Miscanthus is a perennial rhizomatous C4 grass being evaluated in the United States as a potential bioenergy feedstock. Weed control during the first two growing seasons is essential for successful establishment. No herbicides are currently labeled for use in Miscanthus grown for biomass, but herbicides used on field corn might be safe to Miscanthus. Greenhouse experiments were conducted in 2007 and 2008 to evaluate the response of Miscanthus to numerous preemergence (PRE) and postemergence (POST) herbicides. Herbicides with activity only on broadleaf species, whether PRE or POST, did not exhibit injury or reduce Miscanthus biomass. Several herbicides, particularly those with significant activity on grass species, exhibited injury ranging from 6 to 71% (scale of 0 to 100) and/or reduced Miscanthus dry mass by 33 to 78%, especially at the highest rates applied. Field experiments were conducted in 2008 and 2009 with a selection of the herbicides used in the greenhouse experiments to evaluate the response of Miscanthus to herbicides applied PRE, POST and PRE followed by POST. Results from the field experiments generally confirmed those from the greenhouse experiments. PRE herbicides and herbicides with broadleaf-specific activity generally did not produce significant injury or reduce aboveground biomass while herbicides with grass activity tended to cause injury ranging from 22 to 25% and/or reduce biomass by 69 to 78%. With some exceptions, results support prior suppositions that herbicides used in corn are safe to use on Miscanthus and may provide potential herbicide options that growers can use when establishing Miscanthus.

During 1989 and 1990, herbicides were applied to suppress common bermudagrass in a mixed stand of common bermudagrass and ‘Emerald’ zoysiagrass. When the mixed stand was treated with fluazifop at 0.2 kg ha-1 mid-May and 0.1 kg ha-1 1 mo later for two consecutive years, the common bermudagrass cover was reduced from 35 to 7% and the zoysiagrass cover increased from 65 to 85%. Similar results were achieve when fenoxaprop was applied at 0.2 kg ha-1 mid-May and repeated at monthly intervals for a total of four applications each year for 2 yr. The quality of mixed common bermudagrass and zoysiagrass turf was reduced immediately after each treatment; however, zoysiagrass recovered and treatments did not result in permanent damage. Sethoxydim suppressed common bermudagrass during the second year of treatment, but reduced the zoysiagrass stand each year. Ethofumesate applied along or with flurprimidol severely reduced the zoysiagrass stand with an increase of common bermudagrass.

In growth chamber research, infection by Puccinia punctiformis, a rust fungus, reduced flowering and vegetative reproduction in Canada thistle. Disease symptoms were greatest when Canada thistle roots were stored at 5, 10, or 15 C following inoculation. Exposure of roots to different temperatures before inoculation did not affect disease. All Canada thistle clones tested, regardless of gender became diseased although there were differences in susceptibility to P. punctiformis.

Greenhouse and laboratory studies were conducted to determine the effects of tank-mixing the sodium salt of dicamba (Na-dicamba) with imazethapyr on the efficacy and foliar absorption of imazethapyr, applied with non-ionic surfactant (NIS) or methylated seed oil (MSO), by shattercane, giant foxtail, and large crabgrass. The effects of various salt formulations of dicamba and the addition of ammonium sulfate on efficacy, 14C-absorption and on foliar spray retention by the same species were also evaluated. Na-dicamba antagonized imazethapyr efficacy by reducing 14C-absorption. Using MSO instead of NIS prevented antagonism when Na-dicamba was applied at 70 and 140 g/ha and reduced the severity of the antagonism at greater application rates by greatly increasing 14C-absorption compared to NIS. Reductions in 14C-absorption and spray retention were due to the salt formulations of dicamba rather than the parent acid. The addition of ammonium sulfate prevented dicamba antagonism of imazethapyr toxicity to grassy weeds by maintaining 14C foliar absorption and spray retention at normal levels.

Turf managers traditionally avoid seeding cool-season turfgrass in spring due to summer annual weed interference and poor growing conditions for cool-season grasses. Siduron is the most accepted herbicide for weed control in spring-seeded tall fescue, but it has low residual activity and does not control many weeds other than crabgrass. Isoxaflutole, mesotrione, and quinclorac were evaluated as alternatives to siduron. Single applications of these herbicides controlled crabgrass equivalent to or better than siduron. Sequential applications of isoxaflutole, mesotrione, or quinclorac effectively controlled smooth crabgrass without injuring tall fescue. Isoxaflutole and mesotrione controlled broadleaf plantain, henbit, and yellow woodsorrel; quinclorac marginally controlled henbit; and siduron did not control broadleaf weeds. Turfgrass cover 9 wk after seeding was dependent on environment and equivalent between treatments except at a location with predominately broadleaf weeds where siduron treatments resulted in less cover due to weed infestation. Sequential applications of isoxaflutole, mesotrione, and quinclorac provide an effective, safe option for chemical weed control during establishment of cool-season turfgrass.

