Tall morningglory [Ipomoea purpurea (L.) Roth] seeds were germinated at various temperatures and dry weight conversion measured at 24, 48, 72, 96, and 120 hr. Germination and dry weight conversion were slower at the lower temperatures although both occurred. Tall morningglory could germinate and become established over a wide range of temperatures. Some herbicides were effective in reducing germination, and dry weight conversion was reduced most with the dithiocarbamates followed in sequence by the amides, benzoic acids, uracils, dinitroanilines, phthalamic acids, triazines, and ureas.

The question of when to control weeds traditionally has been approached with the calculation of critical periods (CP) based on crop yields. The concept of economic critical period (ECP) and early (EEPT) and late (LEFT) economic period thresholds are presented as a comprehensive approach to answer the same question based on economic losses and costs of control. ECP is defined as the period when the benefit of controlling weeds is greater than its cost. EEPT and LEFT are the limits of the ECP and can be used to determine when first and last weed control measures should be performed. Calculation of EEPT accounts for the economic losses due to weed competition that occur between planting and postemergence weed control. In this way it is possible to better evaluate the economic feasibility of using preplant or preemergence control tactics. The EEPT for DCPA application is analyzed in the context of onion production in Colorado. The EEPT for DCPA application was calculated from an empirical regression model that assessed the impact of weed load and time of weed removal on onion yields. The EEPT was affected by control efficacy, weed-free yield, DCPA cost, and onion price. DCPA application was economically advisable in only one of 20 fields analyzed because of the tow DCPA efficacy (60%).

Wild poinsettia germination was at least 95% when exposed to solution pH of 2.5 to 10 or solution osmotic potential of up to −0.8 MPa. No germination was observed at pH 12 or osmotic potential of −1.5 MPa. Light was not required for germination. Seed germinated at temperatures ranging from 20 to 40 C with maximum germination of 97% at 35 C. Wild poinsettia had the highest emergence (80%) from seed placed 2 to 4 cm below the soil surface, while 20% of the seed planted at 14 cm emerged. Wild poinsettia germinated over a wide range of conditions, which explains why it is becoming an increasingly serious problem.

The aerobic rate of disappearance of isopropalin (2,6-dinitro-N,N-dipropyl-cumidine) was slower than that of oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide) in soil. The aerobic half-lives for isopropalin were 3.5 months and 13.3 months and for oryzalin 1.40 months and 4.35 months at 30 and 15 C respectively. A simple system was devised to create anaerobiosis in soil at 80% of field capacity. Both herbicides dissipated more rapidly under anaerobic conditions. The first order half-lives at 30 C in anaerobic soil were 0.17 months for isopropalin and 0.34 months for oryzalin. Neither first, second, nor half order kinetics were clearly superior in describing the degradation processes. Arrhenius activation energies suggested that the degradation processes were non-biological.

Greenhouse studies were conducted to determine the extent of translocation from the foliage to fleshy roots, the inherent toxicity, and the fate of radiolabeled and nonlabeled dicamba, picloram, and triclopyr in horsenettle. Roots of horsenettle acted as the major sink for photosynthate accumulation at the 0.2- to 0.5-bloom growth stages as determined by autoradiography. Dicamba, picloram, and triclopyr were translocated into the roots of horsenettle and accumulation continued for at least 16 days. 14C associated with each herbicide found in the roots ranged from 1.3% at 4 days to 3.8% at 16 days. After 16 days, slightly more 14C from plants treated with dicamba and triclopyr (3.8 and 3.6%) than picloram (3.0%) was translocated to roots. These compounds were metabolized slowly in the foliage and roots as determined by thin-layer chromatography (TLC) and autoradiography. In translocation studies with horsenettle shoots, picloram at 1.12 kg/ha killed the treated and untreated shoots and roots. Dicamba and triclopyr at the highest rates killed the treated shoots and partially destroyed the root system. Symptoms were noted on the untreated shoots, but full recovery occurred at 8 weeks. Since each of the herbicides was metabolized slowly and only slight differences in their translocation were observed, the relatively higher herbicidal effectiveness of picloram must be attributed to its greater inherent potency.

