Seed treatment of wheat with benzimidazole fungicides against Septoria tritici under semi-arid conditions

Seed treatment with benzimidazole fungicides ensured complete protection of wheat plants, at least till the fifth leaf stage, from Septoria tritici after artificial inoculation in the greenhouse. Under field conditions, protection against the disease manifested itself as a reduction of disease severity on first leaves and of the number of diseased first leaves. Burning of infested straw at the end of the previous season was more effective in the reduçtion of the disease; its effect led to a drastically decreased inoculum and was therefore expressed on other leaves as well. Plots planted with treated seed yielded significantly more than control plots, while straw burning did not contribute significantly to yield increase. It seems that under semi-arid conditions seedling infection is common, but these conditions are unfavourable for the occurrence of septoria at later stages of wheat growth. Under these conditions the very early seedling development seems critical for further plant development and protection against disease at this stage is reflected in yield. Unpublished data from other experiments support the contention that when plants experience water stress a more efficient disease control does not yield as well as less efficient control (in this case: burning vs. seed treatment, respectively). Under semi-arid conditions, where yields are low and the economical risk of chemical control is high, seed treatment might be a cheap insurance against disease. If conditions become more favourable for wheat growth and disease development, chemical spray may give supplementary protection at a later stage.