Five 2,5-dimethyl-1-pyrrolidinecarboxanilides were effective inhibitors of the Hill reaction. However, only the cis isomers were active; the trans isomers were totally inactive. Experiments were conducted using 14C-5328 (cis-2,5-dimethyl-1-pyrrolidinecarboxanilide). A correlation existed between resistance of various plants to 5328 and their ability to metabolize it to water soluble metabolites. Velvetleaf (Abutilon theophrasti Medic.) and proso millet (Panicum miliaceum L.) seedlings were very susceptible to 5328 and were unable to metabolize it. Tall morningglory [Ipomoea purpurea (L.) Roth] seedlings were highly tolerant to 5328 and converted it completely to its metabolites. Corn (Zea mays L. ‘DeKalb variety XL-45′) seedlings which were slightly susceptible to 5328 injury were able to metabolize up to 90% of the parent compound. Corn foliage uptake of 14C-5328 applied to the soil surface occurred through the adventitious roots.

The persistence of biologically active metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one] and its ethylthio analog [4-amino-6-(1,1-dimethylethyl)-3-(ethylthio)-1,2,4-triazin-5(4H)-one] were compared using an intact-plant chlorophyll fluorescence bioassay technique with oats (Avena sativa L.) and wheat (Triticum aestivum L.). Degradation of metribuzin phytotoxicity at concentrations of 0 to 1 ppm (w/w) ai in a Pond Creek silt loam soil was linear over time, with a half-life of 8 days at 35 C. Initial degradation of the biologically active ethylthio analog was much more rapid than for metribuzin, with a decrease in rate at later time intervals. A quadratic function best described this degradation pattern. The initial degradation rate of phytotoxicity for the ethylthio analog indicated a half-life of 4 days at 35 C. Soil pH had no significant influence on the activity or persistence of either herbicide within the range 4.9 to 6.9.

Carbon-14-labeled 2-chloro-4,6-bis(ethylamino)-s-trazine (simazine) was applied at a low concentration to the root media of rye (Secale cereale L.), soybean (Glycine max L.), and corn (Zea mays L.) plants growing in nutrient solution that contained nitrate or ammonium nitrogen. The shoots of the plants grown on nitrate nitrogen contained more radioactive simazine per unit fresh weight than the plants that were grown on ammonium nitrogen. Less herbicidal injury was observed on soybean plants grown in soil fertilized with ammonium sulfate than on soybean plants fertilized with calcium nitrate.

Research was conducted in 1998 and 1999 to characterize common lambsquarters photosynthesis and seed production as influenced by biotic (crop environment) and abiotic (climate) factors. Treatments were common lambsquarters in soybean, in corn, and in common lambsquarters monoculture. Common lambsquarters net photosynthesis was variable among treatments and differed between years. In 1998, early-season common lambsquarters net photosynthesis did not differ in soybean, corn, or common lambsquarters monoculture. In 1999, early-season common lambsquarters net photosynthesis was greater in corn than in soybean, but did not differ from that of common lambsquarters in monoculture. By midseason in both years, common lambsquarters net photosynthesis was less in soybean than in corn or in common lambsquarters monoculture. By late season in both years, common lambsquarters net photosynthesis was greater in common lambsquarters monoculture than in soybean or corn. Common lambsquarters seed production per plant was greater in common lambsquarters monoculture than in soybean or corn. Common lambsquarters seed production was variable among plants and between years. Practical applications of models to predict weed fitness that are based on photosynthetic capacity will be limited until variability in net photosynthesis and in seed production are better understood.

Aminocyclopyrachlor (AMCP) is a synthetic auxin herbicide that controls primarily broadleaf (eudicotyledonous) weeds. Previous research indicates that St. Augustinegrass is unacceptably injured by AMCP. In light of the fact that synthetic auxin herbicides usually are safe when applied to monocotyledons, the mechanism for this injury is not fully understood. Anatomical response of St. Augustinegrass to AMCP was investigated using light microscopy. Apical meristem node tissue responded with callus tissue proliferation, abnormal location and development of the apical meristem, necrosis of the developing vascular tissue, vascular parenchyma proliferation, and xylem gum blockages. Node tissues away from the apical meristem responded with xylem gum blockages and the stimulation of lateral meristems and adventitious root formation. Root tip response to AMCP treatment was characterized by a loss of organization. Root tip apical meristem and vascular tissue maturation was disorganized. Additionally, lateral root generation occurred abnormally close to the root tip. These responses impair affected tissue functionality. Mature tissue was unaffected by AMCP treatment. All of these responses are characteristic of synthetic auxin herbicide treatment to other susceptible species. This research indicates that AMCP treatment results in St. Augustinegrass injury and subsequent death through deleterious growth stimulation and concomitant vascular inhibition.