A seed remover using a modified water-spray system was constructed to separate weed seeds rapidly and effectively from a silt loam soil A 1-kg soil sample can be washed through the seed remover in 6 min. Using a 500-μ mesh sieve, only 70% of small shepherdspurse seeds were recovered, while 100% of larger seeds of henbit, curly dock, wild oats, and downy brome were recovered. The modified seed remover system reduced the required man-hours by more than 50% compared to previous systems.

A field study was conducted for the 2014 and 2015 growing season in Arkansas, Indiana, Illinois, Missouri, Ohio, and Tennessee to determine the effect of cereal rye and either oats, radish, or annual ryegrass on the control of Amaranthus spp. when integrated with comprehensive herbicide programs in glyphosate-resistant and glufosinate-resistant soybean. Amaranthus species included redroot pigweed, waterhemp, and Palmer amaranth. The two herbicide programs included were: a PRE residual herbicide followed by POST application of foliar and residual herbicide (PRE/POST); or PRE residual herbicide followed by POST application of foliar and residual herbicide, followed by another POST application of residual herbicide (PRE/POST/POST). Control was not affected by type of soybean resistance trait. At the end of the season, herbicides controlled 100 and 96% of the redroot pigweed and Palmer amaranth, respectively, versus 49 and 29% in the absence of herbicides, averaged over sites and other factors. The PRE/POST and PRE/POST/POST herbicide treatments controlled 83 and 90% of waterhemp at the end of the season, respectively, versus 14% without herbicide. Cover crop treatments affected control of waterhemp and Palmer amaranth and soybean yield, only in the absence of herbicides. The rye cover crop consistently reduced Amaranthus spp. density in the absence of herbicides compared to no cover treatment.

Herbicide active ingredients, formulation type, ambient temperature, and humidity can influence volatility. A method was developed using volatility chambers to compare relative volatility of different synthetic auxin herbicide formulations in controlled environments. 2,4-D or dicamba acid vapors emanating after application were captured in air-sampling tubes at 24, 48, 72, and 96 h after herbicide application. The 2,4-D or dicamba was extracted from sample tubes and quantified using liquid chromatography and tandem mass spectrometry. Volatility from 2,4-D dimethylamine (DMA) was determined to be greater than that of 2,4-D choline in chambers where temperatures were held at 30 or 40 C and relative humidity (RH) was 20% or 50%. Air concentration of 2,4-D DMA was 0.399 µg m−3 at 40 C and 20% RH compared with 0.005 µg m−3 for 2,4-D choline at the same temperature and humidity at 24 h after application. Volatility from 2,4-D DMA and 2,4-D choline increased as temperature increased from 30 to 40 C. However, volatility from 2,4-D choline was lower than observed from 2,4-D DMA. Volatility from 2,4-D choline at 40 C increased from 0.00458 to 0.0263 µg m−3 and from 0.00341 to 0.025 µg m−3 when humidity increased from 20% to 50% at 72 and 96 h after treatment, respectively, whereas, volatility from 2,4-D DMA tended to be higher at 20% RH compared with 50% RH. Air concentration of dicamba diglycolamine was similar at all time points when measured at 40 C and 20% RH. By 96 h after treatment, there was a trend for lower air concentration of dicamba compared with earlier timings. This method using volatility chambers provided good repeatability with low variability across replications, experiments, and herbicides.

Palmer amaranth resistance to protoporphyrinogen oxidase (PPO)-inhibiting herbicides has become an increasing problem to producers throughout the southeast region of the United States. Traditionally, these herbicides can be used as foliar-applied and soil-applied in glyphosate resistant (GR) cropping systems to control GR Palmer amaranth. Heavy reliance on PPO herbicides has contributed to the increased selection for PPO inhibitor-resistant (PPO-R) Palmer amaranth biotypes. Dose response greenhouse research was conducted to evaluate the efficacy of soil-applied flumioxazin, fomesafen, saflufenacil and sulfentrazone on a known susceptible (S) and resistant (R) Palmer amaranth biotype. Both R and S populations reached maximum germination at 14 d after treatment (DAT). The data from this study suggests complete control (100%) was achieved for the S biotype at 35 d after treatment (DAT) with all herbicides. The R biotype showed difference among herbicide treatments with flumioxazin and saflufenacil having similar responses in control and fomesafen and sulfentrazone resulting in less control of the R Palmer amaranth biotypes. The calculated relative resistance factor ranged from 3.5 to 6.0, and averaged 5X for the four herbicides. This research indicated that the PPO-R population was still responsive to all tested herbicides, but a low level of resistance was present.

