader F pr LSD (5%) NS 3.14 * Untreated programme excluded from the analysis NS=Not significant (P>0.05) % Untreated Dithane NT Shirlan Tanos Sonata Invader 0 % Foliar Blight (22 Sep) % Tuber Blight Fig 8. Foliar blight and pre-storage tuber blight incidence Auchincruive 2003 (Protocol 1) British Potato Council

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13 Table 3. Foliar blight and pre-storage tuber blight incidence Auchincruive 2005 (Protocol 1) First 3 treatments % foliar blight (15 Sept) % tubers infected (by weight) Dithane NT Epok (2 sprays only) Shirlan Tanos Sonata Invader F pr <0.001 LSD (P=0.05) NS 2.98 Main season fungicide evaluation (Protocol 2) These trials gave a good set of tuber blight data. The ranking orders of the fungicides were consistent in five of the trials (Table 3). The exception was the Rosemaund trial in The ranking order of fungicides in this trial is substantially different from the others, e.g. Ranman gave the poorest control of tuber blight and Curzate M was the second most effective. However, it is important to bear in mind that in the Rosemaund 2003 trial there were no significant differences between treatments (P>0.05). The agreement between multiple ranking orders can be summarised statistically by the Coefficient of Concordance. This coefficient was (significant at P=0.01) for the five trials excluding the Rosemaund 2003 trial. The generally consistent results may be partly due to small differences in foliar blight between core treatments in most of the trials. Tuber blight was therefore generally not confounded by differences in foliar blight in some trials and not others. The actual incidences of tuber blight are summarised in Table 4. Table 4. Ranking order of six fungicides for the control of tuber blight. Pre-storage tuber blight for Rosemaund and total (pre- plus post-storage) tuber blight for Auchincruive Rose d Auch. Rose d Auch. Rose d Auch. Mean Mean* Ranman Shirlan Electis Invader Sonata Curzate M * Rosemaund 2003 results excluded Table 5. Incidence (%) of tuber blight (by weight) in relation to fungicide treatment. Pre-storage tuber blight for Rosemaund and total (pre- plus post-storage) tuber blight for Auchincruive. British Potato Council

14 Rose d Auch. Rose d Auch. Rose d Auch. Ranman Shirlan Electis Sonata Invader Curzate M Untreated F pr NS NS <0.001 < LSD (5%) Although the foliar blight epidemics in the untreated plots at both Auchincruive and Rosemaund demonstrated that the sites were subjected to a disease challenge in all trials. However, the fungicide programmes were generally too robust for the prevailing disease pressure, except at Auchincruive in Where disease pressure was low all of the fungicides tested gave good control of foliar blight. The foliar blight results for 2003 and 2005 are not presented. In the Scottish trial in 2004 the control of foliar blight was significantly better for some fungicide products, e.g. Ranman, Shirlan and Electis, than the others. However, these results are from one trial only and they are put in context in the Discussion. At Auchincruive in 2004 there was a close relationship between the severity of foliar blight in September and the total incidence of tuber blight (r=0.91, F pr.=0.018)(fig. 10). This demonstrated the indirect effect of fungicides on tuber blight control through control of the foliar epidemic. There was a strong relationship in terms of tuber blight control for the fungicides between the two sites in 2004 in spite of the Auchincruive trial having very large differences in foliar blight whereas treatments in the Rosemaund trial gave very similar levels of foliar blight control. In the 2004 season the direct and indirect control of tuber blight were strongly related. British Potato Council

15 % Foliar blight* (6 Sept) Untreated Shirlan Curzate Invader Ranman Electis Sonata F pr LSD (5%) NS % Tuber blight (by weight) < NS=Not statistically significant (P>0.05) *Untreated controls excluded from the analysis Rosemaund % Foliar blight (6 Sept) % Tuber blight (by weight) Untreated Shirlan Curzate Invader Ranman Electis Sonata Fig 9 Effect of main season fungicide treatments on the development of foliar and tuber blight levels (pre storage) at Rosemaund 2004 (Protocol 2) British Potato Council

