The effects of several concentrations of glyphosate [N-(phosphonomethyl)glycine] and siduron [1-(2-methylcyclohexyl)-3-phenylurea] on germination and seedling growth of Kentucky bluegrass (Poa pratensis L. ‘Nugget,’ ‘Prato,’ ‘Fylking,’ ‘Park’), creeping bentgrass (Agrostis palustris Huds. Penncross,’ ‘Seaside’), and red fescue (Festuca rubra L. ‘Pennlawn,’ ‘Wintergreen’) were evaluated in petri dishes under controlled environmental conditions. A high concentration of glyphosate (10-4 M) reduced shoot growth in all but two cultivars. Siduron had no effect. Glyphosate or siduron applied to the soil and incorporated did not affect turfgrass germination or growth. When the glyphosate was sprayed over the soil and on the seed lying on the soil surface, red fescue germination was reduced and shoot growth of Kentucky bluegrass, creeping bentgrass, and red fescue was inhibited at the high rate of glyphosate application (17.9 kg/ha). Under field conditions, none of the glyphosate treatments reduced turfgrass germination or growth.

In rolling topography, soil and water runoff losses can be greatly reduced by conservation production systems. Alfalfa (Medicago sativa L.) is an important crop in Nebraska and other states which is often followed in the crop sequence by corn (Zea mays L.) or sorghum [Sorghum bicolor (L.) Moench]. Three years of field experiments indicated that herbicides can substitute for erosive moldboard plowing to destroy alfalfa without loss in the subsequent corn yield. Herbicides applied just prior to corn planting in the spring gave more consistent alfalfa control than those applied the preceeding fall. The most consistent treatment used for alfalfa control and supplemental annual weed control while producing maximum corn yield was 2,4-D amine [(2,4-dichlorophenoxy) acetic acid] plus dicamba (3,6-dichloro-o-anisic acid) at 1.12 and 0.28 kg/ha, respectively. Atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] plus propachlor (2-chloro-N-isopropylacetanilide) versus no preemergence herbicide was used for annual weed control in addition to the treatments to control alfalfa. This treatment was essential for maintaining corn yields where a non-residual or limited residual herbicide was used for alfalfa control.

Studies of the development and distribution of root systems of intraspecific and interspecific competition were conducted between soybean [Glycine max. (L.) Merr. ‘Lee 68′] and tall morningglory [Ipomoea purpurea (L.) Roth]. Tall morningglory at three plant densities and soybean were grown for 2 yr on a Taloka silt loam. The greatest density of soybean and tall morningglory roots grown under intraspecific competition was in the surface 12 cm and in the center of the row. Greater values of root length and density were during the dryer season. The largest fraction of total root length at a given date also was in the surface 12 cm and decreased with depth. The fraction at a given depth was a dynamic property of the root system during the growing season. When compared with the soybean root system, tall morningglory roots were found at deeper depths and had greater root densities. Little expansion of the soybean root system was found after initiation of the soybean reproductive phase. During this phase, the tall morningglory root system was increasing at a faster rate of growth than the soybean root system. The greatest density of roots grown under interspecific competition also was in the surface 12 cm and at the center of the row. These values were less than those found under intraspecific competition. Root distribution and development are dynamic functions of growth stage, planting density, and plant species.

The fate of 2,4-D [(2,4-dichlorophenoxy)acetic acid] in the soil under winter wheat (Triticum aestivum L. ‘Nugaines’) and fallow cropping schemes was studied under the field conditions of eastern Washington in 1973 and 1974 using formulated dimethylamine salt and isooctyl ester of 2,4-D. Soil samples taken 1 hour after herbicide application showed that amine-treated plots retained considerably more applied 2,4-D than ester-treated plots. The rapidity of 2,4-D breakdown decreased gradually with time, and at the end of 6 months, an average of 0.04 ppm of 2,4-D remained in the sampled soil profile regardless of formulation, application rate, or cropping scheme. Loss of 2,4-D from the soil surface in runoff occurred when the plots were irrigated heavily one day after the herbicide application. The herbicide was also leached into the soil profile by both irrigation and natural precipitation. Herbicide concentrations in the sampled portion of the upper soil profile decreased during the summer and then increased slightly in the fall.

