To minimize the chance of surface water contamination by herbicides, farmers need alternative ways to manage weeds in field crops, such as field corn, that reduce herbicide use. Zone herbicide application (ZHA) reduces herbicide use compared with conventional broadcast herbicide application by (1) banding low herbicide rates between corn rows (≤ 1× normal broadcast registered rate), (2) managing crops to favor crop competition, and (3) banding very low herbicide rates over crop rows (≪ 1× normal rate). The research goal was to compare the relative effectiveness of reduced-rate ZHA with broadcast herbicide application on in-row (IR) and between-row (BR) summer annual weed cover (chiefly giant foxtail and waterhemp species), grain yields, and net returns resulting from herbicide application in field corn. Preemergence ZHA of atrazine + metolachlor + clopyralid + flumesulam was made in zones (i.e., even width bands) at different rates between and over crop rows for three site-years in Missouri, and the 1× rate was 2.24 + 1.75 + 0.211 + 0.067 kg ai ha−1, respectively. Best ZHA treatments (0.29× to 0.30× IR herbicide rates + 0.74× to 0.80× BR herbicide rates) outperformed all reduced-rate broadcast herbicide treatments (0.25×, 0.5×, and 0.75×) based on net returns in partial budget analysis. Yields for highest yielding ZHA could not be distinguished from the 1× broadcast treatments in two of three site-years. Net returns due to herbicide application for the highest yielding ZHA were comparable with the 1× broadcast treatment in all three site-years. For the best ZHA, the 3-yr average for total herbicide applied per unit was 53% of the 1× broadcast rate. ZHA may provide row crop farmers with a new generic option for reducing herbicide rates and input costs while maintaining net returns and reducing the chance of surface water contamination by herbicides.

Amitrole-5-C14 was rapidly degraded in unsterile soil but underwent only minor modification in sterile soil. An unidentified chemical product of amitrole was formed in both sterile and unsterile soil. The principle metabolic product of amitrole was carbon dioxide; however, at least 13 additional compounds were formed. One or more metabolic compounds formed from amitrole are tenaciously bound to the soil and appear to be resistant to degradation.

The herbicidal properties of the sodium salt of 3,5–dinitro-orthocresol were recognized in the early 1930's. The dinitrophenols and dinitrocresols have since found wide use in controlling weeds in corn, peas, beans, potatoes, cotton, grains, forage legumes, and many other field and horticultural crops. The 4,6–dinitro-orthosecondarybutyl phenol (hereafter referred to as DNBP) and its salts are the most widely used compounds of this group in the United States.

A weed survey was conducted on 134 Palmer amaranth (Amaranthus palmeri S. Watson) populations from Mississippi and Arkansas in 2017 to investigate the spread of resistance to protoporphyrinogen oxidase (PPO) inhibitors using fomesafen as a proxy. Fomesafen resistance was found in 42% of the A. palmeri populations. To investigate the resistance basis of different PPO inhibitors, we further characterized 10 representative populations by in planta bioassay in a controlled environment and molecular characterizations (DNA sequencing and TaqMan® gene expression assay). A total of 160 plants were sprayed with a labeled field rate (1X) of fomesafen or salfufenacil and screened for the presence of three known resistance-endowing mutations in the mitochondrial PPX2 gene (ΔGly-210, Arg-128-Gly, Gly-399-Ala). To compare the potencies of fomesafen and saflufenacil, dose–response studies were conducted on two highly resistant and one sensitive populations. The interaction of the two herbicides with the target protein harboring known PPX2 mutations was also analyzed. Our results showed that: (1) 90% of the fomesafen- or saflufenacil-resistant plants have at least one of the three known PPX2 mutations, with ΔGly-210 being the most prevalent; (2) saflufenacil is more potent than fomesafen, with five to nine times lower resistance/susceptible (R/S) ratios; (3) fomesafen selects for more diverse mutations, and computational inhibitor/target modeling of fomesafen suggest a weaker binding affinity in addition to a smaller interaction volume and volume overlap with the substrate protoporphyrinogen IX than saflufenacil. As a result, saflufenacil shows reduced sensitivity to PPX2 target-site mutations. Results from current study can help pave the way for designing weed management strategies to delay resistance development and maintain the efficacy of PPO inhibitors.

