Hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4 (1H, 3H)-dione] effectively controlled herbaceous weeds in a loblolly pine (Pinus taeda L.) plantation in 1975. Pine seedling height increased as a result of weed control following 1 to 3 kg/ha applications but phytotoxic symptoms were evident. A 1976 field study indicated activated charcoal root coatings may reduce phytotoxic action. Hexazinone at 3 and 4 kg/ha applied to either the foliage or the soil was toxic to potted pine seedlings in 1976. The addition of surfactant to hexazinone treatments at 2, 3, and 4 kg/ha increased pine phytotoxicity to unacceptable levels. When hexazinone was applied to soil at 2, 3, and 4 kg/ha, activated charcoal root coatings reduced pine mortality to acceptable levels on Norfolk sandy loam. Charcoal was less effective on Madison clay loam. Pine tolerance on both soils was acceptable at 2 kg/ha.

Aerial sprays of asulam (methyl sulfanilylcarbamate) applied at 3.4 or 6.7 kg/ha to forest plantations in western Oregon effectively controlled western bracken [Pteridium aquilinum (L.) Kuhn var. pubescens Underw.] without damaging Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] seedlings. Asulam also did not damage noble fir (Abies procera Rehd.) seedlings if applied without a surfactant. The half-life of asulam in forest soils ranged from less than 7 to 18 days and vertical movement in the soil profile was minimal. No herbicide residues were found in runoff water from treated areas up to 208 days after application.

We studied the effects of temperature (5, 10, 20, and 30 C) on the phytotoxic activity of decaying quackgrass [Agropyron repens (L.) Beauv.] leaves and rhizomes that were incubated in soils for 0, 1, 2, 4, and 6 weeks. Alfalfa (Medicago sativa L.) seeds were grown for 96 h in water, water extracts of control soils, and water extracts of soil with quackgrass rhizomes or leaves. Dried quackgrass rhizomes and leaves contained water-soluble toxins that inhibited alfalfa seedling development and growth. There was a strong interaction between incubation time and temperature on the development of additional toxins by decomposing quackgrass. High incubation temperature (30 C) accelerated toxin formation and ultimate decay. Intermediate temperature (20 C) delayed toxin formation and decay. Low incubation temperatures (5 C and 10 C) prevented formation of additional toxin. In all extracts of quackgrass and soil that had been incubated for 6 weeks, normal alfalfa seedling number equaled that in water. However, seedling growth varied with incubation temperatures.

Treatment of quackgrass with glyphosate [N-(phosphonomethyl) glycine] in the greenhouse did not influence the toxicity of decaying quackgrass leaves. The highest toxic effect was noted after 1 week of decay on the soil surface.

Absorption of triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid} by tanoak [Lithocarpus densiflorus (Hook. & Am.) Rehd.] leaves was investigated. Greater amounts of 14C-triclopyr were absorbed by immature leaves than mature leaves and by abaxial than adaxial surfaces. Both surfaces of immature and mature tanoak leaves were characterized. Stomata were present only on the abaxial surface and were more numerous on immature leaves than mature leaves. Immature leaves had less epicuticular wax and thinner, more permeable cuticular membranes than mature leaves. Stellate trichome densities were greater on abaxial surfaces than adaxial surfaces and on immature than mature leaves. Absorption of 14C-triclopyr was influenced by each of the leaf surface features studied.

Single over-the-top and directed applications of dicamba (3,6-dichloro-o-anisic acid) were made to cotton (Gossypium hirsutum L. ‘Deltapine 16′). Dicamba applied over-the-top of cotton caused foliage malformation for about 6 weeks. Dicamba (32 g/ha) applied to cotton foliage 3 to 15 weeks after emergence reduced average cotton yields. Applications of 16 to 64 g/ha of dicamba over-the-top of cotton before bloom had less effect on cotton foliage, yield, boll components, and fiber properties than application at bloom. Directed applications of dicamba to the soil or to the base of cotton and soil caused foliage malformation but did not affect cotton yield, boll components, and fiber properties.

Alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] at 3.4 kg/ha, EPTC (S-ethyl dipropylthiocarbamate) + R-25788 (N,N-diallyl-2,2-dichloroacetamide) at 4.5 + 0.4 and 9.0 + 0.8 kg/ha, vernolate (S-propyl dipropylthiocarbamate) + R-25788 at 4.5 + 0.4 and 9.0 + 0.8 kg/ha, metolachlor [2-chloro N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] at 1.7 and 3.4 kg/ha, and metolachlor + procyazine {2-[[4-chloro-6-(cyclopropylamino)1,3,5-triazine-2-yl] amino]-2-methylpropanenitrile} at 1.3 + 1.3 kg/ha were preplant incorporated. These herbicides controlled 95% or more of the barnyardgrass [Echinochloa crus-galli (L.) Beauv.], common lambsquarters (Chenopodium album L.), redroot pigweed (Amaranthus retroflexus L.), Powell amaranth (A. powellii S. Wats.), and yellow foxtail [Setaria lutescens (Weigel) Hubb.] without injuring sweetcorn (Zea mays L. ‘Golden Jubilee’) or reducing corn yields or quality. Similar results were obtained with preplant incorporated applications of butylate (S-ethyldiisobutylthiocarbamate) + R-25788 at 4.5 + 0.2 kg/ha followed by a postemergence application of the amine salt of 2,4-D [(2,4-dichlorophenoxy)acetic acid] at 0.6 kg/ha. Metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] at 0.3 and 0.6 kg/ha and metribuzin + alachlor at 0.6 + 2.2 kg/ha applied preplant and incorporated reduced corn stands, primary ear production, and corn yields significantly. None of the herbicides significantly affected total sugars, reducing sugars, soluble solids, moisture content, or succulence of the corn.

The host range of an isolate of the fungal pathogen Alternaria macrospora Zimmerman from infected spurred anoda [Anoda cristata (L.) Schlecht.] leaves was studied in the greenhouse and growth chamber. The fungus was inoculated to representative plants in the Malvaceae, Solanaceae, Leguminosae, and Gramineae families. Evidence of infection was limited to plants in the Malvaceae, with spurred anoda being the most susceptible species tested. Only negligible damage was incited on cotton (Gossypium hirsutum L. ‘Stoneville 213′) and long staple cotton (G. barbadense L. ‘Pima S–5′), hollyhock [Althaea rosea (L.) Cav.], okra (Hibiscus esculentus L. ‘Clemson spineless’), prickly sida (Sida spinosa L.), velvetleaf (Abutilon theophrasti Medic.), and Venice mallow (Hibiscus trionum L.). Disease symptoms induced in cotton by the spurred anoda isolate of A. macrospora were much less severe than those reported for other isolates of the fungus. Therefore, the spurred anoda isolate may be a specialized form of the fungus.

Experiments were conducted to develop systems for control of American germander [Teucrium canadense L. var. virginicum (L.) Eat.] in corn (Zea mays L. ‘Trojan TXS 105A’). Soil-incorporated, preemergence, and postemergence herbicide treatments were evaluated in greenhouse studies. Soil incorporated applications of EPTC (S-ethyl dipropylthiocarbamate) + R-25788 (N,N-diallyl-2,2-dichloroacetamide), atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] and alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] effectively reduced its growth. Preemergence applications of alachlor and atrazine did not control American germander. Postemergence applications of the dimethylamine salt of 2,4-D [(2,4-dichlorophenoxy)acetic acid] the butoxyethanol ester of 2,4-D and dicamba (3,6-dichoro-o-anisic acid) gave 20 to 41% control. Atrazine + crop oil gave 76 to 84% control. Soil-incorporated treatments of atrazine or EPTC + R-25788 controlled American germander better than alchlor when the rhizomes were planted at depths of 2.5 and 10 cm in greenhouse studies. In field trials American germander was a severe competitor in corn, especially when soil moisture was limited, and had the capability of substantially reducing corn yields when not controlled. EPTC + R-25788 and atrazine applied alone or in combinations as preplant incorporated treatments increased yield significantly and controlled 85 to 99% of the American germander 72 weeks after planting. Atrazine + oil was the only effective postemergence treatment.

