Sweet corn (Zea mays L.) tolerance to dicamba and several other herbicides is due to cytochrome P450 (CYP)-mediated metabolism and is conferred by a single gene (Nsf1). Tolerance varies by CYP genotypic class, with hybrids homozygous for functional CYP (Nsf1Nsf1) being the most tolerant and hybrids homozygous for mutant CYP alleles (nsf1nsf1) being the least tolerant. The herbicide safener cyprosulfamide (CSA) increases tolerance to dicamba by stimulating the expression of several CYPs. However, the extent to which CSA improves the tolerance of different sweet corn CYP genotypic classes to dicamba is poorly understood. Additionally, the effect of growth stage on sweet corn sensitivity to dicamba is inadequately described. The objective of this work was to quantify the significance of application timing, formulation, and CYP genotypic class on sweet corn response to dicamba. Hybrids representing each of the three CYP genotypes (Nsf1Nsf1, Nsf1nsf1, nsf1nsf1), were treated with dicamba or dicamba + CSA at one of three growth stages: V3, V6, or V9. Across all timings, the nsf1nsf1 hybrid was the least tolerant to dicamba, displaying 16% higher crop injury levels 2 wk after treatment and 2,130 kg ha−1 lower ear mass yields compared with the Nsf1Nsf1 hybrid. The V9 growth stage was the most susceptible time for dicamba injury regardless of genotypic class, with 1.89 and 1,750 kg ha−1 lower ear mass yields compared with the V3 and V6 application timings, respectively. The addition of CSA to dicamba V9 applications reduced the injury from dicamba for all three genotypic classes; however, it did not eliminate the injury. The use of Nsf1Nsf1 or Nsf1nsf1 sweet corn hybrids along with herbicide safeners will reduce the frequency and severity of injury from dicamba and other CYP-metabolized herbicides.

The use of a corn–earthworm coculture (CE) system is an eco-agricultural technology that has been gradually extended due to its high economic output and diverse ecological benefits for urban agriculture in China. However, the effect of CE on weed occurrence has received little attention. A 5-yr successive experiment (2015 to 2019) was conducted to compare weed occurrence in CE and a corn (Zea mays L.) monoculture (CM). The results show that CE significantly decreased weed diversity, the dominance index, total weed density, and biomass, but increased the weed evenness index. The 5-yr mean number of weed species per plot was 8.4 in CE and 10.7 in CM. Compared with those in CM, the 5-yr mean density and biomass of total weeds in CE decreased by 59.2% and 66.6%, respectively. The effect of CE on weed occurrence was species specific. The mean density of large crabgrass [Digitaria sanguinalis (L.) Scop.], green foxtail [Setaria viridis (L.) P. Beauv.], goosegrass [Eleusine indica (L.) Gaertn.], and common purslane (Portulaca oleracea L.) in CE decreased by 94.5%, 78.1%, 75.0%, and 45.8%, whereas the mean biomass decreased by 96.2%, 80.8%, 76.9%, and 41.4%, respectively. Our study suggests that the use of CE could suppress weed occurrence and reduce herbicide inputs in agriculture.

A tractor-mounted mist blower was as effective as a high-volume ground sprayer or an airplane sprayer for applying herbicides to control hardwoods in two tests in central Louisiana. Two lb/A of butoxyethanol ester of 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) were slightly better than one, and May treatments were more effective than August treatments.

This paper is a review of and a commentary on the published addresses of WSSA presidents from the founding of the Society through 2000. The paper's assumptions are that the presidential remarks will reveal what the Society has emphasized, what its major concerns and goals have been, and how the presidents have addressed what they considered to be important issues. Seven issues have been addressed by many presidents. These include the importance of agricultural production and profit, the necessity of herbicides, weed science and the environment, the regulation of herbicides, the need for education, comparison of weed science and other plant protection disciplines, and the problem of herbicide resistance.

