NEW FUNGICIDES AND THEIR INTRODUCTION IN WHEAT AND BARLEY SPRAY PROGRAMS IN FRANCE
C MAUMENE and G COULEAUD
Technical Institute for Cereals and Forages, Experimental Research Station, 91720 Boigneville, France
Cereals, mainly represented by wheat and barley, are grown on more than 6 million hectares in France. Several foliar diseases are important on these crops. The most commonly observed disease on wheat is the Septoria complex caused by Septoria tritici and, in some cases, by Stagonospora nodorum. Yellow rust (Puccinia striiformis) is mainly present on susceptible cultivars on the northern coast while brown rust (Puccinia recondita) occurs annually in southern France. The appearance of powdery mildew (Erysiphe graminis) is determined, to a large extent, by the susceptibility of the cultivar. In addition, this disease is of particular importance in specific regions such as Champagne. Eyespot (Pseudocercosporella spp.) is considered to be significant only in the northern part of France where fungicides are broadly applied for this disease. The incidence of Fusarium ear blight is variable depending on the environmental conditions of the year. The main diseases of barley are net blotch (Pyrenophora teres) and leaf blotch (Rhynchosporium secalis).
On average, wheat and barley are sprayed twice per season but the number of applications can range from 1 to 3 depending on the region. A large choice of fungicides is available to farmers with over 30 active ingredients and more than 200 commercial products registered.
The arrival of new active ingredients, such as cyprodinil, quinoxyfen, azoxystrobin, and kresoxim-methyl, is much more than a simple commercial opportunity . Such molecules with new modes of action, novel redistribution properties on and in the plant, or high intrinsic activity contributing to a long residual efficacy allow new possibilities for disease control strategies. The addition of these novel fungicides is particularly welcome and needed because the demethylation-inhibiting fungicides (DMI’s) have been fully exploited during the past 20 years. Thus the availability of new modes of action is of great interest.
Cyprodinil has been successfully introduced in the marketplace since 1993 as an initial spray primarily to control eyespot. This utility is particularly important since existing fungicides no longer give acceptable disease control. Cyprodinil is also used on a large scale on barley, mainly against net blotch, which is no longer controlled satisfactorily with DMI fungicides.
Quinoxyfen, registered in 1997, will be used for powdery mildew control. With strong residual efficacy, it is expected to replace some uses of fenpropimorph and fenpropidin. Quinoxyfen will be applied in mixtures with DMI fungicides and probably in the near future, with strobilurin analogs at appropriate timings for these fungicides. However, the best control of powdery mildew has been obtained with a very early application of quinoxyfen at Zadoks’ GS30. This fungicide may also be useful as an additional spray, when needed, devoted exclusively to powdery mildew control.
Two synthetic strobilurin fungicides with utility on cereal diseases have been recently registered for use in France: azoxystrobin and kresoxim-methyl. The activity of azoxystrobin is moderate against powdery mildew and leaf blotch but excellent against other foliar diseases. It is especially effective against net blotch. The spectrum of kresoxim-methyl is narrower; however, in mixture with epoxiconazole, it contributes to a significantly improved efficacy against powdery mildew as well as other diseases, particularly S. tritici and net blotch.
The introduction of azoxystrobin and kresoxim-methyl offers a broad range of possibilities in developing spray programs for disease control . The most direct way consists of substituting a strobilurin, at reduced or full dose, either alone or in mixture with a DMI, for one of the fungicides currently used. An alternate approach, based on the excellent residual efficacy of the strobilurin analogs, is to build new strategies with a reduced number of applications.
Lastly, it is estimated that fungicides and especially DMI’s have increased wheat yields by 1,5 t/ha during the past twenty years. It is predicted that these new molecules, particularly the strobilurin analogs, will allow further progress.References
1. Maumené C, Couleaud G, Hébrard JP, 1997. Perspectives Agricoles 230, dossier 16 p.
2. Félix I, Bonnefoy M, Bouchié JM, Chevalier B, Desroches B, Machaire M, 1998. Perspectives Agricoles 231, pp. 56-63.