The behavior of the methyl ester of 14C-haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid} in common bermudagrass [Cynodon dactylon (L.) Pers. # CYNDA] stolons was examined in greenhouse experiments at two different seasons. The 14C from the herbicide applied on the leaves of a stolon node translocated no more than 3% of the applied radioactivity to the apex and base. Movement out of stolons was not significant. In early summer less than 1% translocated in each direction; in early fall more than 2% moved to the apex and less than 1% toward the base. Decrease of 14C recovery with time was evident in both seasons, particularly in early summer. Haloxyfop volatilization from the leaf surface apparently plays a significant role in recovery decrease. The 14C found in stolons in early summer was approximately the same as that of early fall, although herbicide remaining available for uptake on the leaf surface was lower in the former season. We suggest that environmental conditions that favor volatilization could enhance uptake.

The physiological responses of corn (Zea mays L. ‘Goldencrossbantam′) and pea (Pisum sativum L. ‘Alaska′) to sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio) propyl]-3-hydroxy-2-cyclohexen-1-one} were investigated. Sethoxydim did not affect excised pea root growth at 1 × 10−4 M but inhibited excised corn root growth at concentrations of 1 × 10−8 M and above. Treating corn impeded root growth with 1 × 10−7 M sethoxydim within 4 h after treatment; however, little histological change of the roots was observed at 48 h. At 1 × 10−6 M, growth nearly stopped within 4 h after treatment, and clear cytological changes of the roots were observed at 24 and 48 h. Sethoxydim inhibited both mitosis and DNA synthesis of excised corn root tips between 4 and 48 h after treatment. Respiration of corn roots measured by oxygen uptake and the TTC (2,3,5-triphenyltetrazolium chloride) test was not affected by the herbicide directly. Sethoxydim (1 × 10−4 M) inhibited IAA-induced cell elongation of corn coleoptile and pea epicotyl by 37 and 12%, respectively. Sethoxydim selectively inhibited the growth of excised root tips of susceptible corn by affecting cell division rather than cell enlargement, and the inhibition mechanism of cell division (inhibition of mitosis) by the herbicide was not by direct inhibition of DNA synthesis or by effects on respiration.

The effects of sethoxydim {2-[1-(ethoxyimino) butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} on the metabolic activity of excised root tips of corn (Zea mays, L. ‘Goldencrossbantam′) were studied under laboratory conditions. Uptake and incorporation of 14C-labeled thymidine, uridine, leucine, glucose, and acetic acid into cell constituents, as well as respiration, increased continuously with time progressions during the incubation period. Sethoxydim did not affect either the uptake of any 14C-precursor into or respiration of the root tip tissue. Although RNA and protein syntheses were not affected by the herbicide, DNA and cell wall syntheses were inhibited 120 min after treatment with sethoxydim. Incorporation of 14C-acetic acid into lipid fraction was inhibited by sethoxydim in a time- and concentration-dependent fashion. This inhibition was observed at a shorter time after sethoxydim treatment than that of any other 14C-precursor. The effect was not observed in the nonproliferative regions of corn roots, whereas cerulenin (a fatty acid synthase inhibitor) inhibited the incorporation of 14C-acetic acid both in proliferative and nonproliferative regions. It is suggested that the inhibition of lipid synthesis by sethoxydim does not play a major role in the mode of action of this herbicide. The effects of sethoxydim, including those on lipid metabolism, are closely associated with proliferative conditions of susceptible graminaceous plants.

The selectivity mechanisms of sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} were investigated by examining absorption of 14C-sethoxydim into tissues of corn (Zea mays L. ‘Goldencrossbantam′) and pea (Pisum sativum L. ‘Alaska′). Greater absorption of 14C-sethoxydim was observed only into the proliferative 2-mm terminals of the excised roots of susceptible corn, and the same result was obtained with corn seedlings in hydroponic culture. Absorption was not affected by 1 × 10−4 M 2,4-dinitrophenol (DNP), which indicated that the absorption of 14C-sethoxydim is probably mediated by a passive transport system rather than an active transport system. The selective herbicidal action of sethoxydim appeared to depend largely on the differential rates of absorption into meristematic regions by the susceptible and tolerant plants.

