Properties of new fungicides for winter wheat and winter barley

Abstract

The objective of this project was to provide information on the biological properties of fungicides under development for cereals in the UK, such that information on how they compared with current commercial standards and how to make best use of them would be available at product launch.

Nine field experiments were undertaken in each of the 1996, 1997 and 1998 harvest years, six on winter wheat and three on winter barley. Sites and cultivars were selected to test the fungicides in severe epidemics of all the major foliar diseases of wheat and barley. Ten new fungicides were investigated during the course of the project. Of these, nine are now commercially available, representing seven active ingredients marketed during the course of the project, or subsequently. These were kresoxim-methyl (in Landmark and Ensign), azoxystrobin (in Amistar and Amistar Pro), metconazole (Caramba) tetraconazole (Eminent), cyprodinil (Unix), quinoxyfen (Fortress) and spiroxamine (Neon). The experimental design was to test single applications of each fungicide at the full recommended rate, at four or five growth stages between GS 30 and GS 59. This allowed the protectant and eradicant properties of each fungicide to be determined. A standard commercial two-spray programme (GS 31/32 and GS 39), designed to give full disease control, was also included, to show the yield potential of the crop in the absence of disease and to determine the contribution towards that yield that could be achieved with each single application.

The main advantage in disease control from Landmark compared with epoxiconazole (Opus) alone was in greater protectant activity on each leaf layer against S. tritici from sprays applied before emergence of that leaf layer, allowing greater flexibility overall in fungicide timing. There was also longer retention of green canopy, particularly on leaves 2 and 3, which resulted in consistently higher yields than those from Opus. Azoxystrobin, used alone as Amistar, showed good protectant activity against Septoria tritici and yellow rust on wheat, but its lack of eradicant activity was evident. When Amistar was used in mixture with Opus, its performance was similar to that from Landmark.

Although kresoxim-methyl, in mixture with fenpropimprph, gave good control of wheat mildew, this is likely to have limited commercial value for mildew control because of the occurrence of resistance to strobilurins, which has now been confirmed in wheat mildew in the UK, albeit at low frequency. The best wheat mildew control was given by Fortress, particularly when applied early. Unix and Neon both showed useful mildew activity, but should be used in mixture for best results.

The superiority of Opus over other azoles for S. tritici control was confirmed, but it showed little improvement over Folicur against yellow rust. One new azole fungicide, metconazole (Caramba) showed many similar properties to Folicur, with slightly greater activity against S. tritici but poorer control of yellow rust. Tetraconazole (Eminent) did not show any improvement over Folicur in activity againstS. tritici, and was weaker against yellow rust.

On barley, the performance of Amistar against net blotch, a disease which has proved particularly difficult to control with older fungicides, was superior to that of any other fungicide, and brown rust control was comparable with that from the best azole, Opus. For Rhynchosporium, the currently available strobilurins are beneficial in azole or morpholine mixture but do not offer the advance in disease control that Amistar does for net blotch. Among other new fungicides, Unix has useful activity against net blotch, mildew andRhynchosporium, but needs to be used in mixture for best effect.