The most economical time to control invading noxious shrubs is at an early stage in the invasion, when stands are sparse. One method of doing this is with a ground spray rig (Fig. 1). With such a rig the problem is to get the guns out from the vehicle so that a reasonable-sized swath can be covered. The out-rigger apparatus described herein can be used to cover a swath of 50 feet where the brush is fairly dense, to 90 feet on sparser stands.

Mile-a-minute (Mikania micrantha Kunth) is a tropical American species and has become a worldwide invasive weed. It was first introduced to mainland China in 1983 in Yingjiang City, Dehong State, Yunnan Province. To assess the origins of populations from Dehong State, Yunnan Province, the genetic structure of 427 individuals from 11 M. micrantha populations from Yunnan, Guangxi, Hainan, and Guangdong provinces were analyzed. A total of 28 alleles were detected in 12 nuclear microsatellite loci. Genetic diversity at the population level was relatively high. An analysis of molecular variance showed that most of the variation occurred within populations (82.73%), and only 18.27% occurred among populations. The genetic differentiation coefficient (FST) was 0.183. The estimated gene flow (Nm) from FST was 1.116. The independent origins of four populations collected from Dehong State, Yunnan Province, was determined by the unweighted pair-group method with arithmetic means clustering and STRUCTURE analysis. Three gene clusters and one admixture gene cluster were found. A Mantel test of pairwise Nei’s genetic distances and pairwise geographic distances revealed no evidence for isolation by distance (r = 0.068, P = 0.343). These results suggest that the post-introduction admixture caused by multiple introductions and high gene flow might contribute to the evolutionary adaptation of M. micrantha. These results could provide a scientific basis for the management of invasive M. micrantha.

The experimental herbicide R-24191 [1-(m-t-butylacetamidophenyl)-3-methyl-3-methoxy urea] inhibited growth of Chlorella sorokiniana Shihira and Kraus, O2 evolution during CO2 fixation by Chlorella and isolated leaf cells of spinach (Spinacia oleracea L. ‘Winter Bloomsdale 769′), the photoreduction of NADP by isolated chloroplasts using water or hydroxylamine as the electron donor, the photoreduction of 2,6-dichloroindophenol by isolated chloroplasts, and O2 uptake by isolated chloroplasts using paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) as the electron acceptor. The phenylurea herbicide had no effect on the last reaction when ascorbate plus 2,6-dichloroindophenol were used as the electron donor. The results indicate that the site of the phenylurea inhibition was in photosystem II between water-splitting and photosystem I.

The herbicide O-(2,4-dichlorophenyl) O-methyl isopropylphosphoramidothioate (DMPA) contains an asymmetric tetracovalent phosphorus. The d-isomer is much less active and the l-isomer more active than dl-DMPA in inhibiting seedling grass growth. Furthermore, low levels of dl-DMPA stimulate root growth of seedling wheat (Triticum vulgare L., var. Soft winter).

Combinations of MSMA (monosodium methanearsonate) with bensulide [O,O-diisopropyl phosphorodithioate S-ester with N-(2-mercaptoethyl)benzenesulfonamide], DCPA (dimethyl tetrachloroterephthalate), or prosulfalin {N-[[4-(dipropylamino)-3,5-dinitrophenyl] sulfonyl]-S,S-dimethylsulfilimine} were applied at various dates of treatment to bermudagrass [Cynodon dactylon (L.) Pers.] and Kentucky bluegrass (Poa pratensis L.) in the spring for large crabgrass [Digitaria sanguinalis (L.) Scop.] control. Bensulide controlled a higher percentage of weeds than did DCPA, regardless of treatment dates. When treatments were delayed until late April in Griffin and mid May in Blairsville, Georgia, large crabgrass control was improved from combinations of MSMA with bensulide compared to bensulide alone. Combinations of MSMA with DCPA improved large crabgrass control when applied in March and April at Griffin and in May at Blairsville. Combinations of MSMA with either bensulide or DCPA performed equally well whether applied as a single tank-mix treatment or as separate applications on the same day. Large crabgrass control was not improved at any date from combinations of MSMA with prosulfalin when compared with prosulfalin alone.

