Performance of a semi-glossy onion hybrid in certified organic onion fields infested with Thrips tabaci and bulb-rot causing bacteria

Abstract

More than one-third of the certified organic farms that produce dry bulb onions in the USA are in the Great Lakes region, while onion thrips, Thrips tabaci Lindeman, and bulb-rot causing bacteria are important onion production constraints. Onion cultivars with semi-glossy foliage have been reported to support fewer thrips and suffer less thrips damage and therefore may provide a non-chemical option for thrips management. However, inconsistent results regarding efficacy of semi-glossy onions to reduce thrips densities have been reported in field studies. Bacteria causing bulb rot can infect onion plants through wounds in leaves, but the relationship between thrips damage and bacterial bulb rot disease needs further investigation. In this study, the performance of a semi-glossy onion hybrid, ‘USDA Maia’, was compared with the commonly grown waxy, thrips-susceptible cultivar ‘Bradley’ on certified organic farms in New York and Wisconsin from 2019 to 2021. Results indicated that thrips abundance was not different between ‘USDA Maia’ and ‘Bradley’. Bacterial bulb rot incidence in ‘USDA Maia’ was either similar or lower than the incidence in ‘Bradley’ in four of six trials, but higher in the other two. Marketable bulb yield in ‘USDA Maia’ was similar to yield in ‘Bradley’ in four of seven trials, but lower in the other three. Positive relationships between thrips density and bacterial bulb rot incidence occurred in one of three trials for both onion cultivars. Similarly, negative relationships between thrips density and marketable bulb yield only occurred in one of three trials, regardless of onion cultivar. ‘USDA Maia’ did not reduce thrips infestations as anticipated, but it was similar in susceptibility to bacterial bulb rot disease and produced similar large bulb yields as ‘Bradley’. While high thrips abundance can potentially increase incidence of bacterial bulb rot disease, wet growing conditions during bulbing was more important.