Carboxylic acid amide (CAA) [Group 40] resistance prevention strategy
CAA fungicides are used against late blight in
potatoes and although the resistance risk is
considered to be low to medium, a
resistance prevention strategy is required.
Introduction
The purpose of this guideline is to help maximise the useful life of fungicides in the Fungicide Resistance Action Committee (FRAC) Group 40 for controlling plant diseases in New Zealand by providing relevant information about the nature of pathogen resistance to this group and guidance on practices that may prevent or reduce the development of resistance.
Disclaimer:
The fungicide and bactericide resistance information in the mode of action group table, the mode of action-based strategies and the crop-based strategies is intended to help manage the effects of pesticide resistance on plant disease control by agrochemicals in New Zealand. The New Zealand Committee on Pesticide Resistance (NZCPR) is a subcommittee of the New Zealand Plant Protection Society (NZPPS). The following parties: NZCPR, NZPPS, any people named in the strategies and any organisation the people may be affiliated with, do not guarantee that the resistance information is complete, consistent, accurate or up-to-date, or that resistance will not develop, or that the degree of resistance will decrease, as a result of the resistance information being used, and the parties accept no liability for loss or damage arising from the use of the resistance information contained in these strategies.
Product perspective
Carboxylic acid amide (CAA) fungicides, which are currently represented in New Zealand by the two active ingredients, dimethomorph and mandipropamid. The CAA group was proposed in 2007 by the Fungicide Resistance Action Committee (FRAC) in Europe under FRAC code No. 40 and includes compounds from the three different chemical groups, cinnamic acid amides (dimethomorph), valinamide carbamates (iprovalicarb) and mandelic acid amides (mandipropamid).
CAA fungicides exhibit translaminar movement and although their mode of action is not clear, it is proposed that they inhibit phospholipid biosynthesis and interfere with cell wall deposition.
| Pathogen | Disease | Crops |
|---|---|---|
| Plasmopara viticola | Downy mildew | Grape |
| Bremia lactucae | Downy mildew | Lettuce |
| Peronospora destructor | Downy mildew | Onion |
| Phytophthora infestans | Late blight | Potato |
Current status of carboxylic acid amide (CAA) resistance
CAA fungicides are considered to be at low to medium risk of fungicide resistance by the Fungicide Resistance Action Committee (FRAC) and resistance management is required. Dimethomorph, which causes cell wall lysis in oomycete fungi (Albert et al. 1988), has shown no cross-resistance to phenylamide fungicides (Jensen & Lundsgaard 1999). Mutants of Phytophthora capsici moderately resistant to dimethomorph were induced in the laboratory with chemical mutagenesis, but not through adaptation (Young et al. 2001). A small proportion of field isolates of P. infestans were found to be tolerant to dimethomorph in Russia, however resistant strains that were induced through repeated treatment of potato plots appeared to have reduced fitness (Dereviagina et al. 1999). Attempts to detect resistant strains in field populations of P. viticola in Germany were unsuccessful, as were attempts to induce resistant strains artifically (Bissbort & Schlosser 1991).
Currently, there appears to be no resistance to CAAs in New Zealand.
Resistance prevention strategy
Observe manufacturer's recommendations for application rate and timing. Exceeding the maximum number of applications per season could increase the risk of resistance development. Apply preventatively when disease levels are low, but disease risk is high. Weather-based disease forecasting criteria are available to help effective timing of fungicides for onion downy mildew and potato late blight.
Grapes
Apply a maximum of four applications per season. Apply CAA fungicides always in mixture with an effective fungicide that has a different mode of action. New Zealand Winegrowers' resistance management recommendation may differ from this guideline.
Lettuce, onions and potatoes
Follow the manufacturers label directions. It is suggested that no more than 50% of the fungicide applications used against late blight or downy mildew should contain a CAA fungicide.
Implementation recommendations
Product labels should include a statement about resistance risk and a recommendation about the maximum numbers of carboxylic acid amide containing fungicides that should be applied.
Acknowledgements
This strategy includes information from The Fungicide Resistance Action Committee (FRAC) about mode of action groups, the occurrence of resistance worldwide and resistance management recommendations.
References
Albert G, Curtze J, Drandarevski CA 1988. Dimethomorph (CME 151), a novel curative fungicide. Brighton Crop Protection Conference. Pests and Diseases Vol. 1: 17-24.
Bissbort S, Schlosser E 1991. Sensitivity of Plasmopara viticola to dimethomorph. Mededelingen Faculteit Landbouwwetenschappen, Rijksuniversiteit Gent, 56 (2b): 559-568.
Dereviagina MK, Elansky SN, Diakov YT 1999. Resistance of Phytophthora infestans to the dimethomorph fungicide. Mikologiya Fitopatologiya 33(3): 208-213.
Jensen CB, Lundsgaard J 1999. ACROBAT R WG - a new fungicide against downy mildew in onions and late blight in potatoes. 16th Danish Plant Protection Conference. Crop protection in organic farming. Pests and diseases. DJF Rapport, Markbrug 10: 213-225.
Young DH, Spiewak SL, Slawecki RA 2001. Laboratory studies to assess the risk of development of resistance to zoxamide. Pest Management Science 57(11): 1081-1087.
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