Barley net blotch: Survey of sensitivity of Pyrenophora teres to fungicides

Abstract

Barley net blotch first came to prominence in the late 1970s, and was the major disease in all winter barley growing areas. Control was achieved with the newly introduced DMI fungicides, propiconazole and prochloraz, and in recent years the disease has been at more moderate levels. The main fungicides used to control net blotch continued to be those in the DMI group, and pathogen sensitivity has been monitored since the 1980s.

In this project, net blotch samples were taken from 25 winter barley crops in England during the early summer of 1999. Over 200 isolates of the pathogen, Pyrenophora teres, were obtained from 22 of these crops and tested for sensitivity to four DMI fungicides ( propiconazole, flusilazole, epoxiconazole and prochloraz ), in a repeat of a similar survey in 1996. In all cases, the mean sensitivity of the isolates was similar to those found three years previously. Therefore, the marked shift in sensitivity that had been occurring from 1988 to 1996 had stopped. The close relationship in sensitivity of isolates between propiconazole and flusilazole was apparent in 1999, as it had been in 1996.

For the first time, isolates were screened to see if any resistance to the strobilurin fungicide azoxystrobin was present in the UK P. teres population. A total of 176 isolates were screened and no resistance was detected.

The anilinopyrimidine fungicide, cyprodinil offers another alternative to the DMIs for net blotch control. Sensitivity to this fungicide was also examined for the first time in 1999. In general, isolates of P. teres were very sensitive to cyprodinil, but the finding of three isolates that made some growth in the presence of the fungicide indicates a variability in sensitivity levels in the population. If farmer use of cyprodinil increases, a shift in the sensitivity of the population might be expected in the future. The results of the survey have been of value in formulating advice to farmers on net blotch control, and were used in the production of the FRAG-UK/HGCA leaflet, 'Guidelines for preventing and managing fungicide resistance in cereal pathogens'.