A COMPARISON OF 6 METHODS TO CONTROL TAKE-ALL IN WHEAT

Take-all is a root disease of wheat caused by the fungus Gaeumannomyce s graminis var. tritici (Ggt). The most common method of control, grow ing wheat after a break crop, is not always feasible. This study compa red the use of a break crop with 5 alternative control methods in a se ries of field experiments in south-eastern Australia. The methods of c ontrol tested were: (1) fungicide added to fertiliser; (2) soil fumiga tion with methyl bromide; (3) applied chloride; (4) seed treatment wit h microbial antagonists; (5) a prior brassica break crop; and (6) a 12 -month-long fallow. Eight experiments were conducted over 2 years but not all treatments were included in each experiment. The most successf ul control methods were growing wheat after a brassica break crop or a long fallow. Both methods gave 72% yield increases over wheat growing after wheat. None of the other methods gave consistent, significant, or profitable yield increases or disease control. The mean yield incre ases in the year of application were 8% for the fungicide, 6% for micr obial antagonists, 4% for chloride, and 7% for fumigation. The probabl e reason that fungicide and microbial antagonists were ineffective was that they were localised in the furrow where they were applied, where as roots became infected in the inter-row space. Probable reasons that chloride was ineffective were that the background soil chloride level s were generally above the responsive range, and that roots became inf ected with take-all after the chloride was leached from the topsoil. T he limitation of fumigation was that it suppressed natural antagonists of the Ggt, apparently leading to reinfection at higher levels than b efore. There was also evidence of Ggt re-infection in the second year after break crops, leading to an apparent 'boomerang' effect. Take-all inocula at the sites were measured in pre-sowing soil bioassays, wher eas disease incidence was determined in seedlings and as 'whiteheads' as crops approached maturity. The only consistent pattern among the me asurements was low disease incidence after break crops and the long fa llow. Otherwise, there were low correlations between the 3 sets of mea surements, suggesting that environmental changes after the soil bioass ay and seedling assessment played critical roles in the progress of th e disease.