Field observations indicate that wheat (Triticum aestivum L.) is considerably more tolerant to soil residues of chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] carbonyl] benzenesulfonamide} than barley (Hordeum vulgare L.). The basis for relative differences in tolerance was investigated by measuring herbicide dose response, uptake, movement, and metabolism using ‘Clark’ barley and ‘Marberg’ wheat. Barley root fresh and dry weights were significantly reduced when roots were exposed to nutrient solution containing 35 mM chlorsulfuron for 1 day. Wheat roots similarly exposed for 3 days to 1.1 mM chlorsulfuron displayed no growth reduction. The small differences in uptake and movement of chlorsulfuron detected in wheat and barley are inadequate to explain the large response difference between the two species. Both species rapidly metabolize chlorsulfuron in 1 day and there is no significant difference in the level of parent compound remaining in barley compared to wheat. A factor other than uptake, movement, or metabolism must account for barley roots greater sensitivity to root-applied chlorsulfuron.

The relationships between microorganisms and velvetleaf (Abutilon theophrasti Medic. # ABUTH) seeds in contact with soil were studied to determine microbial effects on velvetleaf seed viability. The characteristic seed microbial association persisted on velvetleaf seeds placed on the soil surface during 32 days of incubation. The fungal association comprised of Alternaria alternata (Fr.) Keissl., Cladosporium cladosporioides (Fres.) de Vries, Epicoccum purpurascens Ehrenb. ex Schlecht, and Fusarium spp. was detected on over 50% of the seeds during incubation. Establishment of soil microorganisms on 50% of seeds occurred at only one sampling date. Such establishment was largely unsuccessful due to the effective barrier presented by seedborne microorganisms. Seedborne and soilborne microorganisms were unable to reduce viability of velvetleaf seeds in contact with soil as the total viability of all seeds tested exceeded 90% during incubation. Velvetleaf seedborne microorganisms may augment seed longevity on and in soils by acting as a barrier to potential seed decomposers originating from soil.

The effects on leucine uptake and its incorporation into protein by cucumber (Cucumis sativus L. ‘Ashley’) cotyledon tissue following treatments with 2,4-bis(isopropylamino)-6-(methylthio)-s-triazine (prometryne) were determined. Prometryne decreased 14C-leucine uptake both in the light and in the dark. Prometryne decreased leucine incorporation into protein only when the discs were also exposed to over 4 hr of light. Percent of absorbed leucine incorporated into protein was increased by a 4 hr exposure in the light to 10−4M prometryne following a 24-hr dark exposure to this same concentration. Similar exposure to 10~5M prometryne had no effect. Percent of leucine incorporated into protein was decreased by 10-5M prometryne following a 24 hr exposure to this same concentration in the light. However, under these conditions 10−4M prometryne had no effect. It is speculated that the increased percentage of leucine incorporated into protein may be related to increased availability of the absorbed leucine for use in protein synthesis rather than an effect of the herbicide on the rate of protein synthesis

The effects of imazaquin and imazethapyr on cotton planted the year following application to soybean were studied on one silt loam and two clay soils in Arkansas from 1989 to 1991. Imazaquin was applied to soybean at 0.07 kg ai ha−1 PPI and POST, 0.14 kg ha−1 PPI, PRE, and POST, and sequentially PPI or PRE followed by POST at 0.14 kg ha−1 per application. Imazethapyr was applied at 0.035 kg ha−1 PPI and POST, 0.07 kg ha−1 PPI, PRE, and POST, and sequentially PPI or PRE followed by POST at 0.07 kg ha−1 per application. Soil residues of 0.07 kg ha−1 imazaquin and imazethapyr did not injure cotton at any location. Residues of 0.14 kg ha−1 imazaquin applied sequentially reduced cotton shoot dry weight for 6 wk after emergence on clay but not on silt loam soil. The PPI followed by POST sequential imazaquin treatment (0.28 kg ha−1 total imazaquin) delayed initiation of fruiting and reduced yield and lint quality.

Early postemergence application of atrazine [2-chloro-4- (ethylamino)-6-(isopropylamino)-s-triazine] at 0.28 kg/ha in combination with alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] at 0.42 kg/ha plus a non-toxic oil-surfactant blend gave season-long weed control in sweet corn (Zea mays L. var. rugosa ‘Seneca Chief’). Bioassay with oats (Avena sativa L.) showed no detectable atrazine residue in the soil 3 months after herbicide application. In greenhouse studies, the response of Japanese millet (Echinochloa crus-galli L. Beauv. var. frumentacea) to early postemergence application of atrazine and alachlor combinations plus an oil-surfactant blend was synergistic. Soil uptake played a major role in the activity of the herbicides. Formulants used in commercial alachlor when added to atrazine spray, enhanced atrazine activity in a way similar to that of the non-toxic oil-surfactant.