The apex of western ironweed (Vernonia baldwini Torr.) vegetative bud shoots adheres to the tunica-corpus theory. Two layers of cells with the plane of wall formation anticlinal to the main axis (tunica) lie over a body of tissue with no pattern to wall formation (corpus). The bud shoot can be divided into the promeristem, the zone of elongation, and a zone of maturation on the basis of histology. It is suggested that the promeristem may be the seat for dormancy mechanisms in western ironweed and that future investigations be concentrated on this site. There was no evidence of a structural barrier to translocation separating the rhizome and bud shoot.

A 4.6-m-long, segmented, flexible-pipe ropewick applicator was constructed to apply picloram (4-amino-3,5,6-trichloropicolinic acid) to leafy spurge (Euphorbia esula L. ♯ EPHES) and other weed species. Gauge wheels on each ropewick applicator segment permit height adjustments, and a loose, independent, vertical flexing action permits the segments to effectively traverse depressed or raised areas. The applicator was designed for use in pastures with rough, uneven terrain where it is difficult to uniformly wipe herbicide solution on plants with a rigid-pipe ropewick. The applicator was found to be durable and effective in applying picloram to leafy spurge.

Dalapon (2,2-dichloropropionic acid) was applied at 3.3 kg/ha during late May or early June to a well-established grass sward consisting of smutgrass [Sporobolus poiretii (R.&S.) Hitchc], pangolagrass (Digitaria decumbens Stent.), and bahiagrass (Paspalum notatum Flugge. ‘Pensacola’). Two cultural treatments, mowing or roller chopping, and two fertilizer treatments, 0 or N-P-K at 112-25-93 kg/ha were superimposed on the dalapon treatments at four different time intervals in a split plot design. Chopping or mowing 2 weeks after the dalapon treatment resulted in the highest bahiagrass ground cover and smutgrass control with a minimum amount of bare soil. Chopping tended to favor pangolagrass recovery, and mowing favored bahiagrass recovery. Fertilizer application increased pangolagrass ground cover 90-days after treatment, and smutgrass control after 1 yr. Fertilizer application 6 weeks after dalapon treatment generally increased pangolagrass ground cover and smutgrass control. Pangolagrass responded to fertilizer regardless of chopping or mowing. Mowing controlled more smutgrass than did chopping on the non-fertilized plots.

Weed Scientists, like many other agricultural scientists and natural resource land managers, often engage in debate with other members of society about values and perceptions of food and fiber production. The focus of the debate is usually on the tools and tactics to grow crops, produce wood, or manage grazing land. Environmental ethical issues have dominated discussions among the membership of WSSA for decades. Examples include the decade-long debate over 2,4,5-T use in forestry and now water quality and human health concerns about atrazine use in agriculture. Ecology is a scientific discipline that seeks knowledge about the interactions of organism, their environments, and, more broadly, the effect of human activities on them. Because weeds are a consequence of how we grow food, the study of both ecological and human components of agroecosystems should allow weed scientists to construct management strategies that more fully address the production, environmental, and social implications of weeds and weeding.

Replacement series are used by researchers to understand how competition-related variables influence dynamics from the individual to the population and community levels, but this approach has been criticized because of inherent biases associated with plant size differences and density-dependent responses. The use of functional densities instead of demographic densities was proposed to minimize those biases. This work explored three models to determine reference densities for replacement series experiments based on (1) maximum biomass, (2) biomass at onset of diminishing returns (i.e., inflection point), and (3) nitrogen (N)-uptake equivalency. Replacement series experiments were conducted using redroot pigweed (Amaranthus hybridus L.):maize (Zea mays L.) and giant foxtail (Setaria faberi Herrm.):maize proportions of 1:0, 0.75:0.25, 0.5:0.5, 0.25:0.75, and 0:1. The monoculture density for each species was established according to the three models. Density selection criteria resulted in major differences in competitive interactions between species. The use of functional densities at which the biomass accumulation inflection point for the smaller species allowed both species to exhibit either increases or decreases in biomass production depending on competitive interactions for all interspecific mixtures. Conversely, the maximum biomass model favored the larger species, almost completely inhibiting the growth of the smaller species, which resulted in a poor characterization of competitive responses of the smaller species. The N uptake equivalency model resulted in interactions closer to the predicted neutral competition. The model based on the biomass accumulation inflection point was the most sensitive and informative across all interspecific mixtures for both species. We propose that to reduce bias associated with species size differences when determining reference densities for replacement series experiments, at least two criteria must be met: (1) the experiment sensitivity allows measuring and quantifying the competitive responses for both species in all mixtures, and (2) the balance between density and carrying capacity of the system minimizes intraspecific competition.

