Alfalfa is an important forage crop in North America, and it can also be found as a roadside weed in alfalfa-growing regions. Weediness and invasiveness are greatly facilitated by establishment ability, yet little is known about the ability of alfalfa to establish in competitive environments such as roadsides. The primary objective of this study was to estimate the degree of alfalfa establishment without managed cultivation under different seed-dispersal times and disturbance regimes. The study had a split-plot design with two main plots (spring and fall seed dispersal) and five subplots (mowing, soil disturbance, herbicide spray, seedbed, and undisturbed control). The study examined establishment, growth attributes, and reproductive output of alfalfa in response to these treatments. Alfalfa establishment in the undisturbed grass swards ranged between 0.5 and 9.7% (out of the total number of seeds dispersed) across the dispersal times. The density of alfalfa in fall-seeded plots was about 82% lower than in spring-seeded plots. Soil disturbance reduced the density of alfalfa to < 50% of the initial density. Generally, low plant densities were compensated over time by increased numbers of shoots and reproductive units (racemes and pods) per plant. Herbicide application (2,4-D + dicamba) effectively controlled all emerged alfalfa plants, but in some cases, seedling recruitment was observed in the years following herbicide application. Although mowing did not kill alfalfa plants, mowed plants did not produce mature seeds, and as such, mowing may be useful in restricting the reproductive success and population growth of alfalfa. Overall, it is evident that alfalfa is capable of establishing in competitive environments (such as roadside habitats) and rapidly recovering from moderate disturbances. The results of this study have implications for managing roadside alfalfa and for designing novel trait-confinement protocols for alfalfa.

Yellow rattle is a hemiparasitic weed that is becoming increasingly problematic in hay fields in the northeastern United States. The biomass of yellow rattle was assessed in two experiments in which commercially available soil amendments were applied to an infested hay field under no-till management. The amendments were applied in the fall of 2010 and 2011 and included wood ash, biochar, hardwood sawdust, lime, and K. Wood ash applied at a rate of 8,967 kg ha−1 (4 tons per acre) had the greatest suppressive effect and reduced yellow rattle biomass the following summer by 86 and 92% relative to the untreated control in Experiments 1 and 2, respectively. Two additional treatments included in Experiment 2, a doubled rate of wood ash and sawdust applied at a rate of 13,450 kg ha−1, also reduced yellow rattle biomass. No other treatments affected yellow rattle biomass. A partial least-squares regression (PLSR) analysis that included aboveground plant community and soil biochemical data explained only 42.4% of the variation in yellow rattle biomass, suggesting that the mechanisms responsible for the suppression of yellow rattle by wood ash and sawdust are complex. Amending hay fields with wood ash or sawdust may be an effective nonherbicide strategy for managing yellow rattle infestations. Additional research will be required to determine the mechanisms and generality of yellow rattle suppression by wood ash and sawdust amendments to the soil.

At rates as high as 40 lb/A, 1-(2-methylcyclohexyl)-3-phenylurea (siduron) did not reduce the growth of crabgrass (Digitaria spp.) seedlings although it was highly toxic to germinating seeds. Siduron placed at the 2-inch soil depth reduced root growth but not shoot growth of crabgrass. Barley (Hordeum vulgare L., var. Trail) roots, like crabgrass, were more affected than shoots. Carbonyl labeled siduron-14C was absorbed by both barley roots and shoots. Siduron-14C was translocated from roots to shoots but not from shoots to roots. Analysis of the extracts from plants treated at various times revealed that no metabolites of siduron-14C were present. Siduron must be present at the time of seed germination to effectively reduce plant growth.

