The herbicides glyphosate [N-(phosphonomethyl)glycine], hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione], and pronamide [3,5-dichloro(N-1,1-dimethyl-2-propynl)benzamide] were evaluated for effectiveness in quackgrass (Agropyron repens L. Beauv.) control when applied in the fall, a time that is desirable in a short-growing-season area such as Atlantic Canada. Glyphosate at 1.12 kg/ha applied to quackgrass in grain stubble gave good control. Glyphosate at 1.12 kg/ha in late October gave better control than the same rate applied in late September. At low rates of 0.56 and 1.12 kg/ha, glyphosate gave better quackgrass control when fall-applied than when spring-applied. No differences were noted between seasons at the 2.24-kg/ha rate of glyphosate. Pre-treatment with nitrogen at 35 kg/ha 30 or 15 days before application, or on the day of application, did not improve quackgrass control with glyphosate. Pronamide gave fair to good control. Hexazinone at 2.24, 4.48, or 6.72 kg/ha gave poor control when fall-applied, but excellent control when spring-applied.

Oxadiazon [2-tert-butyl-4-(2,4-dichloro-5-isopropoxyphenyl)-δ2-1,3,4-oxadiazolin-5-one] applied early enough for large crabgrass [Digitaria sanguinalis (L.) Scop.] control provided full season goosegrass [Eleusine indica (L.) Gaertn.] control during bermudagrass [Cynodon dactylon (L.) Pers. ‘Midiron’ and ‘Tufcoat’] establishment from sod strips. Prosulfalin {N-[[4-(dipropylamino)-3,5-dinitrophenyl]sulfonyl]-S,S-dimethylsulfilimine}, DCPA (dimethyl tetrachloroterephthalate), pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine] and bensulide [0,0-diisopropyl phosphorodithioate S-ester with N-(2-mercaptoethyl)benzenesulfonamide] gave full season goosegrass control in well-established Midiron bermudagrass, but not during the initial establishment period where open bare soil was present. Napropamide [2-(α-naphthoxy)-N,N-diethylpropionamide] provided long term residual control of goosegrass with some interference with rooting of bermudagrass from stolon nodes. Winter survival of Midiron bermudagrass was superior to Tufcoat bermudagrass. Controlling annual grasses permitted superior bermudagrass growth, and winter survival was improved tremendously. Postemergence goosegrass control was obtained with MSMA (monosodium methanearsonate) and methazole [2-(3,4-dichlorophenyl)-4-methyl-1,2,4-oxadiazolidine-3,5-dione] when repeated several times during the season. A mixture of MSMA and methazole was superior to either used alone. The rate of bermudagrass establishment was increased through the control of goosegrass with herbicides.

Leaflets of 1690 species of Old World and South American Astragalus collected from herbaria at Kew, England; Edinburgh, Scotland; Munich, Germany; and Vienna, Austria were analyzed qualitatively for toxic aliphatic nitro compounds. The catabolites of nitro compounds found in species of Astragalus (nitro-bearing), 3-nitro-1-propanol and 3-nitropropionic acid, are especially toxic to cattle and sheep. A total of 190 of 1624 (12%) Old World species, 30 of 66 (45%) South American species, and a single species of one Astragalus subgenus were positive for nitro compounds. Most Old World species that contained aliphatic nitro compounds were collected in the Middle East and the Union of Soviet Socialist Republics. Nitro compounds were detected in specimens of eight species collected between 1822 and 1836. The nitro-bearing species were chemotaxonomically related and grouped within taxonomic sections. The presence of two or three nitro-bearing species within a section indicated that other species within the same section might also be nitro-bearing.