In field studies conducted under weed-free conditions, soybean yield was not adversely affected with POST applications of AC 263,222 at 18 g ha−1. At 36 g ha−1, soybean height at maturity was reduced in three of five studies and soybean yield in two of five studies. Application of 9 g ha−1 of AC 263,222 to sicklepod at cotyledon to four-leaf (early POST) or at a maximum size of five-leaf (late POST) provided 30 to 48% control. Control was 54 to 73% with AC 263,222 at 9 g ha−1 applied early POST followed by late POST. Regardless of application rate or timing, sicklepod control with AC 263,222 generally was inferior to the standard treatments of pendimethalin plus imazaquin PPI followed by imazaquin late POST or pendimethalin PPI and metribuzin PRE followed by chlorimuron late POST. Compared with the weed-free check, soybean yield was reduced when AC 263,222 was applied at 9 g ha−1 early POST followed by late POST in one of two studies and in two of three studies when applied at 18 g ha−1 early POST.

Postemergence herbicides to control grass weeds in grain sorghum are limited. Acetolactate synthase (ALS) –inhibiting herbicides are very effective at controlling many grass species in many crops; unfortunately, use of ALS-inhibiting herbicides is not an option in conventional grain sorghum because of its susceptibility to these herbicides. With the development of ALS-resistant grain sorghum, several POST ALS-inhibiting herbicides can be used to control weeds in grain sorghum. Field experiments were conducted in 2007 and 2008 to evaluate the efficacy of tank mixtures of nicosulfuron + rimsulfuron applied alone or in combination with bromoxynil, carfentrazone–ethyl, halosulfuron + dicamba, prosulfuron, 2,4-D, or metsulfuron methyl + 2,4-D. In addition, these treatments were applied with and without atrazine. Nicosulfuron + rimsulfuron controlled barnyardgrass, green foxtail, and giant foxtail 99, 86, and 91% 6 wk after treatment (WAT), respectively. A decrease in annual grass control was observed when nicosulfuron + rimsulfuron was tank mixed with some broadleaf herbicides, although the differences were not always significant. In addition, nicosulfuron + rimsulfuron controlled velvetleaf and ivyleaf moringglory 64 and 78% 6 WAT, respectively. Control of velvetleaf was improved when nicosulfuron + rimsulfuron was tank mixed with all broadleaf herbicides included in this study with the exception of atrazine, bromoxynil, and prosulfuron + atrazine. Control of ivyleaf morningglory was improved when nicosulfuron + rimsulfuron was tank mixed with all of the herbicides included in this study with the exception of metsulfuron methyl + 2,4-D. Weed populations and biomass were lower when nicosulfuron + rimsulfuron were applied with various broadleaf herbicides than when it was applied alone. Grain sorghum yield was greater in all herbicide treatments than in the weedy check, with the highest grain yield from nicosulfuron + rimsulfuron + prosulfuron. This research showed that postemergence application of nicosulfuron + rimsulfuron effectively controls grass weeds, including barnyardgrass, green foxtail, and giant foxtail. The research also showed that velvetleaf and ivyleaf morningglory control was more effective when nicosulfuron + rimsulfuron were applied with other broadleaf herbicides.

Adjuvant effectiveness with imazethapyr for kochia control was generally methylated seed oil ≥ nonionic surfactant ≥ petroleum oil in the greenhouse experiments, and methylated seed oil ≥ petroleum oil nonionic surfactant in the field. Oil adjuvants were applied at 2.3 L ha-1 and nonionic surfactants were applied at 0.25% (v/v) of spray volume. None of the adjuvants overcame imazethapyr reduced phytotoxicity caused by simulated rain soon after treatment, posttreatment cold (10 C), low soil moisture, or low soil nitrogen. However, kochia fresh weight reductions usually were the greatest when imazethapyr was applied with methylated seed oil, except in the case when soil had 80 ppm or less soil nitrogen. Kochia control with imazethapyr was enhanced the most by methylated seed oil followed by nonionic surfactant and petroleum oil regardless of relative humidity. High compared to low relative humidity tended to increase control for imazethapyr alone or with nonionic surfactant and decrease control for imazethapyr with oils. Kochia fresh weight reduction following imazethapyr treatment was greatest at 20 C, intermediate at 30 C and least at 10 C posttreatment when used with any of the adjuvants.