Dinoseb (2-sec-butyl-4,6-dinitrophenol) and MBR 8251 [1,1 1-trifluoro-4′-(phenylsulfonyl)-methanesulfono-o-toluidide] inhibited enzymic synthesis of glycerides in vitro. The physiological significance of this inhibition was confirmed in intact wheat [Triticum aestivum L., ‘Mediterranean’ (C.I. 5303)] seedlings; dinoseb and MBR 8251 inhibition of glyceride synthesis in vivo was evidenced by a buildup in free fatty acids and a decrease in neutral and polar lipids. Glyceride synthesis and growth were reduced approximately equally by dinoseb and MBR 8251. However, polar (membrane) lipids were reduced more drastically than growth. It is suggested that dinoseb and MBR 8251 alter membrane structure and function through an inhibition of membrane lipid synthesis. DNP (dinitrophenol) was only slightly inhibitory in either the in vitro or in vivo system. Dinoseb was more effective than MBR 8251 in destruction of cell membrane permeability of intact roots immediately after treatment.

The ecological significance of species diversity within agroecosystems has become a point of interest in recent years. Although the time and spatial scale at which diversity is measured may influence the interpretation of its functional importance, little research has been conducted on methodological approaches to assess the number and relative abundance of agricultural plant species. In this study, we (1) evaluated the applicability of the species-area curve to examine plant species richness and α and β diversity in conventional no-tillage and organically managed spring wheat systems, and (2) assessed temporal changes in plant species richness across systems. Measurements were obtained at three times during two growing seasons in experimental plots and at three times during one growing season on commercial farms in Montana. In accordance with previous studies, management system affected species richness and diversity. In eight of nine studied cases, we detected a positive relationship between species richness and sampled area. In these eight cases, intercepts (α diversity) were higher for the organic systems than for the conventional no-tillage systems. Slopes (β diversity) were higher for the organic system in six of nine cases studied. Species richness declined as the season progressed for both systems, with the organic systems consistently having more species than the conventional no-tillage systems. Despite differences in the species composition and between the experimental plots and commercial farm field size, the patterns of species richness and α and β diversity were relatively constant, suggesting that the processes responsible for the assembly of plant communities in agroecosystems of the Northern Great Plains are similar at a range of spatial scales.

Experiments were conducted to examine the influence of adjuvant, growth stage, air temperature, and soil moisture on nicosulfuron activity, absorption, and distribution in quackgrass. Foliar absorption of 14C-nicosulfuron by quackgrass was greater in one-leaf than five-leaf plants. Total translocation of 14C-nicosulfuron was similar regardless of growth stage. However, nicosulfuron was more phytotoxic to three- and five-leaf than one-leaf quackgrass. Of the absorbed 14C, at least 71 % remained as 14C-nicosulfuron 168 h after application in three-leaf plants. 14C-Nicosulfuron absorption, translocation, and accumulation increased with increasing temperatures and was independent of soil moisture. Under adequate soil moisture conditions (-0.03 MPa), nicosulfuron activity was not influenced by temperature. Nicosulfuron efficacy was not influenced by soil moisture at a cool (11/6 C) temperature. As plant moisture stress increased, due to low soil moisture and increasing air temperature, nicosulfuron efficacy declined. Differences in nicosulfuron efficacy due to growth stage or environmental conditions could not be explained by differential 14C recovery, absorption, translocation, or accumulation. The addition of 28% urea-ammonium nitrate liquid fertilizer (UAN) to 14C-nico-sulfuron plus petroleum oil adjuvant (POA) provided greater 14C absorption than POA alone. Translocation of 14C with POA alone 168 h after treatment (HAT) was similar to POA plus UAN 24 HAT. However, 168 HAT there was no difference in the total amount of radiolabelled material translocated among the adjuvants.

Field experiments were conducted in 1983 and 1984 to measure the interference of wild oat (Avena fatua L. # AVEFA) removed at various stages of development (two to three leaves, two to three tillers, two nodes, and heading), plus treatments with wild oat not removed, and wild oat-free stands on the growth and yield of spring barley (Hordeum vulgare L. ‘Advance’). The final plant density of barley and wild oat was 160 and 170 plants/m2, respectively. Based on aboveground barley biomass and yield, the critical duration of wild oat interference began about the two-node stage and continued until maturity of the barley. Wild oat interference reduced barley biomass, the number of tiller heads/plant, tiller heads/unit area, and tiller grain yield, but not the number or grain yield of the main-stem heads. Wild oat did not affect the soil matric potential or the barley total plant and soil nitrogen contents. However, wild oat did reduce total water and turgor potential in barley at the boot stage of growth, which may have affected tiller head formation.