Visible wheat (Triticum aestivum L.) injury, delay in bloom date, and yield reduction were observed following herbicide treatments in growing wheat. Protein content and volume weight of winter wheat were not significantly affected by any herbicide treatment. Some treatments reduced annual grass and broadleaf population by 90% or more 6 weeks after spraying and maintained weed control 8 weeks in untilled winter wheat stubble. Effective herbicide treatments that caused the least winter wheat injury in 1977 and 1978 included metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] + alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] at 0.3 + 2.8 kg/ha, metribuzin + oryzalin (3,5-dinitro-N 4,N 4-dipropylsufanilamide) at 0.3 + 1.8 kg/ha, metribuzin + pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine] at 0.3 + 2.2 kg/ha, metribuzin + SN-533 [N-ethyl-N-propyl-3-(propylsulfonyl)-1H-1,2,4-triazole-1-carboxamide] at 0.3 + 0.8 kg/ha, and R-40244 [1-m-trifluoromethylphenyl)-3-chloro-4-chloromethyl-2-pyrrolidone] at 1.1 kg/ha. Herbicide treatments that showed the most potential to control annual grass and broadleaf weeds selectively in tillered winter wheat and stubble in 1978 include metribuzin + metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] at 0.3 + 2 kg/ha, metribuzin + oryzalin at 0.3 + 1.4 kg/ha, and metribuzin + pendimethalin at 0.3 + 2 kg/ha.

EPTC (S-ethyl dipropylthiocarbamate), benefin (N-butyl-N-ethyl-α α,α-trifluoro-2,6-dinitro-N-propyl-p-toluidine], butralin[4-(1,1-dimethylethyl)-N-(1-methylpropyl)2,6-dinitrobenzenamine], diclofopmethyl {methyl 2-[4-(2,4-dichlorophenoxy)phenoxy]-propanoate} and 2,4-DB [4-(2,4-dichlorophenoxy)butyric acid] were evaluated in the greenhouse for effects on growth, nodulation, and NH3 production of alfalfa (Medicago sativa L.) and medium red clover (Trifolium pratense L.). Some reduction in nodulation occurred from some rates of the herbicides, but reduction in nodulation was usually associated with reduced plant growth caused by herbicidal injury.

Greenhouse experiments were conducted to evaluate phytotoxicity, absorption, and translocation of thifensulfuron when applied to pea at different rates, droplet sizes, and as dry particles. Thifensulfuron rates that reduced shoot dry weight by 25% were 0.46, 0.59, 0.98, and 1.21 g ai ha-1 for droplet diameters of 110, 155, 300, and 450 μm, respectively. The 14C-thifensulfuron absorption as percent of applied increased twofold, whereas translocation decreased 36% as herbicide concentration increased from 18 to 146 mg L-1 in 980-μm droplets. Small droplets (50 μm) that dried to particles before contact with leaves did not damage pea plants. However, under dew conditions, dry particles damaged peas to a similar degree as liquid droplets. We concluded that small and concentrated droplets of thifensulfuron can damage peas more than large and diluted droplets as a result of increased herbicide absorption.

Solutions containing 3-(m-trifluromethylphenyl)-l,l-di-methylurea (fluometuron) or 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron) were displaced through saturated 250-μ glass beads or through Norge loam soil at two water flow rates. The procedure used allowed uniform application of herbicide solutions to the soil surface and subsequent displacement of the herbicide through soil or glass bead columns at a constant water flow rate. Fluometuron was as mobile as the chloride ion at both high and low flow rates. The shape of the fluometuron distribution curves obtained at the two flow rates were distinctly different. The volume of water required to displace fluometuron through a material that adsorbed the herbicide was greater than that necessary to displace the fluometuron through materials giving a smaller amount of adsorption. More diuron was adsorbed by the glass bead system than fluometuron.

A laboratory experiment was conducted to compare the adsorption and desorption of fluometuron between two soils, one collected from an eastern gamagrass filter strip and the other from a cropped field. Fluometuron adsorption to soil collected from the filter strip was higher than to soil collected from the cropped field. Kd values for fluometuron ranged from 1.9 to 3.6 for soil from a cropped area, compared with 2.9 to 5.3 for soil from the filter strip, indicating a weak to moderate binding affinity for fluometuron. The total fluometuron desorbed ranged from 48 to 79% of that adsorbed, most of which (50 to 59% of the total amount desorbed) occurred during the first desorption cycle with both soils. Approximately 11% less fluometuron desorbed when a filter strip was present. Results indicate that eastern gamagrass filter strips can influence adsorption–desorption processes between fluometuron and a Brooksville silty clay soil by altering the soil properties, specifically soil organic matter.