The basis for chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] caronyl] benzenesulfonamide} antagonism of diclofop {(±)-2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid} was investigated in Italian ryegrass [Lolium multiflorum (Lam.) # LOLMU] and wheat (Triticum aestivum L. ‘McNair 1813′). Chlorsulfuron did not affect the chemical stability or volatility of diclofop in spray mixtures over the time and concentration ranges evaluated. Addition of chlorsulfuron (0.11 μg/μl) to a diclofop (2.0 μg/μl) foliar-applied spotting solution did not affect the absorption, translocation, or metabolism of diclofop in 17-day-old Italian ryegrass or wheat. Italian ryegrass and wheat responded differentially to diclofop alone. At 72 h after treatment, 69 and 40% of labeled diclofop penetrated into Italian ryegrass and wheat leaves, respectively. Although little movement of labeled diclofop occurred in either species, more translocated from the treated zone of Italian ryegrass. At 72 h after treatment, the percentages of 14C recovered as parent methyl ester, diclofop (free acid), and conjugates in treated leaf extracts were 9, 62, and 25%, respectively, for Italian ryegrass, and 50, 20, and 29%, respectively, for wheat. Differential penetration and metabolism of diclofop are the probable bases for selectivity between wheat and Italian ryegrass. The antagonism of diclofop caused by chlorsulfuron does not appear to be due to an alteration of the molecular fate of diclofop in Italian ryegrass.

Ragweed Parthenium (Parthenium hysterophorus L. # PTNHY) was found to exhibit autotoxicity. The active principle(s) were isolated from two parts of the plant using polar system. Principle(s) from the inflorescence were more effective than from the leaves. Leachates derived from the plant decreased percent cell survival and chlorophyll content. Leachates from leaves were more toxic to ragweed parthenium when applied to the foliage than when applied through the roots. The polar allelochemicals were highly effective in preventing rooting and sprouting of stem cutting and in reducing the regeneration potential of mature ragweed parthenium plants.

Common ragweed [Ambrosia artemisiifolia L. # AMBEL (2n=36)] and giant ragweed [A. trifida L. # AMBTR (2n=24)] are two abundant annuals that are widespread throughout northeastern North America. They are also the main cause of hay fever in Eastern Canada. The formation of a hybrid between the two species has been reported only once and just one type of hybrid was recovered; namely, common ragweed × giant ragweed. In order to create additional suitable material for future studies of the biochemical features characterizing the allergenic pollen, the production of reciprocal hybrids between common and giant ragweed was attempted. A number of hybrid plants derived from crosses of the type common ragweed × giant ragweed were easily obtained; the reciprocal crosses, however, failed to produce viable plants. In this last case, evidence of postzygotic barriers of interspecific incompatibility were shown by the presence of underdeveloped embryos contained in the few seeds recovered. Embryo culture techniques, therefore, were used in order to bypass such barriers. By this method fifteen plants of hybrid constitution survived to maturity.

Field experiments were conducted to determine whether aerial and subterranean stem sections taken from Canada thistle [Cirsium arvense (L.) Scop. # CIRAR] plants in four stages of development (spring-vegetative, bud, postbloom, and fall-vegetative) could survive and produce infestations the following year. Partially buried aerial stem sections from all stages of development had greater survival 28 days after planting than completely buried aerial stem sections. Few completely buried aerial stem sections survived. Partially or completely buried subterranean stem sections from Canada thistle at the postbloom stage had the highest survival rate. Few partially or completely buried subterranean stem sections from the other three growth stages survived. Surviving stem sections from spring-vegetative, bud, and postbloom stages of Canada thistle produced adventitious roots that overwintered and produced new infestations the following spring. Surviving stem sections from Canada thistle at the fall-vegetative stage did not develop an adequate root system for winter survival.

