Public concern regarding the use of herbicides in urban areas (e.g., golf courses, parks, lawns) is increasing. Thus, there is a need for alternative methods for weed control that are safe for the public, effective against weeds, and yet selective to turfgrass and other desirable species. New molecular tools such as ribonucleic acid interference (RNAi) have the potential to meet all those requirements, but before these technologies can be implemented, it is critical to understand the perceptions of key stakeholders to facilitate adoption as well as regulatory processes. With this in mind, turfgrass system managers, such as golf course superintendents and lawn care providers, were surveyed to gain insight into the perception and potential adoption of RNAi technology for weed management. Based on survey results, turfgrass managers believe that cost of weed management and time spent managing weeds are the main challenges faced in their fields. When considering new weed management tools, survey respondents were most concerned about cost, efficacy, and efficiency of a new product. Survey respondents were also optimistic toward RNAi for weed management and would either use this technology in their own fields or be willing to conduct research to develop RNAi herbicides. Although respondents believed that the general public would have some concerns about this technology, they did not believe this to be the most important factor for them when choosing new weed management tools. The need for new herbicides to balance weed control challenges and public demands is a central factor for turfgrass managers’ willingness to use RNAi-based weed control in turfgrass systems. They believe their clientele will be accepting of RNAi tools, although further research is needed to investigate how a wider range of stakeholders perceive RNAi tools for turfgrass management more broadly.

Rates of evaporation of dalapon acid and four low-volatile esters of dalapon from open dishes at 38C. in pounds per acre per hour, determined gravimetrically, were dalapon acid, 180; propyleneglycol bis ester, 27; diethyleneglycol bis ester, 1.6; dipropyleneglycol bis ester, 0.83; and triethyleneglycol bis ester, 0.61. Foliar applications on an acid equivalent basis were phytotoxic to seedling oats in the increasing order of propyleneglycol bis ester, acid, dipropyleneglycol bis ester, diethyleneglycol bis ester, sodium salt, and tripropyleneglycol bis ester. Relative phytotoxicities were not altered by subjecting plants to rapid drying after spraying. These compounds did not differ significantly in phytotoxicity when added to the rooting medium of germinating oat plants. The triethyleneglycol bis ester, and possibly other esters of dalapon, may offer practical advantages as herbicides other than those related to volatility.

One of the factors to be considered in the establishment and maintenance of an orchard is the competition from weeds for the available supply of moisture and nutrients. Mechanical elimination of competitive plants is time consuming, expensive, and may not be done as early or as frequently as it is needed each year. The use of herbicides as a supplement to such a program now seems worthy of serious consideration. In some instances, as will be seen below, the use of mechanical methods may be eliminated altogether.

Forage legumes are often injured when herbicides, such as 2,4–dichlorophenoxyacetic acid (2,4–D), are applied to control weeds in fields of grain containing legume seedlings. At times the legume seedlings are not injured materially but in many instances the herbicide applications result in a moderate or even drastic thinning of the stand. Various factors have been suggested to account for the variability in results observed.

Chemical methods offer a quick means of eliminating crabgrass from lawns and other grassed areas. Sodium arsenite, used since 1935, is the oldest of the selective chemical crabgrass killers. In 1947 phenyl mercuric acetate was reported to be effective as a crabgrass killer in the bentgrass type of turf.

Continuous use of heavy machinery in fields and frequent farm traffic sometimes result in soil compaction. Soil compaction reduces the oxygen (O2) concentration in soil capillaries and hence lowers the O2 availability for germinating seeds. We investigated how reduced O2 levels changed germination behavior of weeds to elucidate their potential to adapt to O2-deficient soils (compacted, compressed, and waterlogged soils and soils with hard surfaces). Two similar laboratory experiments were conducted with five O2 treatments (20.9%, 15%, 10%, 5%, and 2.5%). The germination percentage of the invasive weed hairy fiddleneck [Amsinckia menziesii (Lehm.) A. Nelson & J.F. Macbr. var. menziesii] and the common weeds common lambsquarters (Chenopodium album L.) and Persian speedwell (Veronica persica Poir) was not significantly reduced at 15% O2. The germination of scarlet pimpernel (Anagallis arvensis L. ssp. arvensis), silky windgrass [Apera spica-venti (L.) Beauv.], catchweed bedstraw (Galium aparine L.), and knawel (Scleranthus annuus L.) was significantly reduced at 15% O2. The highest germination was obtained at 20.9% O2 for blackgrass (Alopecurus myosuroides Huds.), A. spica-venti, G. aparine, annual bluegrass (Poa annua L.), wild mustard (Sinapis arvensis L.), scentless chamomile [Tripleurospermum inodorum (L.) Sch. Bip.], field violet (Viola arvensis Murray) and the less common weeds A. arvensis and S. annuus. Distribution of flora in the landscape may change on O2-deficient soils by reducing germination of some species such as A. arvensis and S. annuus and favoring others like A. menziesii and C. album. The ability to germinate at 2.5% and 5% O2 may contribute to explain why A. myosuroides and A. menziesii have become successful as weeds on O2-deficient soils, as they maintained a germination percentage between 34% and 58% at 2.5% O2.

