Effect of agronomic practices on disease incidence, severity, and impacts in Montana cropping systems
Ranabhat, Nar Bahadur
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Integrated pest management is at the foundation of sustainable cropping systems. This thesis investigated 1) the influence of alternative host plants and agronomic practices on Wheat streak mosaic virus (WSMV) risk, and 2) how cover crop termination methods influence diseases in grazed organic, tilled organic, and chemical no-till systems. To assess the influence of alternative hosts including volunteer wheat, Bromus tectorum, Setaria viridis, and Zea mays on WSMV incidence and its vector, the wheat curl mite (Aceria tosichella, WCM) movement during the fall, a 'trap plant' capture system was used. In 2013, alternative hosts had similar WCM infestation levels compared to the control in most weeks. In 2014, spring planted B. tectorum and volunteer wheat increased the incidence of WSMV and abundance of WCM compared to control. In a study assessing the impact of planting date and winter wheat variety on WSMV incidence, there was almost no infection of WSMV across resistant wheat varieties. However, Pronghorn, a susceptible wheat variety, had a higher WSMV incidence at the early planting date than recommended and late planting dates. In a companion study of the impact of wheat variety and timing of N application on WSMV incidence, results did not differ across N application timing across resistant varieties. However, early spring N application in 2014 had a higher WSMV incidence compared to fall and late spring N application in Pronghorn and Yellowstone. A study assessing the impact of cropping systems on diseases indicated that disease incidence during the transition to organic period in 2013 and 2014 as well as an established organic year, 2016, was similar at tillering and flowering stages of winter wheat between the grazed organic, tilled organic, and chemical no till system. However, disease incidence was variable between systems at the matured growth stage in 2014 and 2016. In 2015, disease incidence varied between systems at all growth stages. Overall, disease severity was similar in winter wheat between grazed organic, tilled organic, and chemical no till systems, indicating disease is not a major constraint to organic methods of crop production during the transition period.