A field microplot experiment was conducted in 1996 and 1997 to determine the influence of root-knot nematodes on intra- and interspecific interactions between chile pepper (chile) and spurred anoda and between chile and yellow or purple nutsedge (or both) using a substitution design. An additional objective was to determine the influence of London rocket, a winter annual and host plant for root-knot nematodes, on the inter- and intraspecific interactions between chile and spurred anoda. Twelve plant combinations were planted into paired 76-cm-diam microplots at a density of 24 plants per microplot each year. Each pair of microplots had one root-knot nematode–infested and one uninfested plot. One randomly selected plant pair or triplet from each plot was destructively sampled in June, July, August, and September each year. Data included leaf area, plant dry weights (leaf, stem, root or root plus rhizome, chile fruit, and nutsedge tuber), and nematode egg production from the belowground biomass of the different plant species within a 2,355-cm3 sampled soil volume. Chile hosted the highest population of root-knot nematodes, followed by spurred anoda, purple nutsedge, and yellow nutsedge. Few root-knot nematode eggs were recovered from London rocket before incorporation into the microplots each spring. Root-knot nematode populations were higher in 1997 and, as a result, more interactions between nematodes and plant combinations were observed for chile. Spurred anoda and root-knot nematodes reduced chile shoot and root weights to levels not significantly different from zero in 1997. Yellow and purple nutsedge shoots, except for those from the original tuber, were removed throughout the season, and these species interfered less with chile. Spurred anoda was not affected by interspecific interference. Few interactions were observed between the spurred anoda plant combinations and root-knot nematodes. In June 1996, low populations of root-knot nematodes (< 4,000 eggs per gram of root) stimulated spurred anoda growth, but higher populations in June 1997 (> 30,000 eggs per gram of root) reduced spurred anoda growth. Prior presence of London rocket had little consistent influence on spurred anoda or chile. Yellow and purple nutsedge growth variables were affected by interference from chile and the other nutsedge species. Tuber number and tuber weight were higher when plants were infected with root-knot nematodes, particularly early in the season. The enhanced tuber production may increase early-season interference from nutsedge species under production conditions. The results suggest that the presence of root-knot nematodes influences plant interference, but the effect is species specific. Annual plants are affected differently compared with perennial nutsedges, possibly because of the continuous association between the perennials and the parasite.

Photosynthetic growth of 9 of the 11 known species of the family Rhodospirillaceae was strongly inhibited by atrazine. Growth of a wild-type strain of the bacterium Rhodopseudomonas sphaeroides van Niel was almost completely inhibited by 100 μM concentrations of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] and diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea]. These herbicides gave 50% inhibition of growth at concentrations of 35 and 25 μM, respectively. Through continuous culture of the wild-type R. sphaeroides in the presence of 100 μM atrazine, strains of the organism were selected in which photosynthetic growth was highly resistant to both atrazine and diuron. Members of the genus Rhodopseudomonas isolated from two natural ecosystems showed various levels of resistance to 100 μM atrazine, but Rhodopseudomonas showing a high level of resistance were more common among the isolates from a pond-mud sample which had been exposed to runoff from atrazine-treated cropland than from a sample of a lake mud never exposed to triazines.