Investigations were conducted on Euglena gracilis Klebs strain Z to determine the effects of fluometuron [1,2-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea], MSMA (monosodium methanearsonate), glyphosate [N-(phosphonomethyl)glycine], and metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] on cell number, chlorophyll content, and photosynthesis. Euglena cell number was reduced by 65% or more after 48 h with fluometuron levels above 4 X 10-5M. MSMA at 6 X 10-4M reduced cell number 42% after 144 h exposure. Chlorophyll content was reduced 33 to 80% by metribuzin levels of 2 X 10-6M or greater, and fluometuron inhibited chlorophyll content by 30% or more from 4 X 10-6M or greater concentrations. Chlorophyll was reduced 21 to 69% by treatment with glyphosate at 3 X 10-3M, but MSMA appeared to have little effect on chlorophyll except at the high level of 6 X 10-4M at 48 h. Photosynthesis was reduced 50% or more with metribuzin levels above 9 X 10-7M and with fluometuron above 9 X 10-5M. MSMA reduced photosynthesis by 20% at the 6 X 10-3M level, and glyphosate slightly reduced photosynthesis at levels below 1.2 X 10-4M but slightly stimulated it above that level. Chronic effects (Euglena exposed to herbicides 96 h prior to measurement) on photosynthesis indicated a more pronounced reduction from fluometuron than from short-term exposure, little change with glyphosate, but less reduction with metribuzin than from short-term exposure. Metribuzin caused increased respiration rates of 100 to 200% after 100 min of exposure. Respiration was stimulated 20% by glyphosate and relatively unaffected by the other compounds. Removal of Euglena from metribuzin- and fluometuron-treated media to non-treated media resulted in increased levels of chlorophyll to near that of the control. These results suggest that use of these herbicides is not detrimental to non-target algae if the exposure is not intensive.

The influence of soil moisture stress, temperature, and bulk density on the germination and seedling emergence of downy brome (Bromus tectorum L.) was investigated in the laboratory. Reductions in soil matric potential from -2 to -16 bars markedly reduced the percentage and rate of emergence. Seedling emergence was better at constant than at alternating temperatures. At high matric potentials, the rate of emergence was accelerated by warmer soil temperature (20 C), while at very low matric potentials, the percentage and rate of seedling emergence were least restricted at cooler temperatures (10 and 15 C). Soil matric potential did not influence the percentage or rate of emergence of seedlings grown from seed lots harvested during climatologically diverse years. Seedling emergence but not germination was inhibited by increased levels of soil compaction. Soil compaction times moisture interaction were not observed, as measured by final seedling emergence.

The concentration of fluridone {1-methyl-3-phenyl-5-[3-(trifluoromethyl)phenyl]-4(1H)-pyridinone} residue in Miller clay and Lufkin fine sandy loam was determined at various intervals following incorporated and nonincorporated applications in the field. Low levels of fluridone were present in Miller clay after 250 days while up to 25% remained in Lufkin fine sandy loam 385 days after treatment. Incorporation of fluridone increased its persistence in, Lufkin fine sandy loam but not in Miller clay. Fluridone degradation in Miller clay and Lufkin fine sandy loam was more rapid in the field than under controlled conditions. Fluridone degradation in sterilized Brennan fine sandy loam and Hidalgo sandy clay loam was significantly slower than in nonsterilized soil kept under the same conditions. These differences were not observed in Lufkin fine sandy loam and Miller clay.

The effect of metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] on the germination and growth of 14 plant species was investigated. A 10-3 M concentration of the herbicide did not reduce germination as much as 10% for corn (Zea mays L. ‘Pioneer 3369A’), English pea (Pisum sativum L. ‘Thomas Laxton’), sicklepod (Cassia obtusifolia L.), or wheat (Triticum aestivum L. ‘Coker 68–15′) but reduced germination of oat (Avena sativa L. ‘Coker 227′) to 0, lettuce (Lactuca sativa L. ‘Grand Rapids’) to 11%, and peanut (Arachis hypogaea L. ‘Florunner’) to 14%. A 10-6 M concentration did not affect the germination of any species tested. A 10-5 M concentration did not significantly decrease length or fresh weight of corn, morningglory, or wheat roots but had at least some adverse effect on all other species tested. At this concentration root length was less than 2/3 of the control for English pea, cucumber (Cucumis sativus L. ‘Ashley’), radish (Raphanus sativus L. ‘Scarlet Globe’), sicklepod, and soybean [Glycine max (L.) Merr. ‘Ransom’]. Metolachlor was supplied to germinating seeds of barley (Hordeum vulgare L. ‘Barsoy’), English pea, and corn either only in the shoot, seed, or root zone, or to all parts. One kg/ha applied in the shoot zone of barley and corn significantly reduced seedling height and dry weight but had no effect when applied in either the seed or root zone. Application in all zones was approximately twice as detrimental as when applied in only the shoot zone. Application of 4 kg/ha in only the shoot, seed, or root zones of English pea did not decrease seedling height or dry weight but application in all zones decreased these values about 98%. A 10-5 M concentration of metolachlor decreased leucine uptake by cucumber root tips but not its incorporation into protein. A 10-4 M concentration strongly reduced leucine uptake and slightly decreased leucine incorporation into protein.

