Effects of Mykos Gold Granular on Pink Root, White Rot, and Growth of Sweet Onion Near Walla Walla, Washington

Washington State University researchers evaluated the arbuscular mycorrhizal fungi (AMF) inoculant Mykos Gold Granular in commercial sweet onion fields near Walla Walla, Washington. Trials were conducted in a spring-planted crop in 2017 and two fall-planted crops in 2017–2018 to assess effects on onion growth and two soilborne diseases of concern to growers: pink root and white rot. The inoculant was applied in-furrow at planting and compared with untreated control plots using replicated field trials.

In the spring-planted crop, AMF colonization of onion roots increased significantly in inoculated plots compared with controls. Although most growth and yield variables were not statistically different, the number and weight of jumbo bulbs tended to be higher in inoculated plots. In fall-planted trials, onion stand counts were significantly higher in inoculated plots, but disease incidence and severity remained low and were not significantly affected by treatment. Overall, the results suggest the AMF inoculant may provide modest production benefits under some conditions, particularly where soil phosphorus levels are relatively low and untreated seed is used.