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

Timing of application
Arguably the timing of fungicide application is more important than product choice when
trying to control FHB and mycotoxin contamination of grain; no matter how effective the
fungicide if it is applied at the wrong time it will not control FHB. Mid-anthesis is the most
susceptible time for infection of wheat by FHB pathogens (Sutton, 1982) and as such is the
most appropriate time to apply a fungicide spray aimed at FHB. Work carried out by
Homdork et al. (2000) and Matthies & Buchenauer (2000) have both highlighted just how
narrow the window for fungicide application is for optimum control of FHB pathogens.
Matthies & Buchenauer (2000) investigated timing of fungicide application on disease
development using trials artificially inoculated with F. culmorum at mid-anthesis. Fungicide
treatments applied were tebuconazole or prochloraz at 8 days pre, 2 or 9 days post
inoculation. The most effective treatment timing for both fungicides was 2 days post
inoculation. The efficacy of the fungicide treatments decreased with increasing time
interval between fungicide application and inoculation. A similar set of experiments carried
out by Homdork et al. (2000) using F. culmorum inoculation with tebuconazole sprayed at
either 3 days pre and/or 5 days post inoculation, again showed the closer the timing of the
spray and inoculation, the better the efficacy of the fungicide.
Some reports of fungicide failure in the field can be directly attributed to incorrect timing
of application. Milus & Parsons (1994) concluded after testing the efficacy of seven
fungicides against F. graminearum that the prospects for chemical control of head blight
were poor. Fungicides were applied to plots at the end of heading growth stage. To each
fungicide treated plot F. graminearum was inoculated three times, at the beginning, mid and
end of anthesis (this equated to 2, 5 and 7 days post fungicide application). The results
showed no reduction in levels of either head blight or DON following fungicide treatment.
However, as already highlighted, inoculum landing on the ear seven days post fungicide
treatment would not be effectively controlled. A more appropriate growth stage for the
fungicide application would have been mid-anthesis. At this growth stage the time interval
between fungicide application and inoculum arrival at the ear would be at its optimum at
between two and three days.
Application rate
To achieve the optimum efficacy against FHB pathogens a fungicide must be applied at
the manufacturers recommended rate. Work carried out by Nicholson et al. (unpublished
data from HGCA project No. 2067) showed that halving the rate of several fungicides led
to significant reductions in control of FHB disease levels and mycotoxin production.
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