Evaluation of an Onion Soil Amendment to Reduce White Rot Sclerotia in Garlic

Series/Report Number: COARC2014

Abstract: White rot is one of the most important diseases of onion, garlic, and other Allium crops. The pathogen survives in the soil as sclerotia, which specifically germinates in response to chemical compounds elicited by Allium species. Onion soil amendment, a byproduct of onion processing activities, is a potential source of naturally occurring sclerotia germination stimulant compounds. The objective of this research is to determine the effectiveness of onion soil amendment, with and without tarping and fungicides, at reducing S. cepivorum populations in field soils. Field plots were established and treated with onion soil amendment or left untreated. One half of the plots were covered with tarps for 6 days after onion soil amendment application and the other half were left uncovered. Soils were sampled before treatment applications and periodically throughout the season to quantify the number of viable sclerotia in each plot. Garlic was planted and an in-furrow treatment of tebuconazole was applied to half of the plots. Significant effects of onion soil amendment or tarping were not observed and significant interactions were not detected (P > 0.05). The combined effects of onion soil amendment, tarping, and tebuconazole on white rot symptoms, marketable yield, and post-harvest sclerotia populations will be determined after harvesting garlic in 2015.