Dodine (guanidine derivative) [Group U12] resistance management strategy

Black spot Diplocarpon rosae of rose

Updated 2023, R. Beresford and M. Christie

Introduction

The purpose of this guideline is to help maximise the useful life of fungicides in the Fungicide Resistance Action Committee (FRAC) Group U12 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.

Dodine product perspective

Dodine is a guanidine derivative and acts predominantly as a protective fungicide, but also has a small degree of curative action. Its greatest use is in apples for early season control of V. inaequalis (black spot or scab) at about the time of bud break. It should not be used when apple flowers or young fruit are developing because it can induce fruit russet. It is also used against a limited range of other diseases (Table 1).

Four products containing dodine are currently marketed in New Zealand, Aklame, Dodine 400, Nuchem Dodine and Syllit Plus. All are suspension concentrate formulations.

**Table 1:** Pathogens and crops targeted by dodine fungicides.
Pathogen	Disease	Crops
Diplocarpon rosae	Black spot	Roses
Taphrina deformans	Leaf curl	Peaches and nectarines
Venturia inaequalis	Black spot	Apples
Venturia pirina	Black spot	Pears

Current status of dodine resistance

There is no known cross-resistance between dodine and the other fungicides used in the crops for which dodine is registered.

Resistance to dodine first developed in Venturia inaequalis in the United States and Canada during the 1960s and 1970s where it had been used as the only fungicide in spray programmes for 10 years or more (Jones 1981; Sholberg et al. 1989). Dodine resistance has also been reported from Europe and Australia. In New Zealand, dodine resistance was looked for in a field survey in 1994 (Bakker et al. 1995), but no resistant strains were detected. The resistance management guideline for the maximum number of dodine applications per season in apples was changed from six to three in about 2000. Between the mid 1990s and 2012, the average EC50 value (dodine concentration in vitro that inhibits V. inaequalis growth by 50%) in New Zealand surveys had decreased, i.e., sensitivity had increased, probably because of the decreased dodine use (Beresford et al 2013).

Resistance management strategy

Apply a maximum of three applications per season. Wherever practical, alternate each application of dodine with an application of a fungicide from a different cross-resistance group. Observe manufacturers' recommendations for application rate and timing. Exceeding the maximum number of applications per season will increase the risk of resistance development. Apply dodine preventatively when disease levels are low, but disease risk is high. Ensure that spraying equipment is accurately calibrated.

Implementation recommendations

Product labels for products that contain dodine should include an appropriate statement about resistance management. Most dodine products do not currently give resistance management statements on their labels.

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

Bakker GR, Butcher MR, Gaunt RE, 1995. Sensitivity of apple black spot to fenarimol, fluzilazol, myclobutanil, penconazole and dodine in New Zealand. Proceedings of the 48th New Zealand Plant Protection Conference: 7-11.

Beresford RM, Wright PJ, Wood PN, Park NM, Larsen NJ, Fisher BM 2013. Resistance of Venturia inaequalis to demethylation inhibitor and dodine fungicides in four New Zealand apple-growing regions. New Zealand Plant Protection 66: 274-283.

Jones AL 1981. Fungicide resistance: past experience with benomyl and dodine and future concerns with sterol inhibitors. Plant Disease 65: 990-992.

Sholberg PL, Yorston JM, Warnock D 1989. Resistance of Venturia inequalis to benomyl and dodine in British Columbia, Canada. Plant Disease 73: 667-669.