Field studies were conducted from 1987 through 1990 on Sharkey clay to determine effect of weed control treatment (WTRT) on yield and net return from soybean grown with no irrigation (NI) or irrigation (I) during reproductive development. Weed control treatments were: 1) PRE glyphosate plus metribuzin plus metolachlor or pendimethalin, followed by POST bentazon plus acifluorfen or 2,4-DB plus linuron (high WTRT); 2) PRE glyphosate at a rate to kill existing weeds at planting (medium WTRT); or 3) PRE paraquat at a rate to desiccate but not necessarily kill existing weeds at planting (low WTRT). POST cultivation was used in all treatments. Weed ground cover in the high, medium, and low WTRT's was composed of annual grass and moderately competitive broadleaf species, and averaged 7, 25, and 49%, respectively, at harvest in 1990. Yield declined with decreasing weed control in the I treatment after the first year, but average net returns from the high and medium WTRT's were not different, and both exceeded average returns from the low WTRT. Yields from the high and medium WTRT's in the NI treatment were not different, and both exceeded yield from the low WTRT. Average net returns from the medium WTRT were greater than those from the high and low WTRT's in all years. Yield increase from irrigation and difference in average net returns between I and NI declined with decreasing weed control.

The allelopathic potential of hoary cress was evaluated by exposing the seeds and the germinated seeds of winter wheat, alfalfa, crested wheatgrass, bluebunch wheatgrass, and hoary cress to a water extract of dried, hoary cress roots under controlled conditions in an environmental chamber. Germination for all species was reduced in the hoary cress root extract when compared with distilled water, with winter wheat and hoary cress being more tolerant than the other species. Root length of all species was reduced by the extract when compared with distilled water. These data show the presence of phytotoxic chemical(s) that may inhibit germination and initial seedling growth in natural environments. Three glucosinolate compounds were identified in hoary cress root extracts.

Research was conducted in 1995 and 1996 to determine the potential for commonly used volunteer corn herbicides to control volunteer sethoxydim-resistant (SR) corn in soybean. Greenhouse studies showed that the SR corn hybrid tolerated 181 times more sethoxydim than the susceptible sister hybrid. SR corn also tolerated other acetyl CoA carboxylase (ACCase) inhibitors including fluazifop-P, quizalofop-P, and clethodim with 30 X, 27 X, and 7 × magnitudes of tolerance, respectively, compared with the susceptible hybrid. SR corn exhibited the least tolerance to clethodim, with a control rating of 50% (CR50) predicted at 28 g ai/ha. Field studies at Dekalb and Urbana, IL, showed that quizalofop-P, fluazifop-P, and fluazifop-P plus fenoxaprop at 62, 140, and 140 + 47 g ai/ha, respectively, controlled 22% or less of volunteer F2 SR corn at 30 days after treatment (DAT). Clethodim at 105, 140, and 210 g/ha consistently suppressed 23 to 70% of the volunteer SR corn. Dry weight reductions at 60 DAT showed the same general trend as the visual estimates of control. The field results confirmed the greenhouse data, which suggested SR corn had the least amount of cross-resistance to clethodim compared to other ACCase-inhibiting herbicides. In 1996, only AC 299,263 and imazethapyr plus imazaquin suppressed volunteer SR corn and prevented soybean yield loss at both locations. However, no system completely controlled volunteer SR corn.

Effects of a 28% N solution containing urea and ammonium nitrate (28% UAN) and a nonionic surfactant on efficacy, uptake, and translocation of chlorimuron ethyl ester in soybean and broadleaf weeds were investigated. Chlorimuron applied postemergence at 8.8 and 13 g ai/ha with either nonionic surfactant at 0.25% (v/v), 28% UAN at 9.4 L/ha, or nonionic surfactant plus 28% UAN controlled weeds better than without additives. Chlorimuron with nonionic surfactant and with 28% UAN controlled weeds similarly but with 28% UAN injured soybeans least. Chlorimuron with nonionic surfactant plus 28% UAN controlled velvetleaf best but injured soybeans most. Less than 2% of applied 14C-chlorimuron was absorbed in velvetleaf 84 h after treatment (HAT) when no additive was present, but adding nonionic surfactant, 28% UAN, and nonionic surfactant plus 28% UAN resulted in 21, 9, and 32% uptake, respectively, 84 HAT. Nonionic surfactant plus 28% UAN also increased translocation (primarily acropetal) of the 14C. Adding 28% UAN increased 14C-chlorimuron uptake in velvetleaf grown at low fertility but had no effect under high fertility.