Knotweed (Fallopia spp.) is an herbaceous perennial from East Asia that was brought to Europe and North America and, despite control efforts, subsequently spread aggressively on both continents. Data are available on knotweed’s modes of sexual and asexual spread, historical spread, preferred habitat, and ploidy levels. Incomplete information is available on knotweed’s current global geographic distribution and genetic diversity. The chemical composition of knotweed leaves and rhizomes has been partially discovered as related to its ability to inhibit growth and germination of neighboring plant communities via phytochemicals. There is still critical information missing. There are currently no studies detailing knotweed male and female fertility. Specifically, information on pollen viability would be important for further understanding sexual reproduction as a vector of spread in knotweed. This information would help managers determine the potential magnitude of knotweed sexual reproduction and the continued spread of diverse hybrid swarms. The potential range of knotweed and its ability to spread into diverse habitats makes studies on knotweed seed and rhizome cold tolerance of utmost importance, yet to date no such studies have been conducted. There is also a lack of genetic information available on knotweed in the upper Midwest. Detailed genetic information, such as ploidy levels and levels of genetic diversity, would answer many questions about knotweed in Minnesota, including understanding its means of spread, what species are present in what densities, and current levels of hybridization. This literature review summarizes current literature on knotweed to better understand its invasiveness and to highlight necessary future research that would benefit and inform knotweed management in the upper Midwest.

Fluridone has been widely used for control of the submersed aquatic weed hydrilla in Florida for over 25 years. Recently, some hydrilla biotypes were suspected of having developed resistance to fluridone. Laboratory studies were conducted to monitor changes in phytoene and β-carotene contents as a function of suspected susceptible and resistant hydrilla biotypes to fluridone treatment. Hydrilla shoot tips from each biotype were exposed to 5, 10, 15, 20, 30, and 50 μg L−1 fluridone. Higher β-carotene and lower phytoene content was observed in all resistant hydrilla biotypes compared with the susceptible. The susceptible biotype showed an increase in phytoene or a decrease in β-carotene content when treated with as little as 5 μg L−1 of fluridone, whereas much higher doses were needed for the resistant biotypes. EC50 β-carotene values of 9 and 63 μg L−1 fluridone were found in the susceptible and the most resistant biotype, respectively. Consistent levels of hydrilla injury occurred at phytoene/β carotene index values of 5.5–7 and occurred at exposure to 5–10 μg L−1 fluridone in susceptible and 50 μg L−1 in the most resistant biotype. A resistance factor (R/S) was calculated for each hydrilla biotype which ranged from as low as 2X (R1 and R2) to 7X (R5). Aggressive spread of fluridone resistant dioecious hydrilla in aquatic ecosystems can severely impact hydrilla management, and consequently cause substantial and long-lasting ecological and economic problems throughout the southern United States.

Kochia (Kochia scoparia L.), also commonly called fire weed, is one of the most widespread annual weeds in Kansas and the Great Plains region. The origin of the weed in Kansas is obscure but it was introduced into the United States from Europe (1). The plant had been cultivated as an ornamental and apparently much of its present wide distribution is a result of escape from ornamental plantings.

Excellent protection from 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) injury at twice the dose needed for weed control was obtained by dipping the roots of strawberry plants (Fragaria grandiflora Ehrh.) in a 10% slurry of activated carbon before transplanting. Protection was greater when the roots were dipped in the slurry of activated carbon than when activated carbon was applied in the transplant water. Protection was obtained from three different activated carbons. Protection from injury to varying degrees was observed when several other herbicides were used.