Renovation of common bermudagrass [Cynodon dactylon (L.) Pers.] turf to either ‘Tifway’ or ‘Tifdwarf’ bermudagrasses, zoysia (Zoysia japonica Steud. x Zoysia tenuifolia Willd. ex Trin. ‘Emerald’) or centipedegrass [Eremochloa ophiuroides (Munro) Hack.] was undertaken with the aid of herbicides. Glyphosate [N-(phosphonomethyl)glycine] applied to common bermudagrass turf followed by treatments of MSMA (Monosodium methanearsonate) + 2,4-D[2,4-dichlorophenoxy)acetic acid] alone or in sequence with DCPA (dimethyl tetrachloroterephthalate) reduced the cover of common bermudagrass in renovated Tifway or Tifdwarf bermudagrass turf. Dalapon (2,2-dichloropropionic acid) applied alone or in sequence with DCPA, MSMA + 2,4-D, or DCPA + MSMA + 2,4-D also reduced coyer of common bermudagrass in some plantings. Paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) and cacodylic acid (hydroxydimethylarsine oxide) did not reduce the cover of common bermudagrass in turf renovations. Slower growing Emerald zoysia and centipedegrass could not compete with the common bermudagrass that escaped the herbicide applications and renovation was unsuccessful.

Analysis of soil in which corn (Zea mays L.) has been grown annually for 9 yr with or without yearly applications of 3.4 kg/ha atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] indicated that long-term atrazine use had little effect upon soil microbes or biochemical processes. With the exception of a transient inhibition of bacterial growth during the first week after field application, repeated applications did not affect the numbers of viable bacteria or fungi, relative abundance of bacteria producing hydrolytic enzymes, or soil enzyme levels.

Metribuzin [4-amino-6-tert-butyl-3-(methylthio-as-triazin-5(4H)one] degradation by soil microorganisms decreased as the soil pH decreased. Metribuzin and atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] mobility increased with increasing concentration and soil pH. 14C-metribuzin had greater mobility on soil thin-layer plates than 14C-atrazine because of differences in water solubility and basicity. Adsorption increased with decreasing soil pH. The pKa for metribuzin was 0.99 ± 0.08. Adsorption increased gradually as the soil pH decreased toward the pKa of metribuzin. Protonation of the amine group with subsequent adsorption to soil colloids was the postulated reason for the reduction in phytotoxicity, microbial degradation, and mobility of metribuzin at low soil pH levels.

The intraspecific (competition between same species) and interspecific (competition between different species) competitiveness of tall morningglory [Ipomoea purpurea (L.) Roth] in soybeans [Glycine max (L.) Merr.] was evaluated for 3 yr at Fayetteville, Arkansas. Tall morningglory was planted at densities of one plant per 61, 30, and 15 cm of row, and competition duration ranged from 2 weeks to full-season. Soybeans were more competitive than tall morningglory for the first 6 to 8 weeks after emergence. The competitiveness of tall morningglory was dependent upon a rapid increase in photosynthetic area which occurred 4 to 6 weeks after emergence. Reductions in leaf area index (LAI) or plant dry weight and crop growth rate (CGR) of soybeans were closely correlated to percent soybean yield reduction. Tall morningglory could remain in soybeans for 12, 10, and 6 weeks without significantly reducing soybean yield at one plant per 61, 30, and 15 cm of row, respectively. Tall morningglory was three to four times more competitive during the soybean reproductive stage than during the vegetative stage.

Emergence of tall morningglory [Ipomoea purpurea (L.) Roth] seedlings was delayed and reduced as planting depths increased from 1.3 to 5.0 cm. Development of seedlings emerging from 3.8 cm or greater depth was delayed for up to 4 weeks as indicated by dry weight accumulation. In both greenhouse and field studies, chemical control of tall morningglory was generally greater when seedlings emerged from planting depths of 2.5 cm or greater. The competitive ability of tall morningglory, as indicated by yield reduction of cowpea [Vigna sinensis (L.) Endl], was dependent upon both planting depth and duration of infestation. Cowpea yields were reduced more by the tall morningglory plants that emerged from 1.3 cm than by those that emerged from greater planting depths for a given infestation period.

Paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) at 1.1 and 2.2 kg/ha and paraquat + dinoseb (2-sec-butyl-4,6-dinitrophenol) at 1.1 + 0.7 kg/ha controlled redroot pigweed (Amaranthus retroflexus L.) and barnyardgrass [Echinochloa crus-galli (L.) Beauv.] in hops (Humulus lupulus L. ‘Yakima Cluster’) without reducing hop yield or the alpha and beta acid content of the hop cones. Three applications at about 3-week intervals were required to control weeds until harvest. Two applications controlled hop sucker growth. Paraquat at more than 0.6 kg/ha in the third application caused excessive reduction in hop sucker growth.