Autoradiographic studies showed that regardless of whether 5-amino-4-chloro-2-phenyl-3(2H)-pyridazinone (pyrazon) was applied to the leaves or to the roots of sugar beet (Beta vulgaris L.) plants, it moved in the apoplastic system. The pattern of pyrazon distribution from root absorption in sugar beet seedlings was identical at either 35 or 18.3 C. However, root absorption at 35 C was twice as great as at 18.3 C; and translocation of pyrazon into the shoot was more rapid at the high temperature. A major metabolite of pyrazon, a pyrazon-glucose conjugate, was produced in leaves and cotyledons but not in roots of sugar beets. A minor metabolite, less than 5%, was found in sugar beet leaves. Pyrazon was not metabolized by the susceptible species common lambsquarters (Chenopodium album L.). The rate of pyrazon-glucose conjugate formation in pyrazon-infiltrated sugar beet leaf discs was practically identical at 35 and 18.3 C. Therefore, it was concluded that the increased susceptibility of sugar beets to pyrazon at higher temperatures was due to an increase in absorption and translocation of the herbicide at higher temperatures which was not accompanied by a parallel increase in the conversion of pyrazon to its glucose conjugate.

Field experiments were conducted over a 2-yr period to study the comparative morphological development of cogongrass [Imperata cylindrica (L.) Beauv.] ecotypes from 15 different locations throughout the three main regions of Iraq. Plant height and density of stands varied more than 2-fold. The number of flowering heads varied 11-fold for plants collected from the different locations. Mature leaf-blades varied in width from 4.7 to 6.9 mm. These distinct variations indicate the existence of different ecotypes of cogongrass in Iraq.

Yellow foxtail [Setaria glauca (L.) Beauv.], giant foxtail (Setaria faberi Herrm.), giant green foxtail [Setaria viridis var. major (Gaud.) Posp.], robust white foxtail (Setaria viridis var. robusta-alba Schreiber), and robust purple foxtail (Setaria viridis var. robusta-purpurea Schreiber) were grown from seed in pure stands in sand-soil nutrient solution cultures at various nitrogen levels. Within taxa dry weight of herbage differed significantly with nitrogen level, but dry weight of roots did not. Yellow foxtail produced more leaf area than the other four taxa regardless of nitrogen level. At the low nitrogen level, yellow foxtail produced significantly more root mass (dry weight) than the other taxa; giant foxtail was second in root-mass production. The order of root-mass production was the same at medium and high nitrogen levels, but only at a 12-h photoperiod. At a 16-h photoperiod, root production was equal in yellow foxtail and giant foxtail and was significantly greater in these taxa than in giant green foxtail, robust white foxtail, or robust purple foxtail. Generally similar relationships were evident in the root: shoot ratios. The chances for survival with giant foxtail taxa should be better for yellow foxtail than for the other foxtail taxa since yellow foxtail produced more root mass even at low nitrogen fertility, a condition common in undistrubed sites such as roadsides and fencerows.

Two of three herbicides were applied repetitively in each of the years to a dense infestation of Canada thistle [Cirsium arvense (L.) Scop.] in timothy (Phleum pratense L.) and red clover (Trifolium pratense L.) sward in Carroll County, Maryland during the period 1969 to 1971. Picloram (4-amino-3,5,6-tricloropicolinic acid), eliminated red clover from the sward after the first year, and controlled 95 to 100% of the Canada thistle in the third year of treatment. The addition of a non-phytotoxic oil to picloram did not improve its efficiency. Dicamba (3,6-dichloro-o-anisic acid) reduced 57 to 87% of the red clover and 72% of the Canada thistle in the first year at a dosage of 1.12 kg/ha, but effected only 42% control in the third year of treatment. Both an amine and ester formulations of 2,4-D [(2,4-dichlorophenoxy) acetic acid] effected variable Canada thistle control and reduced the red clover stand 10 to 15% following the first application. The timothy yield was not significantly reduced during the 3 years of repeated application of all herbicides, but some necrosis of leaves was noted with dicamba and the high rate of 2,4-D. Soybeans [Glycine max (L.) Merr. ‘Delmar’] planted 1 yr following the last picloram application had curled leaves initially, but outgrew the injury. Soybeans planted 2 yr following the last application of the herbicides showed no significant reduction in yield indicating herbicide residues had been reduced to tolerable levels.