Studies were conducted at Grand Rapids, MN, to determine the effect of giant burreed (Sparganium eurycarpum Engelm. # SPGEU) planted at 6, 12, and 24 corms/m2 on wild rice (Zizania palustris L. ‘K2′) growth and yield. Giant burreed, a spreading perennial, had shoot densities of 21, 29, and 42/m2 at harvest for the 6, 12, and 24 corms/m2 treatments, respectively. Wild rice yield and panicle number were reduced approximately 60% when giant burreed shoot density was 40/m2 or higher when compared to the weed-free control. Giant burreed did not interfere with nutrient uptake of wild rice on a whole-plant basis, and increased N fertilizer application did not reduce losses in dry weight. Giant burreed reduced penetration of photosynthetically active radiation (PAR) from 2 to 35% in the wild rice canopy from the early tillering to the anthesis stage of wild rice development. In growth chamber studies, wild rice dry weight and panicle number were reduced by 46 and 65%, respectively, when wild rice was shaded for 12 weeks and compared to a full light treatment. Reduction of PAR penetration into the wild rice canopy appears to be the major mechanism of giant burreed interference with wild rice.

In a 2-yr field study conducted on a Weswood silt loam soil (Fluventic Ustochrepts), interspecific competition between soybeans [Glycine max (L.) Merr. ‘Hutton′] and velvetleaf (Abutilon theophrasti Medik. # ABUTH) resulted in greater than 40 and 50% reductions in soybean and velvetleaf seed yield, respectively. Leaf area index, number of mainstem nodes, total number of leaves, and plant dry weight of monocultured and intercropped velvetleaf differed significantly as early as 4 weeks after emergence. Interspecific competition had litttle or no effect on soybean morphology before 8 weeks after emergence. Soil water extraction occurred to 1-m depths in a monoculture of velvetleaf (five plants/m2) in 1984 and 1985. Monocultured soybeans (32.5 plants/m2) extracted water from a 1.5-m or greater depth of the soil profile during the same years. Soil water extraction in the intercropped plots resembled that of the monocultured velvetleaf treatment until soybeans attained R6, when soil water was extracted to a 1.5-m depth. The potential for interspecific competition for water existed early in the season before late-season soybean root development. Relative water content and leaf water potential (Ψw1) did not differ (0.05) between monocultured and intercropped soybeans in 1984 or 1985. In 1985, Ψw1 differed between monocultured and intercropped velvetleaf during anthesis. Leaf water potential values in the youngest, fully expanded leaves were approximately 0.3 and 0.4 MPa lower during midmorning and midday hours, respectively, in intercropped and monocultured velvetleaf. Transpiration and stomatal conductance did not differ between monocultured and intercropped soybeans or velvetleaf at any time during 1984. Photosynthetic and transpiration rates, stomatal conductance, and Ψw1 were lower in intercropped than in monocultured velvetleaf during anthesis in 1985, suggesting interspecific competition for soil water. Soybean water relations were not affected in either year. The data suggest that soybean yield reductions in soybean-velvetleaf interspecific competition are attributable to resource limitations other than water in south-central Texas.

Data obtained from two experiments were used to identify and describe factors affecting crop loss due to weeds in forage stands. Timothy (Phleum pratense L. ‘Champ′) was established in presence or absence of barley (Hordeum vulgare L. ‘Bruce′), red clover (Trifolium pratense L. ‘Florex′), broadleaf weeds, and grass weeds. Botanical composition, soil water, soil nutrients, light interception, and plant cover were determined 4 and 6 weeks after seeding, and crop yield was determined at periodic forage harvest dates. Principal components analyses permitted the extraction of 12 factors and regression analyses demonstrated that these factors can be used to describe crop yield. Each factor can be estimated either by obtaining the rotated factor scores or by selecting a representative variable that can be substituted for the rotated factor scores in the regression models. The approach described in this paper should be tested with other crops and other weed complexes. It is suggested to use weed density in combination with weed and crop cover data to predict crop loss.

Effects of a natural mixed stand of giant green foxtail [Setaria viridis var. major (Gaudin) Pospichel # SETVM] and fall panicum [Panicum dichotomiflorum Michx. # PANDI] on soybean [Glycine max (L.) Merr. ‘Union’ and ‘Essex′] biomass and seed yield were investigated during 1981, 1982, and 1983. Plots maintained weed free for 2 weeks after soybean emergence produced yields equal to those maintained weed free for the season despite any grass reinfestation. Grasses growing naturally with soybeans for 8 weeks after soybean emergence did not reduce crop yields. Weeds not removed after 8 weeks reduced soybean yields by decreasing the number of pods per plant. Under drought conditions, yield reduction due to grass competition did not occur until 12 to 16 weeks after soybean emergence. Hand-established densities of 1 grass plant/7.5 cm of crop row reduced soybean yield by 0 to 11%. Natural grass infestations reduced soybean yield by 21 to 41%.