16 Untreated Shirlan Curzate Invader Ranman Electis Sonata F pr LSD (5%) % Foliar Blight* (5 Sept) < % Tuber blight (by weight) < *Untreated controls excluded from the analysis Auchincruive % Foliar blight (5 Sept) % Tuber blight (by weight) Untreated Shirlan Curzate Invader Ranman Electis Sonata Fig 10 Effect of main season fungicide treatments on the development of foliar and tuber blight levels (pre + post storage) at Auchincruive 2004 (Protocol 2) Discussion Early season fungicides (Protocol 1) The choice of fungicide for the first few sprays in a programme is often difficult for growers. This is because initially there is little crop present to intercept the fungicide spray, and growers are often reluctant to use the more expensive fungicides at early growth stages when most falls onto the soil. The fungicides tested gave a similar level of foliar blight control. This was surprising given that the cultivar used was very susceptible, five of the six trials were inoculated between 1 and 7 days after the first fungicide application and in three of the trials there were Smith Periods during the time that the different fungicides were applied. It should be remembered that the source of blight in these trials was external to the crop. It is likely that different results would have been obtained had the source of inoculum been from infected seed or perhaps oospores, i.e. within the crop and active earlier. It is surprising that Auchincruive in 2003 differences between treatments were not observed because there were three Smith periods and the average spray interval was nearer 9 than 7 days. However, there were two periods with very high air temperatures at critical times and these greatly restricted the development of blight. British Potato Council

17 The results suggest that the critical factor determining whether the most effective fungicides give superior control is not only the presence of limited active blight but also when this coincides with high-risk conditions. At Auchincruive in 2003, when foliar blight risk was generally low, the application of Shirlan four times from c. 100% emergence gave significantly better control of tuber blight than some other fungicide treatments. This result was not repeated in the 2004 trial, most likely because the fungicide treatments were overwhelmed by the very large number of zoospores being washed down into the soil during the 2004 growing season. The 2005 growing season was not favourable for foliar blight development but three early applications of Shirlan did not give good control of tuber blight. The different results obtained with early Shirlan application in the 3 years are difficult to explain. It is likely that the effectiveness of Shirlan applied at this timing and its effect on tuber infection later in the season does not just depend on the severity of foliar blight and therefore the number of zoospores challenging tubers. Further work would be required to investigate this. When to start a spray programme has long been a concern to both growers and agronomists alike. It is invariably a compromise in terms of justifying the cost and not wasting expensive fungicide on bare soil when the plants are relatively small. There is also the question of justifying the use of such treatments as the GB potato industry is committed to the optimum use of pesticides, and supports the activity of the Voluntary Initiative as a means of minimising the environmental impacts of crop protection products. Main season fungicide evaluation (Protocol 2) The trials provided strong data for the relative fungicide efficacies against tuber blight. The overall ranking order was Ranman TP, Shirlan, Electis, Invader, Sonata and Curzate M. There is good agreement between these results and the latest blight fungicide effectiveness table produced by the Fungicides Sub-Group of EU.NET.ICP. In that table the fungicides are rated, Ranman [+++], Shirlan [++(+)], Electis, Invader and Sonata [++] and Curzate M [0], where +++ equals a very good effect, ++ a good effect, + a reasonable effect and 0 equals no effect. There was a surprisingly strong correlation between the tuber blight results for the fungicide treatments at Rosemaund and Auchincruive in 2004 (r=0.9, F pr.=0.019). The two sites differed in weather conditions and disease pressure. As a result the indirect effect of the fungicide programmes on tuber blight control was evaluated in the Auchincruive trial, whereas in the Rosemaund trial, it was essentially the direct effect that was being tested. The control of tuber blight by fungicides is said to be indirect when the fungicide treatment significantly affects the severity of foliar blight. It is considered to be a direct effect on the tuber infection process itself when the fungicide treatments result in similar severities of foliar blight. In one of the trials (Auchincruive, 2004) there were very large differences in foliar blight between treatments. However, the results of one trial cannot accurately indicate relative efficacy in foliar blight control. This is particularly the case here because the results obtained in the trial are unlikely to be typical for the fungicide products tested. The weather pattern in 2004 was unusual, and the trial tested the persistence of products and their ability to withstand removal from the plant by exceptionally high rainfall. In interpreting the results it is important to know that 10, 48 and 38 mm of rain fell 6, 7 and 8 days after the fourth spray. This deluge happened just before the next spray was due and provided a very severe test of the rainfastness of the fungicide treatments. As expected given the high rainfall in 2004, the effectiveness of the core treatments in terms of foliar blight control quite closely reflected the relative rainfastness of the fungicides. British Potato Council