Nitralin (4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline) controlled grasses and 3-[p-(p-chlorophenoxy)phenyl]-1,1-dimethylurea (chloroxuron) controlled broadleaf weeds in soybeans (Glycine max (L.) Merr.) as well singly as when combined. In 1 year out of 2, nitralin and chloroxuron in combination caused more plant injury than either herbicide alone. The combination of nitralin (0.56 or 0.84 kg/ha) with chloroxuron (1.68 kg/ha) reduced seed yields 37% from the value obtained with chloroxuron alone (1.68 kg/ha).

The effects of treatment with twelve metabolites of trifluralin [2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl) benzenamine] on the gross morphology and ultrastructure of trifluralin-susceptible (S) and -resistant (R) biotypes of goosegrass [Eleusine indica (L.) Gaertner. # ELEIN] root meristems were examined. Unlike trifluralin, ten of the twelve metabolites including the major metabolites of trifluralin caused no root tip swelling even at water-saturated concentrations. Two of the minor metabolites, 3-methoxy-2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine (TR-36M) and N-(2,6-dinitro-4-(trifluoromethyl)phenyl)-N-propylpropanamide (TR-40), caused root swelling when applied as a saturated solution. The most effective metabolite, TR-36M, caused root swelling at 10 μM or greater concentrations. Because trifluralin caused swelling of the root tips even at a 0.01 μM concentration, trifluralin is 1000-fold more effective than the most herbicidally active metabolite. Both herbicidally active metabolites are also much less effective than trifluralin at increasing the mitotic index. Structural studies indicate that the two herbicidally active metabolites arrest mitosis at prometaphase due to the loss of spindle microtubules, similar to trifluralin. Cortical microtubules are also affected by the highest concentrations of these two metabolites. A resistant biotype, in which mitosis is unaffected by trifluralin, was unaffected by any of the trifluralin metabolites.

Field experiments were conducted during 1968 to 1970 to determine the influence of time of herbicide application on control of kudzu [Pueraria lobata (Willd.) Ohwi]. Picloram (4-amino-3,5,6-trichloropicolinic acid) effectively controlled kudzu when applications were made as early as May 22 and as late as October 28. Acceptable control was obtained with rates of picloram 0.34 kg/ha or higher. In contrast, (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T) was most effective when applied during the first half of summer. Essentially no control of kudzu was obtained from 2,4,5-T applied 1 week before the first killing frost.

Absorption of ethyl ester of chlorimuron by excised velvetleaf root tissue was investigated. Chlorimuron uptake increased rapidly, reaching a maximum after 2 h. After 4 h, however, a portion of the previously absorbed herbicide was lost to the external solution. The temperature coefficient (Q10) for chlorimuron absorption between 15 and 25 C was 1.9. The herbicide uptake was severely inhibited by metabolic inhibitors, DNP and KCN, and by anaerobic conditions (anoxia). Results of permeation experiments indicated that chlorimuron did not accumulate in the root tissue against a concentration gradient, and Ci/Co reached 1.0 after a 2-h permeation period. Chlorimuron efflux was continuous and after 2 h of washing the tissue in a herbicide-free solution, 90% of the previously absorbed herbicide was removed, suggesting that its accumulation in the tissue was reversible.

Various surgical cuts were used to induce germination of dormant barnyardgrass [Echinochloa crus-galli (L.) Beauv. # ECHCG] caryopses. Greater percentages of germination were obtained when the cuts were made closer to the embryo. However, removal of only the caryopsis coat covering the coleoptile or midembryo axis induced up to 10% germination compared to 70% germination for caryopses with the coat covering the radicle removed. Dormancy of barnyardgrass was not caused by the inability of the embryo to imbibe, imposed mechanical resistance of the caryopsis coat, or presence of an inhibitor. A wounding response, other than ethylene production, by the cut caryopses was possibly responsible for stimulating germination. Similar responses to cutting observed in afterripened caryopses were consistent with the suggested hypothesis.

