The troublesome weed Johnsongrass [Sorghum halepense (L.) Pers.] is predicted to expand its range under climate change. In the process, it is likely to become more competitive in corn (Zea mays L.) production areas of the northeastern United States and southern Canada. A replicated greenhouse experiment was conducted to measure interspecific and intraspecific competition between an S. halepense biotype from central New York State (northern range edge) and corn under drought and well-watered conditions. Drought stress significantly reduced the biomass and height of corn and S. halepense in both rounds of the experiment (P < 0.001). Drought stress increased the root-to-shoot ratio of S. halepense (P < 0.001) and reduced the root-to-shoot ratio of corn (P < 0.001). In one run of the experiment, corn produced 19.3% more aboveground biomass (P < 0.001) and 6.6% more height (P < 0.001) when competing with an S. halepense plant (interspecific competition) than when competing with a second corn plant (intraspecific competition). Drought conditions increased the advantage of corn plants grown under interspecific relative to intraspecific competition (P = 0.012). In that round of the experiment, biomass of S. halepense was 12.9% higher under intraspecific competition than interspecific competition in the well-watered treatment and 15.5% higher under intraspecific competition than interspecific competition in the drought treatment (main effect of competition, P = 0.002). Differences between competition treatments were smaller in the other round of the experiment (P > 0.05). Our findings suggest that the New York S. halepense biotype used in this study may not be as competitive as biotypes found in this weed’s range core in more southern regions of the United States. However, anticipated effects of climate change may increase the abundance and competitiveness of this species in the northeastern United States.

The interplay of management decisions involving soybean (Glycine max L.) planting date, herbicide programs, and herbicide application timings is critical to optimize soybean performance and weed control in Southern Great Plains soybean production systems. This research sought to evaluate soybean yield potential and the level of weed control as influenced by early‐, delayed‐, and late‐ planting dates and various combinations of preemergence (PRE), early‐postemergence (EPOST), and mid‐postemergence (MPOST) weed management programs. A field study was established in Bixby, OK in 2017 and 2018 under irrigated conditions and in Perkins, OK in 2017 under dryland conditions, consisting of three planting windows (early, delayed, and late) of XtendFlex soybean, with or without a PRE (chlorimuron + flumioxazin + pyroxasulfone + glyphosate + dicamba) combined with EPOST or EPOST + MPOST (glyphosate + dicamba) versus no in‐season applications. The gap in late‐planted soybean yield potential, compared to early‐planted soybean, was exacerbated in the dryland systems (1346 kg ha⁻¹) versus an irrigated system (2311 kg ha⁻¹). Use of PRE provided 60% weed control until MPOST and increased yields by 657 kg ha⁻¹ and 457 kg ha⁻¹ for delayed and late‐planted soybean, respectively. Late‐planted soybean with EPOST + MPOST provided up to 50% weed control, but lack of biomass production for cultural control reduced weed control by 29% compared to early‐ and delayed‐planted soybean. From an agronomic management standpoint, the time of soybean planting is influential on the success of weed control measures and soybean yields in double‐cropping system in the Southern Great Plains, particularly with late‐planted soybean.

Plant mapping was introduced in soybean, but its illustrative capabilities in stress response are yet to be implemented. Methods to track the soybean physiological response are explained in this note by mapping pods in a coordinate system. A growth chamber study was conducted to measure the specific impact of simulated moisture stress on crop yield and pod development across three stages of crop growth. The treatment growth stages were R2, R3, and R5 (Full Bloom, Beginning Pod, and Beginning Seed, respectively), with two moisture stress durations of 7 and 14 days. A coordinate system was developed to understand soybean pod setting and yield by plotting each unique point on the plant using a set of numerical coordinates. This method summarizes soybean morphology during its vegetative and reproductive growth. Utilizing this method, we found that the growth stages during which moisture stress is experienced and the duration of the stress determined and influenced the location of pods on the soybean plant. The stress level factors impact the yield on the mainstem and branches by pod capacity at different magnitudes. This encoding procedure assists in tracking the location of aborted pods. It protects the yield by retaining pods, thereby leading to a better understanding of the stress experienced by these plants.

Palmer amaranth ( Amaranthus palmeri S. Watson) is among the most economically damaging weeds in the United States and has evolved resistance to numerous herbicides, including glyphosate. This fast-growing species has expanded its range into different regions, including New York State, where glyphosate-resistant (GR) populations are now found. We evaluated how temperature modifies two components of weed risk, sensitivity to glyphosate and competitiveness against corn ( Zea mays L.), under growth chamber conditions. First, we performed a dose–response study testing glyphosate efficacy for a GR A. palmeri biotype from New York State and a glyphosate-susceptible (GS) biotype from Nebraska. Tests were conducted at low (25/15 C), medium (30/20 C), and high (35/25 C) day/night temperatures. The nontreated GS biotype produced greater biomass at low versus high temperatures. This biotype was highly sensitive to glyphosate across all temperatures. In contrast, biomass of the nontreated GR biotype did not vary with temperature. This biotype was less sensitive to glyphosate across all temperatures. Our second study tested whether temperature modifies the impacts of A. palmeri on corn biomass at four planting densities (zero, one, two, or four A. palmeri with one corn plant). We used the same three temperature regimes and the same two A. palmeri biotypes as the dose–response study. There was no evidence that the biotypes, at any planting density, were more competitive with corn under elevated temperatures. In fact, the biomass of A. palmeri decreased with increasing temperatures while corn biomass did not vary. In the competition study, the GS biotype from Nebraska had higher biomass than the GR biotype from New York. Overall, these results do not support the hypothesis that increasing temperatures would exacerbate the risk posed by the tested A. palmeri biotypes in corn. Instead, these two A. palmeri biotypes may be highly problematic under temperatures already occurring in New York State.