Anilinopyrimidine management strategy

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

R.M. Beresford
Plant & Food Research, Private Bag 92169, Auckland 1142, New Zealand

(revised December 2004)

A new fungicide resistance management strategy for apple black spot (Venturia inaequalis) has been put in place and supersedes the individual Mode of Action strategies shown elsewhere on this site for apple black spot in pipfruit.

The new strategy is available here.

Introduction

This fungicide use strategy is designed to avoid or delay the development of resistance of plant pathogens in New Zealand to anilinopyrimidine fungicides. It has been developed from previously published information (Beresford et al. 1999) in consultation with the New Zealand agricultural chemical industry (Agcarm Inc.) and is based on recommendations from the Fungicide Resistance Action Committee (FRAC) in Europe.

Anilinopyrimidine product perspective

Anilinopyrimidine fungicides have a site-specific mode of action in the targeted fungal pathogens that interferes with biosynthesis of the amino acid methionine and inhibits secretion of hydrolytic enzymes. They show no crossresistance with other fungicide groups, but there is cross-resistance among the active ingredients within the anilinopyrimidine group. Their spectrum of activity ranges from cereal diseases, such as powdery mildew and eyespot, to botrytis in grapes and black spot (scab) in apples. In New Zealand they are currently used against diseases of horticultural crops (Table 1). They have protective and some degree of systemic curative activity. Of the three anilinopyrimidine fungicides that have been commercialised (cyprodinil, mepanipyrim and pyrimethanil), cyprodinil and pyrimethanil were introduced into New Zealand in the mid- to late-1990s (Table 2).

**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

**Table 2:** Anilinopyrimidine fungicides marketed in New Zealand.
Common name	Trade name
cyprodinil	Chorus in Switch with Fludioxonil¹
pyrimethanil	Scala, Pyrus

¹Fludioxonil is a phenylpyrrole fungicide and is in a different cross-resistance group to the anilinopyrimidines.

Current status of anilinopyrimidine resistance

No instances of anilinopyrimidine resistance have been recorded in New Zealand. Overseas laboratory and field studies have shown that there is a risk of resistance development in Botrytis cinerea and Venturia inaequalis. Resistance in B. cinerea involved a single gene mutation resulting in a qualitative shift in sensitivity in field isolates and field resistance in grapes involving a loss of disease control.

Monitoring in European vineyards under normal disease control practice in 2002 has indicated a low frequency of less sensitive B. cinerea isolates, but no loss of disease control. Venturia inaequalis sensitivity monitoring has not revealed field resistance.

Resistance prevention strategy

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 when disease levels are low.

Implementation recommendations

Product labels should include a statement about resistance risk and a recommendation about the maximum numbers of anilinopyrimidine fungicides that should be applied.

**Table 3:** Anilinopyrimidine use guidelines for specific crops.
Crop	Disease	Recommendations
Grapes	botrytis bunch rot	Maximum of two applications with anilinopyrimidine-containing products may be used per season where up to six botrytis-specific treatments are made. Maximum of three applications with anilinopyrimidine-containing products per season where more than six botrytis-specific treatments are applied. See also: More detailed recommendations for the use of anilinopyrimidine products to control botrytis bunch rot in wine grapes
Apples	black spot, powdery mildew, botrytis dry eye rot	Maximum of four applications per season of products where an anilinopyrimidine is the only fungicide active ingredient in the spray mix. Maximum of five applications per season where anilinopyrimidines are applied in mixture with an effective dose of a black spot fungicide from a different group. Use anilinopyrimidine-containing products early in the season when temperatures are cool.
Peaches and nectarines	blossom blight stage of brown rot	Maximum of four 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.

Acknowledgements

This resistance management strategy has been compiled with assistance from Jack Richardson (Agcarm Inc.), George Follas (Syngenta Crop Protection) and Max Moore (Bayer CropScience).

Reference

Beresford R, Pak H, Manktelow D, Follas G, Hagerty G 1999. Strategies to avoid resistance development to anilopyrimidine fungicides in New Zealand. Proceedings of the 52nd New Zealand Plant Protection Conference: 176-178.