Assessing the contribution of ethaboxam in seed treatment cocktails for the management of metalaxyl-resistant Pythium ultimum var. ultimum in Pacific Northwest spring wheat production

Hard red spring wheat is an important crop in the Pacific Northwest and is a component of a 3-year crop rotation involving soft white winter wheat; cool season pulse crops such as pea, lentil and chickpea; and canola. Pythium root rot and damping-off have long been observed as an annual problem, particularly in spring planted crops. As such, a seed treatment that includes metalaxyl is very common. Recently, an increase in the incidence of Pythium damping-off highlighted that there is an emerging population of Pythium spp. that are resistant to traditional seed treatments containing metalaxyl. The use of alternative chemistries to manage Pythium root rot and damping-off has gained regional interest to increase crop health and improve yields. The effectiveness of ethaboxam was evaluated along with two other seed treatment cocktails in controlling metalaxyl-resistant Pythium in replicated field experiments of spring wheat over three growing seasons in northern Idaho. Emergence, seedling characteristics, plant height, yield and test weight were assessed. The addition of ethaboxam to metalaxyl-containing seed treatment blends consistently increased emergence and yield of spring wheat compared to seed treatment blends containing metalaxyl only. First leaf length, an indirect measure of early season Pythium damage, was longest in seed treatments containing ethaboxam and the average number of tillers was lower, likely due to increased emergence, than non-treated seed. These results indicate that ethaboxam can improve disease control in spring wheat production when applied as a seed treatment in combination with metalaxyl, specifically in the presence of metalaxyl-resistant Pythium spp.