Combinations of copper sulfate pentahydrate (hereinafter referred to as CSP) at 1.0 ppmw copper plus 0.1 to 2.0 ppmw 6,7-dihydrodipyrido-(1,2-a:2′,1′-c)pyrazinediium ion (diquat) resulted in higher accumulations of copper in hydrilla (Hydrilla verticillata Casp.), egeria (Egeria densa Planch.), and southern naiad (Najas guadalupensis Spreng. Magnus) when compared to plants which received only CSP. A contact period greater than 24 hr was necessary before the higher amounts of copper were detected in those plants treated with the combinations. Water samples from outdoor, plastic pools 7 days after treatment with CSP at 1.0 ppmw of copper plus 1.0 ppmw of diquat contained 25% less copper than pools treated with CSP. Samples of hydrilla and southern naiad removed 7 days after treatment of the pools with the combination contained 77 and 38% more copper, respectively, than samples from those pools treated with only CSP.

Site of uptake, absorption, translocation, and metabolism of ethofumesate were studied to determine the differential responses of annual bluegrass, creeping bentgrass, and perennial ryegrass. Using barriers to isolate foliage or soil, the primary site of ethofumesate absorption was found to be the foliage. Symptoms resulting from foliar and over-the-top spray applications of ethofumesate to annual bluegrass included stunting of growth, epinasty, swelling of the crown, darker green color, and fusing of expanding leaf blades. Averaged over the course of the experiment, annual bluegrass, creeping bentgrass, and perennial ryegrass absorbed 33, 11, and 13% of ethofumesate applied. No ethofumesate was detected distally from the treated leaf, but overall translocation of 14C 14 d after treatment (DAT) was 2.2, 5.8, and 2.2% of the absorbed 14C for annual bluegrass, creeping bentgrass, and perennial ryegrass, respectively. Ethofumesate was rapidly metabolized in each species with half-lives ranging from 4.5 to 7 d. The three grasses had metabolized, on average, 67% of the absorbed ethofumesate 14 DAT.

Italian ryegrass is a major weed problem in wheat production worldwide. Field studies were conducted at Fayetteville, AR, to assess morphological characteristics of ryegrass accessions from Arkansas and differences among other Lolium spp.: Italian, rigid, poison, and perennial ryegrass. Plant height, plant growth habit, plant stem color, and node color were recorded every 2 wk until maturity. The number of tillers per plant, spikes per plant, and seeds per plant were recorded at maturity. All ryegrass accessions from Arkansas were identified as Italian ryegrass, which had erect to prostrate growth habit, green to red stem color, green to red nodes, glume (10 mm) shorter than spikelet (19 mm), and medium seed size (5 to 7 mm) with 1 to 3 mm awns. However, significant variability in morphological characteristics was found among Arkansas ryegrass accessions. When Lolium species at the seedling stage (1- to 2-wk-old plants) were compared, poison ryegrass was characterized as having a large main-stem diameter and wide droopy leaves, whereas perennial ryegrass exhibited a short and a very narrow leaf blade. These two can be distinguished from Italian and rigid ryegrass, which have leaf blades wider than perennial ryegrass but narrower than poison ryegrass. Italian and rigid ryegrass are difficult to distinguish at the seedling stage but are distinct at the reproductive stage. At maturity, Italian ryegrass and poison ryegrass seeds are awned, but perennial and rigid ryegrass seeds are awnless. Poison ryegrass awns were at least 4-fold longer than Italian ryegrass awns. Perennial ryegrass flowered 3 wk later than the other species. Poison ryegrass glumes were longer than the spikelets, whereas Italian ryegrass glumes were shorter than the spikelets. Morphological traits indicate that some Italian ryegrass populations are potentially more competitive and more fecund than others.

Imazaquin {2-(4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl)-3-quinolinecarboxylic acid} site of uptake and toxicity from soil application were investigated in yellow nutsedge (Cyperus esculentus L. #3 CYPES) and purple nutsedge (C. rotundus L. # CYPRO). Imazaquin concentrations of 0.1 to 0.5 ppmw inhibited yellow nutsedge shoot emergence completely, while purple nutsedge shoots emerged at the lower concentrations. Herbicide placement above the tuber reduced shoot emergence and shoot and root dry weights of both species more than did placement below the tuber. Increasing herbicide rate increased the number of tuber buds that sprouted. Three-day-old nutsedge propagules absorbed 14C-imazaquin from both rhizome shoots and roots and the herbicide moved both acropetally and basipetally in nutsedge propagules.