Turfgrass managers are concerned about zoysiagrass (Zoysia japonica Steud.) injury from nonselective herbicide treatment during winter dormancy. Research was conducted to assess factors affecting spray penetration into semidormant ‘Meyer’ zoysiagrass canopies and to evaluate absorption and translocation of [14C]glyphosate and [14C]glufosinate into green leaves and subtending stolons. Absorption of [14C]glyphosate and [14C]glufosinate was up to four times greater in stolons than in leaves. Zoysiagrass leaves treated with [14C]glufosinate had more rapid 14C absorption than those treated with [14C]glyphosate. More 14C translocated out of the treated area following [14C]glyphosate treatment compared with [14C]glufosinate and moved more readily from stolon to leaves than from leaves to stolon. When extended-range, flat-fan spray tips (XR) were positioned 61 cm above zoysiagrass, 73% and 11% of recovered colorant was extracted from dormant vegetation in the upper and lower canopy levels. Turbo TeeJet® spray tips (TTI) deposited fewer droplets into the upper canopy and more droplets into the middle and lower canopy regardless of position above the turf surface. Increasing pressure from 103 to 414 kPa increased droplet velocities from XR and TTI nozzles and decreased droplet diameters of XR nozzles. Droplet diameters were also substantially increased when using TTI nozzles compared with XR nozzles. Droplet diameter and associated mass were more determinant of turfgrass canopy penetration than droplet velocity. At 60 L ha−1 of carrier volume, 23% of colorant reached the lower canopy level, and this quantity increased by 2.3% per additional 100 L ha−1. When carrier volume was reduced from 584 to 60 L ha−1, 48% less colorant was delivered to the lower canopy level. Given that subcanopy stolons are always present and absorb more glyphosate and glufosinate than leaves, practices such as avoiding induction-type nozzles, raising spray height, and reducing spray volume can reduce herbicide delivery and potential injury to semidormant zoysiagrass.

Harvest weed seed control (HWSC) is an effective technique for managing wild radish (Raphanus raphanistrum L.), a weed that retains its seed until harvest. However, earlier flowering time (leading to increased seed shedding before harvest) is a risk to HWSC effectiveness. This study investigated the effects of repeated HWSC on the evolution of R. raphanistrum flowering dates, using two methods: an adaptation of the SOMER model that included flowering genes (called SOMEF); and a mathematical calculation of the endpoints of flowering date evolution utilizing the relevant life-history equations. In weed management systems with highly effective herbicides, the additional use of HWSC predicted R. raphanistrum population extinction. Low weed numbers and rapid extinction meant that any gradual evolution in days to first flower (DFF) was insufficient to lead to HWSC evasion. In alternative management systems with less vigorous herbicide control and using HWSC, modeling predicted a maximum 2- to 3-d reduction in DFF. In contrast, mathematical calculations of the phenotypes maximizing seeds returned to the seedbank predicted an endpoint to evolution of 12-d earlier flowering, which matched field observations. However, genetic change postulated by the mathematical calculations was not hampered by a restriction to changing DFF allele frequencies. Unknown accompanying genetic changes could affect germination dates or flowering triggers.

Simulation modeling that included only flowering genes failed to predict the magnitude of an observed 12-d reduction in DFF. Differences between the 12 d observed in the field (and predicted using mathematical calculations) and the modest changes demonstrated in this field-based modeling study are postulated to be due to unaccounted evolutionary changes in R. raphanistrum.