Field experiments were conducted in 1974 and 1975 to evaluate the effect of seven herbicides applied preemergence and two herbicides applied postemergence on weed growth around 7-yr-old pecan [Carya illinoensis (Wang.) K. Koch ‘Elliott’ and ‘Desirable’] and 3-yr-old peach [Prunus persica (L.) Batsch ‘June Gold’] and to observe herbicidal tolerance as noted from visually expressed phytotoxicity. After 12 weeks, the best control of bermudagrass [Cynodon dactylon (L.) Pers.], purple nutsedge (Cyperus rotundus L.), and wild blackberry (Rubus cuneifolius Pursh) was obtained with glyphosate [N-(phosphonomethyl)glycine], napropamide [2-(α-naphthoxy)-N,N-diethylpropionamide] + glyphosate, and napropamide + terbacil (3-tert-butyl-5-chloro-6-methyluracil) + paraquat (1,1′dimethyl-4,4′-bipyridinium ion). The most effective overall control of yellow nutsedge (Cyperus esculentus L.), camphorweed [Heterotheca subaxillaris (Lam.) Britt. & Rusby], dogfennel [Eupatorium capillifolium (Lam.) Small], large crabgrass [Digitaria sanguinalis (L.) Scop.], and Florida pusley (Richardia scabra L.) resulted from napropamide + terbacil + paraquat. Herbicides used caused no visible toxicity to the immature pecan or peach trees.

Ethofumesate, [(+)-2-ethoxy-2,3-dihydro-3,3-dimethyl-5-benzofuranyl methanesulfonate] applied preemergence provided selective control of annual bluegrass (Poa annua L.) in perennial ryegrass (Lolium perenne L.) overseeded on dormant bermudagrass [Cynodon dactylon (L.) Pers. X C. transvaalensis Burtt Davy ‘Tifdwarf’] golf greens. Control in excess of 95% was obtained with single applications at the 2.2 kg/ha rate in 2 of 3 yr, but multiple applications were required when ethofumesate was applied at 1.1 kg/ha or less. Ethofumesate caused temporary cessation of bermudagrass growth when applied in the fall. February applications slowed the spring transition to bermudagrass.

Mathematical growth analysis techniques were used to study the effects of simulated field temperatures and chilling events on the growth of the exotic noxious weed itchgrass (Rottboellia exaltata L. f.) and adapted varieties of corn (Zea mays L. ‘DeKalb XL43’ and ‘DeKalb XL395′), and soybean [Glycine max (L.) Merr. ‘Corsoy’, ‘Williams', and ‘Tracy’] in climate-controlled greenhouses and growth chambers. Itchgrass grew vigorously and produced seed in temperature regimes simulating the warmest 4 months of the growing season in the Gulf Coast states (30/25 C, day/night), the central Midwest (27/21 C), and the northern Midwest (23/18 C). At 30/25 C day/night, itchgrass produced 707 g of dry matter and 1907 seed per plant after 119 days. Itchgrass produced 621 g dry matter and 1429 seed at 27/21 C and 499 g dry matter and 1160 seed at 23/18 C. Itchgrass and adapted varieties of corn and/or soybeans were grown in four additional temperature regimes simulating the first 5 weeks of the growing seasons for corn and soybean at Madison, Wisconsin (19/11 C day/night); for soybean at Carbondale, Illinois (24/20 C); for corn at Waycross, Georgia (20/14 C); and for soybean at Baton Rouge, Louisiana (27/23 C). After 24 days of growth, half the plants in each regime were exposed to 3 days of chilling (11/4 C for Madison, 17/10 C for Carbondale, 15/6 C for Waycross, and 24/18 C for Baton Rouge) and returned to the original growth regimes for recovery. The chilling treatments reduced dry matter production, net assimilation rate, and leaf area duration more in itchgrass than in corn or soybean. After recovery, the previously chilled itchgrass plants had greater reductions in height, leaf area, and dry weight, compared to unchilled controls, than did corn or soybean. Weed/crop ratios in height, leaf area, and dry weight for itchgrass/corn were significantly reduced by chilling. In the two cooler regimes, weed/crop ratios in leaf area and dry weight for itchgrass/soybean were significantly reduced by chilling. Because of its sensitivity to cool temperatures, itchgrass, is unlikely to be an important early-season competitor with corn or with soybean outside the South.