Sublethal amounts of 2,4-D [(2,4-dichlorophenoxy) acetic acid] were applied to several vegetable crops in order to determine effect on yield and quality in a simulated drift experiment. Tomato (Lycopersicon esculentum Mill.) and root crops were most sensitive to 2,4-D; as little as 2.1 g/ha of acid distorted tomato fruit shape and elongated radish (Raphanus sativus L.) roots. All root crops were rendered unmarketable by 10.4 g/ha and gross yields were reduced by exposure to 104 g/ha. Yield of peppers (Capsicum frutescens L. var. grossum) was increased by exposure to 2.1 g/ha and severely depressed by 104 g/ha. Cucumber (Cucumis sativus L.) fruit shape was distorted at 11 g/ha and yield was reduced slightly. Lettuce (Lactuca sativa L.), onion (Allium cepa L.), and cabbage (Brassica oleracea L. var. capitata) were least sensitive to 2,4-D. Exposure to 20.8 g/ha did not reduce yields of lettuce or cabbage. Onion yields were reduced by application of 104 g/ha. Bush bean (Phaseolus vulgaris L.) yield was decreased by exposure to 22 g/ha, but potato (Solarium tuberosum L.) yield increased at 16 g/ha. Herbicide residues in the crop foliage were proportional to the degree of exposure. Residue analysis combined with foliar symptoms may be useful in predicting crop damage following 2,4-D drift.

The diphenyl ether, oxyfluorfen [2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl)benzene], exerts a very strong and rapid bleaching effect upon intact microalgae such as Scenedesmus acutus. Carotenoids, and subsequently chlorophylls, are destroyed concurrently with ethane formation and inhibition of photosynthetic oxygen evolution. These herbicidal effects are not observed before an activation time of approximately 2 h, during which photosynthetic electron transport is necessary. Diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] inhibits oxyfluorfen activity during this activation time, but not thereafter. Isolated spinach chloroplasts (Spinacia oleracea ‘Atlanta’) evolve ethane after a light-incubation phase in the presence of oxyfluorfen as well as paraquat (methylviologen, 1,1′-dimethyl-4,4′-bipyridinium ion). Depending on their chemical constitution, diphenyl ethers apparently act differently and multifunctionally. The effects described for oxyfluorfen are believed to represent the primary mode of action of bleaching diphenyl ethers.

Control of common milkweed (Asclepias syriaca L.) with postemergence herbicides was investigated in greenhouse and field experiments. In greenhouse experiments, amitrole (3-amino-s-triazole), dicamba (3,6-dichloro-o-anisic acid), glyphosate [N-(phosphonomethyl)glycine], and combinations of amitrole + dicamba, dicamba + 2,4-D [(2,4-dichlorophenoxy) acetic acid], glyphosate + 2,4-D, and glyphosate + dicamba reduced regrowth of 6-week-old common milkweed as compared with the untreated check. Postemergence herbicides commonly used in corn (Zea mays L.), sorghum [Sorghum bicolor (L.) Moench], and soybeans [Glycine max (L.) Merr.] had little effect on emerged common milkweed. Removal of common milkweed top-growth as early as 1 day after treatment did not effect subsequent growth reduction from glyphosate at 0.3 kg/ha or higher. In the field, satisfactory control (70% or better) of common milkweed was obtained with glyphosate at 2.2 kg/ha applied at the early or late bud growth stage. Plots plowed 1 day after application of glyphosate at 2.2 kg/ha still retained satisfactory control of common milkweed 1 yr after treatment. Herbicides applied with a herbicide glove or a roller applicator resulted in common milkweed control similar to that obtained from broadcast spray applications.

