Two methods (visual assessment and a bioassay) of detecting the presence of G. graminis var. tritici in wheat stubble were compared. Of the stubble visually assessed as infected, only 4 % was not confirmed as infected by the bioassay. On the other hand, the bioassay showed that 41 % of the stubble visually assessed as free of infection was incorrectly assigned.

Bioassays of wheat stubble were used to study the survival of G. graminis var. tritici in the field. There were marked differences in survival between the two localities investigated. At Ceduna the number of macro-sites with stubble (crowns) containing viable G. graminis var. tritici dropped from 90 % in early February to 82 % in midNovember, while at Turretfield the drop was from 96 % in late January to 30 % in late August. In another experiment at Ceduna, the survival of G. graminis var. tritici in field soil was studied using a bioassay of soil cores. There was only a small drop in the incidence of G. graminis var. tritid in cores removed at regular intervals from the takeall patch over a period of nearly one year.

A bioassay was used to study the effect of various storage treatments on the survival of G. graminis var. tritici in soil cores removed from a take-all patch. There was no significant change in the incidence of the fungus when the soil was maintained either dry (-250 to -980 bars) and cool (15°C), or moist (-4'0 to -7,0 bars) and cool (15°C). When maintained very dry (-980 bars or less) and hot (35°C) or wet (-0'1 to -0,2 bar) and cool (15°C) there was a significant reduction in disease incidence, but considerable levels of viable fungus were still present after 45 weeks storage. Only in wet hot soil (-0'1 to -0,2 bar and 35°C) was the fungus eliminated rapidly.

A method of using grain yield to estimate the incidence of G. graminis var. tritici in the field is described. It was found that a map based on yield alone underestimated the actual incidence. However, when incidence and grain yield were coupled by the use of an "incidence-yield" regression established on a few sites, a map showing estimated levels of G. graminis var. tritici was obtained without destroying the experimental area. Bioassays of stubble and of soil cores were used to establish the actual incidence of G. graminis var. tritici; the former gave better results.

The presence of viable G. graminis var. tritici in field soil was detected by a bioassay. Wheat seedlings were grown in undisturbed soil cores maintained under standard conditions for 4 weeks. The percentage of roots infected per core was the main parameter chosen to give an estimate of the level of G. graminis var. tritici inoculum in the core. Some variability between cores from the same site was observed, but this could be reduced by taking cores over plant remains within take-all patches. In this way, high and reasonably uniform levels of inoculum could be obtained to study the effect of various treatments on the incidence of G. graminis var. trifici.