Studies were conducted to evaluate the effect of wild oat (Avena fatua L. # AVEFA) interference in lentils (Lens culinaris Medik). An infestation of 32 and 65 wild oats/m2 maintained up to 5 weeks in the field did not reduce lentil grain yield. However, 32 wild oats/m2 reduced yields 32% when allowed to remain for 7 weeks and 49% if they remained until harvest time (11 weeks). Sixty-five wild oats/m2 reduced grain yield 42 and 61% for the same time periods, respectively. In the growth chamber, 69 wild oats/m2 reduced lentil plant dry weight 29% if allowed to remain for 3 weeks, 61% for 5 weeks, and 72% for 7 weeks (harvest time). The field data suggest that wild oat control measures may be delayed for several weeks after lentil emergence without reducing crop yield.

Field studies were conducted in Saskatchewan to evaluate the effect of herbicides on annual canarygrass (Phalaris canariensis L.) and associated weeds. Bromoxynil (3,5-dibromo-4-hydroxybenzonitrile) at 0.35 kg ai/ha, tank mixes of bromoxynil at 0.28 kg/ha plus the ester of MCPA [(4-chloro-2-methylphenoxy)acetic acid] at 0.28 kg ae/ha, linuron [N′-(3,4-dichlorophenyl)-N-methoxy-N-methylurea] at 0.28 kg ai/ha plus MCPA amine at 0.56 kg/ha, or propanil [N-(3,4-dichlorophenyI)propanamide] at 1.0 kg ai/ha plus MCPA ester at 0.28 kg/ha resulted in annual canarygrass seed and dry matter yields equal to the unsprayed check and excellent wild mustard (Sinapis arvensis L. # SINAR) and cow cockle (Vaccaria pyramidata Medik. # VAAPY) control. Metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one] at 0.21 kg ai/ha plus MCPA amine at 0.56 kg/ha reduced the crop stand in 1 out of 5 yr and seed yield every year. Postemergence application of difenzoquat (1,2-dimethyl-3,5-dipheny1-1H-pyrazolium) at 0.84 kg ai/ha or flamprop [N-benzoyl-N-(3-chloro-4-fluorophenyl)-DL-alanine] at 0.53 kg ai/ha, or preplant-incorporated triallate [S-(2,3,3-trichloro-2-propenyl)bis(1-methylethyl)carbamothioate] at 1.40 kg ai/ha optimized wild oat (Avena fatua L. # AVEFA) control with seed yields. Diclofop {(±)-2-[4-(2,4-dichlorophenoxy)phenoxy)propanoic acid} at 0.70 kg ai/ha severely damaged annual canarygrass in all years. Triallate applied at 1.40 kg/ha preplant or preemergence incorporated marginally reduced the crop stand and seed yield compared to the untreated controls in tolerance tests.

Field experiments were conducted to evaluate placement techniques for preemergence applications of pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine] in grain sorghum [Sorghum bicolor (L.) Moench.]. The first technique consisted of row shields mounted behind the planter units. Shields maintained an untreated strip over the crop drill and allowed successful crop establishment with pendimethalin at 1.1 kg ai/ha, despite a simulated, intense rainfall of 3.8 cm within 24 h after planting. A second technique, which consisted of a special nozzle arrangement, was evaluated in no-till grain sorghum. The nozzle arrangement allowed a broadcast herbicide application but maintained an untreated strip over the crop drill. No stand reductions occurred using this technique at pendimethalin rates of 1.1 and 2.2 kg/ha. In a growth chamber experiment, preemergence applications of pendimethalin severely injured grain sorghum when the soil was wet at the time of emergence, but injury was reduced under hot, dry conditions.

Field evaluations were made on the effects of imazaquin {2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-3-quinolinecarboxylic acid} on Florida beggarweed [Desmodium tortuosum (SW) DC. # DEDTO] and sicklepod (Cassia obtusifolia L. # CASOB) control in peanuts (Arachis hypogaea L.). Crop yield was reduced at 392 and 504 g ae/ha and with preemergence applications. Florida beggarweed control was not achieved with this herbicide. Maximum sicklepod control (approximately 80%) was achieved with 392 and 504 g/ha applied postemergence. In a separate study, several herbicide systems utilizing imazaquin were compared to a standard weed control program. All these systems provided weed control and yields that were comparable to the standard weed control system; thus the inclusion of imazaquin offered no advantage over the standard system.