Aerial applications of 20% tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N-dimethylurea} pellets at 2.2 kg/ha (ai) in the spring effectively controlled post oak (Quercus stellata Wangenh.), blackjack oak (Q. marilandica Muenchh.), water oak (Q. nigra L.), yaupon (Ilex vomitoria Ait.), winged elm (Ulmus alata Michx.), downy hawthorn (Crataegus mollis Scheele), gum bumelia [Bumelia lanuginosa (Michx.) Pers.], and willow baccharis (Baccharis salicina Torr. & Gray) in the Post Oak Savannah of Texas. Tree huckleberry (Vaccinium arboreum Marsh.), black hickory (Carya texana Buckl.), honeylocust (Gleditsia triachanthos L.) and cedar elm (Ulmus crassifolia Nutt.) were partially controlled by 2.2 kg/ha of tebuthiuron. Canopies of buckbrush (Symphoricarpos orbiculatus Moench), southern dewberry (Rubus trivialis Michx.), American beautyberry (Callicarpa americana L.), and persimmon (Diospyros virginiana L.) were reduced for about two growing seasons after which the woody species recovered. American beautyberry appeared to increase in abundance by the third growing season after control of the other woody species. Honey mesquite [Prosopis juliflora (Swartz) DC. var. glandulosa (Torr.) Cockerell], eastern redcedar (Juniperus virginiana L.), and Texas persimmon (Diospyros texana Scheele) were not controlled by tebuthiuron at 2.2 or 4.4 kg/ha, and saw greenbrier (Similax bona-nox L.) and peppervine [Ampelopsis arborea (L.) Koehne] apparently increased following application of tebuthiuron.

As a result of applying arsenicals as herbicides, desiccants, or soil sterilants, soil As levels can increase under some conditions. Three arsenicals, sodium arsenite, (NaAsO2), cacodylic acid, (hydroxydimethylarsine oxide), and MSMA (monosodium methanearsonate) were applied to bare soil at 1, 2, and 10 times the recommended maximum application rates. After incorporation, radishes (Raphanus sativus L.) and soybeans [Glycine max (L.) Merr.] were planted as indicator crops to assess the phytotoxicity of accumulated soil As residues. Soil As residues increased at all levels of application. However, only 50% of the As applied at 10 times the recommended rate was found after seven annual applications, regardless of the source. Total losses of As from the soil averaged 14 to 15% of that applied each year. At 10 times the recommended rate, As generally reduced radish and soybean yields, but seldom reduced yields at the two lower rates. Results indicated little danger of As residue accumulating to phytotoxic levels under normal application rates.

Combinations of MSMA (monosodium methanearsonate) with bensulide [O,O-diisopropyl phosphorodithioate S-ester with N-(2-mercaptoethyl)benzenesulfonamide], DCPA (dimethyl tetrachloroterephthalate), or prosulfalin {N-[[4-(dipropylamino)-3,5-dinitrophenyl] sulfonyl]-S,S-dimethylsulfilimine} were applied at various dates of treatment to bermudagrass [Cynodon dactylon (L.) Pers.] and Kentucky bluegrass (Poa pratensis L.) in the spring for large crabgrass [Digitaria sanguinalis (L.) Scop.] control. Bensulide controlled a higher percentage of weeds than did DCPA, regardless of treatment dates. When treatments were delayed until late April in Griffin and mid May in Blairsville, Georgia, large crabgrass control was improved from combinations of MSMA with bensulide compared to bensulide alone. Combinations of MSMA with DCPA improved large crabgrass control when applied in March and April at Griffin and in May at Blairsville. Combinations of MSMA with either bensulide or DCPA performed equally well whether applied as a single tank-mix treatment or as separate applications on the same day. Large crabgrass control was not improved at any date from combinations of MSMA with prosulfalin when compared with prosulfalin alone.

