Definition of infection period for field infection of scald in Victoria

Abstract

Conditions suitable for infection of barley with Rhynchosporium secalis were determined by exposing seedlings to inoculum from scald-infected barley plants growing in the field. Maximum infection occurred when the duration of leaf surface wetness was c. 12 h and the average temperature during those periods was c. 6¦C. On this basis potential infection periods were defined as periods of leaf surface wetness of >12 h duration with an average temperature of >6¦C during the period. Meterological records indicated that during the 1983-89 growing seasons there was an average of 91 periods of leaf surface wetness per year at Walpeup and 104 at Horsham and that c. 20% were potential infection periods. The modal duration of leaf surface wetness category was >9-12 h at Horsham and >0-3 h at Walpeup and the modal average temperature category during periods of leaf surface wetness was >6-9¦C at both locations. None of the six most commonly occurring combinations of duration and temperature during periods of leaf surface wetness met the criteria for potential infection periods defined above.