In field studies, herbicides were applied at various times to different plots during the summer and fall at two locations over a 3-year period to control winter weeds in nonoverseeded bermudagrass [Cynodon dactylon (L.) Pers.] turf. Annual bluegrass (Poa annua L.) control was higher at Griffin for all herbicide applications made in October when compared with herbicide applications made at the same rate in July, August, or September. At Lawrenceville, optimum annual bluegrass control was obtained when bensulide [O,O-diisopropyl phosphorodithioate S-ester with N-(2-mercaptoethyl) benzenesulfonamide] was applied in August, terbutol (2,6-di-tert-butyl-p-tolyl methylcarbamate) applied in either August or September, benefin (N-butyl-N-ethyl-α,α,α-trifluoro −2,6 dinitro-p-toluidine) applied in September, pronamide [3,5-dichloro-N-(1,1-dimethyl-2-propynyl) benzamide] applied in either September or October, and simazine [2-chloro-4,6-bis(ethylamino)-s-triazine] applied in October. DCPA (dimethyl tetrachloroterephthalate) did not control annual bluegrass satisfactorily at either location, regardless of dates of application. The control of several broadleaf weeds was generally higher when herbicides were applied in October at Griffin and when applied in September or October at Lawrenceville when compared with earlier treatments. Bensulide applied in October was the only herbicide that satisfactorily controlled parsley-piert (Alchemilla microcarpa Boissie Reuter).

The influence of surfactant type and concentration on the efficacy of asulam {methyl [(4-aminophenyl) sulfonyl] carbamate} for controlling rhizomatous johnsongrass [Sorghum halepense (L.) Pers. # SORHA] was evaluated in field and greenhouse studies. Under field conditions, nonoxynol (9 to 10 POE) [α-lp-nonylphenyl)-w-hydroxypoly (oxyethylene)] applied at concentrations of 6% (v/v) with asulam at 2.8 kg ai/ha reduced rhizomatous johnsongrass biomass by 35%, with no consistently significant difference in asulam's performance between surfactant concentrations of 0 and 3% (v/v) being observed. Asulam applied with nonoxynol at concentrations of 3 and 6% (v/v) reduced sugarcane (Saccharum interspecific hybrids) yields and significantly offset any advantages from increased johnsongrass control. In greenhouse studies, where johnsongrass foliage was washed either 0, 1, 6, 24, or 48 h after treatment (HAT), the degree of johnsongrass control with asulam was generally not affected by the type of surfactant (paraffin-base petroleum oil-surfactant blend or alcohol-surfactant-water mixture) used. At least 48 h was needed to insure adequate basipetal translocation, hence maximum inhibition of rhizome regrowth with asulam applied alone. Increasing the surfactant concentration shortened this interval to 48 h (0.25%) to 24 h (0.5 to 1%) to 6 h (3%) to 1 h (6%).

Triallate [S-(2,3,3-trichloroallyl)diisopropylthiocarbamate] mixed with soil (1.5 ppmw) stimulated coleoptile extension, reduced the length of the primary leaf, but had no effect on mesocotyl development of wild oat (Avena fatua L.) grown in soil in a growth chamber. Incubation of the triallate-treated soil for as long as 20 weeks at constant temperatures (10 C, 16 C, and 20 C) did not reduce phytotoxicity. Triallate phytotoxicity was similar at soil moisture levels of either 5% greater than wilting point or 5% less than field capacity. The phytotoxicity remained the same after a freezing cycle during an 8-week soil incubation. Phytotoxic effects of triallate were markedly reduced as soil organic matter increased.

Representative species of six genera of marine unicellular algae (Chlorococcum sp., Dicrateria inornata Parke, Dunaliella tertiolecta Butcher, Nannochloris sp., Isochrysis galbana Parke, and Monochrysis lutheri Droop) were treated in unialgal culture with 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron), 1-butyl-3-(3,4-dichlorophenyl)-1-methylurea (neburon), 3-(p-chlorophenyl)-1,1-dimethylurea (monuron), and 1,1-dimethyl-3-phenylurea (fenuron). Tests were conducted at salinities of 5, 10, 20, and 30 parts per thousand (ppt). The herbicides depressed concentration of carbohydrate in all species. Dunaliella tertiolecta was most resistant; its carbohydrate content decreased 9.2% at 5 ppt salinity and 17.9% at 30 ppt. Chlorococcum was most susceptible; its carbohydrate content decreased 49.1% at 5 ppt and 65.6% at 30 ppt salinity.