The life cycle of Notaris bimaculatus Fab. and the influence of this weevil on the control of quackgrass [Agropyron repens (L.) Beauv.] with glyphosate [N-(phosphonomethyl) glycine] were studied. Observations on this insect in 1978 and 1979 showed that its life cycle occurs in close association with quackgrass. The adult weevils feed on quackgrass culms and caryopses and use the inside of the culms for ovipositing. Adult populations, measured in quackgrass infestations during the summer months, ranged from 3 to 44/25 sweeps of an insect net. Larvae emerge from the eggs after 2 weeks, feed down the inside of the culms, chew an exit hole, and move into the soil where they attack the rhizomes. Larval numbers ranged from two to six/28 dm3 of soil during the summer months. Larvae feed on the rhizome surface or enter the rhizomes where they devour the vascular and cortical tissue. In dense quackgrass sods treated with glyphosate at 1.7 kg/ha, feeding damage on quackgrass rhizomes caused by the larvae reduced the control of quackgrass by disrupting the translocation of glyphosate in the rhizomes. Although soil-borne larvae of several insects were found in quackgrassinfested soil, larvae of N. bimaculatus were always present. Controlling these soil-borne insect larvae with a soil-applied insecticide for 2 months before applying glyphosate resulted in significantly increased quackgrass control. Shoot regrowth several months after the application of glyphosate at 1.4 kg/ha to quackgrass grown in cages infested with 400 adult weevils was 298 and 611 shoots/m2 in the 1979 and 1980 experiments, respectively. Similar glyphosate applications to weevil-free quackgrass resulted in only 26 and 15 shoots/m2 in the 1979 and 1980 experiments.

Field experiments were conducted with the recirculating sprayer (RCS) at Lincoln, Nebraska from 1974 through 1978. Different spray pressures, spray nozzles, and spray volumes with the RCS showed no significant differences in shattercane [Sorghum bicolor (L.) Moench] control or soybean [Glycine max (L.) Merr.] injury when herbicides were applied at three stages of weed growth. When shattercane was treated in a grain sorghum [Sorghum bicolor (L.) Moench] field, poor weed control and excessive crop injury occurred during treatment at the early growth stage as compared with treatments applied 2 weeks later. The final treatment date gave selective weed control in grain sorghum, but many of the shattercane heads had already developed viable seed. A weed-to-crop height differential of at least 45 cm resulted in maximum weed control with minimum crop injury. Common milkweed (Asclepias syriaca L.) control in soybeans varied considerably, but treatments giving over 80% control were glyphosate [N-(phosphonomethyl)glycine] at 1.1 to 4.5 kg/ha applied through the RCS. Other herbicides were less effective. Volunteer corn (Zea mays L.) was controlled selectively at 75 to 100% in soybeans with glyphosate or paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) when applied through the RCS. Shattercane was controlled 95 to 100% in soybeans with glyphosate at 3.4 kg/ha. Unless spray drift and splash can be prevented when using the RCS, glyphosate and paraquat will not give selective control when applied to weeds growing in grain sorghum. Glyphosate applied through the RCS, however, can be a selective method of controlling weed escapes in soybeans because soybeans are not as sensitive to glyphosate as is sorghum.

The combination of salts at the approximate ratio found in saline irrigation water, (NaCl 41.9 mM, CaCl2 20.9 mM, and MgCl2.6H2O 10.5 mM), with either 1 mM EPTC (S-ethyl dipropylthiocarbamate) or 0.1 mM CDEC (2-chloroallyl diethyldithiocarbamate) induced a greater reduction of root length, shoot length, and fresh weight of tomato (Lycopersicon esculentum Mill. ‘VF-315’) relative to either factor alone. The osmotic pressure of this salt solution is 0.40 MPa (mega Pascal), which is equivalent to 4.0 bar or ca. 4.0 atm. Similar results were found in lettuce (Lactuca sativa L. ‘Great Lakes–659’) using salts at 0.30 MPa (NaCl 31.4 mM, CaCl2 15.7 mM, and MgCl2.6H2O 7.3 mM) combined with either 0.75 mM EPTC or 0.2 mM CDEC. In tomato, the inhibition was additive for each parameter measured. In lettuce, however, the effect on fresh weight and shoot length was synergistic and the effect on root length was additive. Calcium chloride was the single salt component of the mixture, which when combined with either EPTC or CDEC, induced a significant reduction of root length, shoot length, and fresh weight in tomato relative to either factor alone. No additional reduction in growth was found in lettuce when each individual salt was combined with either EPTC or CDEC.

