The FRAC Azanapthalene (AZN) Working Group was formed in 2010 to generate common resistance management recommendations for the fungicides quinoxyfen and proquinazid.
The above mentioned fungicides are grouped together under the FRAC Code No. 13.
Quinoxyfen and proquinazid are Azanaphthalene fungicides with a narrow spectrum of activity limited to powdery mildew of cereals and broadleaf crops of which grapevines, cucurbits and fruiting vegetables are key markets segments. Both fungicides act on early stages of mildew development and are protectant only products. European wheat powdery mildew baselines were established between 1995 and 1996 for quinoxyfen (Holloman et al. 1997) and between 1999 and 2002 for proquinazid (Genet & Jaworska 2009). Baselines for Erysiphe necator were generated in Europe for both molecules around 1999-2000 (Green & Duriatti 2005, Genet & Jaworska 2009). First commercial sales of quinoxyfen occurred in the EU on wheat and barley in 1997 and on grapevine in 2000. Commercial launch date for proquinazid was in 2006 on cereals and 2007 on grapevines.
The exact site of action of these two fungicides is not known. Quinoxyfen effects have been linked to early cell signaling events in wheat powdery mildew (Blumeria graminis) during germling differentiation (Wheeler et al. 2003). Recent studies have shown that quinoxyfen appears to target serine esterase activity, with a downstream perturbation in signal transduction (Lee et al. 2008). Studies conducted on wheat powdery mildew have shown that proquinazid stimulated the expression of host genes classically associated with resistance responses including genes in ethylene-mediated response pathways, phytoalexin biosynthesis, cell-wall strengthening and active oxygen production (Crane et al. 2008).
Low frequencies of Blumeria graminis isolates with reduced sensitivity to quinoxyfen were first detected in 2001 whilst a small increase in the frequency of Erysiphe necator isolates with reduced sensitivity to quinoxyfen was first detected at the start of routine monitoring in 2003 (Green & Duriatti 2005). A clear cross-resistance pattern between quinoxyfen and proquinazid has been demonstrated in grape powdery mildew (Erysiphe necator) while a looser relationship was observed in Blumeria graminis (Genet & Jaworska 2009). The mechanism of resistance is unknown. For resistance management purposes, quinoxyfen and proquinazid must be managed together under FRAC Group 13.
Powdery mildew is usually regarded as a high-risk pathogen with regard to fungicide resistance therefore it is important that resistance management recommendations be strictly followed.