A 4-yr study was conducted to evaluate the response of rice (Oryza sativa L. 'Starbonnet′) to sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl-3-hydroxy-2-cyclohexen-1-one}, haloxyfop {2-[4-[13-chloro-5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid}, fluazifop {(±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid}, and quizalofop {(±)-2-[4-(6-chloro-2-quinoxalynyloxy)phenoxy] propanoic acid}. In general, rice was more sensitive when herbicides were applied at panicle initiation than at the tillering stage of development. Quizalofop severely reduced rice yield when applied wih a surfactant. Applied at tillering, sethoxydim at 210 g ai/ha did not reduce rice height, grain yield, milling yield, or seed quality.

Postemergence applications of imazaquin {2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-3-quinolinecarboxylic acid} controlled higher levels of purple nutsedge (Cyperus rotundus L. # CYPRO) in common bermudagrass [Cynodon dactylon (L.) Pers.] and hybrid bermudagrass (′Tifgreen’ and ‘Tifdwarf′, C. dactylon × C. transvaalensis Burtt-Davy) than monosodium salt of methylarsonic acid (MSMA). Control was better at 560 or 840 g ai/ha of imazaquin than at lower rates. Postemergence applications of imazaquin plus 2240 g ai/ha of MSMA controlled more purple nutsedge than equivalent rates of imazaquin alone. Preemergence applications of imazaquin were not effective. Bermudagrass discoloration was observed in some experiments on turfs mowed at a height of 1.3 cm or less but usually disappeared within 2 to 3 weeks, especially when MSMA was used in combination with imazaquin. No injury was observed on bermudagrasses, zoysiagrass (Zoysia japonica Steud. ‘Meyer′), St. Augustinegrass [Stenotaphrum secundatum (Walt.) Ktze. ‘Raleigh′], and centipedegrass [Erernochloa ophiuroides (Munro) Hack.] maintained at mowing heights above 1.3 cm.

A field experiment was conducted to evaluate weed control systems in a conservation tillage rotation of grain sorghum [Sorghum bicolor (L.) Moench.] – cotton (Gossypium hirsutum L.) – wheat (Triticum aestivum L.). Herbicide systems included fall and spring/summer inputs of high and low intensity. Tillage regimes were no-till (NT) and reduced-till (RT) systems; the latter included fall primary tillage followed by spring stale seedbed planting. Both tillage systems utilized controlled traffic lanes and wide, raised beds. Effective johnsongrass [Sorghum halepense (L.) Pers. # SORHA] control required intense herbicide inputs at one or both application periods, i.e., in the fall and/or spring/summer. Grain sorghum and cotton yields for the most intense weed control system, which included high inputs in both the fall and spring/summer, were not superior to systems that included high inputs in only one of the two application periods. Seedling johnsongrass emergence occurred before spring planting in RT (but not in NT) in 2 of 3 yr, and control measures were ineffective. After 3 yr, the predominant weeds were johnsongrass and browntop panicum (Panicum fasciculatum Sw. # PANFA).

Weed control, yield, quality, and net return in reduced-cost and standard weed control systems were studied in “Sunbelt runner’ peanuts (Arachis hypogaea L.) planted in a twin-row pattern in 1982 to 85 at Tifton, GA, and 1982 to 84 at Headland, AL. Reduced herbicide rates and/or less expensive herbicides were used to decrease weed control costs. In years and locations where weed populations were low there were no differences in weed control, crop yield, or quality. The lowest cost treatment, which included three applications of paraquat (1,1′-dimethyl-4,4′-bipyridinium ion), caused reduced weed control at both locations in 1982 and reduced yield in 1982 and 1984. None of the systems consistently resulted in the highest weed control, crop yield, or quality. A system including reduced rates of preplant-incorporated herbicides followed by two applications of paraquat performed as well as the standard system but cost about 40% less. Due to low cost and generally high yields this system resulted in consistently high net returns. Results indicate that the potential exists for reducing herbicide inputs without sacrificing yield or quality.