Fall applications of 0.14 kg/ha of picloram (4-amino-3,5,6-trichloropicolinic acid) to musk thistle (Carduus nutans L.) rosettes controlled musk thistle stems better and more consistently than fall applications of 2.2 kg/ha of 2,4-D amine [(2,4-dichlorophenoxy)acetic acid], 0.6 kg/ha of dicamba (3,6-dichloro-o-anisic acid), or a mixture of 0.3 kg/ha dicamba + 1.1 kg/ha of 2,4-D. Dry conditions in 1975 and cool conditions in November, 1976, hampered control with all herbicides except picloram. In spring applications when growing conditions were favorable, herbicide differences were usually not significant. For all herbicides, treatment of bolted stems did not control musk thistle satisfactorily. Picloram was superior for reducing stems 12 to 18 months after application in 2 of 3 yr. Residual control resulted principally because the herbicide killed many seedlings and first-year rosettes at the time of application.

Diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea], prometryn [2,4-bis(isopropylamino)-6-(methylthio)-s-triazine], and trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) were applied pre-plant in safflower (Carthamus tinctorius L. ‘AC-1′) for 6 yr at two locations. Diuron and prometryn reduced crop stands in 2 of 6 yr on the sandier soil at Mesa. Growth of sorghum [Sorghum bicolor (L.) Moench ‘Amak R-10′] in the greenhouse in soil collected 10 months after each herbicide application was reduced by 1.7 kg/ha of trifluralin in 3 of 6 yr in the Yuma silty clay loam and by both rates of trifluralin in 1 of 6 yr in the sandier soil at Mesa. Growth of barley (Hordeum vulgare L. ‘Arivat’) was not reduced in soil treated with any herbicide at either location. Herbicides did not accumulate in winter-planted safflower.

Six crop species were irrigated with water that contained up to several times more glyphosate [N-(phosphonomethyl)glycine] than would be expected in irrigation water as a result of spraying ditchbank vegetation. In June or July 1976, sugarbeets (Beta vulgaris L.), alfalfa (Medicago sativa L., ‘Vernal’), grain sorghum [Sorghum bicolor (L.) Moench], field beans (Phaseolus vulgaris L., ‘Pinto’), tomatoes (Lycopersicon esculentum Mill., ‘Roza’), and squash [Cucurbita moschata (Duch.) Duch. ex Poir.] were sprinkler-irrigated with water that contained glyphosate at 0, 0.02, 0.22, or 2.2 ppmw. These concentrations were applied continuously for 8 h to make total applications of 0, 0.01, 0.1, and 1.1 kg/ha, respectively. No injury symptoms developed in any of the crop plants. Yields of treated crops were equal to those produced by untreated plants.

An oat (Avena sativa L. ‘Dal’) primary root bioassay procedure was used to study the persistence of eight dinitroaniline herbicides in soil. Sensitivity of the bioassay to the herbicides depended on the length of time roots were exposed to the herbicide treatments. Root inhibition increased with time of exposure. Herbicide persistence was studied under growth chamber, greenhouse, and field conditions. The herbicides remained biologically active the longest under dry and cool soil conditions. At 5 C, little change in herbicide activity was observed over an 8-month period. Under greenhouse conditions, the herbicides in wet soil dissipated rapidly, as compared with those in dry soil. Soil samples taken from depths of 0 to 7.5 cm and from 7.5 to 15 cm in the field showed that the herbicides were retained primarily in the surface 7.5 cm. Small amounts were found from 7.5 to 15 cm only shortly after the herbicides were applied. Dinitramine (N4,N4-diethyl-α,α,α-trifluoro-3,5-dinitrotoluene-2,4-diamine) was the only herbicide tested of which soil residues from spring field applications were not detected the following fall.

Redroot pigweed (Amaranthus retroflexus L.) and robust foxtail [Setaria viridis (L.) Beauv. var. robusta-alba Schreiber (RWF) or Setaria viridis var. robusta-purpurea Schreiber (RPF)] were investigated regarding their ability to interfere with soybean [Glycine max (L.) Merr. ‘Amsoy 71′] at different weed densities and soybean row spacing throughout two growing seasons. Final weed densities for each species tended to reach a common value because of intraspecific interference regardless of the initial density. With cultivation, a narrow soybean row spacing (38 cm) resulted in less weed growth than did a wide row spacing (76 cm) but with no cultivation, the trend was reversed. Soybeans provided less interference to foxtail than to pigweed during both growing seasons. Interference from foxtail adversely affected soybean yield components and soybean seed yield more than did pigweed interference. Water-stress conditions in 1976 increased the intensity of weed interference and reduced soybean seed yield more severely than in 1975 when moisture was adequate throughout the growing season.