| dc.description.abstract | Smutgrass (Sporobolus indicus) is an aggressive, perennial bunchgrass that invades introduced and native pastures primarily in the southeastern part of the United States. It is problematic to agriculture in range and pasture and is not usually found in row crops. Smutgrass’ prolific seed production allows it to overpower desirable grasses by simply outnumbering them, and its size allows it to outcompete for sunlight. It invades grazed pastures and hay fields making the land difficult to traverse for humans, equipment, and for the animals inhabiting the land. Smutgrass is also undesirable as a food source for cattle. The broad range of variables involved in herbicide applications can make achieving effective weed control challenging. These include application timing, equipment, methodology, weather and many other factors. The impact of these variables has been researched extensively on several weed species; however, no research has been published evaluating application equipment type and the methodology to determine if it can impact herbicide efficacy in smutgrass. There are four primary objectives of this research endeavor. First, determine which herbicides are most effective on smutgrass in individual plant treatments. Second, determine if the inclusion of a pre-emergent, residual herbicide with common post-emergent treatments can increase smutgrass control. Third, determine if nozzle type will impact the efficacy of herbicides in broadcast smutgrass control. Lastly, determine whether different methods of individual plant treatment impact the efficacy of herbicides, including aerial application, foliar ground-based and post-directed ground-based application. Individual plant applications of various rates of glyphosate, liquid hexazinone, solid hexazinone and glyphosate + imazapic, at all rates used, provided 100% control of smutgrass within thirty days and continued to cause complete necrosis to ninety days. Liquid hexazinone treatments, half hexazinone tablets and the low rate of glyphosate alone tended to be the safest to the desirable grasses, recovering to 100% by the end of the study. The bermudagrass treated with the middle rate of glyphosate and low rate of glyphosate + imazapic was highly variable in recovery, with both having 30% or more difference in recovery between locations after ninety days, the high rate of glyphosate recovered poorly to 25-50% and middle and high rate of glyphosate + imazapic were highly injurious and bermudagrass recovered to a maximum of 55%, and a minimum of 0%. Including indaziflam as a pre-emergent following a post-emergent herbicide did not cause a significant difference in the number of newly emerged seedlings. Prior to the indaziflam applications, three treatments received labeled rates of hexazinone, and one received glyphosate. Glyphosate reliably controlled the smutgrass in both years while also causing severe damage to desirable grasses, only being tolerated by 3% of desirable grass in the plots four weeks after application. However, the desirable grass recovered to 53-75% by 18 weeks after PRE-applications. Hexazinone applications failed to adequately control smutgrass the first year, concluding at 25% control, while providing 96-100% control the second year. However, the desirable grasses at both locations fully recovered in both years by 18 weeks after PRE applications. When evaluating control by nozzle selection, there was no significant difference within herbicides by nozzle selection in this research. However, this study showed that an application of glyphosate three to four weeks before an application of hexazinone significantly increased smutgrass control at 98%, compared to hexazinone alone at 89-90% control. Glyphosate followed by hexazinone (59-60%) was significantly more injurious to desirable grasses than hexazinone alone (84-85%) at 40 weeks. By 46 weeks, glyphosate followed by hexazinone recovered to 76-79% and was not significantly different than hexazinone alone (87- 88%) at the conclusion of the study. When applying hexazinone to individual plant treatments, targeting the foliage caused 100% necrosis in all plants by thirty days and continued to 240 days, but applying hexazinone post-direct did not cause 100% necrosis until springtime, 240 days after treatment. Applying post-direct to target the smutgrass roots also caused significantly more damage to desirable grasses around the plant (37% tolerance) at 75 days compared to foliar application (84% tolerance). Both methods recovered to 100% bermudagrass tolerance by 240 days. Lastly, when applied as individual plant treatments, hexazinone and glyphosate + hexazinone provided similar levels of smutgrass control regardless of whether applied from the ground or the air. Hexazinone applied alone to smutgrass resulted in NDVI readings of 32-22 and 91-94% control, while desirable grass tolerance was 93-95% and significantly better than any other herbicide and not significantly different than the untreated check. Smutgrass treated with Glyphosate + hexazinone had NDVI readings of 16-30 and provided 94-100% control with a significant amount of injury to desirable grass (73-74% tolerance). Glyphosate alone applied by hand (17-20) did cause significant reduction in smutgrass NDVI readings compared to glyphosate applied from a UAS (26-30), but there was no significant difference by method for smutgrass control or desirable grass tolerance. | |