When wheat seedlings are injured by trichloroacetate (TCA) the leaves turn yellow in much the same manner as do those on plants growing in media where the nutrients are unbalanced. Accordingly, there is the possibility that TCA may have some effect on the intake of plant nutrients, and that injury was actually the result of nutrient starvation.

Water stargrass (Heteranthera dubia (Jacq.) Mac. M.) is a perennial, rooted, aquatic plant indigenous in the shallow lakes, ponds, and slow rivers of the eastern United States. It thrives in the drainage canals of northeastern Arkansas. This area is basically a reclaimed swamp with intermingled soils ranging from pure sand to heavy clay, and the water table is very close to the surface. Water stargrass reduces the carrying capacity of the drainage ditches, resulting in a rise in the soil water table and in flooded or waterlogged soils. Water stargrass makes its greatest growth in the spring during the season of heaviest load on the drainage canals.

In weed control, soil sterilization is that process whereby the soil is altered so that it will no longer sustain the higher forms of plant life. In most common use the term refers to the application of chemicals to the soil surface. The sterile effect obtained is not instantaneous but develops as the chemical is carried down through the soil with water or after mixing the chemical with the soil by tillage. The sterile effect obtained is not permanent as leaching, fixation, or decomposition by microbes reduce the toxic effect with time. The length of time chemicals will remain active as soil sterilants varies. Highly soluble materials will be removed much more rapidly than will relatively insoluble compounds.

The acid and amine formulations of 2,4-dichorophenoxyacetic acid (2,4-D) can be extracted from soybean seed simultaneously or separately. The method consists of partitioning first between ethyl ether and citrate-phosphate buffer and then between carbon tetrachloride and citrate-phosphate buffer. Quantitative determination of the 2,4-D can be made by means of chromatography.

Treatment of woollyleaf franseria, Franseria tomentosa Gray, with 2,4-dichlorophenoxyacetic acid (2,4-D) at three locations in Nebraska showed that June treatments were much more effective in reducing the stand than those made in July and August. The isopropyl ester and butoxyethanol ester of 2,4-D were somewhat more effective than the triethanolamine salt. Rates of 2 and 4 lb/A gave the most consistent results.

Weed control has been a major problem in Hawaiian pineapple production. Hand-hoeing and mechanical cultivation gave way to activated oil emulsion sprays in the 1940's. The 1950's brought the use of preemergence herbicides especially 3–(p–chlorophenyl)–1,1–dimethylurea (monuron). Each method has brought a shift in species distribution. Today, large-seeded species and vegetatively-propagated species are less well-controlled than in the days of contact weeding with oil emulsion sprays. There is need for selective herbicides which will control the weeds which escape the present program.

Indoleacetic acid (IAA) stimulates the incorporation of radioactivity derived from methionine-methyl-C14 into a fraction of sesbania hypocotyl that is insoluble in 80 per cent alcohol or 60 percent acetone, but is soluble in hot water. Incorporation of C14 into “hot water soluble material” was stimulated by IAA, 2,4-dichlorophenoxyacetic acid, 2,5-dichlorophenoxyacetic acid, 2,4,5-trichlorophenoxyacetic acid, naphthaleneacetic acid, 2,3,6-trichlorophenylacetic acid, 2-methoxy-3,6-dichlorobenzoic acid, 4-amino-2,5-dichlorobenzoic acid, and 4-amino-3,5,6-trichloropicolinic acid. All compounds were stimulative at 1 × 10-5M.

