Amendments to Statutory Conditions of Use of Quinone outside Inhibitor (QoI) Fungicides - Further Information
News Update No. 70 Annex
25 April 2003
Further Information - Questions and Answers
1. What is a QoI
QoI stands for Quinone outside Inhibitor. Products with this mode of action work by binding to the Qo site of cytochrome b thus inhibiting cell respiration. They were previously called STAR (Strobilurin Type Action and Resistance) fungicides. They include the strobilurins azoxystrobin, kresoxim-methyl, picoxystrobin, pyraclostrobin and trifloxystrobin, and the oxazolidinedione famoxadone.
2. Why are PSD taking this action?
Samples of Septoria tritici collected from sites throughout the UK have been found to contain individuals that have a reduced sensitivity to QoI fungicides and carry a genetic mutation that is known to cause resistance in other pathogens. Although there have been no confirmed cases of disease control failure, at a few sites in 2002 QoI fungicides used in disease control programmes appeared to perform less well than expected. The action is intended to reduce the likelihood of resistant strains of Septoria being selected and reaching levels where they would have a serious effect on the performance of QoI fungicides in the field. It will also reduce the likelihood of resistance developing in other pathogens that cause crop diseases.
3. I have product in store that still carries an old label without the limit of two applications. Can I still apply it more than twice to my cereal crops?
No, the amendments to the statutory conditions of use take immediate effect.
4. Where can I get advice on what products to use as partners for solo QoI containing products?
Your crop consultant should be able to advise you on the best products to use in your situation. A list of other sources of information are shown in the box on the right.
5. There is still no evidence of disease control failures. How do you know that the presence of the resistance mutation means this will result in an increase in resistance leading to control failures?
Evidence from similar situations, including powdery mildew resistance to QoI fungicides, suggests that there is a very high probability of increasing levels of resistance developing in Septoria that could have a serious effect on the performance of QoI products. Given the importance of QoI products in cereal production we feel that it is prudent to take these steps now to try and ensure their continued activity in the future.
6. How do we know this is a new phenomenon? Could these genes have been present all along?
The genes have probably always been present in populations of Septoria but at a very low level. There has been an ongoing programme monitoring the sensitivity of QoI fungicides to Septoria tritici since they were first introduced. 2002 was the first year in which any real evidence of an increase in the occurrence of the resistance gene was found detected in Septoria tritici.
7. What would happen if these restrictions are not put in place?
The opinion of the Fungicide Resistance Action Group UK (FRAG-UK) is that there is a high probability that without these restrictions practical levels of resistance may occur in Septoria tritici, and control of the disease would be compromised. There would also be an increased risk of other pathogens developing resistance. This would leave growers without the disease control benefits of the QoI’s that they have experienced in the last few years.
8. Do these measures go far enough and are they the right measures? Should we not restrict use to only a single application?
The restrictions are to be imposed because about 20% of cereal crops are being treated with more than two applications. Two foliar sprays are justified under present circumstances and should not contribute to a further change in resistance status if the other measures advocated are adhered to.
Evidence from other situations indicates that the most important measures for preventing or delaying the development of resistance are to avoid continuous selection pressure and to use other means of control. By restricting the number of foliar applications of QoI containing products to two, used specifically in combination with robust doses of effective partner products, the period during which the fungus is under selection pressure to develop resistance is limited. By only using QoI fungicides in mixture with other active substances effective against the same disease, any fungi that are resistant to QoI products will be controlled by the other product and will not therefore become dominant in the population.
9. Will these measures have any effect now that resistance has been detected?
We have not found conclusive evidence of poor control in the field. These measures are designed to stop the situation deteriorating to the point where resistance does become a practical problem. Monitoring will continue however and further steps will be taken as necessary.
10. Why do we need to restrict the number of applications AND apply in mixture? Is this not overkill?
Restricting the use of QoI fungicides to two foliar sprays still results in significant selection pressure for resistance and would probably be insufficient on its own. If this was the only strategy adopted then further restrictions, perhaps to one spray per season or even to limiting use to alternate seasons would need to be adopted. The use of mixtures is also unlikely to be an effective strategy on its own. Because all fungicides behave slightly differently the ideal partner for a given QoI product will depend on the situation. QoI fungicides often remain active for a very long time. Many of the partner products are less persistent and therefore leave periods when the QoI fungicide alone is giving disease control, and therefore exerting selection pressure for resistance. Also partner products are unlikely to be equally effective against all the different diseases.
11. If use in mixtures is so important should PSD not either withdraw the approvals for solo QoI products or place a statutory restriction on them so that they can only be applied in mixture?
Both actions have been considered by PSD and FRAG-UK. We believe that there can be an advantage with the solo QoI products in allowing the most appropriate mixture partner to be selected for different situations and that this may actually reduce the resistance risk. Some solo QoI products also have important uses in other crops and these may be lost if the solo products were withdrawn.
We are encouraging the manufacturers and crop consultants to devise control strategies that will give farmers/growers specific advice on the best mixtures to use. Details of some sources of additional information are in the panel on the right.
PSD will be carefully monitoring the situation and if it becomes apparent that solo products are not being used in mixture with suitable partner products, further action, which may include the revoking of approvals, may be taken.
12. What role does dose play in selecting for resistance?
It remains unclear whether frequent applications at high or low doses are most likely to cause resistance. The prevalence of resistance in the population may be a critical factor so that the optimum dose to minimise resistance selection varies depending on the level of resistance in the population. However, scientists agree that it is important that partner products are used at robust effective doses and that continuous selection pressure is avoided. Hence the limitation to two applications and advice to apply robust doses of partner products.
13. Why is this a regulatory matter? Is this within PSD’s remit?
It is part of the regulatory requirements that pesticides can only be approved if they are effective. Allowing ineffective products onto the market would permit the unnecessary use of pesticides which would run counter to the government’s policy of pesticide minimisation. Resistance risk analyses and the implementation of effective resistance management strategies are specific requirements under the newer Plant Protection Products Regulations (PPPR) under which many QoI fungicides are registered.
14. Do these changes have any effect on the use of QoI fungicides on crops other than cereals?
No they do not. However, PSD in liaison with FRAG -UKare looking at the resistance management strategies for all uses of QoI fungicides and may take further action in relation to these if necessary. In the meantime growers should ensure that they follow any existing resistance management strategies either on the label or on the Specific Off-Label Approval (SOLA) document. If no guidance is provided or, they should follow the guidelines proposed by Fungicides Resistance Action Committee (FRAC). These are available on their website at http://www.frac.info/frac/work/work_qolf.htm