Asulam (methyl sulfanilylcarbamate) at 3.3 or 4.5 kg/ha gave 54% and 61% control, respectively, when applied only to the initial infestation of rhizomatous johnsongrass [Sorghum halepense (L.) Pers.] in sugarcane (Saccharum interspecific hybrids). When applied both to the initial infestation and to the regrowth, 81% and 88% control, respectively, were obtained. Both the single and dual asulam treatments produced yields of sugar that were about double the yield of an untreated check and about 90% of the yield of a hand-weeded check. Sugarcane cultivars ‘CP 52-68′, ‘CP 65-357′, ‘CP 61-37′, and ‘L 62-96’ were highly tolerant to single applications of asulam at 4.5 and 6.7 kg/ha and to dual applications of asulam at 3.4 kg/ha. Some cultivars were moderately injured by dual applications of asulam at 4.5 kg/ha.

Growth chamber studies showed crabgrass [Digitaria sanguinalis (L.) Scop.] to be more tolerant than witchgrass (Panicum capillare L.) to simazine [2-chloro-4,6-bis(ethylamino)-s-triazine] and atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine]. Both grasses were more susceptible to simazine than to atrazine. The s-triazines were taken up by both weed species in equal quantities, but witchgrass translocated larger amounts of simazine and atrazine to the shoots. The greater sensitivity of witchgrass to simazine appeared to be due to the increased translocation of unchanged simazine to the shoots. Greater sensitivity of witchgrass to atrazine was attributed to increased translocation of atrazine to the shoots and less metabolism of the s-triazine to hydrophilic metabolites. It was concluded that the hydrophilic metabolites were the peptide conjugates formed by the enzyme glutathione-S-transferase.

Metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazine-5(4H)one] applied preemergence resulted in increased phytotoxicity with increasing soil pH. In the field, fall panicum (Panicum dichotomiflorum Michx.) control, number of dead corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] plants, and crop injury ratings increased, and plant height and grain yield decreased as the soil pH increased. In the greenhouse, corn and soybean grown in soil showed decreased dry weights due to metribuzin as pH increased. By contrast, the pH response to metribuzin was not evident in nutrient-sand culture, indicating that, in soil, pH affected the availability of metribuzin for plant absorption.

Metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazine-5(4H)one] residue analysis of soil samples showed greater amounts of residue extractable at soil pH 6.7 than 4.6. Metribuzin leaching increased with increasing soil pH. Metribuzin disappearance from soil followed pseudo first-order kinetics. The half-life of metribuzin decreased as soil pH increased and increased at all soil pH levels as depth of sampling increased. The decreased activity and decreased rate of metribuzin dissipation at lower soil pH is apparently due to protonation and increased adsorption.

Methazole [2-(3,4-dichlorophenyl)-4-methyl-1,2,4-oxadiazolidine-3,5-dione] and metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazine-5(4H)one] were evaluated in separate experiments for postemergence control of large crabgrass [Digitaria sanguinalis (L.) Scop.] and goosegrass [Eleusine indica (L.) Gaertn.] and on tolerance of centipedegrass [Eremochloa ophiuroides (Munro) Hack.], St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze], and bermudagrass [Cynodon dactylon (L.) Pers. ‘Common’]. Methazole was also evaluated on tolerance of Kentucky bluegrass (Poa pratensis L. ‘Common’). Metribuzin applied at 0.6 kg/ha and methazole at 1.1 kg/ha as single treatments controlled 82 and 87% goosegrass, respectively. Repeated treatments were needed for similar control of large crabgrass. These treatments did not permanently injure bermudagrass or centipedegrass. St. Augustinegrass was severely injured when treated with single applications of methazole at 1.1 kg/ha or metribuzin at 0.6 kg/ha while Kentucky bluegrass was severely injured by methazole applied at any rate. Methazole caused moderate to severe injury to bermudagrass when applied at 2.2 kg/ha in each of two applications and to centipedegrass when applied at 4.4 kg/ha in each of two applications.

A survey determined the extent and severity of the infestations of four species of Carduus thistles in the United States. In the mainland United States, 360 counties of 3068 have economically important infestations of musk thistle (Carduus nutans L.), the Appalachian and midwest regions harboring the greatest infestations. Plumeless thistle (Carduus acanthoides L.) and Italian thistle (Carduus pycnocephalus L.) are of economic importance, but have limited distribution. Welted thistle (Carduus crispus L.) is approaching pest status only in Virginia.

The sorption equilibria and relative mobility of metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] were evaluated on 16 soils from the lower alluvial flood plain of the Mississippi River as a function of soil properties. Metribuzin sorption and mobility were significantly correlated with each other and both parameters were significantly associated with clay content, organic matter, and water content at 0, 0.33 field capacity (FC), and 15 bars tension. Prediction equations for adsorption (K1 = −1.10 + 0.08 FC) and mobility (Rf = 0.81 − 0.015 FC) indices were developed based on water content at 0.33 bar tension (FC). A competitive effect was observed between the combination of various levels of clay and organic matter as related to metribuzin adsorption.