Six herbicides were evaluated at two rates on sweet potatoes [Ipomoea batatas (L.) Lam. ‘Georgia Red’, ‘Georgia Jet’] with and without cultivation from 1972 through 1976. Cultivation with a ground-driven rotary hoe about 2 weeks later improved the control of late-season broadleaf weeds such as Florida beggarweed [Desmodium tortuosum (Sw.) DC] and showy crotalaria (Crotalaria spectabilis Roth.). Cultivation improved weed control where vernolate (S-propyl dipropylthiocarbamate), DCPA (dimethyl tetrachloroterephthalate), and napropamide [2-(α-naphthoxy)-N,N-diethylpropionamide] were applied. The improved weed control in cultivated treatments resulted in increased sweet potato yields in 1972 and 1973, which also were the years with the highest weed populations.

Large quantities of viscous, non-crystalline epicuticular waxes were observed on leaves of three goldenweed (Isocoma) species. Based on weights of residues from single 15-s chloroform extractions, wax on leaves of field-grown plants of the least herbicide-susceptible species, common goldenweed [I. coronopifolia (Gray) Greene], increased from 71 mg/dm2 in March to 286 mg/dm2 in October, which was two to four times greater than the amount present on other goldenweed species. Similar quantities were produced by leaves of glasshouse-grown plants, but maximum wax production occurred during summer months. The epicuticular wax of fully expanded leaves decreased with age. The amounts of epicuticular wax on individual plants growing within a field population varied by a factor of four.

Plots of western false hellebore (Veratrum californicum Durand), treated in 1968 and 1969 with 2,4-D [(2,4-dichlorophenoxy)acetic acid] at 2.2 kg/ha, were reexamined in July 1979 to determine vegetative changes, especially any increases in the production of desirable species and long-term control of western false hellebore. Grass, sedge, and rush production had doubled, and broadleaved plant production, excluding western false hellebore, which was eliminated, decreased on treated plots. Western false hellebore had not reinvaded the treated plots; control remained at 100% for 10 yr. Removal of the western false hellebore on treated plots allowed an increase in grass, sedge, and rush production of 1,500 kg/ha over check plots.

Common sunflower (Helianthus annuus L.) interference in onions (Allium cepa L. ‘Yellow Granex PRR’) was studied at different weed densities and periods of interference. Onion yields were reduced when the highest density (360/m2) of common sunflower interference with onions from 6 weeks after emergence and when sunflower at densities of 50/m2 and 5/m2 interfered for 12 and 15 weeks after emergence, respectively. Yield was not reduced if the crop was kept weed-free for 2 to 12 weeks after emergence with the shortest weed-free periods of 2 and 6 weeks requiring high light irradiance and high soil temperature and intermediate soil moisture. Climatic factors were more useful than weed density in explaining differential interference of sunflower in onions. Onion yield was negatively linearly correlated (P<0.05) with sunflower fresh weight, but was not linearly correlated with sunflower height.

Absorption coefficient (k), infinite reflectance (Ri), and scattering coefficient (s) were tabulated for five wavelengths and analyzed for statistical differences for seven weed species. The wavelengths were: 0.55 μm, 0.65 μm, 0.85 μm, 1.65 μm, and 2.20 μm. The Ri of common lambsquarters (Chenopodium album L.), johnsongrass [Sorghum halepense (L.) Pers.], and annual sowthistle (Sonchus oleraceus L.) leaves at the 0.85-μm wavelength were significantly (p = 0.05) higher than for sunflower (Helianthus annuus L.), ragweed parthenium (Parthenium hysterophorus L.), or London rocket (Sisymbrium irio L.). Annual sowthistle had the largest k value, and Palmer amaranth (Amaranthus palmeri S. Wats.) had the smallest k value at the 0.65-μm chlorophyll absorption wavelength. In general, johnsongrass, ragweed parthenium, or London rocket had the largest s values among the five wavelengths, whereas annual sowthistle and Palmer amaranth were usually lowest.

