EFFECT OF EYESPOT CONTROL ON THE YIELD OF WINTER-WHEAT AND EYESPOT DAMAGE IN BELGIUM

In Belgium and most cereal-growing countries of Western Europe, eyespot (Pseudocercosporella herpotrichoides) is no longer considered as highly damaging to winter wheat, but still remains a major element of decision with farmers when contemplating fungicide application at the stem elongation stage. This paradox stems from the fact that users often associate increases in the yield subsequent to treatment with the activity of the fungicide against eyespot even though the most commonly used fungicide (prochloraz) is also effective against Septoria tritici blotch. This may result in questionable interpretations of field trial data. The matter was investigated in 1994 by observing the field behaviour of 6 winter wheat cultivars subjected to an artificial inoculation with eyespot and a natural Septoria epidemic. Applications of chlorothalonil, which is specifically active against Septoria tritici blotch, and prochloraz, which is active against both Septoria and eyespot were made in order to discriminate the respective effects of the 2 diseases on the yield of winter wheat The low level of yield losses caused by eyespot was again evidenced. The yield increases obtained with the fungicide applications at the first node and last leaf stages mainly resulted from the control of Septoria tritici blotch in both eyespot inoculated and uninoculated plots. Whatever the fungicide used (chlorothalonil or a mixture of chlorothalonil and prochloraz), the fungicide applications always resulted in higher yield increases in the eyespot-inoculated plots. Eyespot control is only economically advisable if associated with control measures against Septoria, which are actually sufficient to ensure high yields. This is probably the reason why, in the absence of Septoria, eyespot control did not give satisfactory results in previously conducted trials. The present trial confirms that eyespot does not result in significant yield losses as long as it is not producing white heads. The presumably overrated influence of eyespot control in winter wheat protection programs is discussed.