Turfgrass managers can reduce foliar bleaching of smooth crabgrass from mesotrione by tank-mixing triclopyr ester with applications. These tank mixtures also have potential to enhance smooth crabgrass control compared to mesotrione alone. The objectives of this research were to evaluate the influence of triclopyr on the efficacy, absorption, and translocation of mesotrione in multitiller smooth crabgrass. In field experiments, tank-mixing triclopyr at 560 or 1,120 g ae ha−1 with mesotrione at 140 g ai ha−1 applied sequentially or at 280 g ha−1 applied singly provided excellent control (> 90%) of multitiller smooth crabgrass in tall fescue. These treatments were more effective than mesotrione alone and fenoxaprop at 195 g ai ha−1 that averaged 66 and 81% control after 6 wk, respectively. Mesotrione alone at 280 g ha−1 bleached smooth crabgrass 53% at 2 wk after initial treatment (WAIT), and was 14% greater than the 140 g ha−1 treatment. Sequential treatments of the low mesotrione rate bleached smooth crabgrass 16 to 22% from 3 to 5 WAIT. Triclopyr tank mixtures reduced smooth crabgrass bleaching from mesotrione on all dates to < 5%. Tall fescue injury was not detected at any evaluation date. In laboratory experiments, smooth crabgrass reached peak foliar absorption of 14C-mesotrione at 24 and 168 h after treatment (HAT; 23% and 15%) when mesotrione was applied with triclopyr at 1,120 and 0 g ha−1, respectively. Triclopyr reduced translocation of radioactivity 12% at 72 and 168 HAT, compared to 14C-mesotrione alone. Enhanced foliar uptake of mesotrione from triclopyr tank mixtures might improve control of multitiller smooth crabgrass compared to mesotrione alone. Reduced foliar bleaching from triclopyr is associated with less translocation of mesotrione or derivatives in smooth crabgrass.

Mesotrione provides PRE and early POST control of annual bluegrass during Kentucky bluegrass establishment from seed, but applications do not effectively control multitiller plants. The physiological effects of growth stage on efficacy and the basis of mesotrione selectivity between species is not well understood. The objectives of this research were to evaluate mesotrione behavior in these species at three growth stages: pretiller (3 to 5 leaves), 1-tiller, and multitiller (5 to 7 tillers). In greenhouse experiments, a single mesotrione application at 280 g ai ha−1 injured pretiller, 1-tiller, and multitiller annual bluegrass 54, 33, and 11% at 4 wk after initial treatment (WAIT), respectively. A sequential application of mesotrione increased injury to pretiller and 1-tiller annual bluegrass by 20 and 17% from a single treatment, respectively. Sequential mesotrione applications caused at least 14% injury to multitiller annual bluegrass and Kentucky bluegrass at all growth stages and did not reduce tillering compared to the nontreated. Annual bluegrass absorbed 34% more root-applied 14C-mesotrione than Kentucky bluegrass in hydroponic culture, but relative differences (Bq g−1) among growth stages were not detected for both species. Averaged across growth stages, annual and Kentucky bluegrass absorbed 31 and 35% of the applied radioactivity after foliar treatments, respectively. However, averaged across species, multitiller plants metabolized approximately two times more 14C-mesotrione than pretiller and 1-tiller plants. Overall, the selectivity of mesotrione for annual bluegrass control during Kentucky bluegrass establishment results from differential levels of root absorption. Mesotrione has limited efficacy for controlling multitiller annual bluegrass due to enhanced degradation compared to pretiller and 1-tiller plants.

Asia minor bluegrass (AmB) is a major weed impacting rapeseed production in Dongting Lake District, China. Growth chamber experiments were conducted to determine the influence of environmental factors on germination and emergence of AmB. The optimum constant temperature for germination was around 20 C. Seeds showed germination percentages above 60% under 22/15 and 24/19 C day/night temperature regimes. Seeds could germinate in the dark, but light exposure significantly enhanced the germination percentage. More than 50% of seeds germinated over a pH range between 4 and 10. Seeds were highly sensitive to osmotic stress, and germination was completely inhibited at an osmotic potential of −0.4 MPa, indicating that it was favored by a moist environment. Increasing salinity reduced germination of AmB seeds from 58% at 0 mM to 13% at 80 mM NaCl. The highest seedling emergence (62%) was observed when seeds were placed on the soil surface, and no seedlings emerged from seeds placed at a depth of 5 cm. This work shows that the climate and soil conditions in Dongting Lake District are suitable for AmB seed germination and that no-till fields, where seeds remain on the soil surface, promote the successful establishment of the weed.

