| dc.description.abstract | Management of noxious weeds is an evolving task in agriculture, especially with the current state of herbicide resistance in dominant weed species globally. Johnsongrass (Sorghum halepense) has been consistently ranked as one of the world’s worst weeds, and is considered a high-risk species for the evolution of herbicide resistance (Johnson et al. 2014). Johnsongrass is particularly difficult to control in its crop relative, grain sorghum (Sorghum bicolor), due to the genetic similarities between the two species. Novel tactics for integrated management of this species is thus imperative. Harvest weed seed control (HWSC), developed originally in Australia, is an emerging strategy for minimizing viable seed addition to the soil, but its success depends on the proportion of seeds that are retained on the weed and available for capture during crop harvest and the efficiency of the harvest machinery in separating the weed seed for subsequent destruction. There is also a critical need for developing integrated programs that include chemical and non-chemical options for johnsongrass management in grain sorghum. This study had two specific objectives. First, a four-year field survey (2016-2019) was conducted in multiple locations across Texas and Arkansas to assess johnsongrass seed shattering and determine proportion of seeds that are available for capture by the combine during grain sorghum harvest. Johnsongrass produced as high as 5,929 seeds/m2 in Texas and 808 seeds/m2 in Arkansas, of which >80% was available for capture (at the harvest height) at the time of grain sorghum harvest. Periodic seed shattering assessments showed that individual johnsongrass plants retained >80% of the seeds within the crop harvest window. For the second objective, a four-year study (2016-19) was conducted in College Station, Texas and Keiser, Arkansas involving multiple combinations of integrated management practices in an acetolactate synthase (ALS)-inhibitor-resistant grain sorghum cultivar (Inzen™), including the use of preemergence and postemergence herbicides, desiccant application prior to harvest, HWSC, disking the field after harvest and treating the regrowth with a graminicide. Johnsongrass plant density and soil seedbank size declined drastically when multiple strategies were combined, compared to a standard herbicide-only program. Results of this study show high feasibility for implementing HWSC as part of an integrated program for managing johnsongrass in grain sorghum in the southern US. | en |