Glyphosate [N-(phosphonomethyl)glycine] and EPTC (S-ethyl dipropylthiocarbamate) did not reduce significantly the percent germination of either ‘Saranac’ or ‘Vernal’ cultivars of alfalfa (Medicago sativa L.) grown in petri dishes. Glyphosate at 10−5 M significantly reduced shoot length of both cultivars. Vernal alfalfa appeared to be more susceptible to glyphosate than the Saranac cultivar. Soil applications of glyphosate also had no effect on percent emergence of either cultivar and reduced plant height only of Vernal when applied to the soil at 17.9 kg/ha. Applications of glyphosate at 2.2, 4.5, and 9.0 kg/ha to a Kentucky bluegrass (Poa pratensis L.) sod in a simulated sod seeding alfalfa establishment study in the greenhouse reduced dry weight of both alfalfa cultivars; Vernal was affected more adversely than Saranac. Application of 2.2 kg/ha glyphosate in four management systems showed that a 3-day planting delay after spraying reduced growth inhibition of alfalfa seeded in treated sod. These results were similar to those obtained with paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) in these management systems. Kentucky bluegrass clippings treated with paraquat 3 days or less before contact with alfalfa seedlings significantly reduced seedling dry weight. Clippings treated with glyphosate did not reduce alfalfa seedling dry weights significantly.

Karbutilate [tert-butylcarbamic acid ester with 3(m-hydroxypheny)-1, 1-dimethylurea], formulated as a ball 1.34 cm in diameter, was applied to brush-infested rangeland with fixed-wing aircraft and in a grid pattern by hand at an average density of four balls/12.4 m2 (1.83-m spacing). Control of woody plants with karbutilate applied by hand in an exact grid pattern was not different from aerial applications at the same rate. Based on evaluations at least 24 months after application, karbutilate at 0.56 or 1.12 kg/ha did not control honey mesquite [Prosopis juliflora (Swartz) DC. var. glandulosa (Torr.) Cockerell] in the subhumid Post Oak Savannah or semiarid Rolling Plains of Texas. At 2.24 kg/ha, canopy reduction of honey mesquite averaged 70% with 20 to 25% of the population killed. Post oak (Quercus stellata Wangenh.), blackjack oak (Quercus marilandica Muenchh.), yaupon (Ilex vomitoria Ait.), or winged elm (Ulmus alata Michx.) in Post Oak Savannah were not killed by 2.24 kg/ha. Karbutilate eliminated all vegetation in a 25 to 45-cm diameter circle, depending on concentration of active ingredient in the ball, the year of treatment regardless of vegetation region. The bare areas were revegetated within 2 yr following application in the Post Oak Savannah. However, bare areas in sodgrasses, primarily tobosa [Hilaria mutica (Buckl.) Benth.] and buffalograss [Buchloe dactyloides (Nutt.) Engelm.], where 1.12 and 2.24 kg/ha were applied averaged 20 to 30 in diameter, respectively, 32 months after application to sandy clay loam in the Rolling Plains.

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 laboratory bioassay showed that inhibitors of gibberellin synthesis (flurprimidol, paclobutrazol, and uniconazole) reduced plant height but did not affect physiological parameters such as photosynthesis, respiration, and chlorophyll content in two weedy submersed aquatic plants, hydrilla and Eurasian watermilfoil. Eurasian watermilfoil was sensitive to these compounds at concentrations as low as 0.75 μg L−1. Hydrilla sensitivity was in the range of 75 to 750 μg L−1. The three compounds reduced main and lateral stem lengths in hydrilla; however, at 75 μg L−1 the number of lateral stems and roots was greatly increased over untreated controls resulting in a stoloniferous growth habit. Dominant growth form of treated Eurasian watermilfoil was a single shortened stem with numerous compacted buds. Photosynthesis, respiration, and chlorophyll content were not affected in either plant at nontoxic dosages in which stem reduction was obtained. Both plants required only a 24-h exposure to maintain main stem length reduction for 6 wk after transfer to untreated medium. Our results indicate that these gibberellin synthesis inhibitors would be effective in reducing plant height in aquatic systems.