Methods were developed and tested for mapping the distribution of Scotch broom, an invasive shrub species expanding its range and disrupting native species and habitats in several parts of the world. During spring, the Scotch broom produces yellow flowers. Landsat imagery during the flower bloom period and during summer was acquired for several years for a study area on Vancouver Island, British Columbia, Canada. Ground-based reflectance measurements plus statistical separability tests were conducted to determine the effectiveness for identifying Scotch broom with Landsat spectral bands, band ratios, vegetation indices, and combinations of bloom and nonbloom imagery. Maximum likelihood classifications of three Scotch broom density classes (dense, ≥ 75% cover; moderate, 25 to 75%; low, 10 to 25%) and other land covers were run with various image and band sets and tested against independent reference sites. Accuracies of classifications using the better band combinations for moderate and dense Scotch broom patches combined were on the order of 80%, with unreliable results for sites of low Scotch broom density. Scotch broom patches less than 0.5 ha were often missed. Some commission error occurred (areas erroneously classified as Scotch broom). Suggested improvements are the use of time series of classifications over multiple years, incorporating knowledge of Scotch broom spread mechanisms or temperature and elevation limitations, and use of higher resolution satellites if the expense warrants it. Despite some limitations, a satellite-based remote sensing approach may be useful for aspects of Scotch broom management.

Weeds often limit productivity of organic cropping systems. Radish is a fast-growing, potentially allelopathic cover crop that has the potential to improve weed management in organic systems. To evaluate the effect of radish on density, cover, and biomass of weeds in organically managed corn, 2-yr field experiments were conducted over 4 site years. Four cover-crop planting treatments (fall-only, spring-only, fall + spring, and no cover) were tested in factorial with three cultivation treatments (standard [three to four passes], false seedbed [standard with a false seedbed], and reduced [two passes]). All plots were tilled before planting. Shoot biomass averaged 3,057 kg ha−1 for fall-seeded radish and 385 kg ha−1 for spring-seeded radish. Radish cover crops generally did not improve management of weeds during the corn growing season. However, in the absence of a false seedbed, fall-seeded radish reduced field pennycress density from 9 to < 1 plant m−2 and horseweed density from 6 to 2 plants m−2 in spring in site years where these weeds were present. Fall-seeded radish also reduced cover of summer annual weeds during the fall cover-crop growing season from 4 to 0% in 1 site year, preventing these weeds from setting seed. Radish cover crops did not affect corn grain yield.