Two Nicotiana tabacum L. cultivars, ‘North Carolina 88’ and ‘Coker 319′, were grown in a charcoal-filtered greenhouse and treated with three different herbicides according to the herbicide labels. Labeled rates (X) for diphenamid (N,N-dimethyl-2,2-diphenylacetamide), isopropalin (2,6-dinitro-N,N-dipropylcumidine), and pebulate (S-propyl butylethylthiocarbamate) were 9.2 kg/ha, 2.3 kg/ha, and 6.2 kg/ha, respectively. Three weeks after treatment with 1/2X, X, or 2X rates of herbicide, half of the plants were fumigated with 15 μl/liter ozone for 2.5 h for four consecutive days. North Carolina 88 and Coker 319 grew equally well and were equally sensitive to ozone injury. Ozone reduced plant height and levels of reducing sugars and total nonstructural carbohydrates of both cultivars. Isopropalin, at X and 2X, reduced the ozone sensitivity and growth of both cultivars, while the X rate of pebulate reduced the ozone sensitivity of North Carolina 88. The chemical composition of the plants was not correlated with the sensitivity of the tobacco plants to ozone-induced injury. The major factors governing fleck intensity, growth, and chemical compositions were ozone and herbicide treatments.

Wheat (Triticum aestivum L., var. Selkirk) was most susceptible at the late tiller stage to 4-amino-3,5,6-trichloropicolinic acid (picloram) as determined from weekly applications in the field and the degree of injury increased with rate of picloram. Wheat injury from picloram was manifested by lower kernel yield, greater protein content in the kernels, and reduction in plant height. A reduction in the length of the stem occurred while the length of the flag leaf sheath was not affected. Picloram increased kernel size in 1966 but reduced it in 1965. Picloram did not influence germination of kernels from treated plants. The addition of (2,4-dichlorophenoxy)acetic acid (2,4-D) to picloram tended to increase wheat injury at the 2 to 4-leaf stage.

This paper gives an overview of computer assisted molecule design using quantitative structure activity relationships (QSAR). In deriving a QSAR for a set of compounds, one should be aware of possible properties one can use to correlate with the activity of this set of compounds. The paper describes some of the traditional and also more recently used properties that can be calculated. The traditionally used properties have been those calculated for the substituent groups that were varied on a particular scaffold, whereas the more recently used properties are those calculated on the molecule as a whole. One of the most recently used properties for comparative purposes are fields around the molecules. The technique is termed comparative molecular field analysis (CoMFA). The statistical techniques used to correlate the properties with the activity are also described and, finally, a case study is described. The case study shows the application of traditional and 3D QSAR (CoMFA) techniques on some photosystem II inhibitors.

Competitiveness of noogoora burr and fierce thornapple in irrigated cotton was assessed using area-of-influence methodology. Lint yields were regressed against distances from the weeds using spline regression. The resulting regression curves were used to estimate areas of influence and yield losses, which were further modeled as functions of weed size to understand weed competitiveness. Cotton lint yield reductions averaged 36 and 12%, with maximum distances of influence of 1.71 and 1.65 m for noogoora burr and fierce thornapple, respectively. Economic thresholds for control using hand hoeing were related to weed size. Thresholds for average-size weeds were one cocklebur in 195 m and one fierce thornapple in 73 m of cotton row.

A great deal of energy in recent months has been expended in worrying about energy. The procurement, allocation, utilization, and conservation of energy sources have been probed countless times and viewed from almost every possible vantage point. The word “energy” now shares the stage with the word “environment.”

