3. Fusarium mycotoxins in cereals - Plant Research International ...

anthesis with a mixed conidial suspension of FHB pathogens showed that tebuconazole (as
Folicur) effectively controlled the toxigenic Fusarium species present on the ear, but
showed little control of the non-toxigenic M. nivale. However, the application of a
strobilurin fungicide, azoxystrobin (as Amistar), controlled M. nivale but not the Fusarium
species present. Similar differential control by tebuconazole and azoxystrobin has also
been reported in trials naturally infected by FHB pathogens (Simpson et al., 2001).
Differential control of fusaria and M. nivale also exists within the MBC group of fungicides,
however this has arisen through the widespread development of resistance in populations
of M. nivale (Locke et al., 1987; Pettitt et al., 1993).
Other products with good efficacy towards fusaria responsible for FHB, include
metconazole [as Caramba (Jennings et al., 2000)], prochloraz [as Sportak (Matthies &
Buchenauer, 2000)], and epoxiconazole and carbendazim [as Opus and Derosal WDG
respectively (Nicholson et al., unpublished data from HGCA project No. 2067). Many of
the strobilurin fungicides, such as azoxystrobin, trifloxystrobin and kresoxim methyl, show
good efficacy towards M. nivale.
In most cases the reduction in disease symptoms which followed fungicide application also
gave a reduction in deoxynivalenol (DON) contamination of grain compared to control
plots. However, under certain circumstances it has been reported that application of some
fungicides can lead to increases in DON levels in the field (Jennings et al., 2000). Trials
carried out in 1998 and 1999 showed that following the application of azoxystrobin DON
levels in grain increased in 1998, but not in 1999. The difference in the two years was the
FHB pathogen mixture found on the ear. In 1998, M. nivale and F. culmorum were both
detected on the ear in control plots, whereas in 1999 M. nivale was not detected. This
suggests that the combination of FHB pathogens found on the ear is important in
determining whether increased DON production occurs following the application of
azoxystrobin. Where both M. nivale and F. culmorum were present on the ear the removal of
M. nivale, through use of azoxystrobin, reduced competition on F. culmorum, resulting in
increased DON levels in grain. Where M. nivale was absent from the ear, the application of
azoxystrobin did not alter competition between FHB pathogens and had therefore no
effect DON levels. Similar increases in DON have also been seen from 'on-farm' data
(Turner et al., unpublished data). In 1998, a survey carried out on UK wheat grain indicated
the predominant pathogen was M. nivale, with low levels of Fusaria also present (Turner et
al., 1999). Examination of the fungicides applied to each field analysed for toxin and FHB
pathogen indicated that where azoxystrobin was applied to the ear the level of DON was
higher than where there was no azoxystrobin application.
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