A weevil [Rhinocyllus conicus (Froelich)] host specific to Carduus, Cirsium, Silybum, and Onopordum, was introduced into Gallatin County, Montana, for biocontrol of musk thistle (Carduus nutans L.). Releases were made in 1969, 1971, 1972, and 1973 on local musk thistle infestations. The insects became established and overwintered successfully. In 1974, R. conicus was found over a 1,280-km2 area of the county in seed heads of musk thistle. Weevil larvae severely infected the primary flowers, but only a few secondary and later flowers were attacked. Seed production from infected primary flowers was greatly reduced, and other factors influenced reduction of seeds from secondary and later flowers.

Field studies were conducted to determine the effect of common cocklebur interference in early-maturing (maturity group IV) soybean planted in April, May, and July. Common cocklebur density and length of interference did not affect soybean height, canopy width, or node number at any planting date. Removal of common cocklebur 4 weeks after emergence (WAE) prevented reduction of soybean leaf area, stem dry weight, dry leaf weight, dry pod weight, and seed yield. Aboveground biomass for common cocklebur emerging in July was less than biomass of April or May plantings. Common cocklebur planted into soybean 2, 4, or 8 wk after soybean emergence did not reduce soybean yield. Under parameters of this study, planting date was not a significant factor in yield reduction. Interference from one common cocklebur plant per 1.8, 0.9, and 0.3 m of soybean row for 8 wk reduced yields 7, 14, and 30%, and full-season interference reduced yields 16, 33, and 65%, respectively. The Arkansas Weed Management Computer program closely predicted actual yield loss for early-maturing soybean.

14C-Sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} was rapidly metabolized by quackgrass [Agropyron repens (L.) Beauv. ♯ AGRRE], barnyardgrass [Echinochloa crus-galli (L.) Beauv. ♯ ECHCG], alfalfa (Medicago sativa L. ‘Saranac’), and navy bean (Phaseolus vulgaris L. ‘Seafarer’). One hour after application, 46, 27, 38, and 46% of the total 14C in the ethyl acetate-soluble fraction from treated leaves was sethoxydim, respectively. After 24 h, less than 2% was sethoxydim in any species. Nine metabolites were found, seven of which cochromatographed with photo- and thermal-transformation products of sethoxydim. Two metabolites, previously shown to be phytotoxic to barnyardgrass, contained the majority of 14C up to 24 h after application. Quantitative or qualitative differences in the metabolites of treated leaves could not account for the observed differences in selectivity.

Spectrophotometric and chemical analyses indicated that photodecomposition of 3-amino-2,5-dichlorobenzoic acid [amiben] in water solution occurred rapidly during exposure to, sunlight or light from fluorescent sun lamps. Slow but definite photochemical alteration occurred when dry amiben on filter paper was exposed to light from the sun lamps. Several reaction products were separated by paper chromatography. Loss of herbicidal activity from 10-3 molar aqueous solutions of amiben approximated disappearance of amiben determined colorimetrically. Photochemical inactivation of the formulated triethylamine salt of amiben in aqueous solution was slower than that of chromatographically pure amiben. A method involving diazotization of amiben with nitrous acid and coupling the diazo form with chromotropic acid was suitable for quantitative determination of amiben.

Applications of disodium methanearsonate (DSMA) killed Johnsongrass foliage in field and greenhouse experiments. Control of regrowth following treatment increased with increasing rates, but there was no indication of translocation to rhizomes. DSMA toxicity did not change in 20 to 80 gpa water, but somewhat less control was obtained in 10 gpa. Addition of a surfactant to spray solutions increased toxicity. Control was not affected by stage of Johnsongrass growth, but observations indicated increased control during droughty conditions. Repeated usage provided seasonal Johnsongrass control equal to that obtained with sodium 2,2-dichloropropionate (dalapon), although more frequent applications were necessary.

Ten herbicides were applied preemergence to proso millet (Panicum miliaceum), three Amaranthus species, and Chenopodium album L. The herbicides were either incorporated or left on the soil surface and plots were either sprinkler or furrow irrigated. The phytotoxicity of some herbicides was increased by soil incorporation and/or sprinkler irrigation. Some were unaffected by method of irrigation, and others were not affected by incorporation. Grass and broadleaf weed control were affected differently by incorporation and irrigation. When incorporated with furrow irrigation, five herbicides developed weed control patterns indicating a movement similar to salt movement. A more complex pattern occurred with non-incorporated herbicides.

Toxicity of 3,6–endoxohexahydrophthalic acid (endothal) was measured by the inhibition of growth of germinating flax roots, compared to known standards. In the field, endothal applied at 0.3 to 10.0 ppm was not detectable after an average of 2½ days, and a maximum of 4 days. In aquaria, endothal at these rates was detectable much longer than this, and much longer when the aquaria contained only water than when they also contained mud and plant debris.