The capacity for photosynthetic acclimation to light intensity in Sakhalin knotweed (Polygonum sachalinense F. Schmidt) was studied by growing plants in four light environments [out-of-doors in full sun and under 50% shade, and in a growth chamber at 800 μE m2 sec-1 photosynthetically active radiation, 400 to 700 nm (PAR) and 150 μE m-2 sec-1 PAR], and then determining, with an infrared gas analyzer (IRGA), the photosynthetic rates of single leaves exposed to a range of light intensities from 100 to 2000 μE m2 sec-1 PAR. The plants grown in high light had higher photosynthetic rates throughout the range of 100 to 2000 μE M-2 sec-1 PAR. Maximum photosynthetic rates were 37 mg CO2 dm-2 h-1 for plants grown in full sun out-of-doors and 16.5 mg CO2 dm-2 h-1 for plants grown in low light in the growth chamber. There was no indication of positive adaptation to low light intensity in Sakhalin knotweed. Differences in light-saturated photosynthetic rates were closely related to differences in mesophyll conductance and chlorophyll content per unit leaf area.

A collection of common purslane (Portulaca oleracea L.) ecotypes from various locations around the world was assembled at the University of Illinois. Applications of nitrofen (2,4-dichlorophenyl-p-nitrophenyl ether) to the various ecotypes showed that 3 of the 26 ecotypes [India, Mexico, and Florida (Sanford)] exhibited some degree of tolerance. This marginal tolerance rapidly disappeared as the rate of nitrofen increased beyond 0.56 kg/ha. All of the ecotypes tested were susceptible to applications of oxyfluorfen [2-chloro-2-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl)benzene]. Oxyfluorfen was toxic to common purslane plants at rates as low as 5 g/ha. Treatment of ‘Hybelle’ (tolerant) and ‘Rio Verde’ (susceptible) cabbage (Brassica olerace var. capitata L.) cultivars with 3.36 kg/ha nitrofen reduced plant fresh weight to 82% and 62%, respectively, of control. Oxyfluorfen at 0.15 kg/ha reduced fresh weight to 60% and 27% for Hybelle and Rio Verde, respectively. Applications of nitrofen at 3.36 kg/ha reduced plant fresh weight in Hybelle the same amount as 100 g/ha oxyfluorfen and 70 g/ha in Rio Verde.

Silky windgrass is a serious weed in central and northern Europe. Its importance has escalated in recent years because of its growing resistance to acetolactate synthase (ALS)-inhibiting herbicides. This study investigated the resistance level for three herbicide sites of action in eight silky windgrass populations, collected in fields neighboring a field where iodosulfuron sodium salt–resistant silky windgrass had previously been found. Target site resistance (TSR) and non–target site resistance (NTSR) mechanisms were identified, and a spatial gradient distribution hypothesis of ALS resistance was tested. Populations showed large variations in ED50 values to iodosulfuron, with resistance indices (RIs) ranging from 0.1 to 372. No cross-resistance was found to other herbicide groups with the same site of action as iodosulfuron. In contrast, resistance was observed to the acetyl-CoA carboxylase inhibitor, fenoxaprop ethyl ester (RI from 0.7 to 776), while the activity of prosulfocarb, an inhibitor of long-chain fatty-acid synthesis, was unaffected. Iodosulfuron-resistant phenotypes were associated with NTSR, while fenoxaprop ethyl ester resistance was caused by both NTSR and TSR (Ile-1781-Leu mutation). A large-scale trend in the spatial distribution of resistance to ALS indicated a decreasing resistance with increased distance from an epicenter. After finer-scale analysis, less than 0.05% of the residual variation could be attributed to spatial autocorrelation. The spatial resistance pattern was not correlated with the dominant wind direction, while there was a correlation between the resistant phenotype and type of crop. This study underlines that NTSR mechanisms do not always confer broad resistance to different herbicide subclasses and site of action, hence the complex relationship to resistant phenotype. NTSR mechanisms, in particular detoxification, were present at different levels for the herbicides tested in the silky windgrass populations of this study. The factors contributing to the spatial distribution of resistance remain elusive.