Herbicide applications often do not reach their full potential because only a small amount of the active ingredients reaches the intended targets. Selecting the appropriate application parameters and equipment can allow for improved efficacy. The objective of this research was to evaluate the effect of droplet size on efficacy of six commonly used herbicides. Atrazine (1.12 kg ai ha−1), cloransulam-methyl (0.18 g ai ha−1), dicamba (0.14 kg ae ha−1), glufosinate (0.59 kg ai ha−1), saflufenacil (12.48 g ai ha−1), and 2,4-D (0.20 kg ae ha−1) were applied to seven plant species using an XR11003 nozzle at 138, 276, and 414 kPa and a AI11003 nozzle at 207, 345, and 483 kPa. Each herbicide, nozzle, and pressure combination was evaluated for droplet size spectra. Treatments were applied at 131 L ha−1 to common lambsquarters, common sunflower, shattercane, soybean, tomato, velvetleaf, and volunteer corn. Control from 2,4-D was observed to increase approximately 12% on average for all species except common lambsquarters as droplet size increased from medium to very coarse (Dv0.5 303 to 462 μm; Dv0.5 is droplet size such that 50% of spray volume is contained in droplets of equal or smaller size). Control with atrazine was near 95% for common lambsquarters, common sunflower, and soybean. Atrazine provided the greatest shattercane control using a medium (Dv0.5 325 μm) droplet, whereas the same droplet size provided the lowest tomato control. Control of common lambsquarters, shattercane, and tomato with cloransulam-methyl increased 79% when decreasing droplet size from extremely coarse to fine (Dv0.5 637 to 228 μm). Dicamba control of common lambsquarters increased 17% using a medium droplet compared with a fine droplet (Dv0.5 279 to 204 μm). Dry weight of common sunflower and soybean was reduced 21% using dicamba when using a very coarse spray compared with a fine spray classification (Dv0.5 491 to 204 μm). Common lambsquarters control using glufosinate increased 18% using a fine spray classification (Dv0.5 186 μm) compared with medium (Dv0.5 250 μm) and both very coarse droplet sizes (Dv0.5 470 and 516 μm). Conversely, tomato and velvetleaf control with glufosinate was maximized using a very coarse (Dv0.5 470 and 516 μm) or extremely coarse droplet (Dv0.5 628 μm) with increases of 11 and 25% compared with a fine spray (Dv0.5 186 μm). Saflufenacil control of volunteer corn was 38% greater using extremely coarse droplets (Dv0.5 622 μm) than fine, medium, and very coarse spray classifications (Dv0.5 257 to 514 μm). Overall, spray classifications for the herbicides evaluated play an important role in herbicide efficacy and should be tailored to the herbicide being used and the targeted weed species.

Bell pepper is an economically important vegetable crop that is often impaired by weeds. Management of weeds in bell pepper is required to minimize yield loss because this crop does not tolerate weed competition. Several herbicides have been reported as selective for bell pepper, but research supporting their use for weed control in this crop is limited. Several herbicides were screened in a greenhouse to assess effects on plant biomass, and eight were selected that appeared to be safe for bell pepper. These herbicides, in addition to oxadiargyl, were then evaluated at two different Chilean locations, using different application timings. We measured the effects on plant injury, fruit yield, and the need for additional hand weeding on transplanted bell peppers. The herbicides clomazone, napropamide, pendimethalin, and S-metolachlor caused minimal foliar chlorosis and necrosis but did not affect fruit yield at either location. Pretransplant-incorporated application (PTI) caused no effect on fruit yield from the herbicides evaluated, whereas applications 2 wk (POST2) and 8 wk (POST8) after transplanting reduced fruit yield significantly. For weed management, the best combination was PTI + POST2 + POST8, which reduced the hand-weeding time by 30% compared to the control, at both locations. Based on our results, clomazone, pendimethalin, and S-metolachlor were the most effective treatments applied after transplanting, whereas all herbicides tested were selective for bell pepper when applied and incorporated before transplanting. Results presented here provide new insight into herbicides that can be used to manage weeds in bell pepper and shows that timing of herbicide application is critical to prevent injury to this crop.

Previous research has demonstrated that late and sequential applications of glyphosate and glufosinate can have adverse effects on glyphosate- and glufosinate-resistant canola. Similarly, imidazolinone (IMI)-resistant canola may be affected negatively by late applications of imidazolinone herbicides. Field trials were established across the Northern Great Plains region from 2010 to 2012 to examine the response of IMI-resistant canola yield, yield components, and seed quality to late and sequential applications of imazamox. Plots received either a single imazamox application at the two-leaf, six-leaf, bolt, or early bloom stages or sequential applications at the two-leaf followed by six-leaf, two-leaf followed by bolting, and two-leaf followed by early bloom stages; an unsprayed control was included for comparisons. Results indicated that in most site-years there was no effect of imazamox application timing on IMI-resistant canola yield, yield components, or seed quality. These results suggest that late and sequential applications of imazamox to IMI-resistant canola should have little effect on canola production, even if they are made beyond the recommended six-leaf stage. In situations where growers are forced to make late applications (beyond six leaves) to IMI-resistant canola, using solely imazamox appears to minimize adverse effects on seed yield and quality.