Reduction of spore spread of common bunt (Tilletia tritici) via combining equipment

Summary

The disease common bunt (Tilletia tritici syn. T.caries) has become a more frequent problem in Europe during the last 15 year. In organic farming, common bunt causes serious problems for seed producers, and many seed lots are discarded due to contamination with Tilletia tritici. Due to the biology of Tilletia tritici, with spores loosely attached to the surface of the grain, there is a risk that spores can be disseminated via grain handling equipment, including combine harvesters. Preventive efforts should focus on the role of grain handling equipment, and how the fungus life cycle can be broken. We have investigated the dissemination of spores via the combiner after harvesting infected fields. We conducted six trials over three years, counting the number of spores in up to seven emptyings of the combiner. Up to 4 emptyings with non-contaminated grains are needed in order to achieve an acceptable low level of contamination. Using Denmark as a case, we discuss several important factors influencing disease spread via harvest equipment. It is concluded that one easy preventive strategy is to avoid using the first 4 emptyings of the combiner. This method should always be combined with analysis of seeds for spore load.