The rate and final germination percentage and emergence of green foxtail [Setaria viridis (L.) Beauv.] was found to be very dependent on the soil temperature and moisture conditions at the time of seeding. In contrast, the germination and emergence of wheat (Triticum aestivum L. ‘Sinton’) was only slightly affected over the temperature and moisture range of the study. In laboratory studies, a temperature decrease from 20 to 15 C caused a 53- and 12-h delay in the time to reach 50% germination of green foxtail and wheat, respectively. Soil moisture was found to have a greater effect than soil temperature on green foxtail germination. At −5.3 bars water potential, the final germination percentage of green foxtail was less than at the higher water potentials. A further decrease in the water potential to −6.5 bars effectively reduced green foxtail germination to zero. Wheat germination was delayed only slightly, and the final germination percentage remained unchanged over the range of 0 to −15.3 bars water potential. In field studies, a soil temperature decrease from 22 to 14 C caused a 6-day delay in the time of 50% emergence of green foxtail, and the emergence of wheat was delayed only 1 day by a similar decrease in temperature. Field studies showed that when the soil was moist (0 to −4 bars) and soil temperatures were warm (20 to 25 C), green foxtail emerged within a few days of wheat. However, when the soil was dry (-4.0 to −6.5 bars) and soil temperatures were low (15 to 20 C), green foxtail emerged 7 to 14 days after wheat. The intensity of green foxtail competition was greater when green foxtail emerged within a few days of wheat than when green foxtail emerged 2 weeks after wheat.

Dalapon (2,2-dichloropropionic acid), tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea}, and hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione] were evaluated for smutgrass [Sporobolus poiretii (R.&S.) Hitchc] control in bahiagrass (Paspalum notatum Flugge.) pastures. Dalapon and hexazinone provided the best smutgrass control but injured the bahiagrass. Forage treated with hexazinone at 1.7 kg/ha or less recovered within 6 months; however, the effects of the initial injury from dalapon at 2.2 kg/ha could be detected for as long as 2 yr after treatment. Dogfennel [Eupatorium capillifolium (Lam.) Small] and broomsedge (Andropogon virginicus L.) replaced smutgrass and bahiagrass removed by dalapon. Higher rates of tebuthiuron than hexazinone (3.4 vs. 1.1 kg/ha) were required to control smutgrass adequately.

Field and growth chamber experiments were conducted to determine the effects of surface soil moisture on the phytotoxicity of alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] to grain sorghum [Sorghum bicolor (L.) Moench. ‘Funk 623 GBR’], which was unprotected or protected with CGA-43089 {α-[(cyanomethoxy)imino] benzeneacetonitrile}. In field tests, neither alachlor nor metolachlor was phytotoxic to unprotected grain sorghum when the surface soil remained dry until the sorghum had emerged. CGA-43089 protected sorghum emerging from moist soil that had been treated with alachlor or metolachlor at rates of 2.24 or 3.36 kg/ha. Growth chamber tests showed that CGA-43089 was less effective in protecting sorghum from herbicide injury when Ships clay was continuously wet [110% field capacity (FC)] from time of planting to emergence (3 to 5 days) than when soil was wet for only 1 or 2 days prior to emergence. In contrast, if the surface soil remained dry until the coleoptile reached the soil surface, alachlor and metolachlor had little effect on sorghum even when no protectant was present. When sorghum was planted in Arenosa sand containing 5% organic matter, protected sorghum grew as well as the control even under continuous high moisture conditions. Metolachlor incorporated into the root zone at a rate of 20 ppm had no effect on either protected or unprotected sorghum. Alachlor and metolachlor were most phytotoxic when placed in the surface 1.25 cm of moist soil or when incorporated. The coleoptile was the most susceptible plant part. Thus, the key to grain sorghum response to these herbicides was in herbicide placement and availability to the coleoptile. Under conditions normally leading to phytotoxic effects from alachlor or metolachlor, grain sorghum growth was significantly better from seed protected with CGA-43089 than from unprotected seed.