Few herbicides are available for use in lettuce and hand weeding is required for commercially acceptable weed control. More effective herbicides are needed. Here field evaluations of pendimethalin and S-metolachlor for weed control in transplanted lettuce are reported. Pendimethalin was evaluated PRE at rates between 0.6 and 6.7 kg ai ha−1, and POST at 1.1 and 2.2 kg ha−1. Both pendimethalin PRE and POST applications were safe to transplanted lettuce and provided similar weed control. Pendimethalin PRE at rates of 1.1 kg ha−1 and higher provided better weed control than the industry standard, pronamide at 1.3 kg ha−1. S-Metolachlor PRE was evaluated at rates between 0.6 and 5.6 kg ha−1. S-Metolachlor at rates up to 2.8 kg ha−1 caused little or no crop injury or yield reduction in transplanted lettuce, and S-metolachlor at rates of 1.4 kg ha−1 and higher improved weed control compared with pronamide at 1.3 kg ha−1. Pendimethalin and S-metolachlor are not labeled for transplanted lettuce, but we suggest that labeling be pursued at rates of 1.1 and 0.7 kg ha−1, respectively. Pendimethalin at 1.1 kg ha−1 applied PRE or POST improved weed control by 57 and 42%, respectively compared with pronamide. S-Metolachlor PRE at 0.7 kg ha−1 was less effective on weeds than pendimethalin, but maintained weed control level similar to pronamide. Pendimethalin and S-metolachlor have potential for use in transplanted lettuce production and provide alternatives to current transplanted lettuce herbicides.

Potato, dry bean, and sugar beet production have increased markedly in recent years on irrigated cropland in Alberta, Canada. Concerns exist about declining soil quality and increased soil erosion when these low-residue crops are grown in sequence in short-duration rotations. A 12-yr rotation study was conducted to determine the merits of adopting various conservation practices (reduced tillage, cover crops, composted manure) and longer-duration rotations to develop a more sustainable production system for these row crops. This article reports on weed density and weed seedbank data collected in the study. Weed densities recorded prior to applying postemergence herbicides indicated that conservation compared with conventional management treatments had greater weed densities in 30 to 45% of the cases in 3-, 4-, and 5-yr rotations. In contrast, a 6-yr conservation rotation that included 2 yr of timothy forage resulted in similar or lower weed densities than rotations with conventional management practices. Residual weed densities recorded 4 wk after applying postemergence herbicides were only greater in conservation than conventional rotations in 2 of 12 yr, regardless of rotation length. Weed seedbank densities at the conclusion of the 12-yr study were similar for 3- to 6-yr rotations under either conservation or conventional management. These findings indicate that implementing a suite of conservation practices poses little risk of increased weed populations in the long term. This knowledge will facilitate grower adoption of more sustainable agronomic practices for irrigated row crops in this region.

Pendimethalin control failures on tall morningglory are critical shortcomings in weed-control programs for chile pepper in New Mexico. Using weed seedbank augmentation, we conducted a field study to (1) determine if pendimethalin control of tall morningglory is affected by tall morningglory seedbank density, and (2) identify weed community factors that influence labor for removing the tall morningglory plants that escape pendimethalin. The field study was complemented with a growth chamber study conducted to clarify the effects of pendimethalin rate on the putative association between tall morningglory seedbank density and pendimethalin control outcomes. Under field conditions and after square-root transformation of the dependent variable, the effects of seedbank density on seedling escape density were described with natural logarithmic functions. Although pendimethalin control of tall morningglory decreased with increasing seedbank density, seedbank additions increased labor requirements for removing tall morningglory at only a site-year characterized by low population densities in the indigenous weed community. In growth chambers, increasing pendimethalin rate negatively influenced the effects of increasing seedbank density on pendimethalin control failures. This study shows that pendimethalin control of tall morningglory is reduced when seedbank densities of this species are high. Knowledge of seedbank density effects on specific control outcomes may influence grower attitudes on management strategies that target weed seedbanks.

Field studies were conducted in 2013 at Houlka, MS and 2014 at Houston and Pontotoc, MS to determine the influence of yellow nutsedge density on 'Beauregard' sweet potato yield and quality. Treatments established 2 wk after transplanting (WAP) were yellow nutsedge densities of 0, 5, 10, 15, 30, 40, 50, and 90 shoots m−2 within the planted row. No. 1 and marketable yield loss were fit to a rectangular hyperbola model. In 2013 predicted yield loss of no. 1 and marketable grades ranged from 23 to 96% and 18 to 80%, respectively for yellow nutsedge densities of 5 to 90 shoots m−2. In 2014 predicted yield loss of no. 1 and marketable grades ranged from 7 to 74% and 6 to 67%, respectively for yellow nutsedge densities of 5 to 90 shoots m−2. Yellow nutsedge shoot density increased linearly from 2 WAP to harvest. At Houston and Pontotoc, yellow nutsedge shoot density increased 2.3 and 7.6 times, respectively, for every one shoot present at 2 WAP.

Yellow and purple nutsedge are common in the southeastern United States, and both perennial species are difficult to control in organic crop-production systems. Tubers are generally confined to the upper portions of the soil profile and are vulnerable to desiccation when brought to the soil surface. A peanut digger is a common implement found in the coastal plain region of the southeastern United States and has shown promise controlling perennial nutsedges in fallow sites. The peanut digger undercuts perennial nutsedges, deposits weeds on the soil surface, and exposes weeds to desiccation. However, rainfall after tillage with the peanut digger allows displaced nutsedges to survive. As part of a senior-level class project, undergraduate mechanical engineering students from Auburn University designed and constructed a cart attached to a peanut digger that collected nutsedges. Key features included a custom hitch that allowed the correct plane of movement and a hydraulic conveyor system that discarded the perennial nutsedges off-site, away from the field. The prototype was tested in a fallow location in the summer of 2014 with a yellow nutsedge infestation averaging 148 plants m−2. One week after the initial field test, tillage using the peanut digger with specialized cart reduced yellow nutsedge densities in the tilled area by > 99%.

Four field experiments were conducted over a 2-yr period (2012 and 2013) in winter wheat to evaluate POST herbicides for the control of glyphosate-resistant (GR) giant ragweed. POST herbicides were evaluated for winter wheat injury and GR giant ragweed control, population density, and aboveground biomass. The herbicides used in this study provided 54 to 90% and 51 to 97% control of GR giant ragweed at 4 and 8 wk after treatment (WAT), respectively. At 8 WAT, auxinic herbicide treatments or herbicide tank mix/premix treatments that contained auxinics provided 78 to 97% control of GR giant ragweed. Reductions in GR giant ragweed population density and aboveground biomass were 62 to 100% and 83 to 100%, respectively, and generally reflected the level of control. The results of this research indicate that Ontario, Canada, corn and soybean growers should continue to incorporate winter wheat into their crop rotation as one component of an integrated weed management (IWM) strategy for the control of GR giant ragweed.

Take a walk in many no-till fields that will be planted to a crop or stroll across lawns or golfcourse greens in the spring, and it is not hard to spot the small, white flower of the star-of-Bethlehem (Ornithogalum umbellatum L.). Star-of—Bethlehem is an aggressive weed of lawns, pastures, gardens, and many no-till agriculture fields of the temperate regions of the United States and indeed the world (Hagerman and Young 2004; Johnson and Nice 2015).