DUAL action mixes of new strobilurin chemistry with the best of the latest generation of triazoles topped French septoria trials in 1997.
The extensive series of treatments used by Frances leading agrochemical trials organisation, the ITCF, demonstrated that while the strobilurins were most likely to give yield increases from preventive early treatment, triazoles were a necessary part of successful later applications where a kickback effect was required.
Claude Maumené, who heads the ITCF fungicide programme, found that the strobilurins, like the latest generation of triazoles such as epoxiconazole, are dependent on full-rate applications to get the maximum effect. But even at half-rate a strobilurin/triazole combination will give more yield than a reduced rate triazole on its own.
Results from early treatment against septoria highlight the role of the strobilurins in preventing fungal development. Applied at second node, it was Ogam, the BASF formulation of kresoxim-methyl with epoxiconazole, which showed the greatest (71%) control of septoria and the best yield response of 1.22t/ha.
However, not far behind this full-rate treatment was a mixture of half-rate Amistar (azoxystrobin) with half-rate Opus (epoxiconazole), full-rate Vista CT (fluquinconazole + chlorothalonil), and three-quarter rate Opus with a litre of Daconil (chlorothalonil).
Putting treatment off until flag leaf emergence produced different results which favoured the curative action of the triazoles. Ogam (73%) still excelled but was just pipped for control (74%) by a quarter-rate Amistar with threequarter-rate Opus. Yield response was exactly the same at 1.9t/ha.
For these later treatments, straight Opus and Tango Duo (epoxiconazole + tridemorph) moved up in the league table for control although there were still good yield responses to triazole-based mixtures containing some strobilurin. This may be explained, according to Mr Maumené, by the additional effect of the likes of Amistar on fusarium and ear diseases which were prevalent in 1997.
The yield results which show the better response from later applications are based on single applications of fungicides, and ITCF maintains that growers planning a single fungicide spray are still best advised to use it around flag leaf emergence.
In an ITCF mildew trial in the Champagne region, the new active ingredient quinoxyfen (Fortress) shows the greatest control (90%) closely followed by Ogam and a Fortress plus Opus tank mix.
ITCF has tried out a number of combinations of low rate quinoxyfen with low rate triazole with good results. Quinoxyfen, costing around £23/litre in France, is the first product from a new family of fungicides.
"It appears to be a preventive product with little curative effect," says Mr Maumené. This suggests use at the onset of infection and ITCF advise using it instead of a morpholine at the ear 1cm stage.
Alternatively, quinoxyfen at a reduced rate can be used later in a mixture with those triazoles already known to mildew.
Despite the good mildew control given by Ogam, ITCF points out that its French price of around £42/litre means it wont be an economic alternative against mildew alone. It is more likely to be justified where there is a strong risk of septoria, but the trials also had good results from a mixture of cyprodinil (Unix) with a triazole on crops attacked by eyespot, mildew and septoria.
Nor does Mr Maumené yet dismiss the value of using a morpholine on those wheat varieties less susceptible to mildew.
Brown rust trials by ITCF demonstrated the value of an early treatment as soon as first symptoms were seen. Waiting a further two weeks produced slightly poorer control. Products containing strobilurins performed well but the trials results suggest the triazole component played a major part in their success.
As expected, the eyespot trials were dominated by cyprodinil (Unix) in various combinations. The addition of a strobilurin component boosted control and yield responses in the three eyespot trials conducted by ITCF. Best results came from a combination of Unix with Amistar although azoxystrobin on its own is not approved for eyespot control in France. The combination preferred by ITCF – 0.8kg Unix plus 0.5 litre Amistar – yielded slightly less than a mix with 0.8 litre Amistar but was favoured for the lower cost of treatment.
The power of the strobilurins was, however, exhausted in ITCF fusarium trials which were dominated by tebuconazole and metconazole products. The main infection tackled was Fusarium culmorum, which was introduced artificially and is the main fusarium species found in France.
• The trials information and table results in this article first appeared in the French agronomy magazine Cultivar which featured the 1997 fungicide trials by the ITCF.
Continental growers are often first with new wheat
fungicides. David Millar reports on French trials.