18 Another factor that needs to be considered when interpreting the results of this particular trial (Auchincruive, 2004) is that there were no opportunities for kick-back activity to be demonstrated. It is only possible to take advantage of curative activity if fungicides are applied sufficiently soon after high-risk conditions. The 2004 season was characterised by the risk conditions frequently lasting for more than 2 days. This, together with the sprays being applied routinely, did not allow curative properties to be expressed. Although the severities of foliar blight in most of the trials were low, the disease threat in each was considerably higher than that in the vast majority of commercial crops. The variety of potato used for the trials, King Edward, has a resistance rating of 3 for foliar blight. In 2004 only 17.6% of the potato crop area grown in GB had a rating equal to or less than 3. In addition, the untreated plots together with very many non-sprayed infector areas in the trials provided a much greater in-crop inoculum source than is common in commercial practice. It should be noted that under these conditions most of the fungicide programmes and products provided good control of foliar blight. This suggests that under the blight threat conditions in which most growers crops are grown most of the fungicide products tested will give good control of foliar blight. However, when disease pressure is very high, for example as at Auchincruive in 2004, or when fungicides are badly timed or poorly applied, then the potentially large differences between fungicides are revealed. The low levels of foliar blight at both sites and the slow blight epidemics often resulted in a high incidence of tuber infection. This demonstrates the relationship between the amount of inoculum available to infect tubers at different times during the growing season and tuber infection. It is a strong knowledge transfer message to the GB industry and demonstrates the need to maintain fungicide programmes up to and after haulm desiccation treatment. At Rosemaund in 2004 there were high levels of tuber blight and this is likely to be a function of the speed of the foliar blight epidemic. A relatively slow blighting epidemic extends the period of exposure of tubers to inoculum. British Potato Council

19 Conclusions Early season fungicides (Protocol 1) The data generated so far clearly show that there is a benefit in disease control from early fungicide treatment when blight is present in a locality note that these sites were inoculated with the pathogen. Where the fungicide programme was started very early and short application intervals maintained, the choice of fungicide was frequently not that important for foliar blight control. However, tuber blight was sometimes significantly influenced by fungicide. Shirlan applied prior to canopy closure may in some circumstances contribute to the direct control of tuber blight but the effect does not appear to be consistent in different conditions. In 2005, in conditions not conducive to an aggressive foliar epidemic, there were no differences in foliar blight between any of the fungicide treatments. However, at Auchincruive, two early applications of Epok or Fubol Gold resulted in very good control of tuber blight. The effect of the two phenylamide products was long lasting, approximately 11 weeks. The results of this study do not change the current advice to UK growers. This is to use systemic fungicides early in the life of a crop to take full advantage of their mobility within the plant during the rapid growth phase of the crop. In addition, the first fungicide application in a spray programme should be made when the haulm is meeting along the rows and not as early as 100 % emergence unless local risk is judged to be extremely high. Defining this level of risk remains very much a local decision. Main season fungicide evaluation (Protocol 2) The overall ranking order of the fungicides for tuber blight control was Ranman TP (most effective), Shirlan, Electis, Invader, Sonata and Curzate M (least effective). It is reassuring to know that there are products available which are effective tin replacements. It should be noted that the products were applied repeatedly from the end of rapid haulm growth until desiccation whereas full rate fentin fungicides were usually limited to the final two or three sprays of the programme. The low levels of foliar blight at both sites and the generally slow blight epidemics often resulted in a high incidence of tuber infection. The trials present extremely good examples of the relationship between prolonged production of inoculum on the haulm and high levels of tuber infection. This is a strong reminder of the need to maintain fungicide programmes up to, and to the end of haulm desiccation. Under low risk conditions all of the fungicide programmes evaluated gave good control of foliar blight. The 2004 results showed that there is some very effective fungicide chemistry available to GB growers but when disease pressure is intense and weather conditions delay sprays being applied, blight is very difficult to contain. It is important for growers to appreciate that different fungicide products have different strengths and weaknesses, and these need to be known in order to use the most appropriate fungicide(s) for the circumstances. For example, as demonstrated at Auchincruive in 2004, fungicides with curative activity can only be curative if British Potato Council

20 applied sufficiently soon after high-risk conditions. Timely information on local highrisk periods is vital to their successful use. Where do we go from here? There are many new fungicides in the development pipeline, and continued independent evaluation of their performance would give GB growers a good understanding of their attributes so that blight control can be optimised. One example of this would be relating weather conditions to curative activity and also a better appreciation of the resistance to removal by rain of different products under field conditions. There is a strong case for evaluating fungicides at both high and low blight risk intervals, i.e. at both 7 and 10 days. This would stretch products and would also allow for a better assessment of the different chemistry. Different varieties do have different resistance characteristics to both foliar and tuber blight. There has been some work showing that it is possible to reduce fungicide inputs on more resistant cultivars but further work is necessary to provide sufficient results to give agronomists and growers the confidence to use this approach extensively. (N.B. A preliminary study has been commissioned by the BPC in 2006 to explore the issue of flexibility in spray intervals on potato cultivars with different levels of foliar blight resistance). Consideration should also be given to the use of PLANT-Plus, or another forecasting scheme, at the two sites to compare in-crop blight risk with routine spray programmes. The two protocols have not addressed fungicide protection during rapid haulm growth. This is frequently the most difficult crop growth phase in which to control blight because of all the new growth between fungicide applications. British Potato Council, 4300 Nash Court, John Smith Drive, Oxford Business Park, Oxford, OX4 2RT