The herbicide mixture 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) + 2-chloro-N-isopropylacetanilide (propachlor) was applied preemergence broadcast and in band widths of 18, 36, and 53-cm to corn (Zea mays L.). All herbicide treatments were applied as 1.1 kg of atrazine + 2.7 kg of propachlor per treated hectare. One row-middle cultivation and one rotary hoeing were also imposed on the herbicide treatments as variables. The 18-cm band of atrazine + propachlor with supplementary cultivation was as effective in controlling weed growth and maintaining corn yield as were wider herbicide bands or a broadcast treatment. Broadcast treated corn without row-middle cultivation produced significantly less grain than the handweeded check both years of the experiment. The average ratio of weed dry weight to reduction in corn yield was 0.8 to 1. Cultivation of row middles reduced average end-of-season weed yields 80%. Cultivator effectiveness on an 18-cm herbicide band equalled that measured on wider herbicide bands. Rotary hoeing reduced early season weed yields 82 and 38% in 1970 and 1971, respectively.

Our objective was to evaluate the cost/benefit of a single herbicide application or targeted grazing of invasive annual grasses during restoration of partially invaded sagebrush steppe ecosystems used for livestock production. The cost/benefit model used is based on estimating the production of vegetation in response to implementing management and modeling cost/benefit economics associated with that prediction. The after-tax present value of added animal unit months (AUMs) obtained was lower than the present value of after-tax treatment costs after 20 yr for a single herbicide treatment, but higher than the present value of after-tax treatment costs for the grazing management scenario. Even at the highest weed utilization level, the value of added AUMs did not offset the cost of the treatment after 20 yr. However, the grazing treatment resulted in a value of added AUMs higher than the costs after 20 yr. Depending on the invasive weed utilization level, break-even points with targeted grazing occurred at anywhere from the first year to 7 yr. This assessment clearly shows that grazing management can be economically viable for managing annual grass-infested rangeland. In the future, models like the one used here can be improved by incorporating the rangeland management and restoration benefits on the wide variety of goods and services gained from rangeland.

Itchgrass is an aggressive weed species in tropical agroecosystems. Because of phytosanitary restrictions to exports, pineapple producers must use a zero tolerance level for this species. An understanding of itchgrass seedling emergence would help producers to better time POST control. The objective of the present study was to characterize itchgrass seedling emergence patterns and develop a predictive model. Multiple field experiments were conducted in four agricultural fields in Costa Rica between 2010 and 2011 for a total of 9 site-years. Itchgrass consistently showed a biphasic emergence pattern, with a first emergence phase that was faster and more consistent across site-years than the second one. Weibull + logistic models based on chronological time (R2adj = 0.92) and thermal time with Tbase = 20 C (R2adj = 0.92) provided the best fit for the combined emergence data for two experimental locations in 2010. Both models predicted itchgrass seedling emergence adequately for most site-years, but the thermal-time model was more accurate (R2adj = 0.64 to 0.86) than the chronological model (R2adj = 0.31 to 0.74), especially when temperatures were high. Both models showed high accuracy in the first emergence phase but tended to underestimate emergence rate during the second phase. The models predicted 50% emergence at 14 d or 80 growing degree days and the stabilization of the first emergence phase at approximately 25 d or 200 growing degree days. Thus, these models can be used to properly time itchgrass POST control. More research is needed to understand the regulatory mechanisms responsible for the variability of the second emergence phase.

As a follow-up to greenhouse studies, acetolactate synthase (ALS) (EC 4.1.3.18) was extracted from one imidazolinone (IMI)-susceptible (S) and three IMI-resistant (R1, R2, and R3) smooth pigweed populations, and activity was assayed in the presence of imazethapyr, chlorimuron, thifensulfuron, and pyrithiobac. ALS inhibitor concentrations, required to reduce enzyme activity by a specified percentage compared with the untreated control (I p), were determined for each herbicide using regression analysis, and resistance ratios were calculated from these values. An I 50 value of >35 μM imazethapyr was calculated for all R populations compared with a value of 3.4 μM for the S population. With chlorimuron, thifensulfuron, and pyrithiobac data sets, pairwise comparisons of regression coefficients were used to determine significant differences between regression lines. Using this technique, it was established that ALS from R3 was more sensitive than ALS from S to inhibition by chlorimuron and thifensulfuron. Also, ALS from R2 and R3 displayed increased sensitivity to pyrithiobac compared with ALS extracted from the S population. We have confirmed enzyme-level resistance to imazethapyr in all R populations and have documented negative cross-resistance in some R populations to ALS inhibitors other than imazethapyr.

Field studies of seasonal sprouting of wild garlic (Allium vineale L.) bulbs showed that all the soft offset, aerial, and central bulbs sprouted, but only 20 to 34% of the hardshell bulbs sprouted after a short after-ripening period. Each fall, a percentage of the remaining hardshell bulbs sprouted, but after 4 years 16% of the hardshell bulbs were still dormant. Embryonic shoots of all bulb types sprouted when excised following the after-ripening period. In addition to a short after-ripening period, hardshell bulbs had a prolonged dormancy due to some mechanism which resides in, or was controlled by, the tissue surrounding the embryonic shoot.

