Effect of Previous Crop, Seedborne Inoculum, and Fungicides on Development of Stagonospora Blotch

Stagonospora blotch of wheat has been difficult to control in the eastern United States. The objectives of this research were to evaluate the effects of field inoculum, seedborne inoculum, and seed treatment and foliar fungicides on Stagonospora blotch development and to develop more effective management strategies. In 1995 and 1996, similar experiments were established in "infested" and "clean" fields using two seed lots of Coker 9543 ("low" and "high" levels of seed infection) and six seed or foliar fungicide treatments. Planting in clean fields, planting seed with a low level of seedborne inoculum, treating seed with difenoconazole or triadimenol + thiram, and applying propiconazole or tebuconazole to the foliage all contributed toward reducing leaf infections by Stagonospora nodorum, severity of leaf and glume blotch, and incidence of S. nodorum in the harvested seed. Propiconazole alone was the least effective treatment. Planting in an infested field tended to negate the beneficial effects of low level of seed infection and fungicide seed treatments. Crop rotations and tillage that allow wheat debris to decompose before the next wheat crop along with difenoconazole or triadimenol seed treatment to reduce seedborne inoculum should be sufficient to avoid serious losses. In fields where wheat is grown every year, tillage and seed treatment would still be helpful, but a foliar fungicide at GS 8 may be necessary for adequate control. Applying an effective fungicide to seed appears to be a more efficient means of reducing seedborne inoculum than does producing seed with low levels of inoculum.