Reducing the risk of onion bacterial diseases through managing irrigation frequency and final irrigation timing

Abstract

Onion bacterial diseases pose a serious economic risk to growers as they can lead to catastrophic crop losses. Moisture in the plant canopy plays a critical role in onion bacterial disease development by dispersing the pathogens onto plants (e.g., in splashing water) and keeping conditions conducive for bacterial growth. For this reason, irrigation management can be a promising avenue for controlling bacterial diseases in regions where irrigation is used widely, particularly overhead irrigation. This study investigated the effects of in-season irrigation frequency and timing of the final irrigation on onion bacterial bulb rot and marketable bulb yield over the 2020 and 2021 growing seasons in Washington State’s semi-arid Columbia Basin, using overhead irrigation. Irrigating twice as often but for shorter periods did not increase the incidence of onion bacterial diseases or affect yield compared to longer, less frequent irrigation events under the conditions of this experiment. However, timing of the final irrigation did influence bacterial disease incidence. Irrigating until the tops (leaves and necks) had fallen over on 90% of onion plants led to culling of more bulbs at harvest as a result of bacterial rot and more bulbs with bacterial rot after five months in storage compared to plots in which irrigation was stopped two weeks earlier, at 5–10% tops down. Ending irrigation at 5–10% tops down did not reduce marketable yield or affect bulb size distribution. In semi-arid regions, careful irrigation management can be an important part of managing onion bacterial diseases, particularly at the end of the season when onion plants are most vulnerable to neck and bulb infection.

Keywords

• Allium cepa L.
• Bacterial bulb rot
• Pantoea agglomerans
• Burkholderia gladioli pv. alliicola
• Irrigation scheduling
• Overhead irrigation