Anilinopyrimidine (AP) [Group 9] management strategy

Anilinopyrimidine fungicides are
used to control brown rot
Monilinia fructicola in stonefruit.
(Photo: Philip Elmer.)

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 9 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.

Also see the separate mode of action strategy for use of APs for Botrytis cinerea (bunch rot) in wine grapes, here, the crop-based strategies for use of APs against Venturia inaequalis (black spot; scab) in apples, here, and against Monilinia spp. in Summerfruit (here).

Anilinopyrimidine product perspective

Two anilinopyrimidine active ingredients cyprodinil and pyrimethanil are used in New Zealand and these were introduced in the mid to late 1990s. They are used against several important diseases of horticultural crops (Table 1). They have protective and some degree of systemic curative activity and a site-specific mode of action that interferes with biosynthesis of the amino acid methionine and inhibits secretion of hydrolytic enzymes. They show no cross resistance with other fungicide groups, but there is cross-resistance among the active ingredients within the anilinopyrimidine group.

Refer to the ACVM register (https://eatsafe.nzfsa.govt.nz/web/public/acvm-register) for the trade names of products containing cyprodinil and pyrimethanil.

**Table 1:** Pathogens and crops targeted by anilinopyrimidine fungicides in New Zealand.
Pathogen	Disease	Crop
Botrytis cinerea	Bunch rot	Grape
Botrytis cinerea	Dry eye rot	Apple
Venturia inaequalis	Black spot	Apple
Podosphaera leucotricha	Powdery mildew	Apple
Monilinia fructicola, M. laxa	Blossom blight stage of brown rot	Peach, nectarine

Current status of anilinopyrimidine resistance

Anilinopyrimidine resistance involves a single gene mutation resulting in a variable proportion of pathogen strains in a population with substantially reduced sensitivity. In New Zealand, AP resistant strains are present to various pathogens in many crops but do not generally appear to dominate within the pathogen populations, except in the Tasman region where a high degree of resistance in Venturia inaequalis and Botrytis cinerea is known to be present to both cyprodinil and pyrimethanil.

Resistance management strategy

Refer to the crop-based strategies for use of APs against Venturia inaequalis (black spot; scab) in apples (here) and for Botrytis cinerea (bunch rot) in wine grapes (here). For other crops follow the guidelines below:

Observe maximum numbers of applications of anilinopyrimidines for specific crops and products (Table 3).
Adhere to manufacturers' recommendations for application rate and timing for specific products. Reduced rate applications should be avoided.
In determining whether the maximum number of anilinopyrimidines applied per season has been reached, include the cumulative number of all fungicides containing anilinopyrimidine active ingredients (cyprodinil and pyrimethanil).
Apply anilinopyrimidines preventatively before disease becomes severe but when disease risk is high.

**Table 2:** Anilinopyrimidine use guidelines for Summerfruit (peaches, nectarines and cherries). Also see the crop-based strategy for blossom blight in peaches and nectarines (here).
Crop	Disease	Recommendations
Summerfruit	blossom blight stage of brown rot	Maximum of three applications of anilinopyrimidine-containing products per season. Use during the blossom period. During the rest of the season products containing non-anilinopyrimidine active ingredients should be used. It is preferable to alternate each anilinopyrimidine application with a product containing a non-anilinopyrimidine active ingredient.

Implementation recommendations

Product labels should include a statement about resistance risk and a recommendation about the maximum numbers of AP 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.