When postemergence applications of sethoxydim {2-[1-(ethoxyimino) butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} were compared with DSMA (disodium salt of methylarsonic acid), MSMA (monosodium salt of methylarsonic acid), and glyphosate [N-(phosphonomethyl)glycine] for control of johnsongrass [Sorghum halepense (L.) Pers. # SORHA] in cotton (Gossypium hirsutum L. ‘Acala SJ-2′), repeated annual applications of sethoxydim were more successful than other herbicides in protecting yields of cotton and reducing populations of rhizome johnsongrass over time. After the first year of treatment with sethoxydim in 1982, when an 18% yield loss of cotton occurred, populations of rhizome johnsongrass were reduced to the extent that they were no longer a threat to yields in plots treated with sethoxydim in 1983 and 1984. Although DSMA and glyphosate improved yields when compared to cultivated control plots, substantial yield losses occurred every year, and populations of johnsongrass remained unchanged after 3 yr of treatment. Averaged over 3 yr, plots treated with sethoxydim produced 94% as much cotton as weed-free plots, compared to 60 and 45% for plots treated with glyphosate and DSMA/MSMA, respectively.

Corn (Zea mays L. ‘Dixie 18′) leaf discs were incubated in light or darkness in dilute solutions of 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) with and without 6-furfurylamino-purine (kinetin). Kinetin decreased chlorophyll loss in light whereas atrazine had no effect. In darkness atrazine at a concentration of 5 × 10−8M increased clorophyll a retention in the absence of exogenous kinetin; but in the presence of 1.5 μg/ml of kinetin, the herbicide increased loss of chlorophyll a. Increasing the kinetin concentration to 15 μg/ml relieved the effect of 5 × 10−8M atrazine, but 10−7M atrazine increased chlorophyll loss. Higher concentrations of kinetin (150 and 1500 μg/ml) prevented all effects of atrazine. Factorial analysis revealed a highly significant interaction between atrazine and kinetin.

Greenhouse and field studies were conducted to evaluate Oryza sativa response to the simulated carryover of fluometuron, imazethapyr, metolachlor, and norflurazon in dry- and water-seeded culture. In the greenhouse, fluometuron and norflurazon did not affect O. sativa emergence, but reduced O. sativa shoot and root dry weight at all the residue levels. Greater reduction in O. sativa emergence and shoot dry weight was observed with imazethapyr and metolachlor in dry- compared with water-seeded O. sativa. In the field, imazethapyr at 0.04 kg ai ha−1 injured dry-seeded O. sativa both years, but O. sativa yield was reduced only in the second year. Greater O. sativa injury and yield reduction were observed in dry- compared with water-seeded O. sativa with metolachlor at most residue levels. Norflurazon at 0.42 and 0.21 kg ai ha−1 caused greater O. sativa yield reduction in water-seeded O. sativa than in dry-seeded O. sativa in the first and second year, respectively. The results indicate that water-seeded O. sativa has less risk of being damaged by imazethapyr and metolachlor but is more susceptible to residues of norflurazon compared with dry-seeded O. sativa. Thus, choosing the right seeding method following a specific rotational crop herbicide could help to minimize the risk of O. sativa injury from herbicide carryover.

The new scientific discipline, weed control, is the product of research. So long as man has grown crops for his own personal use, he has fought weeds, for nature favors community life for her plants. True there are examples of pure cultures of plants in nature; the white pine forests of the northwest, the buffalo grass prairies, wild rice in the northern lakes. But by and large, the areas now devoted to our major crops, wheat, corn, cotton and forage, were occupied by mixed plant populations and now they are in monoculture or in controlled plant populations and this nature abhors. Hence through the ages and even more today the farmer has been at war with weeds, the invaders of his crops.

Alhagi pseudalhagi (Bieb.) Desv. (camelthorn) was in troduced into California about 1915, and into the State of Washington about 1935. Here, it was declared a primary noxious weed in 1955. Seeds scarified with sulfuric acid germinated 90–98 per cent at 25 C. Some seeds were viable after burial one year in soil or submergence for 9 months in running water. Seedlings in the infested area were found only in bovine manure. Tests indicated scarification and transportation of seed in the rumen could accelerate the spread of camelthorn. Lack of favorable moisture and soil temperature at the same time prevented establishment of camelthorn planted at several locations. Eradication resulted from treatment with 2,3,6-trichlorobenzoic acid (2,3,6-TBA). Three repeated sprays with esters of 2,4-dichlorophenoxyacetic acid (2,4-D) within a growing season gave control; however, control did not appear to be directly related to depletion of reserve foods in the roots.