The effects of nitrogen (N) rate and weed interference on the grain yield of four corn genotypes were investigated in 2002 and 2003 at Ikenne (7°38′N, 3°42′E), Shika (11°11′N, 7°38′E), and Samaru (10°24′N, 7°42′E) in Nigeria. Nitrogen (N) at 0, 30, 60, and 90 kg N ha−1 were the main plot treatments. Weed-free (weeded weekly), low (intrarow weeds only), and high (zero weeding) weed pressure were the subplot treatments. Four corn genotypes (ACR8328 BN C7, Low-N-Pool C2, Oba Super II, TZB-SR) were the sub-subplot treatments. Weed density was higher at Shika and Samaru than at Ikenne, and the order of average weed biomass 8 to 10 weeks after planting was Samaru (271 g m−2) > Ikenne (236 g m−2) > Shika (161 g m−2). Corn genotype and N rate had no effect on weed biomass except at Samaru where fertilized treatments had higher weed biomass than the unfertilized treatments. Corn leaf area (LA) increased with increasing N rate at all locations regardless of weed pressure and genotype, except at Shika where ACR8328 BN C7, Oba Super II, and TZB-SR did not show any clear N response; LA was highest in the weed-free and lowest in the unfertilized treatments for all genotypes and locations, and weed pressure treatments. Low-N-Pool C2 had the highest LA, which was 1.3 times larger than in Oba Super II, which had the lowest LA. Nitrogen rate, weed pressure, and genotypes significantly affected corn leaf chlorophyll content. Chlorophyll content was higher in the fertilized treatments than the unfertilized treatments, and higher in the weed-free treatments than the low or high weed pressure treatments. ACR8328 BN C7 and Oba Super II had significantly more chlorophyll than the other genotypes. Low-N-Pool C2 showed a linear grain yield response with the increase in N rates. ACR8328 BN C7 did not respond to N application. Compared with the results in the weed-free treatment, high weed pressure reduced grain yield in all genotypes by more than 65% at Samaru, 50% at Shika, and 35% at Ikenne.

New trait technology incorporating 2,4-dichlorophenoxyacetic acid (2,4-D) resistance in soybean provides an alternative method to control weeds. However, the effect of postemergence treatments of 2,4-D on aryloxyalkanoate dioxygenase-12 (AAD-12) soybean on injury and yield components has not been reported. Our objectives were to characterize the effect of 2,4-D (dimethylamine salt) rates (0, 1,120, and 2,240 g ae ha−1) and soybean growth stage (V5, R2, or V5 followed by R2) on AAD-12 soybean injury and yield components. Less than 3% soybean injury was observed when 2,240 g ha−1 of 2,4-D was applied to R2 soybean, and less than 1% soybean injury was caused by 1,120 g ha−1 of 2,4-D. Seed yield, seed mass, pod number, seed number, seed per pod, reproductive node number, pods per reproductive node, node number, and percent reproductive nodes were not affected by 2,4-D treatments when applied at the V5, R2, or the V5 followed by R2 soybean growth stage. This research demonstrates that soybean transformed with AAD-12 can tolerate foliar applications of 2,4-D at rates up to 2,240 g ha−1 with no effect on soybean grain yield components.

Downy brome is an introduced Mediterranean annual grass that now dominates millions of hectares of western U.S. rangelands. The presence of this grass has eliminated many native species and accelerated wildfire cycles. The objective of this study was to identify soil additives that allowed germination but inhibited emergence of downy brome, while not affecting germination or emergence of the native perennial grass Hilaria jamesii. On the basis of data from previous studies, we focused on additives that altered the availability of soil nitrogen (N), phosphorus (P), and potassium (K). Most water-soluble treatments inhibited downy brome germination and emergence. We attribute the inhibitory effects of these treatments to excessive salinity and ion-specific effects of the additives themselves. An exception to this was oxalic acid, which showed no effect. Most water-insoluble treatments had no effect in soils with high P but did have an effect in soils with low P. Zeolite was effective regardless of P level, probably due to the high amounts of Na+ it added to the soil solution. Most treatments at higher concentrations resulted in lower downy brome emergence rates in soils currently dominated by downy brome than in uninvaded (but theoretically invadable) Hilaria soils. This difference is possibly attributable to inherent differences in labile soil P. In Stipa soils, where Stipa spp. grow, but which are generally considered to be uninvadable by downy brome, additions of high amounts of N resulted in lower emergence. This may have been an effect of NH4 + interference with uptake of K or other cations or toxicity of high N. We also saw a positive relationship between downy brome emergence and pH in Stipa soils. Hilaria development parameters were not as susceptible to the treatments, regardless of concentration, as downy brome. Our results suggest that there are additions that may be effective management tools for inhibiting downy brome in calcareous soils, including (1) high salt applications, (2) K-reducing additions (e.g., Mg), and (3) P-reducing additions.