Fall treatments with 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) as opposed to cultivation during the growing season reduced hand labor requirements more than 70% for weed control in Japanese holly (Ilex crenata Thumb. Rotundifolia Hort.). The response of Japanese holly to simazine varied from superior growth and quality to severe injury and death. Simazine plus 3-amino-1,2,4-triazole (amitrole) resulted in better control of small weeds than simazine alone in late winter or early spring. Dimethyl 2,3,5,6-tetrachloroterephthalate (DCPA), N,N-dimethyl-2,2-diphenylacetamide (diphenamid), and 2,6-dichlobenzonitrile (dichlobenil) reduced labor requirements for control of annual weeds without any visual response on the Japanese holly. In certain instances, rotations of herbicides were effective for broad spectrum weed control.

The fungicide, Dyrene [2,4-dichloro-6-(o-chloroanilino)-s-triazine], severely injured var. mite of Canada thistle [Cirsium arvense (L.) Scop.]; and the damage resembled that caused by bipyridylium herbicides. Regrowth from treated plants was abnormal. Other arylamino-s-triazines were from slightly to severely phytotoxic to leaf sections of the var. mite. The var. horridum of Canada thistle was not affected by Dyrene or related compounds. Dyrene and metabolites of Dyrene which were phytotoxic to var. mite leaf disks in bioassay tests were isolated from treated var. mite and horridum plants, but none of these compounds injured the var. horridum. One metabolite was found only in the var. mite; the other five occurred in both varieties. The metabolites were apparently formed from Dyrene by conjugation reactions.

The growth response of annual sowthistle (Sonchus oleraceus L.) to anticipated future climate conditions is currently unknown, and thus two parallel studies were conducted dealing with glyphosate-resistant (GR) and glyphosate-susceptible (GS) biotypes of S. oleraceus. The glyphosate efficacy study was conducted using different doses of glyphosate (0 [control], 180, 360, 720 [recommended dose], and 1,440 g ae ha−1) at two different moisture levels (well-watered and water-stressed conditions). In the second study, the growth and seed production of these biotypes were studied under different atmospheric carbon dioxide (CO2) concentrations (450 and 750 ppm) and under well-watered (100% field capacity) and water-stressed (50% field capacity) conditions. Results showed that the GR biotype survived (>68%) at 1,440 g ha−1, but for the GS biotype, no plant survived, and both biotypes were slightly (<10%) affected by moisture regimes. In the elevated CO2 condition, the GS biotype plants were >38% taller and produced >44%, >18%, and >21% more leaves, buds, and seeds, respectively, compared with the ambient CO2 concentration under both moisture regimes. The biomass also increased by 27% in comparison with the ambient CO2 concentration. For the GR biotype, plants at the elevated CO2 level, while they also grew 38% taller in comparison with the ambient CO2 concentration, the numbers of leaves, buds, and seeds and biomass were not affected by this increase in CO2. Results showed that there were minimal changes in response to glyphosate for GR and GS biotypes of S. oleraceus with or without moisture stress. Our study suggests that future climate change with elevated CO2 levels can affect the response of S. oleraceus to glyphosate, and such knowledge will be helpful for weed management in the future.

Studies were conducted to compare weed growth under lighting systems composed of metal halide (MH) lamps and fluorescent-incandescent (FI) lamps. The MH lamps provided more light intensity and over a 6-week period caused plant dry weight to be 60 to 70% more than for plants exposed to the FI lamps. One week after emergence, all plants under the higher intensity MH lamps had larger stems and cotyledons or first true leaves. Six weeks after planting, weeds grown under the MH lamps had larger leaves, shorter internodes, thicker stems, and, in general, more pubescence than plants under the conventional lighting system. Growth habits of weeds exposed to the MH lamps were similar to those observed for field growth plants.

Winter applications of paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) or combinations of paraquat with diquat [6,7-dihydrodipydrido (1,2-α: 2′,1′-c) pyrazinediium ion], propham (isopropyl carbanilate), or pronamide [3,5-dichloro-N-(1,1-dimethyl-2-propynyl)benzamide], usually controlled both winter annual grass and broadleaf weeds in established white clover (Trifolium repens L. ‘New Zealand,’ ‘Louisiana S-1,’ and ‘Tillman’). Diquat controlled broadleaf weeds, but was less effective than paraquat or combinations of paraquat with diquat, propham, or pronamide for grass control. Dichlobenil (2,6-dichlorobenzonitrile) controlled weeds in some experiments. Pronamide and propham usually controlled grass weeds but not broadleaf weeds. In experiments in which clover seed production differed significantly, paraquat or combinations of paraquat with propham or pronamide usually resulted in higher yields than the check. Yields increased more often where treatments included paraquat.