Reciprocal controlled crosses were made in the greenhouse between Gulfmont rice transformed with the bialaphos resistance (BAR) gene and red rice and BAR-transformed Koshihikari rice and red rice to assess the inheritance of glufosinate resistance. All F1 plants were resistant to 2.2 kg ai/ha glufosinate. Ammonia accumulation as a measure of glufosinate resistance in the F1 hybrids was assayed at 4 and 8 days after treatment (DAT). Ammonia accumulation in hybrids 4 DAT was similar to glufosinate treated, transformed rice, while treated nontransformed plants accumulated 14 to 23 times more ammonia compared with the hybrids. The nature of inheritance of glufosinate resistance in F2 rice plants was studied by a glufosinate dip test, a spray test, and ammonia assay. All three tests confirmed that glufosinate resistance, as influenced by the BAR gene, segregated in a 3 (resistant): 1 (susceptible) ratio.

Flaxleaf fleabane is a difficult-to-control weed in dryland minimum tillage farming systems in the northeast grains region of Australia. Experiments were conducted between 2003 and 2005 to identify effective control strategies on flaxleaf fleabane in wheat and sorghum. A preplant application of chlorsulfuron at 15 g ai/ha in wheat controlled flaxleaf fleabane ≥ 90%. The efficacy of early postemergent applications of metsulfuron–methyl at 4.2 g ai/ha varied between years. However, the flaxleaf fleabane was controlled > 85% with metsulfuron–methyl at 4.2 g ai/ha plus MCPA at 420 g ae/ha plus picloram at 26 g ae/ha, or metsulfuron–methyl followed by late postemergent 2,4-D amine at 300 g ae/ha. In sorghum, a preplant application of glyphosate at 900 g ae/ha plus 2,4-D amine at 900 g ae/ha or dicamba at 500 g ae/ha at 1 mo before sorghum planting provided ≥ 95% control. Preplant atrazine at 2,000 g ai/ha controlled flaxleaf fleabane 83 to 100% in sorghum. At-planting atrazine at 2,000 or 1,000 g ai/ha can be applied to control new emergence of flaxleaf fleabane and grasses, depending on the weed pressure and spectrum. Flaxleaf fleabane reduced sorghum yield 65 to 98% if not controlled.

Field experiments were conducted in 1989 and 1990 on silty clay and sandy loam soils to evaluate weed control and soybean yield with early-April preplant incorporation of selective herbicides in stale seedbed soybean followed by non-selective weed control measures at planting. Metribuzin applied PPI early followed by chlorimuron POST coupled with either glyphosate or paraquat PRE controlled sicklepod, pitted morningglory, and hemp sesbania to the same extent of that treatment applied PPI at planting. All stale seedbed treatments with POST applications and glyphosate, paraquat, or tillage at planting controlled pitted morningglory over 70%. However, imazaquin or metribuzin applied PPI early without a POST treatment controlled sicklepod and pitted morningglory poorly. Frequently, applying PPI herbicides at planting increased control compared with early PPI applications, but this was overcome by POST treatments. Early stale seedbed applications of metribuzin did not result in more than 60% control of hemp sesbania, whereas metribuzin applied PPI at planting controlled over 85%. However, metribuzin plus chlorimuron controlled hemp sesbania at least 74%, regardless of application timing or tillage method, whereas no imazaquin treatment achieved over 65% control. All stale seedbed herbicide treatments increased soybean yield compared with the untreated stale seedbed check. Selective herbicide treatments with either non-selective herbicide in a stale seedbed program resulted in equivalent yield to PPI at planting treatments most often, except with metribuzin.

Phytotoxins produced by the naturally-occurring rhizobacterium, Pseudomonas fluorescens strain D7 (strain D7), in shake cultures from several media sources adversely affected downy brome at several growth stages and affected seeds, whole plants, and isolated cells. These uncharacterized phytotoxins inhibited root and shoot growth of downy brome by 80% in a seed germination agar assay at 2 and 400 ng total solids/ml, respectively. In a hydroponics assay, downy brome and winter wheat dry weights were reduced 50% by cell-free broth concentrations of 15 and 26% of the initial broth concentration, respectively, indicating an almost 2x selectivity between winter wheat and downy brome. Plant water use was reduced similarly. Plasma membranes of isolated protoplasts of downy brome were damaged within 2 h by diluted cell-free broth. Cold-precipitated phytotoxins of strain D7 produced in semi-synthetic and synthetic media reduced dry weight of downy brome seedlings by 100 and 89%, respectively, and killed plants rapidly.