Control of velvetleaf (Abutilon theophrasti) at two heights with POST herbicides in Nebraska popcorn

Velvetleaf is an economically important weed in popcorn production fields in Nebraska. Many PRE herbicides in popcorn have limited residual activity or provide partial velvetleaf control. There are a limited number of herbicides applied POST in popcorn compared with field corn, necessitating the evaluation of POST herbicides for control of velvetleaf. The objectives of this study were to (1) evaluate the efficacy and crop safety of labeled POST herbicides for controlling velvetleaf that survived S-metolachlor/atrazine applied PRE and (2) determine the effect of velvetleaf height on POST herbicide efficacy, popcorn injury, and yield. Field experiments were conducted in 2018 and 2019 near Clay Center, Nebraska. The experiments were arranged in a split-plot design with four replications. The main plot treatments were velvetleaf height (≤15 cm and ≤30 cm) and subplot treatments included a no-POST herbicide control, and 11 POST herbicide programs. Fluthiacet-methyl, fluthiacet-methyl/mesotrione, carfentrazone-ethyl, dicamba, and dicamba/diflufenzopyr provided greater than 96% velvetleaf control 28 d after treatment (DAT), reduced velvetleaf density to fewer than 7 plants m−2, achieved 99% to 100% biomass reduction, and had no effect on popcorn yield. Herbicide programs tested in this study provided greater than 98% control of velvetleaf 28 DAT in 2019. Most POST herbicide programs in this study provided greater than 90% control of up to 15 cm and up to 30 cm velvetleaf and no differences between velvetleaf heights in density, biomass reduction, or popcorn yield were observed, except with topramezone and nicosulfuron/mesotrione 28 DAT in 2018. On the basis of contrast analysis, herbicide programs with fluthiacet-methyl or dicamba provided better control than herbicide programs without them at 28 DAT in 2018. It is concluded that POST herbicides are available for control of velvetleaf up to 30-cm tall in popcorn production fields.

Evaluation of POST-Directed Applications of Flumioxazin in New Mexico Chile Pepper

The objective for this study was to determine if POST-directed applications of flumioxazin reduce fruit yield for chile pepper produced on coarse- and fine-textured soils irrigated by furrow. This objective was addressed with a multiyear (2015, 2016, 2017) field study that compared flumioxazin effects on fruit yield against a commercial standard (POST-directed carfentrazone) and the absence of a POST-directed herbicide. The field study occurred at two university research farms that differed in soil texture. On fine-textured soil, treatments included the no POST–directed herbicide control and the following four POST-directed herbicides applied to raised beds: (1) flumioxazin at 107 g ai ha–1applied 4 wk after crop thinning, (2) carfentrazone at 35 g ai ha–1applied 4 wk after crop thinning, (3) flumioxazin at 70 g ai ha–1applied 4 and 6 wk after crop thinning, (4) carfentrazone at 35 g ai ha–1applied 4 and 6 wk after crop thinning. On coarse-textured soil, treatments included the no POST–directed herbicide control and the following three POST-directed herbicides applied 4 wk after crop thinning: (1) flumioxazin at 107 g ai ha–1applied to raised beds, (2) flumioxazin at 107 g ai ha–1applied to furrows, (3) carfentrazone at 35 g ai ha–1applied to raised beds. On fine-textured soil, treatment did not affect fruit yield. On coarse-textured soil, flumioxazin applied to furrows did not reduce fruit yield, but flumioxazin on raised beds reduced fruit yield of some cultivars in 2015 and 2017. Year-to-year variability in both flumioxazin-induced yield loss and soil characteristics suggested that chile pepper sensitivity to flumioxazin was negatively associated with soil organic matter content. In a follow-up greenhouse study, soil organic matter lessened flumioxazin-induced crop injury. In general, this study indicates that recommendations for POST-directed flumioxazin in New Mexico chile pepper will need to be soil-type specific.

Herbicide Control Strategies for Ventenata dubia in the Intermountain Pacific Northwest

Ventenata dubia is an exotic annual grass that has become increasingly invasive in various perennial grass systems throughout the Intermountain Pacific Northwest. Currently, little information is available to landowners about herbicide control options. In our first field study, we evaluated V. dubia control efficacy and perennial grass tolerance of herbicides applied pre-emergence (PRE) at two locations and as an early postemergence (EPOST) application at four different conservation reserve grasslands, with each grassland dominated by different perennial grass species. Treatments included flufenacet plus metribuzin (303 + 76 g ai ha−1 [0.27 + 0.07 lb ai ac−1]), propoxycarbazone-sodium (49 g ai ha−1 [0.04 lb ai ac−1]), rimsulfuron (53 g ai ha−1 [0.05 lb ai ac−1]), sulfosulfuron (53 g ai ha−1 [0.05 lb ai ac−1]), and imazapic (105 g ai ha−1 [0.09 lb ai ac−1]). Rimsulfuron and flufenacet plus metribuzin applied PRE provided > 90% control 10 mo after treatment (MAT). Rimsulfuron and sulfosulfuron applied EPOST provided > 90% control 9 MAT. Herbicide injury to bluebunch and intermediate wheatgrass was negligible across treatments. Imazapic and sulfosulfuron applied EPOST resulted in significant injury to smooth brome and timothy. In our second study, we addressed the following question: Will fall herbicide plus fertilizer treatments improve V. dubia control compared with herbicide treatments alone? We imposed fall herbicide treatments in main plots and fertilizer treatments (fall N, fall P, fall K, fall PK, spring N, NPK) in split plots at three study locations. Herbicide treatments resulted in high levels of V. dubia control. Differences in V. dubia abundance among fertilizer treatments were negligible 9 MAT. Within herbicide control plots, spring N and NPK treatments resulted in significant increases in perennial grass cover and decreases in V. dubia cover (9 MAT). This result indicates that spring N applications timed to the onset of perennial grass growth could be utilized as a component of an integrated management strategy for V. dubia in invaded perennial grass systems.

Influence of Seeding System Disturbance on Preplant Incorporated Herbicide Control of Rigid Ryegrass (Lolium rigidum) in Wheat in Southern Australia

Field experiments were conducted in 2008, 2011, and 2012 to investigate the interaction between seeding system disturbance and PPI herbicides on rigid ryegrass control in wheat. Of the herbicides examined, prosulfocarb +S-metolachlor, and pyroxasulfone provided ≥ 70% control of rigid ryegrass, irrespective of seeding system. In contrast, trifluralin was the least-effective herbicide against rigid ryegrass and was particularly ineffective when used with single disc (10% control) relative to the triple-disc seeding system (80%) in 2012. Trifluralin consistently reduced wheat density when incorporated using single discs (46 to 59%) but not do so with the triple disc or double-shoot knife-point systems. Although there were large differences in crop establishment because of herbicide phytotoxicity, that did not always translate into large differences in yield because wheat was able to recover from reductions in plant density by increasing the spike number per plant. Pyroxasulfone caused no damage to wheat and appeared to be the most suitable PPI herbicide for use with single-disc seeding systems.