Experiments were conducted to study absorption, translocation, and activity of clopyralid and tribenuron in perennial sowthistle. Absorption and translocation were compared in perennial sowthistle at the rosette and bud stage over a period of 9 d. Both 14C-clopyralid and tribenuron were absorbed slowly by perennial sowthistle leaves with 60 and 30% absorption, respectively, 216 h after application. Limited movement of the absorbed 14C was observed for both herbicides with less than 28% of either herbicide exported from the treated leaf. Primary movement of 14C-herbicide within the plant was acropetal; however, no more than 18% of either herbicide was recovered in the upper shoot or buds. After 216 h, 4.4% of the applied 14C-clopyralid and 2.5% of the applied 14C-tribenuron were recovered in the roots and secondary shoots of plants at the rosette stage. Application of either herbicide to perennial sowthistle resulted in a decrease in net carbon assimilation and leaf conductance. Transpiration was reduced in rosette stage plants by both herbicides; however, transpiration in plants at the bud stage was not reduced until 216 h after treatment. Plants treated with tribenuron had lower net carbon assimilation, leaf conductance, and transpiration rates than plants treated with clopyralid. Application of clopyralid at 150 and 300 g ha-1 resulted in visual injury ratings of 65 and 95%, respectively. Tribenuron applied at 10 and 20 g ha-1 gave similar results. Dry weight accumulation was reduced at all application rates compared to untreated plants. Limited absorption and translocation along with high herbicidal activity suggests that small amounts of either herbicide are sufficient to inhibit perennial sowthistle growth.

In laboratory studies, the herbicide 3'-chloro-2-methyl-p-valerotoluidide (solan) when applied to soil was transformed in part to 3,3'-dichloro-4,4'-dimethylazobenzene. The biochemically mediated transformation followed the pattern established previously for 3,4-dichloroaniline-based acylanilides, but the 3-chloro-4-methylaniline intermediate did not accumulate. Compared to 3,4-dichloroaniline-based acylanilides, solan yielded less azo residue and did not inhibit soil respiration, even if applied at 200 times the recommended field rate.

Managing weeds in lawns using cultural practices such as mowing, irrigation, and fertilization may be important in integrated management. A field experiment evaluated the impact of cultural factors on weed populations in St. Augustinegrass turf. Irrigation treatments were daily to replace evapotranspiration (“Daily”), weekly to saturate the root zone only when wilted (“Conditional Weekly”), and as needed to saturate the root zone after severe wilt (“Severely Wilted”). Averaged over 3 yr, the Daily, Conditional Weekly, and Severely Wilted irrigation treatments resulted in 30, 6, and 2% dollarweed cover, respectively. Except for dollarweed and mat lippia, the largest cover of other weeds was under Severely Wilted irrigation. Fertilization rates were 0, 14, or 28 g N m−2 yr−1; in 2002, the highest fertilization rate had the smallest cover of weeds other than dollarweed. Mowing heights were 64, 89, or 114 mm; in 2003, the shortest mowing height had the smallest cover and dry weight of weeds other than dollarweed. After 3 yr of cultural management, most plots were excessively weedy, and turfgrass quality for all cultural management-treatment combinations, in the absence of herbicides, was unacceptable.

Arabidopsis complementary DNA (cDNA) microarrays were hybridized with labeled cDNA from mature leaves and emerging tillers of wild oat to determine if they could identify gene expression profiles in distantly related species. More than 23% of the > 11,000 cDNAs on the array hybridized to the wild oat probe. Transcription patterns detected by hybridization to the arrays are indicators for physiological processes in the tissues tested. Coordinated expression patterns for these genes in Arabidopsis indicate common signals involved in their regulation. The results demonstrate that probing cDNA-based arrays from well-characterized species can provide valuable insight into the signal transduction processes regulating growth and development of poorly characterized species.

Greenhouse and field studies demonstrated that naptalam reduced paraquat activity by as much as 30% on sicklepod, smallflower morningglory, Florida beggarweed, and peanut Sequential application experiments, i.e. naptalam applied 2 or 24 h prior to an application of paraquat, as well as absorption studies utilizing 14C-paraquat, indicated that the antagonism was due largely to reduced paraquat absorption. Scanning electron microscopy revealed that application of naptalam, as well as naptalam applied with paraquat, resulted in amorphous deposits on the leaf surface which may account for the antagonism.

