Dicarboximide (DCA) [Group 2] resistance management strategy
Dicarboximide fungicide use for control of botrytis
bunch rot Botrytis cinerea of grapes should be
limited to two applications per season.
Introduction
The purpose of this guideline is to help maximise the useful life of fungicides in the Fungicide Resistance Action Committee (FRAC) Group 2 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.
Dicarboximide product perspective
Dicarboximide fungicides are active against a limited range of fungi (Table 1). The exact spectrum of activity varies slightly for different active ingredients within this group. Dicarboximides that are currently used in New Zealand are procymidone and iprodione (Table 2). Dicarboximides were introduced in the late 1970s, principally for the control of Botrytis cinerea in grapes. They were used as an alternative to the MBC fungicides, to which resistance had developed in B. cinerea. Dicarboximides were used intensively in European vineyards and resistance in B. cinerea was found within about three years.
The mode of action of dicarboximides has not been fully characterised, but they affect fungal osmotic regulation, as well as resulting in some other nonspecific toxic effects. Dicarboximides are protectant fungicides with low phytotoxicity and short withholding periods. Because of the short withholding period they have been widely used close to harvest. There is cross-resistance amongst all the active ingredients within the dicarboximide group.
| Pathogen | Disease | Crops |
|---|---|---|
| Alternaria citri | Brown spot | Tangelos |
| Botrytis cinerea | Grey mould | Grapes, berryfruit, strawberries, glasshouse tomatoes |
| Botrytis cinerea, Sclerotinia sclerotiorum | Botrytis and sclerotinia diseases | Beans, kiwifruit |
| Monilinia fructicola | Brown rot | Stonefruit |
| Rhizoctonia spp. and Alternaria spp. | Seedling diseases | Brassica seed treatment |
| Sclerotinia sclerotiorum and S. minor | Sclerotinia | Lettuce |
| Sclerotinia sclerotiorum, Alternaria spp., Botrytis cinerea, Stemphylium spp. |
Various diseases | Flowers and ornamentals |
| Sclerotium cepivorum | Allium white rot | Onion |
| Stemphylium spp. | Needle blight | Asparagus |
| Common Name | Trade Name |
|---|---|
| iprodione | Defence, Ippon, Rapid, Rovral |
| procymidone | Fortress, Sumisclex |
Current status of dicarboximide resistance in New Zealand
Resistance of Botrytis cinerea in grapes, berryfruit and glasshouse crops and resistance of Monilinia fructicola in stonefruit to dicarboximide fungicides first appeared in the early 1980s in many countries, including New Zealand. There is a loss of disease control associated with resistance in both these fungi. There is also evidence for a loss of fitness associated with resistance, resulting in a decrease in the frequency of resistant strains when dicarboximides are no longer used. This makes ongoing use of dicarboximides for control of B. cinerea and M. fructicola possible. Some evidence, especially for M. fructicola, suggests that the fitness penalty for resistance strains is becoming less with time. In both B. cinerea and M. fructicola, strains occur with dual resistance to dicarboximides and Methyl Benzimidazole Carbamates (MBCs).
There are unconfirmed reports of reduced efficacy against some turf diseases, but there is no experimental evidence to suggest that resistance is involved. Loss of efficacy when dicarboximide is applied to soil to control Sclerotium cepivorum is caused by enhanced microbial degradation of the fungicide, not resistance.
Resistance management strategy
Observe manufacturers' recommendations for application rate and timing for specific products and the maximum numbers of applications of dicarboximide products for specific crops (Table 3). Exceeding the maximum number of applications per season will increase the risk of resistance development. Use dicarboximides only when conditions favour disease, but when disease incidence is low. Do not use where disease has become well established. Testing of pathogens for dicarboximide resistance is carried out commercially by some laboratories, and is recommended as part of the resistance management strategy.
| Crop | Disease | Recommendations |
|---|---|---|
| Grapes, berryfruit, strawberries, beans, kiwifruit, glasshouse tomatoes |
Botrytis | Maximum of two dicarboximide applications per season, or in a 12 month period. |
| Stonefruit | Brown rot | Maximum of three dicarboximide applications per season. |
| Other crops | Various | Maximum of three dicarboximide applications per season. |
Implementation recommendations
Product labels should include a statement about resistance risk and a recommendation about the maximum numbers of dicarboximide 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.
Reference
Beresford R, Pak HA, Braithwaite M, Surman C 1996. Dicarboximide resistance management strategy. In: Boudot GW, Suckling DM ed. Pesticide resistance: prevention and management. New Zealand Plant Protection Society, Rotorua, New Zealand. Pp. 139-141.
© 2026 New Zealand Plant Protection Society (Incorporated). All rights reserved.