The control of tan spot of wheat (caused by Pyrenophora tritici-repentis: a possible emerging disease in New Zealand

Pyrenophora tritici-repentis, the cause of tan spot of wheat was first recorded in New Zealand in 1979, but only on wheat seed. However, this pathogen has recently been recorded as causing possible yield losses in isolated crops. A small plot trial set up in a central Canterbury crop of cv. Saracen tested several fungicides alone or in mixtures. Control was not entirely effective since tan spot infection was well established when the first applications were made at GS33 (third node detectible). Nevertheless, two triazoles (propiconazole and prothioconazole) and three SDHI fungicides (isopyrazam, bixafen plus prothioconazole and fluxapyroxad plus epoxiconazole) all gave similar levels of control either when applied alone or in mixtures. Two triazoles (epoxiconazole and difenoconazole) were less effective alone, while addition of strobilurin (pyraclostrobin) to mixtures gave little extra control. Several treatments showed significant increases in green leaf retention and final grain yield. The life cycle of the pathogen dictates that management of the over-wintering inoculum in stubble is a probable essential step in control of the disease.