The activity of glyphosate [N-(phosphonomethyl)glycine], formulated as the isopropylamine salt, on in vitro photosynthesis was investigated. When pH 4.7 glyphosate solutions were titrated to a pH equal to that of the reaction media (pH 7.8), glyphosate additions had no effect on whole chain electron transport between coupled photosystem II (PS II) and photosystem I (PS I) in stroma-free chloroplast thylakoids from peas (Pisum sativum L. ‘Morse's Progress No. 9′). Inhibition did not occur even after a 2-h dark incubation of lamellae in a 5-mM solution of glyphosate. Fluorescence studies failed to detect an effect of glyphosate on PS-II mediated electron transport processes or upon light harvesting properties of PS II even after a 2-h glyphosate/chloroplast preincubation. Glyphosate had no effect on cyclic and noncyclic photophosphorylation even after a 100-min dark incubation of chloroplast membranes in a 5-mM solution of glyphosate. Based on these assays it is concluded that glyphosate has no direct effect on the photochemical reactions of photosynthesis when the pH of the active compound is adjusted to that of the reaction mixture prior to addition to a chloroplast suspension.

Research was conducted in 1994 and 1995 to evaluate the field mobility of flumetsulam in three soils of varied texture and organic matter content but constant pH (pH = 6.0 ± 0.1). Flumetsulam was monitored to a depth of 122 cm at 28, 56, and 84 days after treatment (DAT). Flumetsulam concentrations were determined by cotton bioassay, with separate standard curves for various soil–depth combinations. Following a preemergence application of flumetsulam at 224 g ai ha−1, the herbicide was primarily limited to the upper 8 cm of soil, regardless of soil type, year, or DAT. Exceptions to this typically occurred following substantial rainfall amounts early in the season. Beyond 28 DAT, no significant concentrations of flumetsulam were detected below 15 cm. Results from this research suggest that leaching is not a significant route of flumetsulam dissipation in the field.

The effects of five preemergence herbicides on turfgrass quality and control of crabgrass (Digitaria spp.) were measured to determine the influence of thatch on preemergence herbicide activity in Kentucky bluegrass (Poa pratensis L.) turf. Field applications of benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine), oxadiazon [2-tert-butyl-4-(2,4-dichloro-5-isopropoxyphenyl)-Δ2-1,3,4-oxadiazolin -5-one], and prosulfalin {N-[[4-(dipropylamino)-3,5-dinitrophenyl] sulfonyl]-S,S-dimethylsulfilimine} to thatchy Kentucky bluegrass turf in spring caused injury that was apparent during periods of summer stress, while DCPA (dimethyl tetrachloroterephthalate) and bensulide [O,O-diisopropyl phosphorodithioate S-ester with N-(2-mercaptoethyl)benzenesulfonamide] caused little or no injury. The same treatments on thatch-free sites revealed that only prosulfalin was injurious. Adsorption of benefin, bensulide, and DCPA from solution was greater by thatch than by soil; however, the mobility of these herbicides in undisturbed thatch profiles was greater than measured in undisturbed surface soil from thatch-free sites. Thus, turfgrass injury from preemergence herbicides on thatchy sites is due to at least two factors: the greater mobility of preemergence herbicides in thatch than in soil; and the inherent susceptibility of Kentucky bluegrass to injury from preemergence herbicides that come into direct contact with roots and other absorbing organs.

Retention, absorption, translocation, and metabolism of propanil (3′,4′-dichloropropionanilide) in tolerant wheat (Triticum aestivum L. ‘Era’) and susceptible green foxtail [Setaria viridis (L.) Beauv. ♯3 SETVI] were studied to determine the basis of selectivity. Green foxtail retained 7.7 times more spray on a mg/g fresh weight basis than did wheat. Absorption of 14C-propanil by green foxtail was greater than by wheat during most of the 48-h uptake period, but differences in absorption were not large enough for absorption to be a major selectivity factor. Translocation of foliar-applied 14C-propanil was limited in both species; after 48 h, 96.7% of absorbed 14C remained in the treated wheat leaf and 99.7% remained in the treated green foxtail leaf. Limited metabolism of 14C-propanil occurred in green foxtail, with only 6.4% of extractable 14C-propanil metabolized to dichlorolactanilide and unknown 14C-compounds during a 72-h period. Wheat metabolized 65.8% of the extractable 14C-propanil to dichloroaniline and unknown 14C compounds by 72 h after treatment. The results of this research indicate that spray retention and propanil metabolism are the major factors involved in wheat tolerance and green foxtail susceptibility to propanil.