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Onion (Allium cepa L.) bacterial diseases can cause catastrophic crop losses. Chemical and biological control products are not curative and have mixed or limited efficacy at preventing onion bacterial diseases. Cultural management strategies, such as appropriate irrigation and nitrogen (N) management practices, can reduce the risk for bacterial infection and disease progression. This review synthesizes available literature on cultural management strategies to mitigate onion bacterial diseases and identifies knowledge gaps, promising strategies, and limitations. This synthesis revealed that high N fertilizer application rates, the use of overhead irrigation, and late‐season irrigation or rainfall, especially during field curing, can increase bacterial disease pressure. These factors contribute to conducive conditions for bacteria to colonize the foliage and neck of onion plants. Other in‐season strategies, such as reducing the total amount of irrigation or adjusting application rates of nutrients other than N, have not limited losses to bacterial bulb rots while maintaining desired yields. At the end of the growing season, appropriate timing of lifting bulbs (undercutting to sever the roots) and other practices that speed field curing can reduce the risk of bacterial bulb rots. However, it is less clear if topping (removing foliage) before or after curing influences bacterial bulb rots. Conflicting results reported for some cultural management strategies indicate that local conditions, such as climate and soil types, must be considered for optimizing practices to manage onion bacterial diseases. Advancing our scientific understanding and grower awareness of strategies that reduce onion bacterial diseases is a cost‐effective opportunity to avoid losses. Core Ideas: Biological and chemical control options for onion bacterial diseases are not curative and have limited efficacy.Crop cultural management practices can mitigate the risks of bacterial infection and disease progression.In drier climates, drip and furrow irrigation reduce the risk of onion diseases compared to overhead irrigation.High N fertilizer rates or N applications after bulb initiation can increase losses to onion bacterial bulb rot.Appropriate timing of lifting and providing optimum curing conditions for onion bulbs mitigate losses to rot. [ABSTRACT FROM AUTHOR]

Light leaf spot, caused by the ascomycete Pyrenopeziza brassicae, is an established disease of Brassicaceae in the United Kingdom (UK), continental Europe, and Oceania (OC, including New Zealand and Australia). The disease was reported in North America (NA) for the first time in 2014 on Brassica spp. in the Willamette Valley of western Oregon, followed by detection in Brassica juncea cover crops and on Brassica rapa weeds in northwestern Washington in 2016. Preliminary DNA sequence data and field observations suggest that isolates of the pathogen present in NA might be distinct from those in the UK, continental Europe, and OC. Comparisons of isolates from these regions using genetic (multilocus sequence analysis, MAT gene sequences, and rep‐PCR DNA fingerprinting), pathogenic (B. rapa inoculation studies), biological (sexual compatibility), and morphological (colony and conidial morphology) analyses demonstrated two genetically distinct evolutionary lineages. Lineage 1 comprised isolates from the UK, continental Europe, and OC, and included the P. brassicae type specimen. Lineage 2 contained the NA isolates associated with recent disease outbreaks in the Pacific Northwest region of the USA. Symptoms caused by isolates of the two lineages on B. rapa and B. juncea differed, and therefore "chlorotic leaf spot" is proposed for the disease caused by Lineage 2 isolates of P. brassicae. Isolates of the two lineages differed in genetic diversity as well as sensitivity to the fungicides carbendazim and prothioconazole. [ABSTRACT FROM AUTHOR]