DNA microarrays are one of the new tools of genomics that have become quite commonplace in plant science research within the past decade. Essentially, DNA microarrays are an extension of the more traditional molecular biology technique of northern blotting. Unlike northern blotting, however, in which the expression of a single gene is monitored, DNA microarrays allow for the simultaneous monitoring of thousands of genes—or, in fact, potentially all of an organism's genes—in a single experiment. Most of the currently available plant microarrays are designed for crops species or the model plant, Arabidopsis; however, a microarray for at least one major weed species is currently available. Furthermore, cDNA-based microarrays prepared for one species can be used to investigate gene expression in related species. As the technology is maturing it is becoming much more accessible, and now is the time to begin utilizing microarrays in weed science research. Questions related to herbicide activity are particularly well suited for a microarray approach. Additionally, gene-expression profiling via microarrays can be used to address questions relating to weed biology, weed–crop competition, allelopathy, parasitic weeds, and biological control of weeds.

Greenhouse and laboratory experiments were conducted to determine the effect of CGA 362622 on the herbicidal activity of clethodim on goosegrass. CGA 362622 did not affect absorption and translocation of 14C-clethodim by goosegrass. Averaged across the two treatments of clethodim alone and clethodim plus CGA 362622, absorption was 27 and 85% of the applied 14C-clethodim at 0.5 and 96 h, respectively. By 96 HAT, only 0.8% of applied 14C had translocated to the shoot below the treated leaf. Metabolism of clethodim was not affected by the presence of CGA 362622. Three metabolites of clethodim were detected in treated tissue at all harvest intervals. By 96 HAT, 56% of absorbed 14C converted to a relatively polar form when clethodim was applied alone or in the presence of CGA 362622. One day after treatment, the photosynthetic rate in plants treated with CGA 362622 had decreased below the rate in the nontreated check and remained lower until 6 d after treatment. These data suggest that the antagonism of clethodim by CGA 362622 may result from CGA 362622 altering the photosynthetic rate of goosegrass and therefore the sensitivity of acetyl-coenzyme A carboxylase to clethodim.

Plots were planted to corn (Zea mays L., var. Mo. 880) and treated with 0, 2.5, 5.0, and 10 lb/A of 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine) or 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) in 1964 and in 1965. Soybean (Glycine max L., var. Clark 63) forage yields from soil samples collected in the spring, 1 year after application, were not affected by treatments of 5.0 lb/A or less of atrazine. Yields were reduced on soils collected in the fall (6 months) after application. Following 2 years of treatment, substantial reductions in yields of soybean forage occurred. Soybeans planted in the field following 2 consecutive years of herbicide treatment, yielded similarly to the control plots except when rates of 10 lb/A had been applied.

Biennial wormwood is native to North America and has become an important weed problem in soybean and dry bean fields of North Dakota, South Dakota, and Minnesota in the United States and in the prairie provinces of Canada. Intersimple sequence repeat (ISSR) markers were used to study the genetic diversity among six biennial wormwood and one annual wormwood populations. Deoxyribonucleic acid (DNA) sequences from internal transcribed spacer (ITS1 and ITS2) regions of ribosomal DNA and morphological diversity among the biennial and annual wormwood populations were also studied. High levels of genetic diversity were evident with Nei's gene diversity statistic (h) = 0.40 for biennial wormwood and h = 0.36 for annual wormwood. Total diversity of six biennial wormwood populations was H T = 0.40, and 22% of this diversity was among populations (G ST = 0.22). Estimated gene flow among biennial wormwood populations was low (Nm = 0.9), and high levels of differentiation may be due in part to low levels of genetic exchange among biennial wormwood populations. Although biennial wormwood behaves more like an annual than a biennial, the ISSR, ITS, and morphological studies show that the two species are dissimilar.

Persistence and movement of 2,3,6-trichlorobenzoic acid (2,3,6-TBA) in a silty clay loam soil was studied. Single applications of 16 lb/A 2,3,6-TBA were made to field plots on 21 dates from 1955 to 1965. All treated plots were sampled to a depth of 8 ft in 1966, and a few were sampled to a depth of 11 ft. One-foot increments of soil were bioassayed to determine presence of the herbicide. Variation in amount and depth of penetration of 2,3,6-TBA was noted, but the herbicide had persisted in the soil 11 years. Persistence and movement could not be related to moisture before or after treatment, temperature after treatment, or, except for treatments applied in 1964 and 1965, time between treatments and sampling. Residues from fall applications appeared to be slightly greater than those from spring or summer applications.